National Symposium on Geodynamics and evolution

of Indian Shield – through time and space

Commemorating

Golden Jubilee of the Geological Society of India 2008

Organised by

Centre for Earth Science Studies Thiruvananthapuram

On

18–19 September, 2008

Cover design: Geological map of India published by the Geological Survey of India (1993); superposed is the northward drift of India with respect to Asia during the Cenozoic times taken from P. Molnar and P. Tapponier (1975; science, v. 189; pp419-426)

Magma emplacement in Central Indian tectonic zone – An evidence for large scale crustal growth and recycling during Proterozoic: a review (Abhinaba Roy) P-1

Himalayan mountain building and fragile ecosystem (Anshu Kumar Sinha) P-2

Evolution of the Indian Shield – Imprints from Magnetic Data (S.P. Anand and Mita Rajaram) P-3

Frontiers of Metamorphism: influence on evolution of southern Indian shield (Anand Mohan) P-3

Uranium and Thorium metallogeny in India: A Tectonic Perspective (Anjan Chaki) P-4

Dinosaurs of India: Dead but well! (Ashok Sahni) P-7

Near collisional phase of the Indian plate: Biotas and Palaeogeography (Ashok Sahni) P-7

Some facts about the sutures of continental cratons that constitute the Indian subcontinent and the myth of their selective underplating (D. N. Avasthi) P-8

Nellore-khammam schist belt- a plate tectonic model (V.R.R.M. Babu) P-8

Geo-informatics for Geology and Tectonic Mapping in Kammbam Valley, Tamilnadu, India. (G. Balamurugan) P-9

The emerging pattern of crust-formation and recycling history in the Precambrian Dharwar Craton and the Southern Granulite Terrain, southern India: constraints from recent geochronological and isotopic results (Y.J. Bhaskar Rao) P-10

Palaeozoic successions of the Indian Plate (O. N. Bhargava) P-13

Status of hydrocarbon exploration in sedimentary basins of India (P.K. Bhowmick) P-14

Northward flight of Indian Plate and evolution of the Mesozoic-Cenozoic basins (S.K. Biswas) P-14

Antiquity of Bhima/Kurnool (Palnad) Puräna platformal sediments & their Mesoproterozoic connection: New insights from the limestone xenoliths in siddanpalle kimberlite cluster, Eastern Dharwar craton, Southern India (N. V. Chalapathi Rao) P-15

Ground penetrating radar (GPR) and Quaternary tectonic studies in Gujarat region of Western India (L. S. Chamyal) P-17

Tectono-sedimentation during Rift-drift period in Ramnad sub basin, Cauvery Basin (Chandan Chakraborty, M.S. Rana, S. Chandra, N.D. Gideon, M. Giridhar) P-17

Proterozoic orogens and transpressional tectonic regimes in southern India (T. R. K. Chetty) P-17

Temporal Emplacement-Sequence of the Sodic- and Potassic-Granitoids in the Indian Peninsula and its bearing on U-Mineralization (R. Dhana Raju) P-19

Modelling the evolution of the Indian Granulite terrains-few constraints (V. Divakara Rao) P-20

Majhgawan lamproites, Madhyapradesh and Kodomali orangeites, Chattisgarh: petrological appraisal and new insights on their origin (Fareeduddin) P-21

Geology and hydrocarbon prospectivity of Cauvery basin, India (M. Giridhar, Rajesh Sharma, Chandan Chakraborthy, M.S.Rana) P-22

Paleoclimates changes in Indian Ocean on tectonic time scale (D. Gopala Rao) p-23

A new approach to pecision chronicling of regional tectonic events on the Gondwanian Tethyan margin from Arabia to Australia (Jai Krishna) P-24

CONTENTS

Higher Himalayan orogenic channel: its implications on other orogenic belts of the Indian subcontinent (A. K. Jain) P-26

Assessment of additional draft by community wells and their impact on the shallow aquifer in the Coastal belt of Kerala (John Mathai and Unnikrishnan K.R) P-26

Rainwater Harvesting and Ground Recharge-Success stories from Kerala (John Mathai and P.K. Thampi) P-27

Contribution of palaeoflood techniques to flood risk analysis in ungauged rivers: Examples from the Indian Peninsula (V.S. Kale) P-28

High strandlines during the Proterozoic history of the Indian shield: evidences from Purana basins (V.S. Kale) P-29

Cretaceous Continental Flood Basalt Magmatism in India (P. Krishnamurthy) P-30

Palaeogeographic evolution of the Cuddapah basin (G. Lakshminarayana) P-30

Changes in the Long-term Deformation Pattern in the Andaman-Sumatra Trench-Arc Region after the 26 December 2004 Mega thrust Earthquake (S. Lasitha and M. Radhakrishna) P-31

South Indian high-grade domain: a differentially transformed Archaean continental lithospheric segment (T. M. Mahadevan) P-32

Trends of marine researches - Past, Present and Future (T.K.Mallik) P-33

Archean Crustal growth processes as evidenced from the greenstone belts of eastern Dharwar craton, India (C. Manikyamba, Tarun C. Khanna, P.K. Prachiti, K. Raju) P-34

Fractal analysis, microstructures and deformation processes-potential in the Indian context (Manish A. Mamtani) P-35

Petrography, Palaeomagnetism and 40Ar/39Ar Geochronology of the Late Cretaceous –Early Palaeogene Igneous Activity along the West Coast of India (Mathew Joseph, Mireille Perrin, T. Radhakrishna, Jean Marie Dautria, Henri Maluski, G. Balasubramonium and Jossina Punoose) P-36

Tectono- Sedimentatary Evolution of Kerala-Konkan Basin: Implications on Hydrocarbon Prospectivity (J. Mishra, Rama Paul, Radha Krishan, B.K. Rath KDMIPE, ONGC, Dehradun) P-37

Tectono-stratigraphic evolution of Gondwana basins of India with an Outline of Coal development (G. Mukhopadhyay, S.K. Mukhopadhyay, Manas Roychowdhury and P.K. Parui) P-38

Neoproterozoic biotic signatures in the peninsular Indian basins-an overview (Mukund Sharma) P-39

Geo-environmental health hazard due to fluorosis in Chittur-Kollengode area, Chittur taluk, Palakkad district, Kerala (C. Muraleedharan and V. Ambili) P-40

Imprints of Neotectonic dynamism in the fluvial regimes of Palghat low-level, Kerala, south India (M.P. Muraleedharan and M.S. Raman) P-40

Structure, tectonics and Quaternary seimentary facies along SW coast of India (K. M. Nair, D. Padmalal) P-41

Tectonic Framework of Eastern Ghats Mobile Belt : an Overview (J. K. Nanda) P-42

Enigma of Eo- and Paleo-Archaean crustal evolution; constraints from Mesoarchaean cratonic parts of India: A review (S. M. Naqvi) P-43

Basin evolution and tectonics of the Krishna-Godavari basin, India (Nirupama Banerjee, M.M. Rajkhowa, Atul Kumar, A.K. Sinha, and S. Prasad) P-44

Study of magnetic data over the Chattisgarh basin and surrounding area (Nisha Nair, S.P. Anand, V.C. Erram and Mita Rajaram) P-45

Late Quaternary coastal evolution of Alappuzha- Kochi coast (Kerala), SW India (D. Padmalal, K.M.Nair, Ruta B. Lymaye, and K.P.N. Kumaran) P-45

Crustal evolution of the Precambrian terrain in the Iritty- Kottiyoor sector in the vicinity of Bavali shear zone of north Kerala, south India (K. R. Pillay, S. P. Bhutia and R. S. Nair) P-46

Fluorine substitution and high-grade stability of amphiboles in the marbles of Ambasamudram, Kerala Khondalite Belt, India (A. P. Pradeepkumar) P-48

Receiver functions in the Kachchh rift zone, Gujarat, with implications for mantle structure and dynamics (Prantik Mandal) P-48

New geochemical and palaeomagnetic results from the dykes of the Bundelkhand craton: preliminary observations constraining the Proterozoic igneous activity (T. Radhakrishna, Ram Chandra, Balasubramonian and Akhilesh K. Srivastava) P-49

Oligocene- Pliocene stratigraphy of India and cycles of relative sea-level change with reference of hydrocarbon occurrences: an overview (D.S.N. Raju) P-50

Geochemistry of the Neoarchaean greywackes: multi-component mixing in a continental island arc (Rana Prathap, J.G. and Naqvi, S.M.) P-51

Paleoclimatic reconstructions through microfossils specially foraminifera in marine sediments: Indian examples (Rajiv Nigam) P-51

Metamorphic petrology: recent advances and future trends in the Indian context (Ram S. Sharma) P-52

Evolution of Eastern Dharwar Craton: New Geochemical and Isotopic Constraints (M. Ram Mohan, Stephen, J. Piercey, Balz, S. Kamber, D. S. Sarma, and S.M. Naqvi) P-53

Recent advances in Dharwar geology (M. Ramakrishnan) P-54

Prydz Bay and Mahanandi basins: Conjugate rift basins of the Gondwana Land (Rasik Ravindra and Dhananjai Pandey) P- 55

Studies on heavy minerals in the sediments of Kayamkulam lake, Kerala -Its implications on sediment sourcing (Reji Srinivasan and K. Sajan) P-55

Mass movements triggered by subsurface pipe flow in the Western Ghats (G Sankar) P-56

Development of Free and Open Source Web-GIS System for 3D Visualization for Geospatial Data (Sarawut Ninsawat, Venkatesh Raghavan, Shinji Masumoto) P-57

Distribution and geochemistry of platinum group of elements (PGE) from Madawara Igneous Province, Lalitpur, Southern part of Bundelkhand massif (M. Satyanarayanan, Singh S.P, Balaram V, Anjaiah K.V) P-58

Pore water pressure as a trigger of shallow landslides in the Western Ghats of Kerala, India: some preliminary observations from an experimental catchment (S. L. Kuriakose, V.G. Jetten and C.J. van Westen, G. Sankar and L.P.H van Beek) P-59

Evolution and crustal growth of Bundelkhand Craton viz-a-viz Southern Indian Cratons (K. K. Sharma) P-59

Ganga plain foreland basin (I.B.Singh) P-61

Investigation on specific site response on ground motion in varied geological formations in and around Kochi city using Microtremor data, Kerala State (H. N. Singh, V. N. Neelakandan and V. Shravan Kumar) P-62

Evolution of Proterozoic foldbelts of NW Indian craton : A plate tectonic- and asthenosphere-driven hybrid model (S. Sinha-Roy) P-62

Bhavani shear extension in Kerala - a significant zone in the crustal evolution of peninsular India (P. Soney Kurien) P-64

The Precambrian Redox evolution of atmosphere-hydrosphere system: An Indian Perspective (B. Sreenivas) P-65

Progress relating to study of fluid inclusions in metamorphic rocks and future direction of research (C. Srikantappa) P-67

Inverted ferro-pigeonites from c-type charnockites, Dindigul, Tamil Nadu (C. Srikantappa and M.N. Malathi) P-69

Metallogeny in relation to Archaean crustal evolution : A study from the Dharwar Craton of Southern India (R. Srinivasan) P-70

Clay mineralogical records of the intra-volcanic bole horizons from the eastern Deccan volcanic province: plaeoenvironmental implications and Cretaceous/Palaeogene boundary (J. P. Shrivastava, M. Ahmad and Mamta Kashyap) P-71

Synthesis of expected ground motion using Semi-empirical Green’s Function approach and its comparison with observed accelerations in Garhwal Himalaya (N. Subhadra, Simanchal Padhy, T. Sesunarayana and R. Vijayaraghavan) P-73

Probable and definitive events that sculpted southern India (K R Subrahmanya) P-74

Radiometric studies along the Southern Coastal Orissa, Eastern India (N. Sulekha Rao, R.Guin, S.K.Saha and D. Sengupta) P-76

K/T boundary extinctions and paleobiogeography of peninsular India: recent advances from Deccan volcanic province (Sunil Bajpai) P-76

Cretaceous – Tertiary boundary mass extinction due to large bolide impact on Earth (V .C. Tewari) P-77

Teris of Southern Tamil Nadu: Holocene climate history (K.P. Thrivikramji, Joseph, S and Anirudhan, S) P-77

GPS Campaign in Palghat Gap Region – Preliminary Results (K. R. Unnikrishnan) P-78

Predicting disasters (Victor Jetten) P-79

A Plate Tectonic Appraisal of the Eastern Ghats Belt, India (K. Vijaya Kumar and C. Leelanandam) P-80

Evolution of the Western Ghats (Sahyadri), Western India (M. Widdowson) P-81

Magma emplacement in central Indian tectonic zone –An evidence for large scale crustal growth and

recycling during Proterozoic: a reviewAbhinaba Roy

Geological Survey of India, KolkataE-mail: roy_abhinaba@yahoo.co.in

The Precambrian crust of Central India comprising Bundelkhand Craton (BKC) in the north andBastar Craton (BC) in the south was accreted along the ENE-WSW trending Proterozoic Central IndianTectonic Zone (CITZ). Both the cratons evolved independently at least up to late Archaean – earlyProterozoic time. According to the plate tectonic model (Roy and Prasad, 2003) a northward dippingsubduction system leading to continent-continent collision during Mesoproterozoic (c. 1.1-1.4 Ga)explains the growth and assembly of the different lithotectonic units comprising the supracrustal beltswith associated mafic-ultramafic rocks, gneisses, granites and a few linear tracts of granulites within theCITZ. Lithological and tectonic characteristics, metamorphic history along with the availablegeochronologic data from CITZ is correlatable with global Grenvillian orogeny. Magmatism along collisionalorogens are characterized by varied source components as well as melting conditions. The releasedmelts, both juvenile and crustal derived, advects heat to the middle and upper crust. These possibilitieshave been tested in CITZ, which shows significant growth and recycling of continental crust due mainlyto large scale mafic-ultramafic and felsic magmatism. While there is significant involvement of mantle-derived melts in the generation of mafic-ultramafic rocks, and calc-alkaline granitoids (Patino Douce,1999) crustal thickening in the collisional zones on the other hand leads to melting in the lower crust.Emplacement of mafic-ultramafic rocks in different tectonic domains within CITZ has already been discussedby the author elsewhere (Roy and Chakraborti, 2008 in press).

Subduction of the Bastar Craton below the Bundelkhand Craton and consequent continental collisionand attendant suturing is closely associated with the emplacement of significant volumes of mafic-ultramafic rocks in the Central Indian Tectonic Zone. They are distributed in three main tectonic localesdefining the suture zone, magmatic arc and back arc regions (1) The suture zone is marked by theRamakona-Katangi belt (RKG)) containing mafic granulites (metagabbro) of tholeiitic composition. Thepeak metamorphism in RKG belt is presumed to be pre - 1.1 Ga, followed by a steep decompressionalevent during ~ 1.1 Ga (Roy, Abhijit et al. 2006), (2) The magmatic arc continental margin is representedby the emplacement of Betul belt bimodal volcanics and intrusives of mafic and ultramafic composition,metamorphosed to greenschist-amphibolite facies. Although the complete sequence is not preserved thePadhar ultramafic-mafic complex in the Betul belt bears close resemblance with known layered complexes,(3) The back arc region comprises mafic volcanics together with intrusives of ultramafic and mafic rocksof the Mahakoshal belt. Gabbro and dolerite dykes accompanying the volcanics are abundant in theMahakoshal belt, indicating riftogenic setting characteristics of back are basins. In addition, there wasemplacement of a suite of mafic dykes, subsequently deformed and metamorphosed during amphibolitefacies reworking of the Tirodi biotite gneiss of the Sausar Mobile Belt, which coincides with the mainSausar Orogeny (c. 8.0-9.0 Ga).

Collisional environments are characterized by abnormal crustal thickness, synkinematic granitesand thrust tectonics signatures. A granitic rock derived from a variety of sources, mainly due to crustalreworking is a common feature to many collisional belts. Presence of several ductile shear zones in CITZprovided avenues for syntectonic granite emplacement. They are often closely associated with granulites.Mahakoshal belt, bounded by Son-Narmada North Fault (SNNF) and Son-Narmada South Fault (SNSF), ischaracterized by two periods of granite activity accompany with deformation and metamorphism of thesupracrustal assemblages. They include: (i) The Jhirgadandi pluton, Renusagar-Rihand dam granitoidsand Muirpar granites: (c. 1.75 + 0.1 Ga), and (ii) the Dudhi granite gneiss: (c. 1.5 Ga). Jhirgadandipluton is calc-alkaline to alkaline in nature, represented by monzodiorite-monzonite-quartz syenitesuite of rocks. Renusagar-Rihand dam granite is peraluminous and calc-alkaline in nature, representedby quartz diorite granodiorite-adamellite. While Muripar granite is granodiorite to adamellite, Dudhigranite is adamellite to granite in composition. Wide variation in ISr ratios (0.7078-0.7132) indicate

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both juvenile and crusted inputs (Sarkar et al. 1998). Granite emplacement along SNSF is interpreted torepresent a convergent margin setting. There is a progressive increase in ISr with time (0.70398 to0.71543) implying increasing role of crustal component in the genesis of the granitic rocks. The risinggranitic plutons along ductile shear zones (SNSF) caused advective heat transfer to the middle andupper crust and created relatively higher temperature conditions of metamorphism in Mahakoshal belt atlower pressure. In the Betul belt a few ENE-WNW trending sheet-like bodies of granite are emplaced(c.1.5 Ga) as syntectonic intrusives along oblique-slip ductile shear zones. Dioritic rocks occur as smallbodies in association with mafic-ultramafic rocks.

Several phases of synkinematic granites are emplaced (c. 1.1. Ga) as concordant sheets along theENE to WNW trending Tan Shear Zone (TSZ). Compositionally they fall mainly in the granite field with rarevariants of granodiorite and alkali-feldspar granite, showing calc alkaline affinity. Textural and structuralcharacteristics indicate simultaneous emplacement and deformation at moderate depth under compressionaltectonic regime. Geochemical characteristics are suggestive of melt derivation from a hybrid pelite-basalt source. Synmetamorphic calc-alkaline granite magmatism and contractional structures are verywell documented along Tan Shear Zone, latter representing a typical transpressional tectonic regime inan overall convergent-cum-collisional tectonic setting. Synchronous with the Sausar Orogeny (c.1.0-0.9 Ga) granitic magmas derived mainly from the older recycled crust were emplaced in the Sausar belt.

It is envisaged that there are two major episodes of granite magmatism in CITZ. The earlier one(c.1.8-1.5 Ga), melts derived from both mantle and crustal sources, is conspicuous in the northern part(viz. near SNSF and in Betul Belt) coinciding with the onset of subduction. This event is possibly coevalwith the emplacement of voluminous mafic-ultramafic rocks in Mahakoshal and Betul belts. The later eventof granite magmatism (c.1.2-0.9 Ga), melts derived from recycled thickened continental crust and channeledmainly through TSZ, took place during the continent-continent collision and immediately following it.

Himalayan mountain building and fragile ecosystemProf. Anshu Kumar Sinha

Former Director BSIP,LucknowB602, VIGYAN VIHAR,Sector 56,

Gurgaon 122003, Haryana.E-mail: anshuksinha@gmail.com

The Himalayan arc extends about 2,500 km from northwest to southeast incorporating from westto east the loftiest peaks,viz., Nanga Parbat(8,125m), Everest(8,848m), and Namcha Barwa(7,755m).Thewidth of the belt varies from 250-350 km.The mighty Himalayas and the Karakoram ,embodying thelargest concentration of lithospheric mass, grew south of the Pamir.The Himalayas consist a fascinatinggeological record of Precambrian to present and terminate both east and west with spectacularsyntaxial bends.

The collision of India with Asia is the most facinating event to have occurred in the past 100Ma.It is responsible for uplift of the Himalayas and Tibet and rejuvenating tectonic architecture of Karakoramand Kun Lun,thus resulting changes in the Earth’s orography and consequent climate change aredirectly tied to this ongoing collisional event.This collisional event has been argued for long to haveresponsible for geological, geochemical and climatological consequenses of global extent. The upliftingprocess is still going on with the approximate rate of one cm. per year with continued erosion anddenudation. The eroded material from its rugged topography is repeatedly and regularly being shedinto different depositional settings within the Himalayas to Bay of Bengal Arabian Sea by youthful rivers drainage network.

Global warming responsible for recession of Himalayan glaciers at alarming rate is a serious matterof concern for the survival of humal civilization in the Indo-Gangetic plain.

The stress and strain caused due to plate motion is responsible for frequent earthquakes in thisregion making enormous loss of human life.

Key word: Himalayas, Global Climate, Plate Tectonics, Human survival

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Evolution of the Indian shield – imprints from magnetic dataS.P. Anand and Mita Rajaram

Indian Institute of Geomagnetism, Navi Mumbai – 410 218.E-mail: aerospl@yahoo.co.uk

The surface cover often obscures the sub-surface extension of the surface geology and it is in thiscontext that the aeromagnetic data can play a very crucial role in delineating the sub-surface structures,thereby throw light on the evolution of the Indian sub-continent. From the available aeromagnetic dataon a reconnaissance scale, an aeromagnetic anomaly map of Peninsular India (from 8°N to 25°N) iscomplied. The cratons, major tectonic units & their sub-units, structural features etc are clearly broughtout in the anomaly map. Major magnetic sources in the Peninsular India are related to iron ores, schistbelts, dykes swarms, high grade granulites and mineralized zones along faults. The Euler solutions depictthe block structure and fractured nature of the Indian Crust. Aeromagnetic data of Peninsular India wasdivided into several windows each with dimensions varying from 400km X 400km to 500km X 500km anddepth to bottom of the magnetic layer (Cuie Isotherm Depth) computed. Since aeromagnetic data wasnot available above 25°N, we utilized the available Magnetic Lithospheric Model (MF5) derived fromChamp Satellite data over the sub-continent and using an iterative forward modelling approach calculatedthe Curie Isotherm Depth for the whole sub-continent. Regions of exhumed crust and mobile belts showa thinner magnetic crust than the cratons, in both the derivations. The derived Curie isotherm depthmap is in accordance with the basic structural trend of the major tectonic units within the Indiansubcontinent. The curie isotherm along the EEW trending CITZ (including the Narmada Son Lineament)appears to divide the Indian subcontinent into northern and southern block with the structural trendsin the northern block being essentially ENE-WSW (Bundelkhan- Vindhyan ), the blocks to the southbeing NW-SE (related to Bastar , Deccan, Singhbhum); further, the blocks to the west along the Marwarblock and to the east along the EGMB show a NE-SW trend all in keeping with the basic structural trendof the Indian subcontinent. We further utilize the 1D conductive, steady state heat flow model for thecontinent, to calculate the heat flow associated with different tectonic units of the Indian sub-continentand prepared a proxy-heat flow map of the country incorporating thermal conductivity from the publishedliterature. . The proxy heat flow map can be divided into three zones; zone-I with heat flow values lessthan 35mW/m2, zone-II with heat flow values larger than 56mW/m2 and zone-III with intermediatevalues, with zone-I corresponding to the cratonic regions and Zone-II representing the mobile belts,Mesozoic sedimentary basins and collision zones. Also an attempt has been made to compare the heatflow values thus calculated with the actual heat flow measurements and the results were explained interms of the conductive and advective heat flow. Results of these will be presented.

Frontiers of metamorphism: influence on evolution ofsouthern Indian shield

Anand MohanDepartment of Geology; Banaras Hindu University

Varanasi – 221 005E-mail: anand.abhu@gmail.com

Earth evolution is mostly the consequence of dissipation of Earth’s heat through time. This involvesseveral phenomena, but the wide-ranging study of pressure-temperature-time variation in the rockrecord (ie, metamorphic petrology) is obviously the key. Tracking the pressure-temperature-deformation-time (P-T-D-t) history of individual rocks in tectonic belts (mountain belts, subduction complexes),and comparing such histories among rocks from diverse parts of the same belt (eg, across metamorphiczones, faults) and among different belts, helps us understand the tectonic processes that have shapedEarth’s lithosphere. Frontier areas of focus in Metamorphic Petrology concern the understanding thenew findings of ultrahigh temperature metamorphism (UHTM, cf. Harley, 2008; Kelsey, 2008 and referencestherein), ultrahigh pressure metamorphism (UHPM, cf. Dobrzhinetskaya & Green, 2007 and referencestherein) and characterization of their respective P-T-t paths with major implications for rheological and

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chemical behavior of deep crustal rocks during orogenesis. Researches in the cutting edge of metamorphicpetrology focus on the crustal architecture and tectonometamorphic evolution of orogens; characterizationof P-T-t paths and exhumation of lower crustal rocks; influence of lithospheric thickness variations oncontinental evolution (McKenzie & Priestley, 2007) and role of high temperature dehydration melting(Brown & White, 2008); fluids in Precambrian deep-crustal metamorphism (Ohyama et al , 2007); refinementof internally consistent thermodynamic databases (Holland and Powell, 1998 with updates of 2008)and breakup and assembly of super continents (Muller 2007; Kumar et al., 2007; Brown, 2007).Metamorphic petrology is thus an integral component of the interdisciplinary study of lithosphereevolution through time.

The splendid heritage of high-grade granulites, covering large tracts in southern India, providesan exclusive nature’s laboratory in which to study relationship between UHTM, tectonics and magmatismduring orogenesis (Prakash et al 2006, Mohan, 2002; 2003, 2004). Metamorphic community world overhas vigorously persuaded researches on southern Indian granulites for last several years and significantlyadded to our knowledge towards building a holistic model for geodynamic evolution of polycyclic andpolydeformed granulites, in space and time. The continued international researches on the granuliteterrains of southern India have gained further impetus from International Lithosphere Program (ILP),Lithospheric evolution of Gondwana East from Interdisciplinary Deep Surveys (LEGENDS), UNESCO-IUGS-IGCP-368 and 440 programs. Memoirs of the Geological Society of India, viz; Tectonics of SouthernGranulite Terrane: Kuppam – Palani Geotransect (Ramakrishnan, 2003); Milestones in Petrology and futureperspectives (Mohan, 2003); Indian Continental Lithosphere: emerging research trends (Mahadevan et. al.,2003) besides Geological Society of London, Special Volume 206, 2003); Glimpses on Geosciences Researchin India by INSA (Singhvi and Bhattacharya, 2004); The Indian continental crust and upper mantle (Eds.Leelanandam et al 2007, special issue of Gondawana Research), New perspectives in the study of thePrecambrian continental crust of India: An integrated sedimentologic, isotopic, tectonometamorphic andseismological appraisal (Eds. S. Dasgupta, M. Raith and S. Sarkar (Special issue of Precambrian Research,2008) provide insights on the important outcome of developments in respect of deep continentalstudies vis-à-vis petrology of the southern Indian granulite corridors at the home front. Yet, significantpotential of SHRIMP, IDTIMS and LA-ICP-MS techniques capable of producing high resolution resultsremain largely untapped in southern granulite terrain and Eastern Ghats granulite belt. There is a needto calculate phase diagrams rapidly and automatically to allow experimentation in modelling naturalrocks (different chemical systems; different bulk compositions). Future areas of research call for improvingour most important tools to address questions of linking protolith ages to metamorphic events, exhumationand cooling rates pertinent to Precambrian terrains of South India. The study on tiniest relics in UHProcks (coesite, Sachan et al., 2004) and in UHT rocks (titanium in quartz, Sato & Santosh, 2007) isprojected to generate a nanoscale revolution in Earth Sciences (Mohan, 2005; Hochella, 2008).

Uranium and thorium metallogeny in India: A tectonic perspectiveAnjan Chaki

Director, Atomic Minerals Directorate for Exploration and Research,Hyderabad 500016, India

E-mail: director.amd@gov.in

Uranium metallogeny, being quite wide spread in the Precambrian and Phanerozoic of peninsularand extra-peninsular India, correlates well with the globally recognized time-bound nature and offer excellentinsights into crustal evolution and continental geotectonic reconstructions. The mineralisation is identifiedin several regions, in which the rocks of one or more successive ages are enriched in uranium above normalabundances, such as: (i) Singhbhum province, (ii) Dharwar province, (iii) Aravalli – Delhi province, (iv)Northwestern Himalayan province and (v) Shillong province. A number of deposits have been proved in theabove provinces, some of which are being mined or under various stages of development.

World-wide uranium metallogeny has resulted in very large deposits of up to few hundred thousandtonnes of metal in each of a number of deposits with a large spread in space and time, as well as

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concentration reaching up to 20% or more. These deposits are grouped into as many as fifteen types,delineated by a combination of dominant geological characteristics, such as host rocks and structuralsetting and generally agreed upon processes of ore genesis. However only seven deposit types – Quartzpebble conglomerate (5.43%), Unconformity related (11.69%), Vein (5.84%), Metasomatite (12.14%),Intrusive (5.18%), Iron Oxide Breccia Complex (16.23%) and Sandstone type (27.44%) – account forthe vast majority of world’s known resources of 5.55 million tonnes. In India the present status is thatVein (56.00%), Unconformity related (12.00%), Stratabound type (13.00%) and Sandstone type (17.00%)account for about 1,16,377 tonnes of uranium resources, a picture that may change in future, in favourof Unconformity and Sandstone type deposits.

The time-bound character of uranium metallogeny is now understood to have been constrainedby five major periods, viz., (i) before 2800 Ma: when uranium was fractionated into the upper crustduring late Archaean – Early Proterozoic cratonisation processes with formation of granite terrenes,which provided uranium for subsequent mineralising events; (ii) 2800 – 2200 Ma: cratonisation allowingthe formation of long lived basins and low atmospheric oxygen levels permitting uraninite to be transportedand concentrated as placer deposits; (iii) 2200 – 1200 Ma: atmospheric oxygen built up allowinguranium to be transported in solutions as uranyl ions and subsequently precipitated in marine shelfsediments or at the base of unconformity with overlying continental clastics; (iv) 1200 – 400 Ma: finalmineralisation in some important deposits as well as with alkaline magmatism and Pan-African andBrazilian events; and (v) 400 – 0 Ma: incorporation of organic material into continental clastic sedimentsallowing uranyl ions to be precipitated as sandstone type deposits.

Cratonisation was mostly complete by Ca 2500 Ma, which was followed by a period ofdifferentiation within the crust, that carried uranium to upper most crust, a process which was completedgenerally before 2200 Ma. After the formation of rigid lithosperic plates by this time, extensional basinsstarted developing, with higher rate of fault-controlled and thermal subsidence and enhanced heat flow,where huge thickness of sediments were deposited over the uranium rich upper crust. Even though therewere significant amounts of oxygen in the atmosphere during 2800 – 2200 Ma, reducing conditionswere sufficiently high for detrital transport, deposition and preservation of uraninite derived from LateArchean potassium rich granites, as seen in the Quartz Pebble Conglomerate type of deposits in ElliotLake, Canada and Witwatersrand, South Africa. The first phase of uranium metallogeny in India, is alsoassociated with the oligomictic conglomerates underlying the volcano-sedimentary piles as in Dharwarand Singhbhum cartons, which are derived from the granitoids in the basement.

A major change in mode of transport of uranium happened Ca 2200 Ma due to rise in levels ofatmospheric oxygen, which released uranium in solutions due to chemical weathering of Late Archaeangranites and were transported as uranyl ions. During the period 2200 – 1200 Ma some amount of theuranium were precipitated in shallow marine and lagoonal sequences, which also had substantial amountsof organic matter, to form large deposits as in Oklo, Gabon and also as hydrothermal vein type depositsclosely associated with the marine sediments as in Beverlodge, Canada and Schwartzwalder, USA. Howeverthe most economically significant Unconformity related deposits are formed during this period at ornear to the unconformity between the lower marine sequences (Early Proterozoic) and overlying thicksequences of continental sediments (Middle Proterozoic) as in Athabasca basin, Canada and Pine CreekOrogen, Australia. Circulating hydrothermal solutions in the upper continental clastics and the lowerbasement marine sediments with intrusive granitic bodies are responsible for the high grade mineralisationat the unconformity. This period is also marked by phreatomagmatic volcanogenic process during ~1600– 1500 Ma that have resulted in Iron Oxide Copper Gold (IOCG) deposit in Olympic Dam, Australia, whichis the single largest deposit of uranium hitherto discovered. The deposit is associated with a majormagmatic event, that included outpouring of extensive volcanics and synchronous uranium rich graniticintrusions which hosts the deposit.

In India the major episodes of uranium metallogeny, represented as unconformity related, vein,stratabound and metasomatic types in different provinces, during the Early – Mid - Late Proterozoic, are

6

even more closely associated to the widespread granitic activity in all the continental nuclei of India,viz., Dharwar, Singhbhum, Aravalli and Central India. In the Singhbhum Shear Zone, where polymetallicvein and stratabound types of mineralisation coexist, a possibility of unconformity related settings hasbeen mooted by some workers. Vein type of mineralisation is also seen the Central Indian and Aravalliprovinces. Structurally controlled metasomatic mineralisation in North Delhi Fold belt in Aravalli provincealso has some gross similarities with the above mineralisation. Central Himalayan crystallines and associatedquartzites also have some cases of vein type of metallogeny, which needs to be synthesized with that ofthe peninsular India. In all the above cases, uranium enriched granites intruded in the basementcomplex are envisaged as direct or indirect sources of uranium, from where uranium was mobilised in afavorable geotectonic regime, through structural pathways.

Unconformity related mineralisation has been established in the Srisailam and Palnad sub-basins ofCuddapah basin and in the Bhima Basin, whereas encouraging indications are forthcoming from Papaghnisub-basin of Cuddapah basin and also from Kaladgi basin. In all the above cases the association offertile uraniferous granites are particularly remarkable, as the continental or marginal marine sequencesdirectly rests over uranium rich granites. A few more Proterozoic basins such as the Chhattisgarh-Indravati-Abujmarh, Vindhyan-Bijawar and Shillong basins are identified as having potential for hostingsuch mineralisation. The uranium mineralisation along a 180 Km long belt in Vempalle dolomiticlimestones, along the southern and western margin of Cuddapah basin, occur in this time frame with astratabound nature, and is also related to the fertile basement granites of Ca 2500 – 2200 Ma.

The 1200 – 400 Ma period is associated with alkaline complexes, pegmatites such as the gabboric– alkaline magmatic suite of Greenland, and Pilanesberg Complex, South Africa which are mostly associatedwith vast potential reserves of not only uranium, but also thorium, REE, zirconium and other metals. Themagmatic activity associated with Pan-African and Brazilian events are responsible for alaskite hostedRössing deposit, Namibia, vein type mineralisation in Zambia – Zaire copper belt and Jaquaribeana foldbelt and Serido geosyncline, Brazil. Thorium metallogeny as thorianite in Sri Lanka and as uranothorianitenear Fort Dauphin, Madagascar are also notable. In India the alkaline complexes of southern and easternIndia are associated with uranium, thorium, rare metal and rare earth element metallogeny, which thoughsub-economic are very significant in terms of deciphering the crustal tectonics of the period.

Higher oxygen in the atmosphere from Silurian onwards permitted evolution of land plants andthus it became possible for organic material to be incorporated into continental clastic sediments,which proved to be good hosts for uranium mobilised from granitic source rocks. Continental sedimentsof Mesozoic – Cenozoic age are host uranium in North America, Central Asia, and Mongolia, as wells as inthe Gondwana sediments of Australia, Africa and South America. Uranium metallogeny of this period inIndia include that of Late Cretaceous Mahadek basin in northeastern India and the widespreadmineralisation, though of low grade and fragmented, in the Tertiary Siwalik basin of the Himalayanfoothills. In Meghalaya, the Ca 550 Ma granites have directly provided uranium rich solutions to thecontinental sediments, deposited in a peri-cratonic rift related basin, where the tectonics duringsedimentation provided conducive environment for influx of oxygenated solutions and to precipitate itin the redox interfaces. Extensive Gondwana sediments are also being investigated for similar type ofmineralisation. Alkaline magmatism during Late Mesozoic – Cenozoic in northeastern and western India,related to Gondwana breakup are also associated with uranium, thorium and REE metallogeny.

Thorium mineralisation is not as wide spread in time, but is very abundant and widely dispersed.World’s estimated 6 million tonnes of thorium resources occur in carbonatites (31.26%), placer (24.68%),vein (21.39%) and alkaline rocks (18.43%) and are distributed widely in Australia, USA, Turkey, India,Venezuela, Brazil and other counties. The abundant monazite resources of India, estimated to be 10.21million tonnes with recoverable thorium of 319,000 tonnes, is found in association with an estimated883.69 million tonnes of heavy minerals, including ilmenite, rutile, leucoxene, zircon, garnet andsillimanite. This is of Recent beach placer origin, sourced from the Archaean – Lower Proterozoicprovenance and related with the modern coastal evolution, conducive for the mechanical concentrationsof heavy minerals.

7

Thus it quite evident that uranium rich ‘hot granites’, emplacement during various tectono – magmaticevents that punctuated the diverse tectonic provinces of India, are not only the primary sources ofuranium, but possibly are also the sources of radiogenic heat that provided the thermal gradients requiredfor mobilization and transport of uranium. This time bound metallogeny seen world wide, are also closelyrelated to formation and break-up of super continents from Ur through Rodinia and Pangaea. As with thereconstruction attempts based on different elements of geodynamics and geochemistry, metallogenic provincecorrelations will offer valuable tools in understanding the crustal evolution in a holistic way and offervaluable insights into the crust – mantel – core interactions, mantel heterogeneity and their role incrustal evolution. Moreover a through understanding of the tectonic history of the Indian sub-continentvis-a-vis uranium and thorium metallogeny will have a direct bearing on the exploration and discovery ofnew richer and larger deposits of these important fuel metals.

Dinosaurs of India: Dead but well!Ashok Sahni

Centre of Advanced Study in Geology,Panjab University, Chandigarh-160014

E-mail: ashok.sahni@gmail.com

It is generally not well known that dinosaur fossils from India provide a unique perspective ontheir own evolution as they represent a long lineage starting from some of the oldest records in theworld in the Triassic to the time of their extinction some 65 million years ago. As presently known, thedinosaurs of India have a close relationship to those from Madagascar and South America rather than toLaurasia. In addition, they provide excellent data on reproductive physiology as the Indian LateCretaceous outcrops of the Lameta Formation represent one of the most spatially extensive dinosaurnesting sites in the world both for the plant- and meat-eating dinosaur groups. Furthermore, theirexcreta preserved as “ coprolites “ in and around the village of Pisdura in Maharashtra indicates thenature of their diet and how large cold-blooded reptiles were able to digest their food. This informationhas helped in reconstructing palaeo-environments specially during the latest Cretaceous when the earthwas devastated by catastrophic events in the form of a large asteroid hit and one of the most extensive,intense volcanic activities known on planet earth. Two sections in western India (Anjar) and north-eastern India (Um Shorengkew) have anomalous high spikes of the element iridium at the time of theworld-wide extinction of dinosaurs and 65% of other life forms suggesting that the asteroid fallout mayhave reached the Indian landmass as well.

Near collisional phase of the Indian plate: biotas and palaeogeographyAshok Sahni

Centre of Advanced Study in Geology, Panjab University, Chandigarh-160014E-mail: ashok.sahni@gmail.com

During the last two decades, considerable attention has focused on the regional and global eventsthat have controlled the evolution of Indian biotas and the marked changes in South Asianpalaeobiogeography. These include a surface contact with the Madagascar-South America landmass complextill the Late Cretaceous while active drift was underway; the intense Deccan Trap activity with marinetransgressions again along the major rift systems in the Deccan Volcanic Province; the separation of theSeychelles from the western Indian margin at about the same time with unique present day organisms onboth blocks that pre-date the separation; the global Initial Eocene Thermal Event (IETM) and similar minorevents at the Palaeocene-Eocene Boundary and in the Lower Eocene, increasing biotic endemism as theIndian Plate an island subcontinent with a concomitant rise in marginal lignite deposits both in Pakistanand the western and north-eastern Indian margins; and lastly, on collision, the crossing over of centralAsiatic forms into the Indian Plate and the reversal of drainage in this region as the Himalaya elevated.

8

Some facts about the sutures of continental cratons that constitute theIndian subcontinent and the myth of their selective underplating

D.N.AvasthiC-190, Sarita Vihar;

New Delhi - 110 076.E-mail: dnavasthi@hotmail.com

The agglomeration of cratons, which constitute the Indian subcontinent vary in geologic agesranging from Archaen to Miocene. This provides a great opportunity to study and understand themechanism of inter-plate interactions in the context of plate tectonics. Seismic imaging of the crustsof these cratons and their junctions by the scientists of National Geophysical Research Institute througha number of controlled source seismic profiles has exploded the myth of one plate subducting underanother in case of collision of continental plates. They have established that at the collision margin, thecrusts of the colliding plates do separate at lowermost and uppermost crustal segments. While the lowercrusts of both the plates subduct into the subcrustal mantle, the upper crustal segments rise togetherto form elevated plateaus like Tibet. With the passage of time, the plateaus get eroded and deposited,as for example,the case of Vindhyan and Marwad basins of Proterozoic age. The plateau may get totallyeroded as in the case of Southern Granulite Terrain (SGT) of Archaen age. In fact, the SGT is a complexconglomeration of more than two colliding cratons and 3 to 4 collisions appear to have taken place inPre-Cambrian times. Thus SGT is not only a conglomeration of Archaen cratons but also of multiplemobile belts, of which two are prominent. From these considerations, the subduction of a gradualsliding underplate below the over-riding plate in the collision of continental plates is ruled out. Subductionof lower crustal segments of colliding plates into mantle below takes place at a sharp angle and in slabs,which periodically get detached from the subducting crustal segments.

The physico-chemical properties of the lower crust sharply contrast with those of upper mantleleading to a well=defined boundary in a vertical section of the property of acoustic impedance of thecrust and upper mantle. Any departure from this contrasting picture of acoustic impedance at the crustmantle boundary observed in the regions of mobile belts and in continental deposits over fractured thinoceanic crusts has so far been explained as underplating of the continental crust, without justificationof the physico-chemical process involved, if any. But laboratory experiments of Trubitsyn et al, (2006)and Kincaid and Griffiths (2003), as also a global analysis of S-wave seismic anisotropy by Long andSilver (2008) have demonstrated that the phenomenon of mantle flow around sinking slab as well ascorner flow can bring about the change in the physical property of sinking slab. In this manner, in thecase of conventional model of plate subduction of oceanic crust under another oceanic crust or undera continental crust, the subducting slab gets transformed into a layer having the property of acousticimpedance intermediate to the lower crust of the continental plate and upper mantle. Replumaz (2004)has indicated the existence of such roll back of the mantle about the subducting lower crust of thecontinental plate in south and southeast Asia. The manifestation of this layer in the controlled sourceseismic sections across the mobile belts appears to have led the geophysicists to imagine some sort ofunderplating of the continental crust. However, it has not been possible to explain the selectiveunderplating under mobile belts only, while the same continental crusts overlying the upper mantle atother places show distinct physical properties of lower crust and upper mantle, with no intermediatelayer in between. It is high time that the untenable concept of selective underplating of the continentalcrust is given a decent burial.

Nellore-Khammam schist belt- a plate tectonic modelV.R.R.M. Babu, Andhra University, Waltair, Visakhapatnam-3.

E-mail: vrrmbabu@yahoo.com

The NKSB (L, 600km; W, 5-40km; A, 13,000sq.km) outcrops in Nellore, Chitoor, Praka- sam, Guntur,Krishna & Khammam districts of Andhra Pradesh as a continuous belt & in some places as enclaves in thegranitoids, pegmatites & other intrusives. It is bounded by the EGGB in the east & Cuddapah Basin

9

(CUB) & granitoids in the west. The rock types are meta-pelites, meta-sammites, mafic schists, meta-volcanics etc, which were metamor -phosed to amphibolite grade. The localities that drawn much attentionare- Kandra Igne-ous complex (KIC), Nellore Mica Belt (NMB), Vinjamuru Acid Barium Volcanics, Praka -sam Mafic & Alkaline Province (PMAP), & Chimalapadu Anorthosite Complex (CAC). The NKSB was deformedmore than once. The amphibolite recorded the protolith age- 3.6-3.3Ga. The rocks were metamorphosedto amphibolite grade at ca.2.6Ga when Grea -ter India (GI) was part of the super-continent, Ur (ca.2750-2400Ma). In the NKSB, the granitoids crystallized at a depth of >7km between 2.6 & 2.2Ga, i.e. in thepre-rift & rift stages of Ur & early Wilson Cycle-IV (2.4-1.8Ga). The granitic pegmatites in the NMB wereemplaced at a depth of ~7km in the folded amphibolites, quartz-mica schists & quar -tzites before 2.2Ga. The NKSB formed basement &/or boundary to the CUB between 1.95Ga & 1.6Ga when GI was part ofthe super-continent, Columbia/Nuna (C/N; 1.8-1.5 Ga). The ages1.8-1.6Ga, obtained from minerals &rocks from the CUB, NKSB & EGGB were record of forces & fluxes acted on this region when GI was part ofC/N. The second metamorphic event identified in the Ongole (1.6-1.5Ga) & Vinjamuru areas was the resu-lt of westward thrust of the EGGB & NKSB that ended the deposition in the Nallamalai sub-basin in theCUB when GI was part of C/N. The NKSB & granitoids became the basement to the Godavari Pakhal Basinat ca.1600Ma. The emplacement of syenitoids in the PMAP & EGGB, lamproites (Ramannapeta, Kotakonda,Chelima) took place bet-ween 1.5 & 1.4Ga i.e., in the Early Wilson Cycle-III (1.5-1.05 Ga). The 1.3-1.2Ga ages obtained from syenitoids in the PMAP, minerals & rocks from the NKSB & EGGB indicate therift of C/N Gondwana followed by C/N East Gondwana whereas, the 1.1-1.0Ga ages are evidence for theGrenvillian Orogeny, which was associated with the coalescence of Rodinian East Gondwana, Gondwana& finally, Rodinia (1.05-0.8Ga). The 800-600Ma ages of the minerals in the NKSB indicate the affect ofthe rift of Rodinia whereas, 600-500Ma ages are related to the coalescence of Pangaean East Gondwana,Gondwana & finally, Pangaea (320-230Ma). The westward thrust of the EGGB & NKSB resulted in thecessation of deposition of the Kurnool Group at ca.530Ma. The 400-200Ma ages obtained from theminerals in the NMB indicate the affect of forces & fluxes associated with Pangaea & its rift at ca.230Ma.The Jurassic planar surface in the EGGB & red beds identified in the ONGC drill holes are evidences forupliftment & corresponding break in the deposition in the region. The NKSB became basement to theChennai-Sriperumbudur Gondwana Basin at ca.160Ma. From the East Gondwana the Indian plate rifted &drifted & joined the Australian plate at ca.53Ma. Finally, the present statuses of the NKSB & EGGB,development of the Pennar-Krishna-Godavari Sedimentary Basins were closely related to the collision ofIndo-Australian plate with the Asian & adjacent plates.

Geo-informatics for geology and tectonic mapping inKammbam valley, Tamilnadu, India.

G.BalamuruganCentre for Remote Sensing & Geoinformatics

Sathyabama University; Chennai.E-mail: remotebala@gmail.com

The purpose of the present work was to evaluate the effectiveness of Geoinformatics techniques inorder to improve the harmonization of the cartographic information, as well as to reconstruct the mostdominant geology and tectonic features of the region with unique criteria. For this objective, opticaldata, collected from sensors onboard of Landsat-7 ETM+ image was used. In this study, image processingmethods such as principal component analysis, decorralation Stretch and Band ratio methods wereapplied to highlight lithological features of the Study area. Additionally, SRTM- DEM analysis was alsorealized to expose structural features of the Study area. The anaglyph image produced from Landsat -ETM+ and DEM data has been found as the most suitable method in the visual interpretation of thestructural elements. SRTM data is quite effective in the identification of the most important tectonicstructures, with less detail than optical information, and enhancing the recognition of some olderstructures not so well defined in the optical bands. The results are being checked by the ground-truthstudies. It is possible identify clearly the effects of the extensional tectonic on the satellite images byvisual interpretations based on knowledge. The faults of the neotectonic period of the region can be

10

distinguished clearly, and it is perceived that the motion to the NE-SW direction in general forms theactive tectonics in the region.

The emerging pattern of crust-formation and recycling history in thePrecambrian Dharwar craton and the southern granulite terrain, southern India:

constraints from recent geochronological and isotopic resultsY.J. Bhaskar Rao

National Geophysical Research InstituteHyderabad-500 606, India

E-mail: bhaskarraoyj@ngri.res.in

The Precambrian crust of southern India(Fig. 1) is divisible into two principal regionsbased on grade of metamorphism: 1) the low-to medium- grade granite-greenstone terrainof the Dharwar Craton and 2) regions ofmainly granulite facies rocks, the SouthernGranulite Terrain (SGT) and the Eastern GhatsGranulite Terrain (EGGT). The former regionis divisible into the western and eastern partsof Dharwar Craton (WDC and EDC), which areseparated by the faulted eastern boundaryof the Chitradurga supracrustal belt (CSB).Asreviewed here, the geochronological databased mainly on a combination of wholerockRb-Sr, Sm-Nd and Pb-Pb isochrones and alimited set of zircon U-Pb concordia establisha broad pattern of chronology of majormagmatic and metamorphic events, while Sr,Nd and a small preliminary set of Zircon-Hfisotopic compositions help in tracing eventsof juvenile crust formation and recycling.

The WDC and EDC comprise Archaeansupracrustal belts surrounded by Archaeangneisses and granitoids. The gneisses of theWDC are predominantly tonalite-trondhjemite-granodiorite (TTG), while thoseof the EDC are essentially granodiorite togranite. These constitute a polyphaseassemblage that developed between ca. 3.4Ga and 2.5 Ga. Rocks > 3.0 Ga seem to berestricted to the WDC as there is noconvincing evidence for units > 2.8 Ga in the EDC. U-Pb ages for detrital zircons from metasediments ofthe HSB indicate felsic protoliths upto ca. 3.6 Ga [1], but evidence for rocks of this antiquity is lacking.One of the oldest crustal nuclei of the craton is around the Holenarsipur supracrustal belt (HSB,fig.1).However, temporal and spatial relationships between the supracrustal rocks and the closely associatedoldest gneisses remain inconclusive. This region preserves the oldest yet dated TTG gneisses of ca. 3.33Ga (the Gorur gneiss) and the HSB supracrustal rocks have also yielded a similar age[e.g.,2,3].Elsewherein the WDC, the numerous large tracts of supracrustal assemblages are unequivo cally ensialic and thereis evidence for their deposition between ca. 2.9 and 2.6 Ga. A popular stratigraphic model [4] refers tothis supracrustal association as the ‘Dharwar Supergroup’, which is divisible into the lower ‘BababudanGroup’ and an upper ‘Chitradurga Group’, each comprising several Formations based on unconformable

Fig.1. Simplified geological sketch of Southern part of India shield (Abbrevations explained in text)

74 77 80

8

11

14

Kasaragod

Mangalore Hassan

Mysore

Bangalore

Ongole

Nellore

Chennai

AnanthapurEDCWDC

Tumkur

MK HN

Chitradurga

Arabian Sea

Bay of B

engal

km0 50

CB

TZ

HSB

CSB

Archean

Proterozoic

SGT

TZ

Index

Greenstone/schsit belts

Charnockites

Closepet granites & equivalents

Proterozoic dykesShear zones

Foliation

Peninsular Gneisse

Transition Zone (TZ)

Pa-Ca

India

11

relationships. In detail however, craton-wide stratigraphic correlations remain debatable. Geochemicaland isotopic data of metavolcanics indicate that, at places, even within the same supracrustal belt,volcanic rocks derived from distinct mantle sources occur in close spatial association. Thus, the truegeologic picture is much more complicated than presumed in the prevailing stratigraphic models.

In the Archaean greenstone belts of the WDC, both ultramafic komatiites and mafic tholeiites occurin close spatial and temporal association while boninites have also been reported at few places in theEDC. Some studies attempted to characterize their isotope geochemistry and precise age [5-8]. Apreliminary conclusion from Nd isotopic studies has been that the tholeiites of the Dharwar Supergroup(~2.8-2.7 Ga) were extracted from chondritic and/or mildly enriched mantle sources [7].

A recent study involving in-situ zircon analysis for U-Pb ages, U, Th, Zr, Hf, Y and Yb abundancesand Hf-isotopic compositions by a combination of electron microprobe, LAM-ICPMS and LAM-MC-ICPMS[for methodology, 9] reveal interesting though preliminary information on crust- formation and recyclingevents in the WDC [10]. This study involved a modest zircon population from samples of: 1) fluvialquartz-arenite from the basal quartz-pebble-conglomerate unit of the Dharwar Supergroup, depositionalage ca. 2.9 Ga, 2) low-Al

2O

3 tonalite gneiss from Gorur, close to the HSB, dated previously at ca. 3.3 Ga

and 3) sand samples from rivers draining the south-central part of WDC at locations near Mangalore andHassan, a section across the pre- 3.0 Ga terrain west of the HSB.

The oldest zircon age of 3634±10 Ma (2ó) corresponds to the mean of two detrital grains from thebasal quartzite while rocks of this antiquity are yet to be recognized in the WDC. Initial

176Hf/

177Hf ratios

of these and few other zircons of marginally younger ages(upto ca.3.5Ga) approach chondriticcomposition (å

Hf between +3 and +0.5) suggesting their protoliths may have incorporated older (i.e.

>3.63 Ga) juvenile material with some crustal pre-history. Notably, significant addition(s) of juvenilemagmas into the Dharwar crust between ca. 3.36 and 3.2 Ga is emphasized, a direct example being theGorur tonalite gneiss, which was revisited and dated here at ca. 3346±10 Ma (å

Hf between +4 and +7).

Explanations for the apparent non-involvement of older crust in the genesis of such juvenile magmas areambiguous at this stage. Younger zircons (ca. d” 3.0 Ga) suggest protoliths representing an essentiallyrecycled crust.

In the Dharwar craton, late Archaean granites cover significant proportion of the exposed Archaeancrust, particularly abundant in the EDC. Recent geochemical and isotope data show widespread lateArchaean juvenile plutonism manifest as batholiths including the Closepet granite during 2.55-2.51 Ga.[11-14]. However, such inferences need to be tested by way of more robust tracers like the zircon-Hfisotope signatures.

The Southern Granulite Terrain (SGT), presents a mosaic of Archaean and Neoproterozoic regionalgranulite terrains with peak-metamorphism dated at ca.2.5 Ga and 0.55 Ga respectively (Fig.1). TheArchean and Proterozoic terrains are generally believed to lie across a crustal-scale shear zone system,well known as the Palghat-Cauvery Shear Zone(Pa-Ca,Fig.1), but suggestions for the terrain boundary farsouth of this shear zone have been proposed in the light of geochronological studies in recent years: Nddepleted mantle model age(TDM) mapping[15] and U-Pb zircon and monazite dating[16]. A new data setof major and trace element compositions and Sr-Nd isotopic systematics of charnockitic ortho-gneissesall across SGT indicate contrasting source compositions and genetic environments for the protoliths ofArchaean and Neoproterozoic charnockites [17, 18]. The sources of Archaean charnockites could beeither dominated by a mantle component produced by subduction process during the latest Archaean,with variable extent of incorporation of mid-Archaean (upto 3.5 Ga) crustal components or may haveinvolved an Archaean granulitic lower crust typically with low-initial 87Sr/86Sr. On the contrary, thegenesis Proterozoic charnockites involved greater recycling of older (TDM upto ca.3.2 Ga,) crustalcomponents, in intracrustal melting process within a thickened crust. In the Neoproterozoic domain,there is also evidence for charnockites derived from Neoproterozoic juvenile protoliths(TDM between 1.8and 1.1 Ga) with affinities to syn-collisional or arc magmas.

More elaborate and exhaustive studies deploying new strategies and approaches such as[9] will berequired to firm-up this emerging picture of Precambrian crust formation and recycling episodes in theIndian shield.

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References:

1. Nutman, A.P., Chadwick, B., Ramakrishnan, M., Viswanatha, M.N.(1992) SHRIMP U-Pb ages of detritalzircon in Sargur supracrustal rocks in western Karnataka, southern India. Jour. Geol. Soc. India.,39, pp367-374.

2. Peucat, J. J., Bouhallier, H., Fanning, C. M., Jayananda, M.(1995) Age of the Holenarsipur greenstone belt,relationships with the surrounding gneisses (Karnataka, South India). Jour. Geol., v.103, pp701-710

3. Bhaskar Rao, Y.J., Anil Kumar, Vrevsky, A.B., Srinivasan, R., Anantha Iyer.(2000) Sm-Nd ages of twometa-anorthosite complexes around Holenarsipur: constraints on the antiquity of Archaean supracrustalrocks of the Dharwar craton. Proc. Ind. Acad. Sci. (Earth and Planet. Sci) 109. pp57-66.

4. Swami Nath, J., Ramakrishnan, M.(1981) Present classification and correlation, in Early PrecambrianSupracrustals of Southern Karnataka, In: Swami Nath, J., Ramakrishnan, M. (Eds.), Mem. Geol.Surv.India, v.pp112, 23-38.

5. Balakrishnan, S., Hanson, G.N., Rajamani, V. (1990) Pb and Nd isotope constraints on the origin ofhigh Mg and tholeiitic amphibolites, Kolar Schist Belt, South India. Contrib. Mineral. Petrol., 107,pp 272-292.

6. Zachariah, J. K., Hanson, G. N., Rajamani, V. (1995) Post-crystallization disturbances in theneodymium and lead isotope systems of metabasalts from the Ramagiri Schist Belt, south India.Geochim. Cosmochim. Acta., v.59. pp3189-3203.

7. Kumar, A., Bhaskar Rao, Y.J., Sivaraman, T.V., Gopalan, K., (1996) Sm-Nd ages of Archaeanmetavolcanics of the Dharwar craton, South India. Precambrian Res., v.80. pp205-216.

8. Jayananda, M. Kano, T. Peucat, J.-J Channabasappa, S. (2008) 3.35 Ga komatiite volcanism in thewestern Dharwar craton, southern India: Constraints from Nd isotopes and whole-rock geochemistry.Precambrian Res, v.162.pp160-179.

9. Griffin, W.L., Belousova,E.A,Shee,S.R.,Pearson,N.J.,O’Reailly,s.y. (2004) Archean crustal evolutionin the northern Yilgarn Craton:U-Pb and Hf-isotope evidence from detrital zircons.pp

10. Bhaskar Rao, Y.J., Griffin, W.L., Ketchum, J., Pearson, N.J., Beyer, E., and O’Reilly, S.Y. 2008. Anoutline of juvenile crust formation and recycling history in the Archaean Western Dharwar craton,from zircon in situ U-Pb dating and Hf-isotopic compositions., Abstract, Goldschmidt Conference2008, Geochim. Cosmochim.Acta.V.72, ppA81.

11. Moyen, J.F., Martin, H., Jayananda, M., Auvray, B., 2003b. Late Archaean granites: a typologybased on the Dharwar Craton (India). Precambrian. Res., v.127, pp103–123.

12. Moyen, J.-F., Nedelec, A., Martin, H., Jayananda, M.,(2003a) Syntectonic granite emplacement atdifferent structural levels: the Closepet granite, south India. J. Struct. Geol., v.25. pp611-631.

13. Moyen, J.-F., Martin, H., Jayananda, M.(2001) The Closepet granite (S. India) multi-elementsgeochemical modelling of Crust–Mantle interactions during late-Archaean crustal growth.Precambrian. Res., v.112, pp87-105.

14. Chardon, D., Peucat, J-J., Jayananda, M., Choukroune, P., Fanning,C.M.(2002) Archaen granite-greenstone tectonics at Kolar (South India): Interplay of diapirism, bulk inhomogenous contractionduring juvenile accretion.Tectonics, 32, pp1029-1047

15. Bhaskar Rao, Y.J., Janardhan, A.S., Vijaya Kumar, T., Narayana, B.L., Dayal, A.M., Taylor, P.N., Chetty,T.R.K.(2003) Sm-Nd model ages and Rb-Sr isotope systematics of charnockites and gneisses acrossthe Cauvery Shear Zone, southern India: implications for the Archaean-Neoproterozoic boundary inthe southern granulite terrain. In: Ranmakrishnan, M. (Ed.), Tectonics of Southern GranuliteTerrain. Geol. Soc. India Mem. No.50, pp297–317.

16. Ghosh, J.G., de Wit, M. J., Zartman, R.E.(2004) Age and tectonic evolution of Neoproterozoicductile shear zones in the Southern Granulite Terrain of India, with implications for Gondwanastudies. Tectonics 23, ppTC2005–TC3006.

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17. Tomson, J.K., Bhaskar Rao, Y.J., Vijaya Kumar, T., Mallikharjuna Rao, J.(2006) Charnockitegenesis across the Archaean–Proterozoic terrane boundary in the South Indian Granulite Terrain:Constraints from major–trace element geochemistry and Sr–Nd isotopic systematics. GondwanaRes., 10: pp115-127.

18. Tomson, J.K., Bhaskar Rao, Y.J., Vijaya Kumar, T., and Choudhary, A.K.(2008) Geochemistry and Sr-Nd isotopic systematics of Archaean and Neoproterozoic charnockites from the Southern GranuliteTerrain, South India: Magma genesis and tectonics, Abstract, Goldschmidt Conference 2008,Geochim.et Cosmochim Acta, v.72,ppA951.

Palaeozoic successions of the Indian plateO.N.Bhargava

Formerly with Geological Survey of India103 Sector 7, Panchkula 134109E-mail: onbhargava@yahoo.co.in

During the late Late Preambrian there was a rifting episode that is manifested by the KhewraVolcanics in the Salt Range, Singhi Volcanics in the Tethyan Bhutan and volcaniclastic material in thebasal most Tal of the Lesser Himalaya. This was followed by Cambrian sedimentation in Bikaner district ofRajasthan, Salt Range, the Lesser Himalaya and the Tethyan Himalaya, including the Peshawar basin. Asa response to an orogeny that culminated in Late Cambrian, a regression set in, as a result the sedimentsin the Salt Range, Peshawar (also Hazira), Lesser Himalaya range up to Middle Cambrian, in Kashmir up toearly Late Cambrian and in Bhutan up to middle Late Cambrian. It is not certain if the preservation ofdifferent parts of the Cambrian is result of a diachronous regression or due to variable erosion, or acombination of both. The Late Cambrian Orogeny caused thin skin thrusting, raising of the Cambrianbasin and emplacement of Early Palaeozoic granites. After this event the Salt Range, Rajasthan and theLesser Himalaya remained positive area till Late Carboniferous-Asselian.

The marine transgression in the Tethyan Himalaya took place during Early Ordovician in Peshawarand from Kashmir to Nepal. Clastic sequences were deposited in all these areas. Transgression in Bhutantook place during the Late Ordovician. Late Ordovician (Ashgill) to Early (Llandovery)-Middle (Wenlock)was a period of carbonate sedimentation with reef building activity. The Ordovician-Silurian boundaryinterval is possibly marked by a diastem-a period of ice age in Europe. Except Nawshera, where reefbuilding took place in the latest Silurian to earliest Devonian, other areas witnessed a regression. Thesea returned only during late Early to early Middle Devonian, when sedimentation between Kashmir andUttarkhand was on a vast stable beach. By Givetian the sea deepened and carbonate sedimentationcommenced (Lipak Formation, Syringothyris Limestone), as the basin shallowed in some parts Sabakha-like conditions prevailed, in other parts clastics were deposited. By the Viséan time several parts of thebasin particularly in eastern Spiti, Kinnaur-Uttarkhand were raised, which contributed clasts to the LateCarboniferous-Early Permian diamictites. These diamictites were deposited in the Salt Range, parts ofthe Lesser Himalaya, Rajasthan and Central India. Save Central India, where there are true tillites, inareas the diamictite deposits are referable to fluvioglacial to fluvial. During this period the erosionstripped up to the Lipak and even up to the Muth in Kinnaur and Uttarkhand. In Asselian, these areaswere inundated by cold and rough sea as revealed by ubiquitous presence of Eurydesma. The timeinterval covered by Midian-Kungurian witnessed the Panjal Volcanicity in parts of Kashmir and Zanskarand cessation of sedimentation in remaining parts the Himalaya, the Salt Range and the Peninsula. Themarine condition returned in Dzulfian, when new areas in Chamba and Lahul were inundated. The phosphoritehorizon reported in the Gondwana possibly belongs to this event. There was a period of non-depositionin Late Dorashamian, possibly a submarine break.

The important events during the Palaeozoic in Indian Plate are: i) Rifting in late Eocambrian/Ediacaran, ii) Cambrian sedimentation, phosphate deposition in the Lesser Himalaya basin, which formedan embayment of the Tethys, iii) Emplacement of Early Palaeozoic granites, iv) Late Cambrian Orogeny,nucleation of the Vaikrita Thrust Sheet (=MCT), obliteration and uplift of the Cambrian Basin. The SaltRange, the Lesser Himalaya and the Peninsular part become positive areas, v) Marine transgression in EarlyOrdovician and deposition of conglomerate in Kashmir-Nepal stretch and in Late Ordovician in Bhutan.

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Reef building during Ashgill-Llandovery-? Wenlock, vi) Regression in early to middle Middle Silurian inmost of the areas, vii) Marine transgression in late Early Devonian, viii) Small coral-algal buildup duringFamennian, ix) Uplift of the basin in selected parts of Zanskar-Spiti, Kinnaur-Uttarkhand, Bhutan inTournaisian-Viséan time. On set of glaciation in Late Carboniferous-Early Permian led to regression inshallower part. The glaciers had melted by the time they reached Salt Range and the Himalaya, x) Rifting inthe Gondwana, opening of old lineaments and melting of the glaciers in Asselian raised the sea level andled to transgression in Salt Range, Narbada-Son valleys, Lesser Himalaya foothills and Tethyan part, xi)Cessation in sedimentation during Midian accompanied by Panjal Volcanicity, xii) Transgression duringDzulfian in the entire Tethyan Himalaya, xiii) Period of non-deposition in late Dorashamian.

Status of hydrocarbon exploration in sedimentary basins of IndiaP.K. Bhowmick

Executive Director -Head KDMIPE, ONGC,Dehradun 248195

E-mail : bhowmick_pk@ongc.co.in

The sedimentary basins of India have received attention of geoscientists for hydrocarbonexploration since middle of last century. These petroliferous basins, both on land and offshore, range inage throughout the Phanerozoic. Most of the commercial hydrocarbon discoveries in India are fromCenozoic succession. However, the Mesozoics including Middle-Late Jurassic of Kutch -Rajasthan andCretaceous successions on the eastern Indian coastal basins have relatively lesser hydrocarbon finds. Inview of increased focus on Coal Bed Methane (CBM) exploration, the coal deposits in the PaleozoicGondwana sequences are now gaining increased attention.

Ever since the knowledge of occurrence of flammable hydrocarbons from Jwalamukhi in HimachalHimalayas and drilling of first oil wells of Digboi field in Assam since early part of last century , thehydrocarbon exploration in the country has seen a new era of relevance with the discovery of commercialhydrocarbons in the Cenozoic succession of Cambay basin during 1950ýÿs . However, not all thePhanerozoic basins in India are prospective. Based on the oil exploration activities and successes ,itis observed that a small number of basins produce most of the hydrocarbons.The category of provedpetroliferous basins of India with commercial production include Mumbai Offshore, Cambay, Assam-Arakan, Cauvery, Krishna-Godavari and Tripura-Cachar basins. Another category of basins with knownoccurrence of hydrocarbons, but lacking commercial production include Andaman-Nicobar, Bengal,Mahanadi, Himalayan Foothills and Rajasthan. Another category of basins with no hydrocarbon shows ,but geologically prospective are Kutch-Saurashtra and Kerala-Konkan basins. There is yet another categoryof basins which are in initial phase of exploration viz., Arunanchal foothills, Deccan synclise, GangaValley, Karewas , Mizoram ýÿManipur and Narmada basins.

The status of hydrocarbon exploration in petroliferous sedimentary basins of India along westernmargin (Rajasthan, Cambay, Kutch, Mumbai Offshore and Kerala-Konkan); along east coast (Cauvery,Krishana-Godavari, Mahanadi and Bengal basin); Northeast basins (Assam and Assam Arakan basin) andcentral India basins (Ganga and Purnea ) has been summarized in the present work. Each basin isdiscussed in context with its evolution, tectonics, sedimentary fill and petroleum systems, in light oflatest understanding of these basins and their hydrocarbon prospectivity.

Northward flight of Indian plate and evolution of theMesozoic-Cenozoic basins

S.K. BiswasFormerly with ONGC

E-mail: sanjibkbiswas2001@yahoo.co.in

The Indian Continental plate evolved by rifting from the Eastern Gondwanaland in Late Triassic-Late Cretaceous period, followed by northward drift along an anticlockwise path and collision with theEurasian plate in late Mid-Eocene. The Phanerozic basins of India evolved at different stages of rifting,

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drifting and collision. The separation of Africa shaped the western continental margin in stages duringrifting. The separation of Antarctica in Late Neocomian shaped the eastern margin of the continent. Thenorthern leading edge formed the peripheral foreland basin extending from Rajasthan to Upper Assambordering Himalayan Orogenic belt. Following the separation of Australia, the Indo-Sinian plate convergedtowards India ending up in an oblique collision at its northeastern corner in Late Oligocene. Concomitantlyan island arc formed, on the east - Andaman-Sumatran arc. The floor of the eastern Indian Ocean(including Bay of Bengal) started subducting below the arc as the plates converged and the Andamantrench and Tripura fore-arc prism complex evolved. The incomplete suturing of the Indo-Sinian platesince Oligocene formed the intermontane foreland basin of Assam and the remnant ocean basin ofBengal. Thus, in the present geotectonic set up two active ocean basins flank the Indian plate, aspreading Arabian Sea in the west and a converging Bay of Bengal in the east.

Radially oriented marginal sag basins and intervening highs feature the Tertiary foreland basin. Theseare the inherent passive margin basins on the leading edge of the drifting plate. The intra-cratonicGondwana rift basins, formed during pre-break up crustal distension in Late Paleozoic, occur in the centralpart of the craton associated with the Narmada-Son geofracture. Mesozoic-Tertiary pericratonic rift basinsformed during continental break up, shape the western and eastern margins of the craton. Three intersecting‘rifts’ viz., Kutch, Cambay & Narmada formed around the cratonic block of Saurashtra. The Kutch rift basinwas initiated during the early break up in Late Triassic and aborted in Early Cretaceous. Cambay, Narmadaand Bombay offshore rifts are related to rrr-triple junction. These basins formed during the final breakup ofthe plate in Late Cretaceous and fully evolved during the drift stage as polycyclic basins. The pericratonicrift basins of the east coast of India evolved during Mid-Cretaceous Indo-Antarctican break up along theNE-SW trending Eastern Ghat mobile belt. These basins, Cauvery, Palar and Krishna-Godavari, are rifted/pull-apart basins superposed orthogonally on the NW-SE trending Gondwana basins.

The continent is presently undergoing neotectonic movement under NNE-SSW directed compressivestress due to northerly ridge-push from the Carlsberg Ridge of the spreading Arabian sea and the southerlyback thrust from the northern collision front. Intra-continental geodynamics are controlled by three NE-SW trending mega shears along the trans- continental tectonic lineaments: North Kathiawar-GreatBoundary fault, Narmoda-Son-Dauki fault and Palghat-Eastern Ghat-Hail Hakalula-Naga thrust trends.

Antiquity of Bhima/Kurnool (Palnad) Puräna platformal sediments and theirMesoproterozoic connection: New insights from the limestone xenolithsin siddanpalle kimberlite cluster, Eastern Dharwar craton, southern India

N.V.Chalapathi RaoDepartment of Geology, Banaras Hindu University, Varanasi-221005

E-mail: nvcr100@gmail.com

Proterozoic sedimentary basins are repositories of significant information on the nature andevolution of Earth’s lithosphere, atmosphere and biosphere and their interactions. Hence they are currentlythe focus of increased global attention. Furthermore, the Proterozoic sedimentary basins also constituteexcellent examples to investigate whether the plate tectonics processes displayed by their Phanerozoicanalogues operated in the geological past thereby making their study important both from fundamentalas well as economic point of view e.g. hydrocarbon potential.

The name ‘Puräna’ (= ancient) was given by Holland (1907) to a group of unmetamorphosed andleast disturbed Proterozoic sediments that rest over the metamorphosed and highly deformed Archaeanbasement in the peninsular India. Purana basins include the Cuddapah, Kurnool, Palnad, Bhima, Kaladgi,Godavari-Pranhita, Vindhyan, Chattisgarh, Indravati, Bijawar, Kolhan, Abhujmar and some minor basinsdistributed in Central India. Despite more than a century of study their origin, evolution, agerelationships, fossil content and mineral wealth are not yet fully understood. Rigorous constraints onthese aspects are necessary for their regional correlation.

As there is no record of any igneous activity in the present day exposed Bhima and Kurnool(Palnad) Purana sediments (Fig.1) of southern India, the application of conventional radiometric methods

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to determine the age of the sedimentation is not straightforward. Therefore their ages were, for long,constrained by indirect and relative dating methods involving lithostratigraphic correlations, bio-stratigraphy and comparison of C and Sr isotopes with Proterozoic global isotopic sea-level curves. In arecent paper (Dongre et al. 2008) we have reported the occurrence of a limestone xenolith in one of thekimberlites (SK2) from the Siddanpalle kimberlite cluster, Gadwal granite-greenstone terrane, EasternDharwar craton, southern India, and speculated on its source from the Proterozoic platformal cover, noweroded, of the Bhima/Kurnool (Palnad) Purana sedimentary basins. A Mesoproterozoic age for the carbonatehorizon was inferred based on 1090Ma age of the host kimberlite and the possibility of close linkbetween these two Purana basins.

The purpose of the present communication is to (i) firmly establish a sedimentary carbonatehorizon in the Siddanpalle area by documenting additional limestone xenoliths from even the two pipesof the cluster, (ii) critically evaluate the postulated Bhima and Kurnool (Palnad) platformal Mesoproterozoicconnection in the light of new geological evidences, (iii) speculate on the possible geodynamic reasonsresponsible for the uplift of this geological domain, (iv) propose a new model accounting the primarysource of the alluvial diamonds recovered all along the Krishna river and (v) highlight the need to re-evaluate the uranium potential of the Kurnool basin on the basis of new findings.References

Dongre, A., Chalapathi Rao, N.V. and Kamde, G. (2008) Limestone xenolith in Siddanpalli kimberlite,Gadwal granite-greenstone terrain, Eastern Dharwar craton, Southern India: Remnant of ProterozoicPlatformal cover sequence of Vhima/Kurnool age? Journal of Geology v. 116, pp. 184-191.

Holland, T.H. (1907) Imperial Gazetteer of India. 1:50-103.

Figure 1 Possible Mesoproterozoic connection (dashed lines)between Bhima and Kurnool Puräna sediments.

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Ground penetrating radar (GPR) and Quaternary tectonic studiesin Gujarat region of western India

L. S. ChamyalDepartment of Geology, Faculty of Science, The M. S. University of Baroda

Vadodara-390 002E-mail: lschamyal@yahoo.com

GPR and Quaternary tectonic studies have received a fresh momentum in last decade in parts ofIndia due to the occurrence of devastating earthquakes. The neotectonic deformation and seismicinstability of the Indian plate is related to the continued northward movement of the Indian plate. Thefault controlled basins provide ideal sites for Quaternary sedimentation and are thus considered importantfor understanding the Quaternary tectonic evolution of the Indian plate. The documentation of thesuccessive tectonic events along various faults and related landforms is essential to address thesignificance of Quaternary tectonics in landscape development. As far as the neotectonic and palaeoseismichistory of faults is concerned, the state of art subsurface studies using Ground Penetrating Radar (GPR)is extremely important.

The shaping of the landscape and the Quaternary sedimentation of the Gujarat region is primarilyinfluenced by tectonic movement along faults. The extensive sedimentary exposures in the vicinity ofthe various fault systems of Gujarat help in understanding the neotectonic and palaeoseismic history ofwestern India. Several earthquakes have occurred in historical times along several fault zones of Kachchhbasin and the Narmada Son Fault (NSF). GPR and Quaternary tectonic studies are found useful in delineatingthe past history (late Quaternary) of tectonic and seismic events. An upto date review of thegeomorphological, stratigraphical, tectonic and GPR studies in parts of Gujarat, western India withspecial reference to precise mapping of faults and their neotectonic history will be presented.

Tectono-sedimentation during rift-drift period inRamnad sub basin, Cauvery basin

Chandan Chakraborty1‘, M.S.Rana1, S.Chandra2, N.D Gideon1, M.Giridhar1

1-BSD, KDMIPE, ONGC, Dehradun, 2-OVL, New DelhiE-mail: chanchak2@yahoo.com

Plate reconstruction models indicate that the initial rifting in the Cauvery Basin took place duringLate Jurassic- Early Cretaceous time. Taphrogenetic fragmentation of Archean basement as a result ofrifting related deep seated basement controlled fault system has resulted in the formation of a series ofNE-SW trending( half) grabens and ridges. Ramnad – Palk Bay sub basin is one of the south- easternmost graben limited by Pattukuttai – Mannargudi ridges to the west and Mandapam Delft ridge to theeast and hold sediments of over 5000m thickness at its depocentre, ranging in age from Lower Cretaceousto recent. Both the ridges, especially the former one are the primary provenance for the sedimentationin this sub basin.

Seismic sequence analysis based on chronostratigraphy validated by biostratigraphy and electrologshas been applied in this study. Eight reflectors corresponding to near top of Basement, within Pre-Albian, close to top of Albian, Cenomanian, Turonian, Santonian, Cretaceous and Paleocene have beencorrelated regionally and their relief map as well as corresponding isochronopach maps have been preparedto decipher the depositional model.

A relief map at different levels depicts the changing basin architecture with passage of time. Atbasement level, the deepest Ramnad low with steeper western and gentler eastern flanks in Ramnad subbasin and two lows in Palk Bay area i.e the broader Western Palk Bay low and an elongated, linear EasternPalk Bay low are seen. The Eastern Palk Bay low is comparatively shallower than the western Palk Bay low,which is again divided into northern and southern low separated by intervening higher areas.

Due to high rate of sedimentation coupled with low accommodation space during Pre-Albian time,the Ramnad low has shrunk considerably and the two lows of Western Palk Bay was obliterated. This has

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induced a transpressive force and resulted in selective reactivation of basin opening normal faultsresulting in inversion seen in the Western Palk Bay area. The fault system again became active duringAlbian period resulted in broadening and lengthening of Ramnad low as well as Eastern Palk Bay low.Ramnad low also slightly shifted towards the east.

During Cenomanian time, the main depocentre was shifted towards Eastern Palk Bay off shore.Ramnad low further shifted towards NE and the NE-SW trend of Ramnad and Palk Bay basinal low more orless aligned in the same axis which was positioned differently during Albian time.

The rifting appears to have ceased by end of Early Cretaceous and is followed by a period of ‘drift’.During Turonian time, some drainage output from Pattukottai ridge resulting peneplanation of Ramnadlow due to active sedimentation. The area of the Eastern Palk Bay low was further increased because oftectonic activity and received less sediments. Eastward tilting during Santonian time shifted the spreadof basinal low towards east and a major deep is seen in within Eastern Palk Bay low.

Cretaceous top being an erosional unconformity led to the development of a network of submarinecanyons and channels on K/T surface. This has brought out probable coarser clastics down the dip anda substantial part was being transported in the Eastern Palk Bay low. This factor coupled with easterlytilting resulted major changes at the end of Cretaceous. The NE-SW trending Eastern Palk Bay low hasshrunk and an east-west trending low between north and south of Mandapam Delft ridge has widen anddeveloped as a major low axis. Further easterly tilting of the basin during Paleocene time createdmultiple drainage system originating from Pattukottai ridge. Major sedimentation which was mainlytowards Ramnad low in the earlier time is now seen towards the Eastern Palk bay low which by that timewas aligned in almost east-west direction.

Proterozoic orogens and transpressional tectonic regimes in southern IndiaT.R.K.Chetty

National Geophysical Research InstituteHyderabad-500 007, India

E-mail: chettytrk@yahoo.co.in

The Precambrian southern Indian shield is central to all discussions on the formation and breakuphistory of supercontinents. The Proterozoic high grade metamorphic orogens occurring at the southernand eastern margins of the southern Indian shield, skirting the 3.4 Ga old Dharwar craton, are ofparamount significance. They provide not only better understanding of the lower crustal processes andlithospheric geodynamics, but also contribute to the reconstruction models of Rodinia and Gondwanatectonics. These Proterozoic orogens are well described as Southern Granulite Terrane (SGT) in the southand the Eastern Ghats Mobile Belt (EGMB) in the east coast. The continuity of these orogens is brokenfor a distance of ~400km and disappears in the Bay of Bengal. These orogens expose windows of middleto lower crust with well preserved rock records displaying multiple tectonothermal events and multiphaseexhumation paths. They consist of Archean to Neoproterozoic complexly deformed high grade metamorphicand magmatic assemblages

Recent studies in these orogens have led to the recognition of discrete crustal blocks or terranesseparated by major shear zone systems. The geological characteristics such as fod-thrust tectonics,regional granulite facies metamorphism with isolated UHT characteristics, multitude P-T history,development of lithoshpheric shear zones, emplacement of granitoids, presence of alkaline and anorthositiccomplexes, development of crustal scale “flower structures”, trnaspressional strains, reactivation tectonics,are common in both the orogens. These features make us believe that these orogens represent a singlecontiguous orogen, which is here described as ‘Proterozoic orogen of southern India’ (POSI), which hasbeen subjected to common orogenesis. . In recent years, several multidisciplinary studies led to establishthat the POSI is an important collisional belt in East Gondwana supercontinent exposing a uniquewindow of a wide range of structural levels of orogenic belt marked by large tracts of reworked linearbelts ranging in scale , intensity, and age (2.5 to 0.5Ga) . The intermediate orogenic event (1.0 Ga) ispronounced in the EGMB and it is rarely reported from the SGT. The POSI is characterized by heterogeneous

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distribution of different metamorphic and magmatic assemblages with distinct spatial and temporalstrain variations in shaping the fabric elements in different blocks of the larger orogen. However, theentire orogen shares a common transpressional deformation history during the Neoproterozoic.

Oblique collision and long lived transpressional tectonic regimes during Gondwana amalgamationseem to be responsible for the present disposition, geometry, reactivation tectonics of these orogens.Long lived transpressional tectonic regime was also responsible for steepening the initial low anglecrustal scale structures establishing a subvertical grain conducive to reactivation. The spatial distribution,geometry, kinematics and the transpressional strain of the shear zone systems, which are critical to allconceptual models dealing with tectono-metamorphic history of Proterozoic orogens of southern India,will be discussed.

Temporal emplacement-sequence of the sodic- and potassic-granitoids in theIndian peninsula and its bearing on U-mineralization

R. Dhana RajuFormer Asso. Director, Atomic Minerals Directorate for Exploration & Research, DAE

6-3-124, Hastinapuri, Sainikpuri P.O., Secunderabad – 500 094E-mail: rdhanaraju@yahoo.co.in

Granitoids (sensu lato) constitute the dominant rock type in the Earth’s crust. In India, theirtemporal sequence of emplacement is recorded from Paleoarchean (~3.6 Ga) to Neogene (~0.02 Ga). Theywere also shown as forming both the ‘host’ and more importantly the ‘source’ for diverse types of U-mineralization in India. Critical evaluation of their temporal emplacement-sequence vis-à-vis U-mineralization in the Indian Peninsula, as presented in the following, indicates that broadly there is analternating sequence of emplacement of sodic (Na2O/K2O > 1) and potassic (K2O/Na2O > 1) granitoidsduring this long period, with the former responsible usually for the high-temperature type and the latterfor low-medium temperature type U-mineralization.

1. During the Paleo- to Neo-Archean (3.6 - 2.9/2.5 Ga) period, the Earth’s crust comprises mainlythe sodic granitoids like the Peninsular Gneiss of TTG (tonalite-tondhjemite-granodiorite) compositionin the Dharwar Craton, OMTG (Older Metamorphic Tonalite Gneiss) in the Singhbhum Craton and theBundelkhand Gneissic Complex of the Mewar Craton in Rajasthan. These sodic granitids and their relatedpegmatoids contained most of the U and Th that were migrated from the mantle to the crust. Theycontributed, in an essentially anoxic atmosphere, the high-temperature Th-bearing uraninite, thorite,uranothorite and brannerite, along with other placer minerals like rutile, zircon, monazite and xenotime,all of which are recorded in the paleoplacer-type U-mineralization in the (i) oldest, pyritiferous QuartzPebble Conglomerate (QPC) at Walkunji in Karnataka and other places in Orissa and (ii) meta-arenite(above QPC) in the Arbail-Dabguli area in Karnataka. In the Singhbhum craton, the ‘Singhbhum GraniteBatholith’ (SGB; ~3.4-3.1 Ga)) is composite, mainly sodic of TTG composition. It is the source forcommercial-grade, Mesoproterozoic (~1.6 Ga), essentially structurally-controlled, low-medium temperature,hydrothermal-type U-mineralization as Th-poor uraninite, pitchblende and brannerite in diverse rocktypes, mainly of schists with minor apatite-magnetite-quartz-tourmaline rocks, quartzite and conglomerate,present along the Singhbhum shear zone.

2. During the Paleoproterozoic (2.9/2.5 - 1.6 Ga) period, there was major emplacement of potassicgranitoids, after the major change of atmosphere from anoxic to oxic at ~2.6 Ga, indicated by the firstFe-Mn formation above the Arbail (paleoplacer )-type U-minera-lization. These granitoids are representedby the Closepet granite (2.5 Ga) and its equivalents like the Dongargarh, Malanjkhand and those formingthe basement for the intracratonic, Mesoproterozoic (1.6-1.0 Ga; Purana) basins like the Cuddapah,Vindhyan, Kaladgi-Badami and Bhima. These potassic granitoids constitute both the host and sourcefor different types of commercial-grade, low-medium temperature U-mineralization, manifested as Th-poor uraninite, pitchblende and coffinite. These include the (i) uncorfimity-proximal type in both thegranite and its overlying Srisailam/Banganapalle quartzite in the Cuddapah basin, (ii) stratabound,dolostone-hosted type (Tummalapalle deposit) in the Vemalle formation of the Cuddapah Supergroup

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and (iii) hydrothermal type in both the granite and overlying Shahabad limestone at Gogi in the Bhimabasin.

3. During the Neoproterozoic (1.0 – 0.542 Ga; Pan-African) period, there was emplace-ment ofAnorogenic (A-type) granitoids along major extensional zones of rift, shear and continental epeirogenicuplift in high-grade granulite-gneiss terrains. These granitids carry high-temperature, refractory U-Th-Ti-Rare Metal (Nb-Ta, Li, Be, etc.)-Rare Earth mineralization in the form of Th-bearing uraninite, thorite,brannerite, davidite, columbite-tantalite, fergusonite and samarskite. Examples of these include sodictype (trondhjemite; 0.53 Ga) at Kullampatti, Tamil Nadu and potassic type (1 Ga) at Kanigiri, AndhraPradesh. Furthermore, this period also witnessed (i) albitite-/metasomatite-type, high-temperature U-mineralization (0.5 Ga) as at Rohil-Ghateswar in Rajasthan and (ii) potassic, I- and S-type granitoids,represented, respectively, by the South Khasi batholith (0.75 Ga) and Mylliem (0.6 Ga), which constitutethe source for the Phanerozoic, commercial-grade, low-temperature, sandstone-type U-mineralization(0.07 Ga), manifested as Th-poor pitchblende and coffinite, in the Domiasiat-Wahkyn and adjoiningareas in Meghalaya.

Modelling the evolution of the Indian granulite terrains-few constraintsV. Divakararao

Visiting Professor; Geology Department, Osmania UniversityHyderabad, 500 007.

E-mail: divakararaov@hotmail.com

High grade granulite facies rocks occur in two different tectonic setting in the Indian shield-thecratonic granulites extending from Kuppam in the north to Cape –Comorin in the south(the SCG) andthe Eastern Ghats Granulite Belt,extending from Brahmani in the north-east to Chennai and furthersouth all along the east coast of the Indian shield.

Extensive multidisciplinary data base created on these two terrains (geological, geophysical,chronological,geochemical,structural,thermo-barometric) since last two and half decades by reputedR&D institutes and academicians while could help in having a better understanding of the lithologicalsetup,the structure,the pro-grade and retro-grade metamorphic events ,the chronological controls ,create some problems in modeling the evolution of these two terrains ,their time-space relation and thegranite –gneiss terrain with which the granulite are in direct contact.

The remarkable lithological similarity between the two belts( the charnockite-basic granulite-calk granulite-alkaline and ultramfic rocks-anorthosites-quartzite-granite-leptynite etc ,though the relative abundance ofthe different lithologies from terrain to terrain vary) suggest their formation in similar setup.

Both the terrains exhibit poly metamorphic events (both prograde and retrograde with clockwiseand anti-clockwise events) and the available chronological data clearly show the antiquity of these twobelts with dates suggesting late-Archaean to meso-and neo-Proterozoixc metamorphic events apart fromthe Pan-African which is more pronounced in the SCG with limited evidence in the EGGB.

Chronological data on these two terrains shows broad similarities ,with late-Archaean –early -Proterozoic to ,meso- proterozoic of the protoliths ages of the charnockite-basic granulite suites(calk-alkaline and tholeiite respectively). The alkaline-anorthosite –ultramafic intrusives in both beltssimilarly are of similar age to a large extent. The ultrametamorphic Ghinjee granite(2300 Ma) in SCG andthe megacrystic granites In the EGGB( 1900-2000 Ma) differ marginally probably indicating the shftingof higher thermal activity from SCG to EGGB during that time.

Geochemical investigations on different lithologies from both the belts,especially the charnockite-basic granulte and metapelite suggest that in both the SCG and EGGB the charnockites show TTG(tonalite-trondhjemite-granodiorite) characters and ,the basic granulites are of tholeiite nature and both theterrains have layered as well as massive anorthosites.Occurrence of metapelite-calcgranulite-BIF-limestonevestiges (outliers) in SCG down up to Coimbatore suggest that these metapelite-calckgranulite lithologieswere much more extensive than their present abundance and probably due to the northen tilt of theshield must have been eroded.

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Integrated geophysical studies (gravity, magnetic, MT, seismic etc) to evaluate the sub-surfaceconfiguration of the SCG and EGGB, however show substantial difference in the sub-surface configurationof the belts. The low velocity layers suggested at shallower levels in the SCG are not present in EGGB andthere is an also perceptible difference in the crustal thickness, resistivity, conductivity etc. Most ofthese geophysical signatures are prone to change with tectonics (and hence time), the differencebetween the subsurface confifguration of the two belts must have been altered due to the later, meso-to neo-Proterozoic tectono-thermal events.

Based on a critical analysis of this vast data base on both the SCG and EGGB it can be suggestedthat these two belts have evolved or was part of single terrain which was thrust on the Indian shieldfrom south-east and south with the southern thrust being at a low angle forking throuth the lowgradegranite gneiss shiled resulting in the low velocity layers at shallowe depths while the in the south westthe thrust angle shuld have been near verticle. This model however requires further detailed studies onthe tectonic fabric and the timing of the events to substantiate.

Majhgawan Lamproites, Madhyapradesh and Kodomali orangeites, Chattisgarh:petrological appraisal and new insights on their origin

FareeduddinGeological Survey of India, Bangalore -

E-mail: fareedromani@hotmail.com

The potassic ultramafic igneous rocks that include kimberlites, lamproites, orangeites, minnettes andmonchiquites occur in diverse tectonic settings in all the cratonic regions of the Indian shield. Inconformity with their host tectonic settings and the period of their emplacements, these intrusive/extrusive rocks exhibit significant diversity in their textural, mineralogical, and chemical properties. Thereis an impressive build up of geochemical data and this together with recent description of petrographicfeatures of these bodies help in elucidating there exact petrological classification as per the mineralogical-genetic nomenclature scheme proposed in recent years. The present paper deals with the petrology andpetrogenesis of the two most important diamondiferous diatremes of the Indian shield.

The diamondiferous Kodomali diatreme in the ‘Mainpur kimberlite field’, Raipur district, Chhattisgarhstate, has intruded into the lower part of the platformal sequence of Kahriar Piari group of rocks at 478+/-2 Ma. The diatreme exhibits a distinct macrocrystal texture with polyphase development of olivinesoccurring as coarser and finer macrocrysts in a very fine grained groundmass made of diopside, phlogopite,spinels and secondary serpentine. Extensive microprobe data on the constituent mineral phases ofKodomali diatereme suggest it to have affinities towards South African orangeite. Spinels from anotherdiamondiferous diatreme in the region also show orangeitic affinities. Justification for recognition ofthis region as Paleozoic orangeite field in Indian subcontinent is discussed.

The alkali-ultramafic rock near Majhgawan and its satellite body near Hinota, on the southeasternmargin of the arc shaped Bundelkhand craton and within the Mesoproterozoic Vindhyan basin in CentralIndia hosts the only diamond producing mine in India. Variously classified, 500m x 300 m size, ellipticalshaped body is dominantly represented by several varieties of breccias (from simple granulation tocomplex melt breccias) of ultramafic composition, and shows significant differences in bulk chemistryand mineral compositions with other known kimberlites and related rocks of India. It possesses texturalfeatures (lapilli) suggestive of crater facies volcanic eruption. It contains crustal fragments of surroundingVindhyan sediments but xenolithic fragments either from basement Bundelkhand granitoids or mantleare conspicuous by their absence.

Recently observed shock metamorphic features in olivine as well as the presence of variety offeatures bearing startling resemblance to the chondrules suggest that the Majhgawan ultramafic brecciacontains traces of chondritic components in it. It is interpreted here that the Majhgawan diatreme,largely of lamproitic composition, is the result of a billion year old, impact triggered eruption of mantlematerial where the latter has incorporated the surface remains of the chondritic matter. Much morestudy is called for on this line to understand the textural and mineralogical complexities exhibited bythe Majhgawan body. It is argued that the difficulty in providing a descriptive classification for thisrock within the framework of the IUGS schemes for terrestrial rocks owes mainly to its miss-identification

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as simple rock akin to the known diamondiferous primary sources. Implications of identification ofshock features for our understanding of the genesis of diamonds in the rock are also discussed.

Geology and hydrocarbon prospectivity of Cauvery basin, IndiaM.Giridhar, Rajesh Sharma, Chandan Chakraborthy, M.S.Rana

Basin Research Division, KDMIPE, Dehradun - 248 195

Cauvery Basin a pericratonic rift basin lying towards southeastern part of India came into existencedue to divergent tensional block faulting of continental crust and subsidence during Late Jurassic ageand had a sedimentation history till Recent with alternative transgressive and regressive cycles. Gravity-Magnetic-seismic surveys carried out showed NE-SW trending horsts with intervening lows (sub-basins)which were initiated during rifting. Maximum thickness (>6000m) of sediments are found in the centralparts of basin (Tranquebar sub-basin). Oldest sediments in the sub surface are of Jurassic age reportedfrom northern sub-basin (Ariyalur sub-basin).

The basin underwent two stages during its formation viz., Late Jurassic/Early Cretaceous synriftstage, Late Cretaceous—Recent post rift passive margin stage. The synrift sediments are represented byAndimadam Formation of Pre-Albian to Albian age with a marked unconformity above. This was followedby world wide transgression represented by Sattapadi shale of Cenomanian age followed by deposition ofBhuvanagiri Formation of Turonian age. During Late Turonian a major upliftment has taken place in thebasin, many deep water regimes has been brought to shallower regimes and culminated into anunconformity. During Coniacian eastern tilt of the basin has resulted in widespread transgression whichhas brought out major part of the basin under marine regime with the deposition of Kudavasal shale. Aregular shelf/slope started emerging with deeper bathymetry and deposition of sands represented byNannilam Formation of Santonian-Campanian age. This was followed by another prominent marinetransgression during Campanian to early Maastrichian represented by Porto Novo shale. The end ofMesozoic was marked by upliftment of basin and subsequent erosion led to the formation of canyons andalso resulting in widespread unconformity. Many canyon associated reservoirs of Paleocene to EarlyEocene were proved to be hydrocarbon producers. During Middle Eocene to Late Eocene the entire basinunderwent major tectonic readjustment with easterly tilt followed by widespread transgression with theadvent of easterly prograding shelf margins represented by Karaikal shale. This was followed by majorregression during Late Eocene to Oligocene where delta building activity was very strong withprogradational features represented by Neravy Formation. This was followed by small transgressive eventbetween Late Oligocene to Early Miocene represented by Shiyali Claystone.

Two anoxic events depositing organic rich shales during Middle-Late Albian age(end of synrift stage)and Cenomanian-Early Turonian age have been reported. The shales within Albian-Pre-Albian age are thesource rocks for the entire basin whereas Cenomanian-Early Turonian shale serves as additional source rock.Maximum number of plays is found in the Nagapattinam sub-basin with number of discoveries ranging inages from Pre-Albian-Albian –Oligocene. Hydrocarbons are discovered in fractured basement also.

Hydrocarbons from lower Andimadam Formation are found only in Tanjore sub-basin where thereservoirs have poor petro physical properties whereas at Upper Andimadam levels as in the southwesternrising flanks of Kumbakonam high the reservoir properties are good and discoveries have been made.Basement associated structures of Bhuvanagiri Formation also similar to Andimadam reservoirs thepetrophysical preoperties vary depending on the depth of occurrence. Nannilam Formation sands whichoccur in all the subbasins have better petrophysical properties. Kamalapuram Formation of Paleocene-Eocene age have deposited over Cretaceous unconformity have multistacked reservoirs with heterogeneouspetrophysical properties where discrete sand lenses of relatively small areal extent and irregular sandgeometry are the main constraints. The Neravy Formation sands are also of staked nature with very goodreservoir properties has good hydrocarbon recoveries.

Each sub-basin had its independent sedimentation history irrespective of other sub-basins andthe petroleum system is different. Based on Time-Temperature Index onset of hydrocarbon generationhas occurred around 25mybp (TTI-10) whereas peak generation occurred at 2mybp (TTI-75) in

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Nagapattinam sub-basin. Moderate to average sedimentation rates, associated higher HI values, betterquality of organic matter, higher geothermal gradients might have contributed for better generation ofhydrocarbons in Nagapattinam sub-basin and in the northwestern parts of Tranquebar sub-basin.

Andimadam-Nannilam petroleum system(.) in Ariyalur-Pondicherry sub-basin where fault associatedstructures within basinal parts and pinch outs against northwestern rising fanks, Andimadam-Bhuvanagiripetroleum system(.) in Tranquebar sub-basin fault associated basement controlled structures in thenorthwestern parts,Vertically/laterally drained Andimadam-Neravy petroleum system(.) in Nagapattinamsubbasin where structural/combination traps at Bhuvanagiri/Nannilam Formation level, canyon associatedfans of Kamalapuram Formation and distal delta sands at Neravy Formation level, Andimadam- Andimadampetroleum system(.) in Tanjore subbasin where structures formed at lower Andimadam level, Andimadam-Kamalapuram petroleum system(.) in Ramnad subbasin where deep seated fault associated structures arethe targets of exploration. Recently the exploration activities are focused for basement as well as synriftsequences.

Paleoclimates changes in Indian Ocean on tectonic time scaleD. Gopala Rao.

Emeritus scientist (CSIR), Geology Department, Osmania University, Hyderabad- 500 007E-mail: drgopalarao@yahoo.com

Earth-oceans and atmosphere interact and transfer energy/ matter from one to the other as coupledsystem had prompted to study oceans, sediments and ocean crust to know climates changes - trends,rythms/periodicities and aberrations. They shall lead to better realization and characterize the climatechanges, effects and forces driving them. Studies of the ocean sediments drilled and recovered from theseafloor under aegis of the Ocean Drilling Project had identified the proxy indicators of the climatechange. They are the foraminifer (plankton and benthos), geochemistry and isotopic ratios in sediments,foraminifera, volcanism, corals, aeolian dust particles, sea level changes, chemistry and physics of thewaters and their circulation pattern in space and time. The Cenezoic period climate extremes- Paleocene,Miocene and Pliocene warmth and Oligocene ice age and aberrations are noted. They are synchronouswith plate tectonic events of the past. Such major change in plate’s positions, plate’s reorganizationsoccurred in the Indian Ocean around 90 Ma and 65 Ma. Interestingly around the time, 65 Ma of tectonicevent large outpoured lavas and extinction of biology occurred which is record of the extreme warmthand noted as one of the significant events to believe them as cause and consequence. Their occurrenceat the same time is very convincing to record their impact and intimate relationship to climate changes.

The continued motion of the plates due to sea floor spreading in the Indian Ocean resulted inIndian plate collision with Eurasian plate, closure of Tethys Sea and origin of the Himalayan Mountains.The mountains building by end of Miocene or early Miocene is believed to be the root cause forestablishment of the present day Asian monsoon pattern. Thus they are correlations between tectonicsand climate changes. These findings led to believe 1) plate tectonics played major role in causingextreme warmth of long duration owing to volcanism/carbon budget. and 2) to look for further causeand effect relationship of climate changes. The time of peak volcanism was also marked by high crustalproductions rates due to extrusion of magma from below, low strontium ratios, increase in sea level dueto warmer climates and very high sea levels and high temperatures. Variation in magnetic susceptibilityof sediments was noted to recognize the climates changes- a proxy to indicate climate change. Highstrength of it occurs in case of large magnetic particles due to volcanism or minerals, brought by thereverine systems from land sources due to flooding.

The multi-channel seismic records off Udipi, southwest coast of India and interpreted time sectionshow the eroded surface images developed during Oligocene lowered sea-level ~ 20 Ma i.e. an ice ageand pause in sediment supply. The event is globally noted and records maximum drop in sea levels. Highsedimentation rates during Miocene and Pliocene are noted from seismic images of the Bay of Bengal fansediments which note high rate of sediment deposition under increased precipitation denoting theenvironmental chage/climate. Corals (live and relict) at the sea floor and relict ones at two subsurface

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depths interspersed by sediments are imaged on seismic records in the Gulf of Kachchh, northwest ofIndia. The corals presence and absence, on correlation with sea level variations curves led to believethem due to transgressed and regressed sea level in the gulf during the Late Quaternary period. Thusthey are several proxy indicators of climate change owing to tectonics. Their characteristic differencesfacilitate to easily recognize from the changes due to earth orbital parameters and anthropogeniccauses and their periodicities from the spectra of climate changes. Tectonic processes causing continentalrifting, volcanism, collision and upliftment of continents significantly contribute to climate variationsand essential to consider them while assessing their trend/rythems.

A new approach to pecision chronicling of regional tectonic events on theGondwanian Tethyan margin from Arabia to Australia

Jai KrishnaDepartment of Geology, Banaras Hindu University, Varanasi - 221 005

Precision chronicling of regional extensional tectonic events related to dismemberment ofGondwanaland or otherwise is here conceptually approached through the relatively new tool of sequenceStratigraphy. Recently (Krishna 2006 onwards), possible genetic links have been suggested betweenregional extensional tectonic events and sequence stratigraphic surfaces of 2nd and higher order –maximum flooding surfaces (MFS’s) and sequence boundaries (SB’s). Gondwanaland is here uniquelyconceived of two units – Inner/Axial/Core unit of India-Madagascar-Africa and Outer unit of Australia-Antarctica-South Africa. It is also envisaged that at first the oceanic spreading is inter-unit betweenInner and Outer units and later intra-unit among India, Madagascar and Africa or among Australia,Antarctica and S. America. The extensional tectonics in general during the Mesozoic has proceeded fromnorth to south and east to west.

The Indian Mesozoic mega-sequence begins through origin of Neotethys in Middle Permian andterminates with closure in Middle Paleogene. It includes three 1st order sequences, three 1st order MFS’sand two 1st order SB’s in the Mesozoic that have been precisely dated through recently developed highresolution ammonoid stratigraphic refinement. The basal mid-Permian SB marks the onset of plate-reorganisation efforts both in India – Africa and India – Australo–Antarctica divergent sectors of theGTM as a consequence of inward extended compression from the Tethyan and Pacific margins of theGondwana. The basal SB tectonic event of the mega sequence results in the origin of the Neotethysthrough spreading away of Iran, Afganistan and Lhasa from the Arabo-Indian super-plate. Otherexpressions of the event are mid-Permian subaerial stratigraphic gap (SASG) in non-marine Gondwanabasins, Panjal and Ralakung igneous activities, crustal extension in High Himalaya etc. The intra-Triassic 1st order MFS tectonic event above the Late Anisian Trinodosus Zone witnessed rift-climaxingand maximized subsidence in the High Himalaya basin that led to a thick succeeding Late Anisian –Pleinsbachian HST. The event is widely expressed from Arabia to Australia. The 1st order Early ToarcianNitiscens Zone SB tectonic event marks the drowning of the carbonate platform in high Himalaya,initiation of southward transform sliding of India ( inclusive of Madagascar) against East-Africa alongthe Davies Fracture Zone from subtropics to subtemperate latitudes, large SASG with drastic lithologicalchange etc. along with varied expressions along GTM. The late Middle Oxfordian Schilli Subzone MFStectonic event marks initiation of spreading between NW Australia and Greater India and maximizedsubsidence all over the GTM and associated submarine gaps. The Early Aptian SB tectonic event isexpressed through Rajmahal igneous activity and origin of the Indian Ocean through spreading away ofAustralo-Antarctica from Inner Gondwana unit. The constituents of the Inner unit up to Middle Turonianwere largely held together but for transform sliding on either side of India without involving anyappreciable spreading. The Middle Turonian Helvetica Zone tectonic event initiates oceanic separationof India from Madagascar India, being neighbored by transformed boundaries on either side with transformsliding in opposite directions north to south in the west and from south to north in the east, sufferedanti-clockwise rotation which in-turn prompted reorganization of plates in the region along with expansionand growth of Indian Ocean from India’s eastern to western sector. The oceanic separation of Madagascarfrom India allows its rapid drift towards north. Deccan igneous outpouring took place in Late Maastrichtian

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when the drifting Indian plate passed over the Reunion hot spot that later prompted union and assimilationof India into Asia in mid-Paleogene.

The extent of influence of the tectonic events works as function of tectonic homogeneity of theregion. Until Barremian, the events extended throughout the GTM, during Aptian to Middle Turonian tothe Inner unit and later restricted only to India. The 2nd order MFS’s and SB’s, similarly, precisely date theintra-regional provincial to intra-basinal tectonic events. The sequence stratigraphic approach alsoprecisely dates the origin of the relatively short lived shallow marine corridor type seaways that developedat various stages of the Gondwana dismemberment; (a) Gondic corridor between the East and West

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Gondwana components in late Late Tithonian, (b) Dravidian corridor between India and Australo-Antarctica during Aptian – Albian and (c) Lemurian corridor between India and Madagascar duringConiacian to Early Maastrichtian. Similarly, the Indian East coast took shape during Late Aptian – EarlyAlbian and the Indian West coast during Middle Turonian.

Higher Himalayan orogenic channel: its implications onother orogenic belts of the Indian subcontinent

A. K. JainDepartment of Earth Sciences

Indian Institute of Technology Roorkee, Roorkee– 247667E-mail: himalfes@iitr.ernet.in

The core of the Himalayan orogenic belt is occupied by an extensive metamorphic belt, which hasbeen named as the Higher Himalayan Crystalline (HHC) Belt in the western parts and the Great HimalayanCrystallines in Nepal. It is characterized by (a) NE-dipping slab that is bounded by the Main CentralThrust (MCT) at the base and the Zanskar Shear Zone (ZSZ) near the top, (b) non-coaxial top-to-SWoverthrust-type distributed penetrative ductile shearing across the slab, (c) inverted metamorphismwith garnet- to kyanite-bearing rocks in the lower parts and surrounding the highest sillimanite-k-feldspar grade schist/gneiss which have undergone peak metamorphism ~ 780 0C and 10 kb, (d) associatedmigmatite, in-situ leucogranite and emplaced granitoid sheets, (e) normal metamorphic isograds nearthe top that has undergone top-to-NE extensional ductile shearing within the ZSZ mainly, and (f)differential exhumation phases. This slab-like zone has been visualized as the 15-20 km thick HigherHimalayan orogenic channel with the MCT as one, and the contact between the ZSZ and Tethyan SedimentaryZone (TSZ) as the other wall; and undergoing deformation and exhumation processes in the combinedductile shear and channel flow mode. Initially, most significant pervasive ductile shearing within theHigher Himalayan Shear Zone (HHSZ) creates the ductile shear fabric having overthrust top-to-SWdisplacement sense indicated by down-the-dip plunging lineation. This causes a syn- to post-metamorphicinversion with disposition of highest metamorphic grades in the middle to upper parts, maximum migmatitedevelopment and the lower grade rocks in the basal parts.

During the superposed later phase, laminar flow of rock material joins the ongoing top-to-the SWshearing, giving rise to a zone within the channel near the top with an apparent top-to-NE extensionalshearing. During this phase, migmatite is also continuously generated and associated with near-isothermaldecompression to ~4kb and in-situ granite generation between 46 Ma and 20 Ma, as is evident alongthe Bhagirathi section. Granitic melts remain trapped within slab-like core of the channel till these aresuddenly released from the chamber around 25-20 Ma, and emplaced near the upper channel wall due toan extensional shear zone and rheological variation with the overlying Tethyan sedimentary cover.

Eroded orogenic belts of the Indian subcontinent may not mirror image these characters, whichare so prevalent in the Himalaya, evidences of such processes might have been overlooked and called fordetailed re-examination of other belts, where non-coaxial deformation is prevalent in widespread highgrade metamorphic and granitic terrains of Aravalli, South India and Central India.

Assessment of additional draft by community wells and their impact on theshallow aquifer in the coastal belt of Kerala

John Mathai and Unnikrishnan K.RCentre for Earth Science Studies, Thiruvananthapuram - 695 031

E-mail: mathaicess@gmail.com

Community water supply schemes with open wells as sources have been implemented in the coastalregion in north Kerala. Since the area falls in the coastal belt with areas prone to tidal incursion, theperformance of the source wells and aquifer was monitored for a period of one year to identify zones ofsaline intrusion. The study involved collection of daily rainfall, recording fluctuation of water level everyfortnight in the source wells and observation wells, surveys to estimate the spot height of wells above

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mean sea level, resistivity surveys to determine the nature and extend of shallow aquifer, hydro-geologicalsurveys to characterise the area into homogeneous units and chemical analysis of water samples in twoseasons to estimate the quality of water.

Recent coastal plain, older coastal plain, modified coastal plain with mudflats constitute dominantgeomorphic units in the study area. They are further divided into ridges, swales, mounts and fore dune.Most of the source wells are located in the elevated sandy ridges and mounts where the elevation rangesfrom 6- 8 m amsl. Coastal alluvial formations with sand and sand-clay intercalations constitute thedominant lithology. Hard crusted laterite formations are seen below the red coloured sandy layer to theeastern part while in the west the sandy layer is underlain by organic rich clay layer. The fluctuation inwater level during the rainy period was controlled by the precipitation with the aquifers respondingalmost instantaneously. During the non-rainy period the water level showed a steady decline in a narrowrange of less than 2 m indicating higher water potential and homogeneity of aquifer material. Resistivitysurveys indicate a shallow sandy aquifer of 7-14 m thickness followed by clay rich layers limiting theshallow aquifer. Brackish water is indicated in wells close to the tidal creeks. Chemical analysis of watersamples indicates good potable grade water in the post monsoon period. The pre monsoon data indicatesalinity ingress in two wells close to the tidal creeks.

The study area receives an annual average rainfall of 2907 mm. During the period of observationthe area received 3326 mm of rainfall. The rainfall recharge relationship and availability of water forextraction was computed for each unit separately. The study area receives a total rainfall of 80.99 MCMwhile the present annual recharge is only 11.03 MCM or 13.62% of the total rainfall. Based on thesaturated thickness of the shallow aquifer, the area has the potential of 22.05 MCM for extraction andneeds only 27.5% of the annual rainfall to replenish the aquifer. 73% of the total potential is confinedto the elevated ridges and mounts. The response of the aquifer to the rainfall computed for eachfortnight indicates that during the rainy period the aquifers are recharged and a part of it is drainedout. The real decline in water level starts from December to May a period of six months. The cumulativereduction in the quantity of water in each unit amounts to 1.308, 2.798 and 1.043 MCM in the recentcoastal plain ridges, older coastal plain ridges and modified coastal plain mounts respectively.

Additional draft from community source wells calculated separately shows that in the recent coastalplain there is additional draft of 0.2 MCM. In the other units it is 0.05 MCM and 0.04 MCM only. The netdrawdown on account of these wells is less than 30 cm for a period of six months corresponding to thenon rainy period when compared to the overall draw down of 200 cm.

Rainwater harvesting and ground recharge- success stories from KeralaJohn Mathai and P.K. Thampi*

Centre for Earth Science Studies, Thiruvananthapuram 695 031* Former Head, Geosicences Division

Centre for Earth Science Studies, Thiruvananthapuram 695 031E-mail: mathaicess@gmail.com

Domestic wells tapping the shallow unconfined aquifer are the main source of water in Kerala, thesustainability of which largely depends on the nature of the aquifer and ability to harvest rainwater andrecharge them. Diversity of the terrain with steep slope, abrupt changes in extent and thickness ofoverburden, rapid changes in landuse, skewed rainfall, degradation and depletion of source region etc.impose severe restriction on the selection of methods of rainwater harvesting and groundwater recharge.In addition, development of sustainable sources for the upcoming industrial areas and public institutionswith limitations on the availability of land and absence of perennial water supply is a delicate task.Studies have been conducted in different parts of the state to provide perennial sources of water rightin the campus of the institutions by harvesting the precipitation received in the limited area, arrestingthe surface and base flow and recharging the shallow aquifer through site specific structures. Further,based on the peculiarities of the site, structures were designed to harvest rainwater, recharge theshallow aquifer and exploit it on a commercial basis. A few of the success stories are given below.

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Film and Video Park of KINFRA at Thiruvananthapuram is located on a laterite capped high groundwith moderate slope to the east. The open wells in the area have poor yield and water table fluctuationis about 10 m. Taking into account the topography and presence of a hollow region a percolation pondof 1 ha area was created in the lower part. A sub-surface dyke cum bund with clay core and RR masonryon either side was created adjacent to the pond on the lower part. In the elevated portions rechargepits (3 m depth) were provided in conjunction with storm water drains. The precipitation received in 20ha of land reaches the percolation pond directly and indirectly. The sub-surface dyke cum bund arrestsboth surface and sub-surface flow of water out of the campus. Presently, the entire need of the Park @2.5 lakh lpd is met from this structure.

Another success story is the Ahalia Foundation Hospital project of Kerala Health Care in Kozhippara, Palghat district – Perhaps the largest rain harvesting farm in India A 35 hectare catchment is used forcollection of all rain water falling within it. A subsurface dyke cum bund is erected using LDPE film tocreate a water body with an area of 2 hectare and average depth of 5 m. Using the same technology twomore water bodies were established in the same campus having surface area of 1.5 acres and 2 hectaresrespectively with average water depth of 6 m. After establishment of these water bodies it is noted thatall the surrounding area has a water table level same as that of the reservoir making all surrounding wellsperennial. The presence of the water body has considerably changed the microclimate of the area. Nowafter the implementation of conservation measures and the establishment of the water body throughsubsurface dike there is no scarcity of water in this area even during the peak summer months. It may benoted here that this area of Palghat district is a low rainfall area with the annual rainfall coming toabout 100 cm only.

Other success stories exclusively supported by rain harvesting are Rubber park at Mazhuvannur inErnakulam district, Poabson industries in Calicut, Yenoppaya Medical trust (Mangalore) for supply ofdrinking water, Central Rice Research Institute (Kerala Agricultural University) for storage of water forcultivation of third crop, IGO Complex near Thiruvalla, and KINFRA Industrial Park at Kunnamthanam.

Contribution of palaeoflood techniques to flood risk analysis inungauged rivers: examples from the Indian peninsula

V.S. KaleDepartment of Geography, University of Pune, Pune 411 007

E-mail: vskale@unipune.ernet.in

Extreme floods inundate large areas, uproot people and damage infrastructure. Therefore, suchevents are of a great concern to the engineers and planners. Effective planning and design of flood riskmanagement projects require accurate estimates of flood risk. Flood-risk estimation commonly involvesthe determination of the magnitude (severity) and probability (likelihood) of extreme floods. The gaugerecords in India are usually not longer than 50 years. The goal of engineers is to provide flood protectionfor at least the flood that has a chance of 1 in 100 of being exceeded in any year (aka 100-yr flood).This requires fitting of a statistical frequency distribution to short gauge record and extrapolationbeyond the gauge data. Needless to say such estimates are less accurate and reliable. Palaeofloodhydrological approach holds promise as a robust and practical tool for estimating and predictingextraordinary floods. In ungauged basins or river reaches, palaeoflood records are the only source ofinformation for the historic as well as the modern period. Another advantage of palaeoflood data is thatit provides records that are several times longer than the systematic gauge records in gauged rivers. Therecord of past floods, thus, is a measure of the tendency of a river to produce large-magnitude floodsover a long timescale. It has been shown that palaeoflood data have the same interpretative value as theconventional gauge data.

Palaeoflood technique is especially useful in remote areas where conventional hydrological data arecompletely lacking. In such data-poor river basins, high water marks of recent floods or palaeostageindicators (erosional or depositional) of past floods are used to estimate the associated discharges. Theflood stage indicators include – scour marks or lines, silt lines, slackwater flood deposits, large floodtransported boulders, flood-scarred trees, tree lines, flood debris, etc. These indicators are commonly

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used to estimate the magnitude of the largest flood along a channel. Multiple flood events are naturallyrecorded in certain specific geomorphic situations in the form of single or multiple vertically-stackedsequences of slackwater deposits.

The present study illustrates the use of palaeoflood techniques to generate a discharge estimatefor specific floods for which field evidence of stage are available. Three different rivers in the IndiaPeninsula, each with a different stage indicator, were investigated. Hydraulic models or slope-areamethod were used to generate discharge estimates from stage indicators. The rivers are: Narmada, Tapiand Vel (a tributary of the Bhima River).

The study demonstrates that the palaeoflood approach provides valuable information about extremefloods for risk analysis for both gauged and ungauged rivers that is not normally available from other sources.

Proterozoic high-stands in the Dharwar craton:evidences from the Purana sediments.

Vivek S. KaleKalyani Net Ventures Ltd.,

Industry House, Sr. No. 49, Mundhwa, Pune 411036, IndiaVivek.Kale@teleatlas.com

The Proterozic sedimentary sequences occurring on the fringes of the Dharwar Craton in the Puranabasins provide clues to the environments and processes which operated on this shield after its stabilizationand emergence. These sediments also provide evidences of major cycles of sea-level changes during theProterozoic; that definitely operated on a regional (cratonic) scale. Whether or not they can be correlatedwith global cycles is conjunctural.

The sediments from the Bhima, Kaladgi and Cuddapah basins are examined in this perspective. Theassessment of the sediment accumulation in these basin, their bounding unconformities and thedepositional environments provide excellent clues leading to a first level approximation on the depositionalsystems and sequence identification in these basis.

Based on the available information, it can be infrerred that there were atleast 2 major events of sea-level Highstands (corresponding to II/III Order Eustatic Cycles) during the Proterozoic that have beenrecorded in the Purana sediments from the Dharwar craton. The first major transgressive highstand thatencroached upon this craton (around 1800 -1600 mya) appears to have been preceeded by an event basicmagmatism along the fringes of the craton. This produced massive and comprehensive sedimentary sequencesall along the fringes of the Dharwar craton. The second event (which is recorded all across the south Indianshield) occurred during the Neoproterozoic times (perhaps around 650 + 50 Ma).

These eustatic cycles need to be assessed in the perspective of the global model of Proterozoicsupercontinental assemblies and break-ups. Prima facie, the correlation between is apparent and hasexciting implications on the Proterozic geohistory of the Dharwar Craton. However, absence of accurategeochronological data from the Purana sequences is a major impediment in this modeling.

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Cretaceous continental flood basalt magmatism in IndiaP. Krishnamurthy

Formerly with Atomic Minerals Directorate & Uranium Corporation of India Ltd.,Department of Atomic Energy, India

E-mail: krisviji@gmail.com

The Cretaceous period (145-65 Ma) stands out uniquely in terms of earth’s history, namely therifting and drifting of the Gondwana supercontinent coupled with flood basalt magmatism on both thenewly formed oceans and continental margins. Marine transgressions and mass extinctions were additionalhall marks of this period apparently related to the huge volumes of ‘new crust’ that got added andvolcanism induced climate change. The Rajmahal-Bengal-Sylhet (130-110 Ma), Karnataka-Kerala doleritedykes and St. Mary Is. rhyolites (90-83 Ma) along with the Deccan (70-65 Ma) represent the flood basaltmagmatic provinces that developed during ‘Greater India’s separation and migration. A large knowledgebase on these provinces, notably on the Deccan, had been obtained through international collaborativeprojects which have helped us to understand their evolution. Apart from passive rifting at the earlystages, active rifting, caused by thermal anomalies induced by the mantle plumes, namely Kerguelen,Crozet, Marion at the trailing edge and Reunion at the leading edge, probably caused a protracted timespan for Cretaceous magmatism in India. Non-plume models, invoke ‘rifting and delamination of enrichedcontinental mantle’ for the magmatism.

Although poorly constrained geochronologically, the magmatic cycle, with sub-cycles in the Sylhetand Deccan appear to begin with a minor alkaline-ultra alkaline phase represented by alkali basalts,fenites, carbonatites (e.g. Sung Valley ?, Sylhet; Mundwara, Sirivasan, Deccan) apparently developedduring the early, subvolcanic phases of the magmatism. This is followed by the main and dominanttholeiitic basalt phase manifested as thick piles of flows (500-1700 m) with fairly well defined subgroupsand formations based on mineralogy and chemistry as at Mahabaleshwar, Kalsubai, Toranmal, Mandla andothers. The waning stages are represented by a more heterogeneous suite, dominated by acid rock plugsand flows including ignimbrites and subvolcanic complexes (e.g. Girnar, Phenai Mata, Ambadongar?,Pawagargh, Chogat-Chamardi, Rajula, Alech, Barda) apparently influenced by crustal magma chamberprocesses.

The intensely rifted western Indian coast, Saurashtra coast, Kutch, Cambay, Narmada-Satpura-Taptiregions, show features, such as volcanic vents, fissures, dyke swarms, pyroclastics and others indicatingsource regions for the Deccan basalt plateau. Structures below the trap cover (e.g. Pranhita-Godavari,Mahanadhi and others) have also been postulated as additional source areas. Based on detailed field,petrological, mineralogical and geochemical studies, including Sr-Nd-Pb-O isotopes from a large numberof areas spread over most of the basalt plateau, a variety of processes and upper mantle source rockshave been inferred. The processes include variable degrees of partial melting, poly-baric and poly-cyclicmineral controlled fractionation (Ol/Cpx/Plag./opaque oxides) of parental /primary magmas (picritic tobasaltic), magma mixing (evolved and primitive) and continental crust contamination/assimilationfractionation, either alone or in combination within crustal magma chambers and en route from thesource. Mantle sources inferred include: (a) depleted, MORB source (peridotites) for the least contaminatedand dominant tholeiites (e.g. Ambenali type) (b) transitional and enriched MORB source or metosomatisedlithospheric mantle source for the transitional and alkalic basalts (eg. Rajpipla, Mahabaleshwar andothers), (c) iron-rich ilherzolites, and (c)mixture of peridotite and eclogite within the subcontinentallithosphere wherein the eclogites will almost totally melt to give large volumes of primitive basalts.

Palaeogeographic evolution of the Cuddapah basinG. Lakshminarayana

Geological Survey of India, Coal Wing, Salt Lake City, Kolkata 700091E-mail: glakshmi_1999@yahoo.com

Sediment fill in the crescent shaped Cuddapah Basin consists of quartzite-shale-carbonate assemblageoccurring in the form of mega cyclothems corresponding stratigraphically to the Papaghni, and Chitravati/

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Nallamalai Groups (middle Proterozoic - Cuddapahs) and Banaganapalli and Jammalamadugu Groups (lateProterozoic - Kurnools). Lithofacies attributes and palaeocurrents indicate deposition of the Papaghnisediments was initiated in alluvial fan-shallow marine shelf/ramp setting with palaeo-shorelinecorresponding to the present outcrop limits of Gulcheru Formation in the west. The Peninsular GneissicComplex of the eastern Dharwar craton was elevated enough to enable the onset of alluvial fans thatdebouched into the then newly initiated Cuddapah Basin. Vemapalle Stromatolitic dolomite-chert- shalecycles were deposited in shallow water but the upper chert breccias beds indicate basinal instability atthe closing phases of Papaghni sedimentation. Following an interlude of post Papaghni basalt volcanism,the Chitravati deposition was initiated along Pulivendla shoreline which came into being about 25 kmeast with respect to the Papaghni shoreline. A passive continental margin setting is visualized for thewestern margin of the basin. The basin was open towards east like the present day Bay of Bengal and itseastern shorelines during the Papaghni and Chitravati episodes may have been located elsewhere alonga counterpart crustal fragment during middle Proterozoic. The Nallamalai metasediments are traced beyondthe eastern margin of the Cuddapah basin right upto Podili-Kanigiri igneous complex hitherto consideredto be a part of Nellore Schist Belt (NSB). Evidences for syn-sedimentational volcanism and associatedcatastrophic events are identified in Nallamalai sediments near Kanigiri. The final phase of Chitravati/Nallamalai deposition was accomplished in a shallow epeiric sea wherein the quartzite sheets (Gandikotaand Bairenkonda) were deposited in an intertidal setting for which a newly emerging southeasterlyprovenance also contributed sediment supply to the basin. A major compressional tectonic event at theend of the Nallamalai sedimentation culminated in deformation, metamorphism and igneous activity. Asa result, Nallamalai metasediments progressively became schistose towards east, folded ,faulted andsubsequent erosion resulted in the disposition of discontinuous schist-quartzite belts amidst thegranitic-basic and alkaline complexes. It is for these reasons the eastern limit of the Cuddapah Basinremained poorly delimited. The post-Nallamalai tectonic event may be considered as a manifestation ofamalgamation of Precambrian landmass-Rhodinia. The late Proterozoic Kurnool sedimentation was initiatedover the deformed Cuddapah tracts in several isolated depressions which later coalesced in N-S directionto form a superposed Kurnool sub-basin. Provenance for Kurnool sediments was intrabasinal i.e. olderCuddapahs and the deposition was accomplished in two uninterrupted quartzite-carbonate-shale cycles.The present configuration of the Cuddapah Basin was attained during the post Kurnool epeirogenicmovements. Therefore, it is indicated that the Cuddapah Basin evolution was accomplished in multipleepisodes of sedimentation and tectonism thereby making it an unique geological terrain of India toshow evidence for the reconstruction of Proterozoic crustal fragments.

Changes in the Long-term deformation pattern in the Andaman-Sumatra trench-arc region after the 26 December 2004 mega thrust earthquake

S.Lasitha1 and M.Radhakrishna1, 2

1Department of Marine Geology and Geophysics, Fine Arts Avenue,Cochin University of Science and Technology, Cochin 682 016, India.

2Department of Earth Sciences, Indian Institute of Technology Bombay,Powai, Mumbai-400 076.

E-mail: mradhakrishna@iitb.ac.in

On 26 December 2004, a mega thrust earthquake of magnitude Mw ~ 9.3 struck off the coast ofnorthern Sumatra and ruptured nearly 1300 km of plate boundary up to the Andaman Islands. Therupture zone is 100 km wide and the earthquake gave rise to maximum slip of 20 m. This event wasfollowed by another major thrust earthquake of Mw ~ 8.7 on 28 March 2005 about 300 km furthersoutheast. Historical and recent catalogue of events in the region also shows many great / largeearthquakes which are known to have occurred along the plate boundary as a result of subduction of theIndo-Australian plate beneath Sumatra in an approximately NE direction at an oblique angle to theSunda trench. In the present paper, a detailed analysis of changes in long-term seismic deformation

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after the 26 December 2004 mega thrust earthquake has been carried out along the Andaman-Sumatraarc mainly for two reasons, i) to study the changes that were brought out in the deformation pattern invarious segments of the arc, due to the mega thrust event followed by intense seismic activity all alongthe rupture zone, ii) to update the long-term deformation pattern along and across the arc that will beuseful in identifying areas of increased future seismic hazard.

The results on crustal deformation rates estimated in the Andaman-Sumatra region before (1900 –2004) and after (1900 – 2005) the mega thrust earthquake show drastic change in the long-termdeformation rate in the Sumatra offshore between 0º to 4º. The deformation pattern indicates thedominance of compressive stresses in the fore arc region with the direction of maximum compression inalmost NNE – SSW. While, it is almost normal to the trench in the Sumatran fore arc near Nias islandregion, the compression takes more oblique trend with respect to the trench towards north near AndamanIslands. For the sources OSF2 and OSF3, the extensional deformation rate becomes negligible after themega thrust event. In the source OSF2, where the 26th December 2004 event was located, the compressionaldeformation rate increases from 5.2 mm/yr to 150.5 mm/yr. In the next overlapping window OSF3, whereboth the 2004 December and 2005 March events occurred, the compressional deformation rate changesfrom 7.3 mm/yr to 252.6 mm/yr. In the source OSF4, where only the 28th March 2005 was located, thecompression rate changes from 22.3 mm/yr to 93.1 mm/yr. The deformation velocities suggest that thepartial compression with a component of strike-slip faulting prevailing earlier had transformed into acompletely compressional environment due to the post-tsunami seismic deformation in the Sumatranoffshore. The right lateral strike slip motion prevails all along the SFZ and deformation rate also remainedalmost constant due to absence of major postseismic events, except in source SFZ7, where thecompressional deformation increased from 29 mm/yr to 35mm/yr and extensional deformation increasedfrom 14 mm/yr to 22 mm/yr. All along the Andaman fore arc region, the deformation is predominantlycompressional and show considerable variation along the arc, whereas, the sources in the back arcregion show very little variation in the deformation rates after the mega thrust earthquake. The resultshave been discussed in the light of ongoing tectonics of the region and recommend the need for re-assessment of long-term seismic deformation whenever such mega-thrust earthquakes occur alongseismically active belts.

South Indian high-grade domain:a differentially transformed Archaean continental lithospheric segment

T. M. MahadevanRetd.Director, Atomic Minerals Division

Sreebagh, Ammankoil Road, Ernakulam- KOCHI-682 035E-Mail: tmmahadevan@rediffmail.com

The evolution of the South Indian High-grade Domain (SIHGD) is modeled as the transformation ofan Archaean buoyant lithosphere through the Proterozoic following two distinct styles that distinguishthe Northern Block (NB) from the southern Pandyan mobile belt (PMB).

The Archaean SIHGD developed deep sub-continental lithospheric mantle (SCLM) roots, debatablyto depths of about ~250km, possibly by 2.2 Ga, and moved into more than one phase of extensionalfracturing and exposure to the thermal regimes of the mantle. In the NB, emplacement of several smalldyke swarms and an early syenite-carbonatite complex at Hoganekal dated ~2.2 Ga help to date thecooling and stabilization of the Archaean lithosphere (“cratonisation”) and its enrichment below theArchaean crust. It is suspected the cratonisation process may have had even a greater ancestry. After alapse of a long stable phase, onset of distension and a new thermal regime led to development of the NEtrending Dharmapuri straight belt (rift zone) and emplacement of the well known alkaline ultramafic-syenitic-carbonatitic complexes, within the 1200 —650 Ma time span, (perhaps ~750Ma). Accompanyingextensive metasomatism, brought about an amphibolite facies metamorphic impress on the granulitebasement, resetting the structural trends and possibly radiometric clocks.

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The PMB, in contrast, was greatly involved in the Late Proterozoic Pan-African thermal events (650to 550 Ma) and remained an open system exposed to mantle thermal regimes. The region was exposed toextensive granitic and alkali granite magmatism and influx of alkaline and CO2 – rich fluids, leading togeneration of largely crustal partial melts, migmatisation, charnocktisation and some selectivemineralization. The mobilized melts and fluids, possibly with increments from SCLM sources, were enrichedin large-ion lithophile and high field strength elements and may be expected to have reset the isotopicclocks, imparting new radiometric ages that, in fact, date the metasomatic events. The view that thePMB is a Proterozoic continent based on radiometric dates ignores an Archaean protolithic parentage.

The configuration of SIHGD into the NB and PMB is the result of differential exhumation possiblydue to buoyancy differences and resulted in steep intracontinental faults often designated “sutures”.The faults are of different generations. Listric tendencies assigned to these faults lack evidence. Theextensive exposures of lower crustal charnockitic massifs along the Sahyadri is due also to pro-activeparticipation of the Late Mesozoic coastal rifting and possible uplift by underplating , eastward tilt ofthe continent, followed by erosion and isostatic uplift. Tectonic and geophysical modeling is incompleteif an integration of the Precambrian and Late Mesozoic processes are not reckoned and the several“sutures” are not dated.

SIHGD illustrates how through continued thermal interactions with a buoyant lithosphere and thethermal and (?) fluid regimes of the sub-lithospheric mantle, a buoyant Archaean continent may imbibeyounger features of the Proterozoic and even , perhaps, the Phanerozoic .It may provide an example ofrelevance to Indian continental evolution.

Trends of marine researches - past, present and futureT.K.Mallik.

Former Director, Marine Wing, G.S.I.FD-317, Sector- 3, Salt Lake, Kolkata- 700106

E-mail: tkmallik@rediffmail.com

The sea has been a source of food, recreation, mode of transport, a site for waste disposal anda regulator of climate from ancient times.. The sediments of the sea and the embedded fossils record thehistory of geological events. Ocean contains various mineral resources including oil, gas and gas hydrates.

It is established since 1726 that the observable processes in the Ocean can explain the geologicalevents in the land.. HMS CHALLENGER expedition in 1873-76 raised lot of interest in the scientificcommunity followed by a number of expeditions .In early 19th Century studies were mainly related tosediments, shoreline configuration, earths magnetism, heat flow, seismic survey etc World War I compelledthe development of Echo sounding Technology to understand the submarine topography including configuration of the mid oceanic ridges, valleys, trenches etc. The National Science Foundation, USAboosted the Marine Research by forming the Deep Sea Drilling Project to understand the history andformation of the earth. At the end of World War II emphasis was led to deploy submersibles,. deep towequipments, side scan sonars, TV Camera etc.

In India the initial studies were restricted to the beaches. and coastal sectors after GSI came intoexistence in 1851 . Systemetic study started with the participation in the International IndianOcean Expedition in 1960 and several Institution ,Agencies and Universities began to work on differentaspects . Major studies in the Ocean areas are being carried out by the Marine wing , GSI and theNational Institute of Oceanography.

Studies on different aspects include the mapping the Continental margin , Exploration of Mineraloccurrences, coastal erosion and deposition , seabed morphology, paleo oceanography, palaeoclimate,sea level changes, coastal dynamics, determination of Geophysical, Geochemical, Geotechnical , physical,chemical biological and engineering parameters. of sediments, disposal of wastes, remote sensingapplications, archeological studies etc.. NIO was the lead organization for the first scientific expedition

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to Antarctica Establishment of Seismological and GPSD at the ice continent by NGRI is very creditable.Pioneering studies on Coastal Zone Management ,Wave Studies has been carried out by CESS .Trivandrum First polar research laboratory in Antarctica has been established by he National Centre for Antarctic and Ocean Research . The INCOIS at Hyderabad is responsible to synthesize, generate and coordinatevarious endeavors in the field of ocean observation and provide advisory services to various users.

It is important to delineate problems of future research and indicate the priorities. We shouldfirst aim to solve societal problems related to the coastal zone . .Society is dependent on this zone forits biological diversity, mineral resources, recreational opportunities, fishing industries etc. The systemsatisfies the need for waste disposal and transportation also. Storm surges, sea level rise, erosion andsilting often causes great problems and we have to monitor these problems closely and try to find theprotection.. Multidisciplinary investigation of the sedimentary dynamics and environment should begiven a priority for more benefit of the mankind. A coherent programme for unresolved problems related to fine scale strata architecture in a sedimentary facies and the energy fluctuations in sedimentwater interface are still not clearly understood. Sedimentary dynamics of the shelf and shore faceenvironment should be studied in detail. Interdisciplinary and multistage investigation of particletransport, numerical modeling , facies architecture, coastal behavior etc needs to be studied properly. Modeling studies should help to understand the processes and the response to processes The linkbetween the large scale shelf and marine processes with the terrestrial sediment supply should beproperly understood The sediment dispersal pathways through the estuaries and inlet are still poorlyunderstood and the study will help to know about the bed load ,suspended sediment etc. An integratedapproach is desirable . More and more attention should be paid to near coastal placer deposits ratherthan deposits in the deep sea.. We are in the grip of acute Power Shortage and OTEC can be a solutionfor this problem

Issues related to effect of storm surges, tsunami and earthquake are important We have to understandthe full background to find out the Process-Response model and document the triggering mechanism ofthese hazards The technology to install undersea observations and event detection systems should bethought.. It is essential to collect a baseline data and create a data bank. Coastal hazard managementstudies should form a part of the Marine Geology course.

Proper attention should be given to understand the role of the variety of life that is in the seaand their sensitivity . Role in biochemical cycling of nutrients and the correlation of chemistry withbiology should be established. to understand many processes. Ichnology is another new field whichhas been useful in recognition of environment. Extensive biogenic activity has sometimes causedcoastal erosion in some sectors. Some of the Polychate tubes has been used as a biogenic tool forready and precise estimation of current annual rates of erosion and deposition in coastal profiles andattention should be paid to these types of studies.

There is need to develop suitable infrastructure for the advanced work The educational systemshould improve so that the basic need of understanding the marine science is imparted in the studentlevel itself. There is also an urgent need for evolving integrated national marine science explorationpolicies to avoid repetition and shouldering proper responsibilities by different organizations . It isdesired that for better development, free and rapid flow of information should exists between NationalSurveys, Universities and Research Institutes A multi disciplinary integrated approach is desired toachieve our goal of understanding and solving the problems.

Archean Crustal growth processes as evidenced from thegreenstone belts of eastern Dharwar craton, India

C. Manikyamba, Tarun C. Khanna, P.K. Prachiti, K. RajuNational Geophysical Research Institute, Uppal Road, Hyderabad 500 606

E-mail: cmaningri@yahoo.com

The Archean geological period represents one third of Earth’s history spanning 4.0 – 2.5 Ga duringwhich much of the crust formed and stabilized as cratonic lithosphere. Specifically, the Neoarchean is a

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significant period of crust formation due to voluminous eruption of mafic-ultramafic volcanism, bimodalarc lavas, tonalite-trondhjemite-granodiorite (TTG) batholiths and K-rich granitoids that are excellentlypreserved in different greenstone belts of Dharwar craton. The granite-greenstone terranes of the worldrecord indicate the formation of new continental crust at convergent margins between 2.8-2.6 Ga andsome of them are most intensely mineralized late Archean greenstone belts (Yilgran Craton and SuperiorProvince). During this time, there is a world wide record of multiple events of eruption of komatiite-tholeiite and tholeiite-calc alkaline magmatism. Recent studies have highlighted contemporaneousdevelopment of plume-arc related volcano-sedimentary associations in Canada and India. The geologicaland geochronological connection between the Dharwar, Bastar and Singhbhum cratons and east Antartica,suggested that these two terranes amalgamated during convergence and collision at ca. 2.5 Ga. Accordingto Swain et al. (2004), the tectonothermal history of the Dharwar craton has links with Australia, northChina craton and east Antartica preserving the gological and geochronological evidence for extensiveconvergent margin magmatism and high grade metamorphism between ca 2560-2400 Ma. The Dharwarcraton, preserves a history of tectonothermal event of 3.4 Ga mantle plume, ~2.7 Ga calc-alkalinemagmatism and the orogenic event at ~2.5 Ga. The late Archean lithologies of the Dharwar craton areconsistent with the crustal growth between ca 2560-2500 Ma from different cratons (Australia, China,Canada) interpreted to reflect an evolving arc environment analogous to modern plate tectonic likegeodynamic processes.

The lithological ingredients present in different greenstone belts preserve the evidence of interactionbetween convergent margin tectonics and mantle plume activity responsible for crustal growth in theDharwar craton. High precision major, trace and rare earth elemental data obtained from the ultramafic,mafic and felsic volcanic rocks of Sandur, Hutti, Penakachela, Gadwal and Kadiri indicate the presence ofboninites, high Mg basalts, Nb-enriched basalts, andesites, dacites, rhyolites along with high silica andlow silica adakites. Identification of these rock types having distinct geochemical signatures fromdifferent greenstone belts reflects on their source and tectonic setting. Most of them geochemicallyresembling with magmatic rocks generated at Phanerozoic subduction zones. Some of them are indicativeof plume-arc interaction while few of them exhibit across-arc variation. The available geochemical dataendorses complex arc situations during the Archean period in the Dharwar craton that have contributedfor the crustal growth process in this region.

Fractal analysis, microstructures and deformationprocesses-potential in the Indian context

Manish A. MamtaniDepartment of Geology & Geophysics; Indian Institute of Technology

Kharagpur 721302, West Bengal, IndiaE-mail: mamtani@gg.iitkgp.ernet.in

Mineral grain shapes are influenced by deformation processes that are active on the microscale,which in turn are controlled by factors such as temperature, strain rate, stress, fluids etc. Therefore,quantification of mineral grain boundaries and/or their perimeter shapes can be useful in decipheringdeformation conditions. In this paper, the application of fractal geometry in quantifying mineral grainshapes is highlighted. Samples from the Godhra Granite (southern parts of Aravalli Mountain Belt) aretaken and data are presented from two different fractal geometry techniques (a) ruler dimension (Dr)analysis of quartz grain boundary sutures and (b) area perimeter fractal dimension (Da) analysis of quartzgrains. It is shown that Dr works well as a geothermometer. Da is found useful in identifying strain ratevariations in different parts of the granite, but its application as an absolute strain rate gauge remainsdoubtful. Ruler dimension analysis of magnetite grain perimeters (Dm) in the Godhra Granite is alsoperformed. A negative correlation is found between Dm and grain size of magnetite (dm), which isinterpreted in terms of different dominant deformation mechanisms in the coarse and fine magnetitegrains. Thus, the importance of fractal geometry techniques in analyzing deformation fabrics as well asdeciphering deformation conditions in Indian rocks is highlighted.

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Petrography, Palaeomagnetism and 40Ar/39Ar Geochronology of the LateCretaceous –Early Palaeogene Igneous Activity along the West Coast of India

Mathew Joseph,1,3* Mireille Perrin1, T.Radhakrishna2, Jean Marie Dautria1, Henri Maluski1,G.Balasubramonium2 and Jossina Punoose2

1Geosciences Montpellier, University of Montpellier 2, C60, 34095, Montpellier, Cedx 5, France2Centre for Earth Science Studies, Trivandrum, 695031, 3Geological Survey of India,

Trivandrum, 695013 *Email: mathewj65@yahoo.com

Post-Archaean mafic magmatism in the south Indian shield, is mainly manifested as mafic dykeintrusions. The dykes that occur in the interior of the shield are mostly of Proterozoic age, while thosein the west coast are of late Cretaceous–early Palaeogene age and are related with the final break-up ofGondwanaland. Two discrete magmatic episodes, separated by a short time span (20-15 Ma), have beenproposed for the Phanerozoic dyke emplacements. Dyke intrusions of younger igneous episode (65-69Ma), supposed to be coeval with Deccan continental flood basalt magmatism, constitute the main dykemagmatism in central/north Kerala and Goa region along the coast. The older episode is represented bythe prominent gabbroic dyke in central/north Kerala of c.90-85 Ma age. In Agali-Coimbatore area withinthe western segment of Bhavani shear zone, the predominant dyke emplacement is of Proterozoic age,while dykes related to the 90-85 Ma age are sporadic in occurrence.

Despite large scale weathering and lateritisation throughout the area, we could locate and sample(including central and contact zones) eighteen sites which are quite fresh. Fifteen sites were sampledfrom the NW-SE trending dolerite dykes coeval with the major Deccan activity. The samples belonging tothe older episode of magmatism include one dyke from the Agali-Coimbatore dyke and two sites from theSt. Mary Island volcanics. The coarse grained gabbros were not sampled for the study.

Most of the doleritic dykes are microlithic to porphyritic microlithic in the chilled margins withtypical mineral assemblages of plagioclase, augite, olivine and Fe-Ti oxides. Olivine is often transformedto iddingsite. Fe-Ti oxides occur either as early inclusions within pyroxene or as interstitial and mayconstitute the late crystallization phases. The alterations appear to be of deuteric origin during magmacooling stage.

Selected specimens from each site were subjected to low and high temperature susceptibilitymeasurements to define the magnetic carriers and the thermal stability of the samples. They have indicatedtitanomagnetite to be the main carrier of magnetization. The samples from the older group have shownreversible curves up to curie point, while all samples have shown reversible curves at least up to 350°C.Viscosity index of samples were also determined. It shows a wide range, with 1/3 of the values beingbelow 5 %. Higher values up to 921 were also yielded.

Palaeomagnetic measurements were carried out by step-wise alternating field and thermaldemagnetizations. Except six sites all other sites have yielded characteristic remanent magnetisations.Seven sites have given normal magnetization, three have given reverse magnetization and the other twosites present a new direction. The 90-85 Ma episode consisting of the dyke from Agali-Coimbatore andthe volcanics for the St.Mary Island have yielded mean palaeomagnetic direction (D = 323.3; I = -56.9,N=3, kappa = 71and á95 = 14.7) with a mean VGP (Lat. = 28.8, Long. = 288.1, N = 3 and A95 = 20.7).Samples from site 5, 10, and 16, for which age determinations are not available, have directions and VGPsimilar to the 90-85 Ma rocks (D=340, I = -68.5, N=3, kappa = 129.8 and á95= 10.9 and a mean of Lat.=22.8, Long. = 267.3, N=3 and A95=10.9). But a younger age cannot be ruled out for these doleritedykes. The implication of the new direction (D = 150.9, I = -68.3 and á95= 15.8) from sites 1 and 3 isbeing worked out. The mean for the reversely magnetized vectors is D = 139.3, I = 62, N = 3 and á95 =27.7 with a mean VGP of Lat. = -26.2, Long. = 101.3, N = 3 and A95 = 39.8. The 90-85 Ma dykes of Agali-Coimbatore area are coeval with the volcanism in St. Mary Islands off the Malpe-Mangalore coast and thecontinental flood basalt volcanism in Madagascar and may constitute a part of large igneous provincerelated to Madagascar vs India-Seychelles rifting. The younger 65-69 Ma dyke emplacements are associatedwith the final phase of Seychelles-India breakup.

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Tectono- sedimentatary evolution of Kerala-Konkan basin:implications on hydrocarbon prospectivity

J. Mishra, Rama Paul, Radha Krishan, B.K. RathKDMIPE, ONGC, Dehradun- 248 195

Kerala-Konkan basin is located in the southeastern part of Western continental margin of India ina divergent margin set up. The basin lies to the south of Bombay offshore basin. The basin is boundedby Vengurla arch in the north and extends beyond Cape Comorin into the Indian Ocean to the south.The basin is divided into two sub basins i.e. Konkan basin between Vengurla and Tellichery arch in thenorth and Kerala basin between Tellichery and Trivandrum arch in the south.

The basin evolved due to the thermo-tectonic rifting-drifting of Madagascar from India duringMiddle Cretaceous. Large scale rifting was associated with this continental break up and the basin witnessedan early rift phase during this period. The rifting has taken place along the NNW-SSE Dharwar basementgrain, forming configuration of western margin of India a long relatively straight, rifted passive margin.The event of Madagascar separation represented by ‘older’ traps dated 90-110Ma. Structural style in thebasin is mainly controlled by NNW-SSE trending faults parallel to the coast line and mostly confined to theshelfal part and NNE-SSW faults oblique to the Miocene shelf edge and confined to the basinal part. Aleppeyplatform with thick carbonate sequence is an important structural element of the area.

The sedimentary succession in the basin ranges from Cretaceous-Recent and is broadly divisibleinto two sequences viz. Rift sequence and passive margin sequence. The Lower rift sequence correspondsto rifting and separation from Madagascar during Middle Cretaceous. The overlying Late Cretaceous toRecent represents the passive margin sequence. The basin witnessed the early rift phase in Late Cretaceous,dominantly along the NNW-SSE trends. The Late Cretaceous sediments were deposited as part oftranstensional tectonics. These sediments comprising mainly fine to medium grained glauconiticsandstone, calcareous siltstone, limestone and shale were deposited in a shallow to marginal marineregime with dominant periodic clastic influx. Major part of Early Paleocene is a hiatus in Kerala–Konkanbasin. Late Paleocene marine transgression is seen in all over the basin except on the shallow shelf whereit is represented by continental sands with clay and lignite.

Early Eocene to Middle / Late Eocene period was marked by a basin wide transgression and theentire platform acted as homoclinal ramp with deposition of thick carbonates. End of Middle Eocenewitnessed withdrawal of sea resulting in pronounced unconformity. The Late Eocene carbonates wereeither not deposited or completely eroded off over major part of the basin. Carbonate deposition continuedthrough Oligocene up to Middle Miocene. The end of Middle Miocene experienced severe tectonicactivity and upheaval resulting in erosion and marking the end of carbonate sedimentation. Huge influxof fine clastics was witnessed in the Post- Middle Miocene period.

The hydrocarbon prospectivity of Kerala-Konkan basin appears to be promising because of itsproximity to major hydrocarbon producing Mumbai Offshore basin to the north. Thirteen prospects haveso far been probed by exploratory drilling. Thirteen exploratory wells and one DSDP well have been drilledand hydrocarbon shows have been recorded in some wells. However, no petroleum system has beenestablished in the basin as yet. Source rock studies indicate favourable source facies within Late Cretaceousand Paleocene-Early Eocene clastics. The basin is endowed with good reservoir facies within LateCretaceous clastics, Paleocene-Early Eocene clastics and Eocene- Miocene carbonates, as bioherms,aggrading and prograding shelfal banks, and isolated algal banks. Probable hydrocarbon plays in form ofcarbonate growth and carbonate debris and clastic wedges have been identified.

Speculative Mesozoic and Tertiary Petroleum System Petroleum Systems have been envisaged in thebasin. The Late Cretaceous sediments, deposited as part of syn-transtensional tectonics with hugethickness in those lows, may act as good kitchen over the area. Restricted environment of depositionduring early rift phase and the favourable thermal domain because of proximity of the basin to thespreading center and shallow mantle were conducive for development and maturation of source rocks.The south-western part of Cochin high/Aleppey platform in Kerala basin seems to be promising forMesozoic exploration. Burial history modeling suggests that the Mesozoic sediments are capable of

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producing hydrocarbons. However, establishing the petroleum system elements especially the sourcerock distribution, kitchen areas, charge timing, migration pathways and regional cap remain as themajor challenge for exploration in the basin.

Proterozoic high-stands in the Dharwar craton: evidences from the Purana sediments.

Vivek S. KaleKalyani Net Ventures Ltd.,

Industry House, Sr. No. 49, Mundhwa, Pune 411036, IndiaVivek.Kale@teleatlas.com

The Proterozic sedimentary sequences occurring on the fringes of the Dharwar Craton in the Puranabasins provide clues to the environments and processes which operated on this shield after its stabilizationand emergence. These sediments also provide evidences of major cycles of sea-level changes during theProterozoic; that definitely operated on a regional (cratonic) scale. Whether or not they can be correlatedwith global cycles is conjunctural.

The sediments from the Bhima, Kaladgi and Cuddapah basins are examined in this perspective. Theassessment of the sediment accumulation in these basin, their bounding unconformities and thedepositional environments provide excellent clues leading to a first level approximation on the depositionalsystems and sequence identification in these basis.

Based on the available information, it can be infrerred that there were atleast 2 major events of sea-level Highstands (corresponding to II/III Order Eustatic Cycles) during the Proterozoic that have beenrecorded in the Purana sediments from the Dharwar craton. The first major transgressive highstand thatencroached upon this craton (around 1800 -1600 mya) appears to have been preceeded by an event basicmagmatism along the fringes of the craton. This produced massive and comprehensive sedimentary sequencesall along the fringes of the Dharwar craton. The second event (which is recorded all across the south Indianshield) occurred during the Neoproterozoic times (perhaps around 650 + 50 Ma).

These eustatic cycles need to be assessed in the perspective of the global model of Proterozoicsupercontinental assemblies and break-ups. Prima facie, the correlation between is apparent and hasexciting implications on the Proterozic geohistory of the Dharwar Craton. However, absence of accurategeochronological data from the Purana sequences is a major impediment in this modeling.

Tectono-stratigraphic evolution of Gondwana basins ofIndia with an outline of coal development

G. Mukhopadhyay, S.K. Mukhopadhyay, Manas Roychowdhury and P.K. ParuiGeological Survey of India; Coal wing, Kolkata 700 091

E-mail: ddgcoalgsi@rediffmail.com

Gondwana basins of India occur within the suture zones of Precambrian cratonic blocks of PeninsularIndia along some linear belts. More than 99% of the total resource of coal in our country is presentwithin these basins. The basins are demarcated by boundary faults having graben or half-graben geometry.The temporal evolution of these boundary faults in the context of Gondwana sedimentation is acontroversial issue.

These basins preserve a thick sedimentary pile spanning over nearly 200 million years. However,due to lack of well-constrained data, age of most of the formations is assigned tentatively. This hasresulted in diversified views on both intra- and inter-basinal stratigraphic correlation particularly incase of Upper Gondwana formations.

To address these problems, during the present study, some unique events, well constrained byage data in the other parts of Gondwanaland, like marine flooding surfaces, large scale tectonic eventsor major change in depositional environment have been used as a tool for temporal correlation withinthe Gondwana basins of India. Considering these major events as time planes the lithosequence of

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different Gondwana basins has been classified into different time slots that help in better understandingof basinal history.

Initial sedimentation took place during late Carboniferous or early Permian in troughs formed byglacial scouring over the Precambrian basement. Widespread transgression took place during EarlySakmarian at around 292 Ma as evidenced by marine fossils at the top of Talchir Formation in manybasins of India. Tethyan marine front entered into the low-lying basinal area from north, east and west.During the subsequent regressive phase Karharbari and Barakar formations were deposited with majorcoal seams in a tectonically active environment. Coal seams associated with Karharbari Formation orLower parts of Barakar Formation are generally low ash, inertinite rich and erratic in their distribution.Major coal deposits of all the basins occur within the middle part of Barakar Formation. The thickest coalseam in individual basin has some striking similarity both in their stratigraphic disposition as well aspetrographic make up and likely to represent the first correlatable major coal forming event. In manybasins another period of thick coal development can be recognized within Barakar Formation that marksa distinct change in coal character as well as nature of associated sediments.

A series of marine transgressions are recorded from other parts of Gondwanaland between 271 - 256Ma. Evidence of this transgressive event is present within Barren Measures and its equivalent formationsin the marginal basins of Peninsular India. coal forming environment reappeared in the succeedingregressive phase during the deposition of Raniganj and equivalent formations. Although major coaldeposits are found only in Raniganj, Jharia and Singrauli coalfields but thin coal seams/bands arepresent in almost all the coalfields.

P-T boundary ushered an arid environment in all the basins of India. Large scale extinctionoccurred across the plant and animal kingdom all over the earth. New species appeared that couldsustain the arid condition. The sedimentation in most of the Indian Gondwana basins came to a haltwithin Norian.

This is followed by a period of nondeposition, basinal tilting, erosion and major Faulting. Adistinctly different depositional mileau was established during Early Jurassic when the nature of sedimentschanged completely. New basins opened up along the western margin of Peninsular India. India alongwith other constituents of eastern Gondwana started separating from western Gondwana.

The last phase of sedimentation within the Gondwana basins took place in some isolated areasduring Late Jurassic/Early Cretaceous. Marginal basins along the eastern coast opened up. Extrusion ofTholeiitic lava took place in the form of Rajmahal Trap and Lamprophyre dykes/sills were emplacedwithin Gondwana basins in the eastern part of India. India got separated from Antarctica and Australiamarking the end of the history of Gondwana basins.

Neoproterozoic biotic signatures in the peninsularIndian basins-an overview

Mukund SharmaBirbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow-226 007

E-mail: sharmamukund1@rediffmail.com

Neoproterozoic successions world over are characterized by the large acritarchs, advent of calcareousmetaphyte and metazoan and finally distinct animal remains known as Ediacaran animals. A distinctperiod has been named after this assemblage called Ediacaran Period in Neoproterozoic Era. Neoproterozoicsuccessions in Peninsular India exposed in Kurnool and Bhima basins are ideal sections for the study ofbiotic evidences of this Era. Detailed study of the Narji Limestone Formation has shown the presence ofmany burrow structures and the Owk Shales Formation of the Kurnool Group has yielded varied carbonaceouscompressions and impressions that include Chuaria–Tawuia, Ellypsophysid, Moranid and Beltinid remains.Besides these remains, large acritarchs and helically coiled forms are also recovered the shales. Helicallycoiled forms characteristic of Ediacaran Period include Obruchevella, and Volyniella. The Panium QuartziteFormation has shown the presence of early animal traces. The Koilkuntala Limestone Formation yieldedstructured advanced metaphytic algae. All these evidences collectively indicate the presence of an idealNeoproterzoic succession in Kurnool basin.

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The Halkal Shale Formation and the Hotpet Sandstone Formation of Bhima basin are promisinglithounits that have yielded Ediacaran biota. Abundant well preserved diversified macrofossils preserved ascompressions and impressions have been recorded from the intracratonic argillaceous sediments of theBhima basin in south India. Impressions and compressions in the Halkal Formation belong to Chuariacircularis, Tawuia dalensis, Sinosabellidites huainanensis, Pararenicola huaiyuanensis, Proteoarenicolabaiguashannsis, Daltenia mackenzienis, Morania antique and Beltina danai. In the Hopet Formation are notedanimal traces of Ediacaran Period. The paper discusses the diversity, and biostratigraphic potential ofthese macrofossils specially Chuaria and Tawuia assemblage as biozone and phenomenon of gigantismOccurrence of global marker event like phosphotisation, absence of stromatolites, presence of complicatedforms, gigantism in carbonaceous remains in Halkal Formation of the Bhima basin indicate a latest TerminalProterozoic age. Both these basins are suitable for understanding position of India in the Rodinia as well.

Geo-environmental health hazard due to fluorosis in Chittur-Kollengode area,Chittur taluk, Palakkad district, Kerala.C. Muraleedharan and V. Ambili, Senior Geologists

Geological Survey of India, Ops: TNPK, Unit: Kerala Dharani Bhavan, Manikanteswaram. P.O.Thiruvananthapuram, 695013, 0471-2374594, 2374595. Fax: 0471-2374598

E-Mail: muralee_kal@rediffmail.com

Generally, the interaction with natural materials is believed to be non hazardous. Nevertheless somegeologic materials pose health hazards in certain geo-environment. Fluoride is a trace element and is veryessential for many enzymatic functions and it completely absorbed in the stomach and intestine. 50% ofthe fluorite extracted through kidney. The main retention sites of fluoride are bone, cartilage and dentaltissue. It plays an important role in the prevention of chronic disease (dental carries). Excess consumptionof fluoride may cause dental fluorosis (mottling and staining of teeth) and skeletal fluorosis (increasedbone mass, calcification of ligaments) if consumed for longer period. Fluoride in drinking water can bederived from the weathering of fluoride bearing minerals in the rock, from volcanic activities, springs,fertilizers and industrial waste. Environmental pollution takes place through changes in energy pattern,physical and chemical decay of the materials and abundance of the micro-organism. Quite often environmentalpollution reported after the anthropogenic activities and very rarely due to the decay of natural ores andminerals. Fluoride contamination in ground water was reported in many parts of Kerala particularly in andaround Kollengode-Chittur areas, Palakkad district leading to fluorosis hazards both dental and skeletal arealso reported. To corroborate the idea, 34 random water samples from open and bore well, tap water werecollected in the eastern and northeastern part of the topo sheet No. 58B/10. The study area comprises thePrecambrian basement rock mainly hornblende-biotite gneiss, gneiss and gneissic charnockite traversedby pegmatite and quartz veins. Geomorphic discontinuity-Palghat gap is the geomorphic unit, probably astructural discontinuity. This area is mainly cultivated with paddy and well irrigated. The analytical resultshows that the values range from 1ppm to 9ppm. More than 20 samples gave the value above the permissiblelimit of WHO 1.5ppm. Dental fluorosis is more conspicuous among the children and youngsters. Few casesof skeletal disorder due to fluoride also reported among the elderly peoples. A panic and psychics isprevailed among the youngsters and complained about getting a good alliangs. Thus the fluoridecontamination in ground water became a health and psychics hazard in Kollengode-Chittur area, whichrequire immediate attention, monitoring and mitigation after exploring the provenance.

Imprints of Neotectonic dynamism in the fluvial regimes of Palghat low-level, Kerala, south India

M.P.MuraleedharanDirector, Geological Survey of India, Kerala Unit, Thiruvananthapuram

andM.S.Raman

Geologist(Sr), Geological Survey of India, EG Division, SR, Hyderabad

The prominent low-level landform known popularly as the ‘Palghat gap’ in south India represents atypical interfingering union of various geomorphic entities. The low-level is marked by buried stream

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channels, meander scars and valley flats. Erosional remnants such as exfoliation domes mostly in elongatedoval shapes are widespread. Some of the prominent lineaments present here represent fracture planesresponsible for the formation of escarpment slopes and cuesta scarps in some of the high rising hillocksin the southern extremities of the low-level. The presence of fossil stream channels and meander scarssuggests that the land-blocks sustaining the catchment streams of the rivers have undergone differentialdynamics during the geological past as a result of local inversions of slopes leading to river piracy.

The present day Bharathapuzha River and its tributaries appear like ‘misfit’ streams in the backgroundof the vast alluvial expanses and valley flats adjoining them. Morphometric analysis of three sub-basinsof the Bharathapuzha river system draining the Palghat gap low-level area westwards was carried outwith a view to understanding the fluvial processes in a quantitative way and evaluating their role incarving out the low-level landform. Three major sub-basins constituting the area, viz the Walayar sub-basin, Korai Ar sub-basin and the Kalpathipuzha sub-basin were studied. The various parameters ofmorphogenesis like the stream order, number and length, area of the drainage basins, bifurcation ratio,drainage density, drainage frequency, texture ratio and ruggedness number have been determined separatelyfor the three sub-basins.

The relations of stream order versus stream number and stream order versus stream length were plottedin a semi log graph sheet to decipher the behaviour of these variables in combination with one another. Innormal case, these are to have a simple geometric relationship and the graph should indicate ascendingstraight line relationship from the lower order to the highest. In the present case, in all the three sub-basins, the straight line relationship is present only from the first order to the third and then the thirdorder to the last. This indicates that each of all these three sub-basins suggests the merging of twoindependently behaving minor sub-basins and that the present cumulative sub-basin does not represent afull cycle of evolution. Differential uplifts due to neotectonic events in the recent geological past wouldhave caused the capturing of the lower order basins by the strike streams of the gap area. The zonebetween the third order and fourth order streams in the basins is the zone of uplift and in all probabilitywas the palaeo water divide for the basinal portions which sustain the higher order streams at present.

Structure, tectonics and Quaternary seimentary faciesalong SW coast of India

K.M.Nair, Vakkom Moulavi foundation, Thekkummoodu, Thiruvananthapuram-695037D. Padmalal, Centre for Earth Science Studies, Akkulam-695031,

K.P.N.Kumaran, Agharkar Research Institute, Pune-400011.E-mail: geologistnair@gmail.com

The west coast of Indian Peninsula has its origin in separation from Madagascar, rifting anddrifting of the Indian palate during the period from Cretaceous to Holocene. One significant geomorphicresult of this is the formation of ‘Sahyadri’ and the western marine shelf. The most prominent structuralelements in this are the NNW trending West coast fault and the faults that developed sympatheticthereto. From the analysis of lineaments it is known that there are several sets of faults formed sinceAchaean, most of which are not active now. However, the faults that formed after the India-Eurasia platecollision and trending ENE-WSW and E-W or ESE-WNW seem to be still active as evidenced by the seismicityin association with them. The NNW trending faults, due possibly to the continuing movement of theIndian plate, have a perceptible transform component. At intersections of these faults with the faults inother directions in general and those trending ENE-WSW in particular seem to result in giving rise togeomorphic ruggedness on land.

The fundamental difference between the sedimentary stratigraphy of western and eastern shelfbasins is that the former has witnessed development of carbonate-dominated stratigraphy, while in thelatter, clastics dominate the overall stratigraphic successions. This is primarily due to the location ofthe Sahyadri close to the west coast restricting considerably the area of provenance to supply clastics tothe shelf sedimentary basins. The peninsular west coast sedimentary basins are divided into BombayOffshore Basin and Konkan Kerala Basin. While Bombay Offshore Basin has no representation on land,

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Konkan-Kerala Basin is represented on land by laterally discontinuous stretches of thin Miocene sediments.One significant exception to this is found in a curvilinear area along the coast between 8045/ and 100

15/ N latitudes. This area has its maximum width of ~ 25 km around 90 30/ latitude. Numerous boreholesdrilled for tapping ground water and Quaternary stratigraphic studies have yielded a reliable picture ofthe stratigraphy, facies, paleoecology and tectonics witnessed by the region. This has proved that thisarea is a landward extension of the offshore basin having a sediment fill of ~700m and for the sake ofconvenience, is called the South Kerala Sedimentary Basin (SKSB). Similarly, geophysical surveys anddrilling of hydrocarbon exploratory wells in the shelf adjoining the SKSB have revealed that there areconsiderable similarities between the offshore and onshore parts in terms of structure and tectonics andthe consequences thereof.

The SKSB can be conveniently divided into a southern flank and northern flank separated by acentral depression. The generalized stratigraphic column comprises Vaikom Formation, Quilon Formationand Warkalli Formation of Miocene age and Vembanad formation of Late Pleistocene-Holocene age. Thesouthern flank seems uplifted progressively towards south resulting in exposing Warkalli and QuilonFormations. Similarly, the northern flank also has undergone uplift; but to larger extent and during adifferent time. The result of the uplift of the northern flank is that the Quaternary sediments overlieVaikom Formation. It is estimated that > 500 m of sediments could have been lost from the northernflank as compared to a fraction of this thickness lost in the southern flank.

The offshore basin is characterized by a shelf edge carbonate bank and a possibly mixed clastics-carbonate facies in the area between the bank and the coast. Detailed analysis of seismic data and thestratigraphic columns revealed by the offshore exploratory wells enable a reliable interpretation of tectonicsand its influence on the carbonate build up, paleodrainage and erosional history of the shelf margin.From this it can be reliably stated that the major tectonic events experienced by the SKSB and theadjacent shelf area is largely similar. However, due to topographic irregularities that might have beencreated by the crossing of faults indicated earlier, numerous intrabasinal highs have been created inSKSB. The depressions caused in the process became mostly the sites of lagoons/estuaries. The intrabasinalhighs seem to have contributed much of the Quaternary sediments in the SKSB. One glaring aspect is theaccumulation of detrital laterite, often having thicknesses of 50-80 m in certain stretches. This lateriticsediment has accumulated in mostly lagoonal environments. In many instances the subsurface samplesappear to be a mixture of laterite and gray claystone having varying quantities of lagoonal fauna. Suchsediments usually underlie carbon dated Quaternary sediments (older than 40-45 ka). It would beinteresting and in fact essential to date some of these samples which will yield a clearer picture of thesedimentary history of SKSB, particularly the older part of the Quaternary sequences.

Tectonic framework of eastern ghats mobile belt : an overviewJ.K.Nanda

Geological Survey of India, BhubaneswarE-mail: jknanda_gsi@yahoo.com

Deciphering the tectonic evolution of Proterozoic Eastern Ghats Mobile Belt (EGMB) is importantin the context of models of reconstruction of Rodinia and other ancient supercontinents. The polyphaseintense ductile deformation in the belt and consequent development of major shear zones, a pervasivestrong fabric, regional granulite facies metamorphism locally reaching up to UHT conditions andgeneration of migmatites is a reflection of its complex tectononic history and the causative multipleorogenic movements ranging in age from late Archaean to early Phanerozoic. Magmatic events includemultiple phases of emplacement of alkaline and anorthosite-charnockite-mangerite complexes duringMesoproterozoic. A general gravity high over the belt and a steep gravity gradient across its boundarywith the adjoining Bastar and Dharwar crotons is characteristic. Detailed study of meso- to microscopicstructural features and thermo barometric estimates and precise dating of tectonic events carried out inonly a limited sectors and localities the mobile belt to be a composite high grade terrane with manysubterranes or domains of differing geologic and tectonic history which are separated from each other

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by tectonic boundaries. Major ductile shear zones were described from the western boundary and fromwithin the belt.

1500-500 Ma recurrent alkaline magmatism represented by miaskitic nepheline syenite along thewestern and northern margin of EGMB has been used as evidence of a rift setting and operation of Wilsoncycle. The girdle joining the sites of DARCs is inferred to be a Precambrian suture zone with surfacemanifestation of a terrane boundary shear zone and a westerly verging thrust / nappe in some segments.The boundary of the belt is variable from transitional to a thrust contact. Recent work suggest thatEGMB was thrust into juxtaposition with upper crustal rocks of Bastar craton and the cratonic fringe wasreactivated and preserved an inverted metamorphic signature during collision/amalgamation synchronouswith UHT metamorphism of EGMB. Structural evidences are in support of a hot over cold thrustingprocess. Some authors consider that the terrane boundary shear zones have resulted from obliquetranspressional collison of EGMB with the Bastar and Singhbhum cratonic blocks. They recognised withinthe belt both hotter Archaean and non-restitic Proterozoic granulites of similar collisional tectonicstyles but formed under different thermal regimes. The NE-SW Tel River Shear Zone has been interpretedas the root of this nappe along which several diapiric bodies of ~1000 Ma massive-type anorthosite-leuconorite complexes have been emplaced which are compared with Andean arc roots. While someauthors believe a thrust and collision related horizontal tectonics followed by strike-slip movements tobe responsible for the deformation in the belt, others argued that the early structures are subverticalresulting from a homogenous E-W compression. The well known NW-SE trending Godavari graben and theWNW-ESE trending Mahanadi graben with characteristic geophysical signatures transect the mobile beltand host Gondwana sedimentary formations including coal bearing horizons. While the Godavari grabenmay represent the failed arm of a rift system Mahanadi graben formed through a two-stage rifting inLate Permian to Middle Triassic and evolved parallel to the rifting of Lambert graben in East Antarctica.Recent work suggest that the internal segmentation and structural configuration of the Eastern GhatsBelt (EGB) and its cratonic forelands occurred during late Neoproterozoic–Early Phanerozoic times.Some workers concluded that pervasive high-grade metamorphism in the EGMB and the Rayner Provincerecord the Grenvillian collision, whereas pan-African shear zones between the EGMB and the Archeancratons of India and at Prydz Bay and south of the Rayner Block record the early Palaeozoic assembly. Ithas been inferred that the Eastern Ghats-Rayner Province terrane formed part of Rodinia while the restof sub continental India did not and the Eastern Ghats collage formed and collided with cratonic Indiaonly in Early Phanerozoic and not during global Grenvillian age as was assumed before.

Enigma of Eo- and Paleo-Archaean crustal evolution; constraints fromMesoarchaean cratonic parts of India: A review

S. M. NaqviNational Geophysical Research Institute

Uppal Road, Hyderabad – 500 007Email: naqvimahmood@yahoo.com

“The biggest question surrounding the Eo-Paleoarchaean crust is its demise”. Known Eoarchaeanrocks underlie about 10,000 km2 of the Earth’s crust. Is this small sample of crust represents the geologicalprocesses at that time?

Origin, evolution and destruction of Eo-Paleoarchaean crust remains an enigma, resulting in severalunresolved debates, in spite of the remarkable growth of ‘zirconology’, the early rock record is minisculeand preserved in Acasta gneiss (Slave Province), Itsaq gneisses, North Atlantic Craton (south Greenland,3000 km2), Eastern Pilbara Terrane (Australia) and Kaapvaal Craton. The Early-Mesoarchaean rocks arefound in more than 35 locations distributed world over. These Eo-Paleo-Mesoarchaean blocks of rocksare tectonically preserved in Neoarchaean greenstone belts and extend <500 km across, with an exceptionof Acasta gneiss covering 3000 km2. They form only about one millionth of the modern crust. India hasfive localities in Dharwar, Jaypore-Bastar, Bundelkhand, Singhbhum and Aravalli/Bhilwara Cratons, whereMesoarchaean rocks and Paleoarchaean zircons have been identified. From these regions of Indian

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subcontinent, Holenarsipur Nucleus of Dharwar craton is fairly known and covers an area of more than1000 km2. The gneisses from Holenarsipur Nucleus are dated ~3.4 Ga and detrital zircons ~3.6 Ga. Ifthese Eo-Paleo-Mesoarchaean rocks from world over cratons were originally spread over the vast terrane;their origin, geodynamic setting, genetic model and subsequent large-scale destruction or possiblerecycling must be explained. The evidence for such processes may be preserved in Meso-Neoarchaeangranite-greenstone terranes. Search for the processes of birth and demise of the Hadean and Eoarchaeancrust is one of the central themes of present day research in Earth sciences. The most favored model forthe origin of Eoarchaean crust is the internal melting and fractionation of the mantle plumes. The oldestzircons (4.4 Ga) may also have been crystallized from internal fractionation of the plume lavas. However,certain trace elements such as Sc in these zircons indicate that they are derived from ‘granitoids’. On theother hand the 4.4 Ga old zircons from Jack Hills require a substantially depleted mantle and complimentarycrust with low Lu/Hf ratio. This large extent of silicate earth differentiation is still not visible in 3.8-3.5Ga zircons from several terranes. Several geochemical/isotopic data argue for a substantial primordialcrust that formed 3.85 Ga. These divergent interpretations create an enigma regarding almost completedisappearance of Eoarchaean crust of the Earth. The answer for this problem may be provided by large-scale zirconology and trace element /isotope geochemistry of relicts of older crust and the mantle plumerocks preserved in subsequent sequences.

Basin evolution and tectonics of the Krishna-Godavari basin, IndiaNirupama Banerjee, M.M. Rajkhowa, Atul Kumar, A.K. Sinha, & S. Prasad,

KDM Institute of Petroleum Exploration, Dehradun - 248 195

Krishna-Godavari (KG) Basin, a peri-cratonic rift basin along the East Coast of India, is locatedbetween 150 to 17.50 N and 800 to 89.50 E. It covers an area of 59,000 Km2 both onshore and offshoreand includes the deltas of Krishna and Godavari rivers. The basin comprises of the sediments ranging inage from Lower Permian to Recent with sediment thickness of the order of over 7.0 Km.

The onland part of the basin is under alluvial cover. However there are Permo-Triassic, Late Jurassic-Cretaceous and Tertiary outcrops along the western margin of the basin. The basement is of Archaeanand Proterozoic rocks of the Eastern Ghats. The Krishna-Godavari Basin is characterized by a series of NE-SW trending en-echelon horsts and grabens formed during the Jurassic - Cretaceous break-up betweenIndia and Antarctica. These NE-SW structures overprinted the NW-SE trending Permo-Triassic Pranhita-Godavari Graben. The morphotectonic elements of the basin are defined by deep-seated basementcontrolled fault systems with a series of asymmetric half-grabens and horsts.

The basin evolution shows remarkable correlation with various tectonic episodes of opening ofEast Coast of India. The grabens were filled with thick Middle Jurassic to Early Cretaceous clastics. Therifting ceased and widespread Late Cretaceous clastics buried the ‘horst and graben’ topography. Theonset of passive margin progradation towards the south-east commenced during the Late Cretaceous,and paleo-shelf breaks have been recognized in the sub-surface. During the late Cretaceous to earlyPalaeocene, the Indian plate was tilted down towards the south-east. This event was caused by theuplift of north-western India as it drifted northwards over the Deccan “hot spot.” The Krishna-Godavaribasin was down-warped so that the gradient from source to basin, towards east-southeast was increased.Higher depositional energy of the proto-Krishna-Godavari river system led to an influx of coarse clasticscausing vigorous passive margin progradation to the southeast. The two present-day delta promontoriesbecame established in their present positions in the late Neogene. With the Tertiary base providing theglide plane, slippages and slides controlled by the instabilities generated by rapid sedimentation at ornear shelf edge led to development of growth fault systems in the coastal and offshore areas.

Krishna-Godavari (KG) Basin is the only proven petroliferous basin of India that has potentialreservoirs ranging in age from the Permian to the sub-aqueous channel deposits of Pliestocene. Exploratorydrilling of more than 400 wells in more than 160 structures has resulted in the discovery of over 40 oiland gas bearing structures.

In Krishna Godavari Basin systematic geological mapping of Basin Margin outcrop was initiated in1958 followed by Gravity, magnetic and seismic surveys in onland and offshore areas. The exploratory

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efforts made by ONGC, paid in 1979 with the presence of hydrocarbon in well Narsapur -A, where a gasblow-out took place. Subsequent discoveries were made in Cretaceous and Tertiary reservoirs. In 1987oil was struck for the first time in the clastic reservoirs of Ravva field and gas was discovered in thePasarlapudi field in the onland. The discovery of gas in Permian sediments of Gondwana in Mandapetafield was the only such discovery in India. Thus, sustained exploratory efforts made in Krishna GodavariBasin for over two decades, resulted in one of the prolific petroliferous Basin of India.

Study of magnetic data over the Chattisgarh basin and surrounding areaNisha Nair, S.P.Anand, V.C.Erram and Mita Rajaram

Indian Institute of Geomagnetism, New Panvel (W), Navi Mumbai 410 218E-mail: nisha1711nair@gmail.com

The Archaean Bastar craton (Central Indian craton) bounded by the Proterozoic mobile belts Pranhita-Godavari rift to its southwest, the Mahanadi rift to its northeast, the Central Indian Tectonic/ SutureZone to its northwest and the Eastern Ghats Mobile Belt to its southeast has been a region of greatinterest due to its tectonic and mineralogical importance. Late Archaean to Early Proterozoic sediments,bounded by these rift zones/ mobile belts are metamorphosed to green schist facies which can be seenin Bastar craton. A portion of the aeromagnetic anomaly map of Bastar Craton after IGRF correction,from 20° to 22°N and 81° to 83°E has been analyzed to understand the magnetic response and tectonicstructure. Although Chhattisgarh basin depicts a magnetic low in the anomaly map, it shows some clearNW-SE trending anomalies extending below the basin. Signatures of Charnockites and Iron Ore bodiesare clearly evident in the anomaly map. The aeromagnetic map of this region was subjected to varioustransformations. Signature of a hitherto unidentified NW-SE subsurface fault that cuts across parts ofthe Chhattisgarh basin is evident on the anomaly map and its downward continued map and this couldform zones of mineralisation. On close examination of the geology map, we find that this fault constrainsthe known dykes and Charnockite body from extending south-westwards. A system of EW trending dykeshas been identified from the magnetic anomaly map and its vertical derivative. The magnetic sources inthis region were brought out in the analytic signal map. From the analytic signal map, the distributionof magnetic sources and their extent in the region can be studied. The edges of the Sonakhan SchistBelt are clearly picked up in the analytic signal map and they appear to be continuing below theChhattisgarh basin. This Schist Belt comprises Dharwarian sequence of basal schist, metabasalt, ultramaficsand gabbro overlain by gold bearing silicious tuffs, quartz sericite schist and phyllites with upper mostrhyolite and rhyolite porphyry. Ground magnetic data was collected along a profile of length nearly100km (Kanker-Mainpur road) with a station spacing of 500-800m. Data was also collected along anotherprofile at around 110km to the north of the previous profile. Rock samples were collected during theground survey to provide ground truths like susceptibility for modelling of the profile data. The analysisof these data together with gravity data will be presented.

Late Quaternary coastal evolution ofAlappuzha- Kochi coast (Kerala), SW India

D. Padmalal1, K.M.Nair2 Ruta B. Lymaye3 and K.P.N.Kumaran3

1Centre for Earth Science Studies, Thiruvananthapuram- 695031,2Vakkom Moulavi Foundation Trust,

Thekkummoodu, Thiruvananthapuram-6950373Agarkar Research Institute, G.G.Agarkar Road, Pune-411004

The coastal plains of Kerala in the southwest coast of India record best development of Cenozoicsediments in the stretch between Kollam and Kodungullur, otherwise called the South Kerala SedimentaryBasin (SKSB). The Cenozoic sedimentary deposits comprise the Tertiaries and the Quaternaries. The totalthickness of Cenozoic sediments exceeds 600m in the Ambalappuzha- Alappuzha region. The maximumthickness of Quaternary sediments is about 80m and the remaining is the Tertiaries. The width of thecoastal plains preserving the Cenozoic sediments is much variable and attains a maximum of ~30km

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along the latitude N 70 40’ (Sherthala). Although many studies exist on the Tertiaries of the coastallands, studies on the Quaternaries are scarce. The present study deals with the late Quaternary coastalevolution of the Alappuzha –Kochi coast in the south west coast of India.

A total of seven bore holes were drilled at places like Alappuzha, Muhamma, Pathiramanal,Thannirmukkom, Panavally, Palluruthi and Kochi for collecting sub-surface sediments for sedimentological,palynological and geochrnological studies. The borehole sample collected from Alappuzha is about 20mlong and composed mainly of organic carbon rich, clayey sediments with marine/brackish water shells atdifferent levels. The total heavy mineral content in the sand varies from 1 to 5%. Opaque and sillimaniteare the major minerals in the heavy residue. Traces of zircon, garnet and rutile are also detected in somesamples. Contrary to the Alappuzha site, the borehole samples recovered from Muhamma(32m),Pathiramanal(24m), Thannirmukkom(14m) and Panavally(42m) show sand dominated sediments at thetop and silt and clay dominated sediments at the bottom. The top sand layer is 10-20m thick andcomposed mainly of medium to fine grained quartzose (silica) sand. The heavy mineral content in thislayer is substantially low. As in the case of Alappuzha borehole, opaque and sillimanite are the majorheavy minerals identified in these bore holes too. This indicates a khondalitic provenance to the sands.Absence of less stable minerals in the heavy crop, dominance of well sorted, well rounded to sub-rounded quartoze sand in sediment population points to its maturity and long residence in a highenergy environment prior to deposition in the sampling site. The silt and clay dominated finer sedimentswith broken and unbroken shells of marine and brackish water affinity, lying below the sand indicatesthe initial phase of basin filling/initiation of northerly drift of sediments. The Palluruthi(30m) andKochi bore hole(23m) samples are composed of a complex association of textural facies with interbedsof sand and clay dominated sediments. The heavy mineral residue in the sediments of the Palluruthi andKochi bore holes is composed of hornblende and opaque as the major minerals and hypersthene andzircon as minor minerals. This clearly indicates that the sediments in the Palluruthi-Kochi stretch havebeen derived from hornblende-biotite gneiss and charnockite/ charnokite gneiss that cover in thehinder lands of Vembanad basin north of the Achenkovil Shear Zone (ASZ).

It can be concluded that the coastal areas of Alappuzha- Kochi stretch have been influenced bysediments brought from two distinct petrographic provinces. The absence of khondalitic rocks in thehinder lands of the study area points to the fact that the sand rich sediments of Alappuzha-Panavallystretch have been brought by northerly drift of sediments from the continental shelf south of ASZalignment. The high rain fall, rising sea level and the northerly currents of the late Quaternary (especiallyin Early-Middle Holocene) period is responsible for the reworking and accretion of sediments in the formof ridges and swales in the area. It is this reworking of shelf sediments, in one way or the other, actedas a causative factor for the present day coastal land forms with its peculiar suite of economic resourceslike black sands, silica sands and lime shells in the study area and its adjoining regions. Furthermore,this process played a pivotal role in the enclosing of a part of Lakshadweep Sea as Vembanand lagoon (orthe ‘Vembanad kayal’ in local vernacular.

Crustal evolution of the Precambrian terrain in the Iritty- Kottiyoor sectorin the vicinity of Bavali shear zone of north Kerala, south India

K. R. Pillay, S. P. Bhutia and R. S. NairGeological Survey of India, Unit: Kerala

Dharani Bhavan, Manikanteswaram. P.O. Thiruvananthapuram

The WNW-ESE trending Bavali Shear Zone (BvSZ) in north Kerala, extending from Payyannur in thewest to Sulthan Bathery in the east for about 150 km is a major tectonic feature in the northern part ofthe South Indian Granulite Terrain. The shear zone possibly merges with the E-W trending Moyar ShearZone (MSZ) further east which is considered as a terrain boundary. Mapping on 1: 25,000 scale in an areaof 600 sq km was carried out in the Irity-Kottiyoor sector of North Kerala along and across the shear

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zone to study the crustal evolution of the BvSZ and adjoining areas. The Precambrian rocks of the areaare classified into : (1) Wayanad Group of rocks (WG) comprising metapelites and metaultramafitesequivalent to the Sargurs of Karnataka Craton ; (2) Gneisses and granitoids equivalent to PGC ; (3)Charnockite Group consisting of basic granulites, charnockite and charnockite gneiss ; (4) Vengadmetasedimentary sequence equivalent to the Dharawar Supergroup and (5) Younger acid,alkaline andbasic intrusives. The area has undergone three phases of deformation. The first phase of deformation(D1) is represented by tight, appressed, rootless folds (F1) and the second phase (D2) by open folds (F2).These two events took place during the N-S crustal shortening and burial. The third phase of deformation(D3) is evinced by broad swerves in the limbs of F2 and as tight asymetrical folds, the axial traces ofwhich trend N-S to NNE-SSW. This event indicates E-W crustal shortening. The most dominant planarstructure in the area is mylonitic foliation Sm2 which has a general trend of WNW-ESE with sub-verticalto steep SW or NE dips. The mylonite zone varies in width from 2 to 4 km and the shear sense indicatorspoints to a dextral sense. However, the steep dips of the lineations suggest an oblique slip.

EPMA studies on basic granulite, charnockite, metapelite and hornblende gneiss have brought outvarious mineral phases and its P-T conditions. The gt-opx pair of basic granulite north of BvSZ indicatedmetamorphic temperature of 778°C and pressure of 7.32 to 9.23 kb for the core and 731°C and 7.35 to9.27 kb for the rim.The gt-bt pair and the gt-plg-sil-qtz assemblage of the metapelites of the northernblock (NB) give a temperature of 575°C /8.29 kb for the core and 560°C/9.58 kb for the rim. The highpressures and presence of kyanite in the metapelites indicate deep burial of this crustal segment. Thecore and rim pressures are almost equal, indicating an isobaric cooling (IBC) P-T path. The high pressureregime corresponds to a depth of 30-35 km. Mafic granulites showing retrograded mineral assemblagesindicate 6.5 kb pressure and 583°C temperature which suggest later upliftment of the NB (Ravindrakumarand srikantappa,1984). Gt-bt. pair in hornblende gneiss south of BvSZ gives an average temperature of735°C for the core and 652°C for the rim and these are low when compared to the NB. Pressure estimatesof the southern block (SB) give 6 to 8 kb corresponding to an exhumation level of 23 km (Soney,2000).Thelitho-association which includes high pressure metapelite mineral assemblages along with granulitesindicates deep burial of these rocks. Tectonic models that can be invoked for transport of supracrustalrocks to such great depths are continental –scale underthrusting and continent-continent collision.Both these involve amalgamation of crustal segments which might have differences in litho-assemblageand tectonic history. Lithologic and structural patterns of the NB and SB are broadly similar suggestingthe absence of any suture or subduction zone.

The model which contemplates intra-continental subduction subsequent to upwelling andunderplating of mantle material (Kroner, 1983) can be suggested as a possible mechanism that operatedin the area. An upwelling mantle would have caused crustal extension and basin formation withoutcomplete continental separation. The Wayanad supracrustals representing volcano-sedimentary sequencewere deposited in small platformal basins. Cold sub-crustal mantle delaminated from the overlying crustsank, triggering crustal shortening above it. Further sinking and crustal shortening evidently led totectonic thickening through crustal duplex formation during which granulite facies metamorphism andD1 phase of deformation took place. The transported crust might have remained there under high pressureconditions for a long time as indicated by the IBC P-T path. After a prolonged period of crustal growththrough ensialic magamatism, the area experienced a major upliftment as suggested by the mineralassemblages characteristic of an ITD P-T path. The difference between the exhumation levels of the NBand SB is due to differential upliftment along the WNW-ESE trending BvSZ. Shearing is post-F2 and it hastransposed both F1 and F2 folds. Thus, the mylonitic rocks of BvSZ represent a much later tectonic eventcompared to the earlier tectono-metamorphic events. Upwelling and underplating of mantle in a thickenedcrust later led to extensional tectonism along BvSZ. Alkaline rocks such as syenites and syenites andalkali granites were emplaced during the onset of rifting. This was followed by emplacement of gabbrobodies and then BvSZ closed as an aborted rift. Age data of alkaline bodies indicate that this eventoccurred during the Pan-African times. The area has not experienced any major tectono-magmatic eventafter this except the emplacement of a few dolerite dykes during the Mesozoic.

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Fluorine substitution and high-grade stability of amphiboles in the marbles ofAmbasamudram, Kerala khondalite belt, India

A. P. Pradeepkumar Lecturer, Dept of Geology, Govt College, Nattakom, Kottayam - Pin

E-mail: geo_pradeep@yahoo.com

The marbles of Ambasamudram (8° 41' 60 N, 77° 28' E), are part of the Kerala Khondalite Belt, inthe Southern Granulite Terrain of India. The presence of humite-bearing mineral assemblages, as well asthe location within the disputed Tenmala–Achenkovil Shear Zone has lead to extensive studies on theserocks and their assemblages. Metamorphic conditions of 650–850°C and 5.5–8.0 kb have been established.A wide variety of minerals like clinohumite, humite, chondrodite, norbergite, spinel, calcite, dolomite,diopside, chlorite, talc, amphiboles, scapolite, sphene etc exist.

EPMA data show the amphiboles to be calcic with XF 0.13–0.41 (Tremolite: 0.13; Tremolitic HB:0.16; Magnesio HB: 0.26; Edenite: 0.33; Edenitic HB: 0.355; Pargasitic HB: 0.36; Pargasite: 0.41), and(Ca + Na)B e” 1.34 and NaB < 0.67. All the C-sites are filled in most of the analysed amphiboles, with Mg> AlIV > Ti > Cr e” 0. The M4 site occupied by the B-cations has Ca as the major occupant (1.966–1.663apfu), with Ca > Fe > Mg > Mn. The average T-site occupancy is 7.985 apfu. The A-site is occupied by Ca,Na, K. In the Ambasamudram marbles the amphiboles are Al-saturated and coexist with high-MgO-Al2O3spinels. The homogeneous Al-rich edenites and pargasites indicate high grade conditions. In Al-dolomitesamphibole composition depends on the composition of the coexisting minerals like Fo, Dol, Cal andupon the nature of the fluid. The activity of the tremolite component of the amphibole is fixed by theassemblage amph–cal–dol–ol–spl and that of the fluid by the equilibria Tr + 11Dol = 8Fo + 13Cal + 9CO2+ H2O. The assemblage Fo + Spl fixes the tshcermakitic (Ts) component, according to the equilibriaMgAl2O4 + MgSiAl_Al_ = Mg2SiO4. The edenitic component is not fixed by an independent variable.

Introduction of Na as an aqueous species will not change amphibole composition, but limits theappearance/disappearance of pargasite in an association at constant P–T. Its introduction as a fluidcomponent into cal + fo + spl leads to pargasite precipitation. This mechanism for pargasite existed inthese humite-bearing marbles. The possible reactions are: 12Fo + 23Cal + 3Spl + 15CO2 + 3H2O + 2Na+ =Prg + 19Do + 2H+ and 3Fo + 17Cal + 3Chl + 9CO2 + 2Na+ = 2Prg + 13Dol + 9H2O + 2H+. Since all othercomponents were fixed by dol + cal + fo + chl + spl, only Na2O and K2O had chemical gradients. Pargasitetakes its components from all available neighbouring mineral phases and the excess MgO forms dolomite.The presence of NaCl and KCl in metamorphic fluids causes the continuous modification of the tremolitecomponent with increasing temperatures. This produces edenites and pargasites from tremolite at highT and this exchange is also responsible for the higher temperature upper limit of amphibole stability incertain parts of the area, compared to the pure CaO–MgO–Al2O3–SiO2–H2O–CO2 marble system. The bi-modal calcic-amphibole compositions in the Ambasamudram marbles indicate non-equilibrium conditionsof formation.

Receiver functions in the Kachchh rift zone, Gujarat,with implications for mantle structure and dynamics

Prantik MandalNational Geophysical Research InstituteUppal Road, Hyderabad-500 007, India.

E-mail: prantikmandal@yahoo.com

Analysis, stacking and inversion of teleseismic radial receiver functions have been performed usingbroadband data of teleseismic events recorded during 2001-2007 at fifteen stations in the Kachchhregion, Gujarat, India, covering an area of roughly 150 km x 120 km. In general, strong Ps conversionsfrom the Moho and sediment-basement transitions characterize the radial receiver functions. The inversionof stacked radial receiver functions delineates a marked crustal thinning of 4-7 km and an asthenosphericupdoming of 6-8 km beneath the central part of the Kachchh rift relative to the surrounding unriftedparts of the Kachchh rift zone (KRZ), a result that agrees with the findings from the old continental rift

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zones around the world. The coincidence of the area of updoming of Moho as well as asthenosphrere andaftershock activity beneath the central Kachchh rift zone suggests the presence of a confined body ofpartial melt (perhaps the imprints of the Deccan mantle plume), which might be the cause for high CO2mantle fluid flow and aftershock activity in this recently non-volcanic, intracontinental Kachchh riftzone. The forward modeling of later arrivals on the radial RF corresponding to 410 km and 660 kmdiscontinuities reveals a 4.8-7.2% decrease in Vp and a 7.9-10.2% decrease in Vs in the depth range415 to 655 km, suggesting a 10 km decrease in the mantle transition zone (MTZ). A thin LVZ (at 320-415 km) atop 410 km discontinuity is also noticed, which has also been reported beneath the Precambrianplatforms, in association with either Mesozoic or Cenozoic mantle plumes. Hence, given the slow seismicvelocities in the mantle and thinning of the LAB and MTZ, it can be inferred that mantle beneath theregion is warm having low strength. The results from this study and other Global tomographic studiesconfirm the presence of low shear velocity anomalies associated with the K/T boundary Deccan mantleplume up to a depth of 660 km. This study also confirms a typical continental passive rift model with awarm mantle beneath the Kachchh rift zone, Gujarat.

New geochemical and palaeomagnetic results from the dykes of theBundelkhand craton: preliminary observations constraining the

Proterozoic igneous activityT. Radhakrishna1, Ram Chandra2, Balasubramonian1 and Akhilesh K. Srivastava2

1Centre for Earth Science Studies, Trivandrum 695 0312Department of Geology, Bundelkhand University, Jhansi-284 128

*Email for correspondence: tradha1@rediffmail.com

New major and trace (including rare earth) element analysis on fifty mafic dyke samples andpalaeoamgnetic investigations of twenty seven dykes have been carried out on dykes covering thewhole of Bundelkhand craton. The dykes petrographically are doleritres to gabbro in grain size andcontain plagioclase, clinopyroxene and opaques mineral assemblage with typical ophitic to subophiticand intergranular igneous textures without metamorphism or strong deformation. However, clouding orturbid appearance of plagioclase and occasional bending of lamella twinning and urlitisation andcloritisation are seen.

Our plaeomagnetic analysis includes detailed alternate field demagnetizations at close intervals(2.5 mT) on all samples (over 300 samples from 27 sies) and thermal demagnetizations on representativesamples because the former has been successful to delineate characteristic remnant magnetizations(ChRM) at least ten cores have been drilled from each dyke to constitute a site. The results displaycomplex magnetic structure and the success rate of obtaining coherent within-site ChRMs, as in similarPrecambrian dyke swarms, is quite low, probably because of their greater age. Nevertheless, the ChRMdirections at least three discrete ChRMs could be delineated suggesting that the dykes manifest multiple(at least three) igneous events. Thermomagnetic study of heating/cooling cycle using BartingtonTemperature – Susceptibility system (at 2°C interval from RT to 700°C) suggest that titanomagnetite asthe dominant magnetic mineral. The ChRM directions registered in these dykes are incidentally comparedwell with the directions recorded in the mafic dyke swarms in the Dharwar craton. These palaeomagneticcomparisons and the available Ar/Ar isotopic age data suggest that the dyke magmatism in the Bundelkhandcraton is of Palaeoproterozoic.

Our new geochemical data from the dykes in the entire geographic area of the Bundelkhand suggestthat the dykes are of tholeiitic basalts as reported earlier in the dykes from Lalitpur-Jhansi sector.Geochemical trends and the incompatible element ratios cannot be distinguished either in geographicdistribution or in terms of their field orientations or in terms of the distinct palaeomagnetic directions.Bivalent plots show general fractionation trends that can be explained by fractionation of ferromagnesianphases. Chondrite normalized rare earth element patterns and mantle normalized incompatible elementpatterns of the dykes from Bundelkhnad region generally mimics the trends from the Proterozoic dykesfrom Dharwar craton, south India. Detailed analysis of the palaeomagnetic and geochemical data are inprogress to understand the position of Bundelkhand craton in the Palaeoproterozoic continental

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reconstructions and the nature and development of mantle sources for the Palaeoproterozoic magmas inIndian subcontinent.

Indian subcontinent.

Oligocene- Pliocene stratigraphy of India and cycles of relativesea-level change with reference of hydrocarbon occurrences: an overview

D.S.N. RajuFormerly with ONGC, 10th, Siddhartha Enclave, G.M.S. Road, Dehradun- 248001, India.

E-mail: rajudsn1@gmail.com.

The Oligocene-Pliocene strata of India occupy an envious status in holding major reserves of oiland natural gas. The Oligocene-Pliocene reservoirs are spread from Mumbai offshore( including the giantoil field), Ratnagiri offshore, Cambay, Assam, Tripura, Mahanadi, Andaman (noncommercial at present )and Cauvery basins.

An effort is made to document the litho-, bio-, chrono-. cyclo- and sequence -stratigraphy,paleobathymetry, relative sea level changes and transgressive-regressive cycles. Special attention ismade towards Indian stages and biochrons (the smallest divisions of chronostatigraphy) besides standardglobal stages as a framework towards dating and correlation of strata of hydrocarbon bearing reservoirs.The major geologic and biotic events associated with this geological time interval are also discussed.

The Indian stages, biochrons (in bracket) and their equivalent global standard stages are: RamanianStage (RAM-I and RAM-II) early to middle Rupelian, Waiorian Stage (WA-I, WA-II and WA-III with furtherfiner subdivisions)- late Rupelian-Chattian, Aidaian Stage (AID-I, AID-II and AID-III)-Aquitanian,Vinjhanian Stage (VIN-I, VIN-II and VIN-III)- lower to middle Burdigalian) and Thrupuandian Stage(THI-I and THI-II)- Late Burdigalian to Serravalian. Attempt is also made to propose biochrons for deepwater facies based on the publications of M.S.Srinivasan and his research scholars. We have achieved inbuilding a high-resolution biochronostratigraphic framework for the Oligocene-Pliocene surface andsubstance strata of Indo-Pacific province.

Paleomagnetic studies on Siwaliks of North India, Barails-Bhubans of Assam- Arakan contributedtowards improving the dating of poorly fossiliferous strata. Dating by stronsium isotopes was attemptedbut not up to the accuracy required.

The major geological events during this interval include drops of sea-level and associated hiatusesduring late Eocene, Mid/late Oligocene and late -Middle to Late Miocene between Zone N11 (3Ma) andzone N18 of latest Miocene, Miocene Himalayan orogenic movement (HOM) to around 16.4 Ma leading tothe development of Siwalik fore deep, HOM-II during 2.58Ma to 3.60 Ma, very high rate of sedimentationafter 2.5 Ma, collision of India and Burma plates, paleotemperature fluctuations (for e.g. a drop of 60Cduring early Oligocene), mass extinction of foraminifera at the Eocene- Oligocene boundary and changesin biota close to the top of Zone N 12. We have also gained some knowledge in respect of cycles of sealevel change and biosequence stratigraphy.

In the Oligocene exposed succession of Kutch,7(possibly 8) cycles/Para sequences are recognizedin a shallow marine set up. In Narimanam and Adiyakkamangalam structures of Cauvery Basin, 6 to 7sequences are recognized in a bathyal setup of Oligocene. These cycles are close to the number of globalcycles but it is difficult to tie- up cycle to cycle to cycle. Earliest Miocene witnessed a major transgressionin several basins of India. In the succession of the Aidaian Stage two marine incursions are observed inKutch while a number of cycles are known from Mumbai offshore. In the Vinjhanian Stage, the host ofMumbai giant oil field, as many as 9 fourth order cycles defined by fossil MFSs are recognized in Kutchoutcrops and Mumbai offshore in a shallow inner shelf to marginal marine set up. Hydrocarbon reservoirsare linked with such low amplitude and high frequency cycles with bounding diastems, in westernoffshore.

In Ravva oil field of Krishna-Godavari Basin about 8 third order cycles are recognized based on quantitativeforaminiferal studies and their number is close to global cycles. Late Miocene productive intra-slope fans of KDstructure, Krishna Delta, is the result of a post N-11 (Middle Miocene) drop in sea-level.

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Geologic times scale 2004/2008 (Gradstein and others) achieved a zero error in dating stageboundaries within the Neogene. Can we achieve such an accuracy in dating subsurface strata of Indiawith available tools and methods.

Geochemistry of the Neoarchaean greywackes:multi-component mixing in a continental island arc

Rana Prathap, J.G. and Naqvi, S.MNational Geophysical Research Institute

Uppal Road, Hyderabad – 500 606, IndiaE-mail: ranangri@yahoo.com

The greywacke-shale assemblage of the Ranibennur Formation of the Shimoga schist belt (2.7 Ga)of southern India is interlayered with calc-alkaline volcanic rocks including adakites, and is interpretedto represent a remnant continental arc succession. These meta-sediments are mineralogically and texturallyhighly immature and exhibit heterogeneous compositions that are expressed as large-scale variations intheir major- and trace- element composition including HFSE (High field strength elements), REE (Rareearth elements) and inter-element ratios. Fractionated REE patterns show slightly enriched HREE. Weakand negative Eu anomalies are characteristic features of these rocks, which along with HREE enrichmentappear to be inherited from the current-bedded arenites and arenaceous matrix of Quartz-Pebble-Conglomerate (QPC) present in the source region and lower part of the succession. Archaean zircons areknown to be enriched in HREE. A two-component mixing model of TTG (tonalite-trondhjemite-granodiorite)and basalt is unable to explain the observed composition of the greywackes of the Ranibennur Formation.Instead, a five-component source (comprising TTGs, basalts, amphibolites, arenites and banded ironformations) is identified on the basis of REE, HFSE and transition element distribution. Mixing of TTGand basalt in 1:1 proportion with addition of arenaceous matrix of QPC, garnetiferous amphibolites andbanded iron formation explains the sediment composition. Debris derived from garnetiferous amphibolites,arenites and the arenaceous matrix of the QPC at the base of the Dharwar Supergroup has elevated Zr, Hf,Y and Yb concentrations. Contribution from the banded iron formation of the Bababudan Group appearsto have elevated the Fe2O3 of the GSRF. Geochemical discrimination parameters (Th-Sc-La) along withQFL (Quartz-Feldspar-Lithic fragments) detrital modes suggest that deposition of these sediments tookplace in an active continental marginal arc predominantly as deep-water turbidites. The entire assemblageof Bababudan-Shimoga schist belts, which begins with mature arenites, QPC and terminates with avolcanic arc sedimentary sequence. Stromatolites along the western margin of the Shimoga schist beltwith arenites followed by turbidites, BIF and volcanic rocks indicate the change from stable to unstableconditions and thus these data demonstrates the transformation of a passive margin into a continentalisland arc margin. Transformation from the passive margin conditions to the active continental islandarc setting was probably triggered by spontaneous development and nucleation of a subduction zone.

Paleoclimatic reconstructions through microfossils specially foraminiferain marine sediments: Indian examples

Rajiv NigamNational Institute of OceanographyDona Paula, Goa -403004

E-mail: nigam@nio.org

The present global scenario poses multiple environmental problems associated with global warmingdue to green house effect. Anthropogenic contributions are now considered as cause for acceleratedsea level rise, changes in monsoonal rainfall pattern, increase in intensity and frequency of storms etc.Obviously, In order to foresee the future variability in climate, there is an increased awareness about thepast climatic changes. However, climate prediction is a very delicate task and needs a thorough knowledgeabout the past. Past records have been maintained for not more than past 100-150 years, beyond whichwe would need proxies to give us information about the past climate. During the past few decades,microfossils, especially foraminifers have become the prime source to paleoclimatic reconstructions.

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We produced the updated curve for the Late Pleistocene - Holocene sea level fluctuations alongthe west coast of India. We succeeded in demonstrating that, as compared to present, sea level waslower by ~100 m at about 14,500 years Before Present (BP), ~60 m at about 10,000 years BP and higherthan present ~6000 years BP. With the help of sea level curve, we could solve few of the unresolvedissues pertaining to ancient human civilizations, like dockyard (first Naval dock yard of the world asclaimed by archaeologists) at Lothal (a ~4000 years old Harappan Settlement and Neolithic settlements(at 30-40 m water depth) in Gulf of Khambhat. A similar compilation of the available data to produce anupdated composite curve for the Bay of Bengal is need of the hour.

Monsoonal rain is among one the most important elements of climate. The results based on coresamples off Karwar, clearly showed high rainfall around 4000 and 3500 years BP and reversals of rainfallcondition since 3500 years BP with a marked low at 2000 years BP. Geophysical and palynologicalinvestigations also support these findings. In addition to this, a cyclicity of approximately 77 years inconcentration of drought years was also deciphered. There is a possibility of correlation between inferredmonsoon intensity cycle and Gleissberg solar cycle.

Storms and/or tsunamis are most severe natural calamities that affect Indian coasts which causesa huge loss of lives and wealth. To predict such events, the knowledge of past events during the historicas well as pre-historic periods is very much required. The recent study reveals the utility of foraminiferato decipher paleo storms / tsunamis. One of the most storm-prone areas of the west coast of India, theKachchh, was studied in search of presence of such signatures. The study shows that after ~8,000 yearsBP, older sediments of ~10,000 to ~12,000 years BP age, were eroded from the deeper region by severestorm(s)/tsunamis, transported and redeposited in the shallower region thus giving rise to an invertedsequence deposited between ~8,000 and 7,000 years B.P.

A slight change in the climatic condition will lead to the migration or extinction of the fishes,which would in turn affect the economy of the country. Along the Indian coast line, no direct evidenceis available to understand the migratory changes of fishes in the past. Quest for an additional tool todecipher such eventualities in the past guided us to fish remains-Otoliths. Otoliths are calcified concretionsfound within the membranous labyrinth of bony fishes, have been traditionally used for determining theage of fishes by counting the growth rings. Oxygen isotope studies on Otoliths help the palaeontologistsin determining the paleoclimate / paleotemperature, and are as useful as foraminifera and other calciumcarbonate bearing shells. A conceptual frame work is proposed to exhibit how otoliths can be used todetermine history of changes in fisheries pattern through the Holocene.

All these studies indicate that paleoclimatic reconstructions help to understand nature and timingof natural climatic variability along with hazardous events. Such information, through extrapolationcan also provide the idea of future changes. However such studies are still fragmentary and more effortsare required to produce reliable and comprehensive understanding of past climatic changes.

Metamorphic petrology: recent advances and future trends in theIndian context

R. S. SharmaDepartment of Geology, Rajasthan University, Jaipur

E-mail: sharma.r.sw@gmail.com

An attempt has been made here to compile the advancement with time of Metamorphic Petrologyand its supporting disciplines in terms of field, theory, and experiment. The development of the petrologicalscience, marked by milestones, has received contributions from Indian geoscientists at each benchmark,beginning from preparation of geological maps, mapping of metamorphic zones and isograds on thepattern of Barrovian zones in Scottish Highlands; computation of P-T conditions of metamorphism withthermodynamic approach, advancing newer models of geothermometry (Gt-Bt, Cd-Gt, Gt-Cpx thermometers)and geobarometry (Cd-Gt-Sil-Qz and Gt-Opx-Plag-Qz barometers) and also geothermobarometers for silica-deficient pelitic compositions by petrologists at IITs and Universities. Impressive results have beenarrived at from the P-T-t paths for different terrains, especially Eastern Ghats mobile belt, Western andCentral Indian fold belts, relating crustal thickening and heating of metamorphic terrains in depth. Withthe realization that time is the essential parameter to calibrate geological processes and rates of change,

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Indian petrologists developed facilites at selected Institutions (MNGRI, PRL, GSI, and some universities)in the last two decades for isotopic dating of rocks and minerals. A greater impetus in petrologicalresearch came through foreign collaborations when origin of charnockite became a central theme tounderstand the physical and chemical proceses in the middle and lower crustal domains. Time honoutred,the Indian geoscientists have extensively applied modern and traditional tools (polarizing microscope,SEM, and EPMA) and meaningful conclusions have been arrived at to understand genesis of fold beltsand cratonic regions of the Indian shield. The analytical tools enhanced computational power andimproved theoretical understanding to extract quantitative information from rocks, providing insightsinto the current research in petrology, like continental reconstructions and mantle compositions, therebytransforming the field of metamorphic petrology in the coming years.

Evolution of eastern Dharwar craton:new geochemical and isotopic constraints

M. Ram Mohan*1, Stephen, J. Piercey2, Balz, S. Kamber2, D. S. Sarma1 and S.M. Naqvi11 National Geophysical Research Institute, Hyderabad-500 007, India. Email:rammohan@ngri.res.in)2 Department of Earth Sciences, Laurentian University, Sudbury, ON, Canada.

E-mail: rammohan@ngri.res.in

The Neoarchean Eastern Dharwar Craton is distinct from the Meso-Neoarchean Western DharwarCraton due to the predominance of K-rich granitoids and auriferous greenstone belts. The evolution andassembly of the Eastern Dharwar Craton (EDC) has been a matter of debate. One prominent hypothesisenvisages a plume growth model (Jayananda et al., 2000) while others propose a subduction model(Chadwick et al., 2000; Naqvi, 2005).New fluid mobile element (FME), trace element, and Pb-Nd isotopic data for TTG and felsic metavolcanicrocks from Sandur, Hutti and Kushtagi greenstone belts provide new constraints on the petrogeneticprocesses that led to the formation of TTG and felsic rocks within these belts. The åNdt of these rocks arevariable with åNdt ranging from +0.12 and –7.55, indicating that none of these rocks are uncontaminatedand entirely mantle-derived. Rather, they originated from evolved magmas that had been variablycontaminated by crust. In terms of Pb isotopes there is a clear geographic progression. Relative to theposition of mantle and crust evolution lines, the Pb isotopic data suggest that the rocks from Sandurgreenstone belt were derived from a mantle source that had been contaminated by pre-existing ancientcontinental crust (i.e. > several hundred Ma than the greenstone belt), whereas the Kushtagi and Huttigreenstone rocks exhibit variable but less contamination with crust of more juvenile character. Theisotopic variations can either be explained by heterogeneous mantle sources with relatively constantdegree of crustal contamination, or an originally homogeneous mantle source that subsequently wascontaminated by continental crust at variable levels and possibly variable age (older in the west, youngerin the east). The high field strength element (HFSE) and other trace elemental systematics indicate aconvergent margin setting for these rocks, whereas the FME systematics such as B, Be and As argue morefor an oceanic arc origin. Fractional crystallization was also an important mechanism during the evolutionof these rocks. Based on these data, it seems improbable that the EDC formed from plume activity.Rather, it may be inferred that the Neoarchean magmatism of EDC is related to subduction zone processes,the details of which need further refinement.References:

Chadwick, B., Vasudev, V.N and Hegde, G.V (2000) The Dharwar Craton, Southern India, interpretedas the result of Late Archean oblique convergence. Precambrian Research, v. 99, pp. 91-111.Jayananda, M., Moyen, J.F., Martin, H., Peucat, J.J., Auvray, B and Mahabaleshwar , B (2000) Late Archean(2550-2520 Ma) juvenile magmatism in the Eastern Dharwar Craton, Southern India: constraints fromgeochronology, Nd-Sr isotopes and whole rock geochemistry. Precambrian Research, v. 99, pp. 225-254.Naqvi, S.M (2005) Geology and evolution of the Indian plate (from Hadean to Holocene ~ 4 Ga to 4Ka). Capital publishing Company, New Delhi, 450 pp.

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Recent advances in Dharwar geologyM.Ramakrishnan

Formerly with Geological Survey of IndiaE-mail: emarkay@hotmail.com

There has been a recent explosion of geoscientific data in the Dharwar craton that has revolutionizedour understanding of this classical greenstone-granite terrain. Two significant advances in our knowledgeof the craton are: (1) The demarcation of an older group of narrow schist belts and widespread enclavesof Sargur Group (3.3-3.1 Ga) from the large array of younger schist belts of Dharwar Supergroup (2.8-2.6Ga); (2) The division of the greenstone terrain into the Western (WDC) and Eastern (EDC) Dharwarcratons on the basis of significant differences in lithology, metamorphism and isotopic age.

Sargur Group consists of minor shelf facies rocks (including BIF) associated with a prominentkomatiite-tholeiite suite, intruded by ultramafic-mafic layered complexes (with minor anorthosite aswell as chromite and titano-magnetite). It is extensively intruded by Peninsular Gneiss (3.4-3.0 Ga).The younger Dharwar Supergroup of WDC consists of quartzite-basalt alternations and BIF, followed by anunstable shelf association of polymict conglomerate, quartzite-carbonate-pelite-Mn/Fe formationculminating in greywacke pile at the top. Pillowed mafic volcanics form in deeper waters contemporaneouslywith the unstable shelf at the margin. The Dharwar Supergroup of EDC consists of a dominant maficvolcanic suite underlain by a thin screen of dismembered shelf lithologies. Polymict volcanic conglomerateand felsic volcanic-volcaniclastic rocks occur as the youngest unit. The Dharwar lithological associationshows a gradual transition from WDC to EDC suggesting a gradual change in depositional and tectonicsettings with the median Sandur belt marking the transition.

Peninsular Gneiss (PG) is a dominant TTG suite that is established as the basement for DharwarSupergroup in WDC. On the other hand, the gneisses of EDC are minor units in relation to the voluminousgranitoids. They belong to the granodiorite-quartz monzonite-granite suite (2.7-2.5 Ga) that intrudesthe Dharwar Supergroup of EDC. This granite-gneiss suite is distinguished from PG as a younger granitoidcomplex that is called by some authors as Dharwar Batholith.

The EDC and WDC are separated by the Chitradurga Boundary Shear Zone with linear body of ClosepetGranite occurring in the vicinity. The contact is a diffuse zone marked by the gradual transition oflithological ensembles of greenstones and granitoids of both WDC and EDC. Closepet Granite (2.5 Ga) asa distinct entity in the craton has been questioned by some who included it as part of DharwarBatholith, but it appears to be a stitching granite between WDC and EDC.

The WDC and EDC are together involved in the younger Dharwar orogeny (2.7-2.5 Ga) that culminatedwith the profuse invasion by younger granitoids in the EDC (“granite bloom”) and sporadic graniteintrusions in WDC. The cratonisation was complete with the emplacement of mafic dyke swarms at 2.4-2.2 Ga. The craton was tilted gently to the north during the Proterozoic, progressively exposing thedeeper crustal sections towards the south, with the E-W trending granulite-gneiss terrain runningorthogonal to, but still retaining the regional N-S structural grain.

The Archaean Karimnagar granulite belt occurs as a narrow linear belt on the shoulder of Godavarigraben, and has a gradational contact with the greenstone terrain of EDC. This granulite belt representsthe deeper part of the craton in the northeast, exhumed by faulting along the Godavari graben. This beltis closely associated with the shelf facies lithologies of Warangal Group that may represent an oldersequence than the Dharwar of EDC.

It is now accepted by most workers that the Dharwar craton represents an Archaean accretionaryorogen that evolved by subduction of oceanic lithologies. There are however differences of detail invarious models. An alternative model of sagduction coupled with gravity flow has also been suggested.

Much remains to be done to project this classical terrain as one of international renown like thegreenstone-granite terrains of Canada, South Africa and Australia. The available geochemical,thermobarometric and geochronological data are very limited in terms of the vastness of the Dharwarterrain. Instrumental analysis has grown by leaps and bounds in recent years in terms of quality, quantity,methodology, rapidity and sophistication. For example, U-Pb and Th-Pb dating, as well as trace element

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and REE data acquisition are the norm everywhere, and we need to catch up with these trends speedily.The vast strides made by China and Japan in these fields in recent years should be an eye opener to us.In order to augment the tempo of our studies, a large scale multi-institutional effort is called for on awar footing. A note of caution is needed: while generating a vast database, the ground truth should berevisited in the sampling areas for instrumental analysis.

Prydz Bay and Mahanandi basins: conjugate rift basinsof the Gondwanaland

Rasik Ravindra and Dhananjai Pandey*National Centre for Antarctic and Ocean Research, Goa, India

* Email: pandey@ncaor.org

East Antarctica occupied the centre space in the Gondwanaland super continent. ThePrydz bay of EastAntarctica and the Mahnadi river basin of India constitute a conjugate rift system. The Prydz bay iscurrently occupied by Lambert Glacier system that marks one of the most prominent features of theeastern Antarctica. It extends for more than 650 km from its northern coast over the East Antarcticshield. The rocks in these regions, apart from the middle Proterozoic also include Permian–Triassic–Cretaceous sediments. As this part of Antarctica was supposed to be juxtaposed with the east coast ofIndia, the northeast–southwest orientation of the Prydz Bay basin is suggested to be influenced byrifting between India and Antarctica. The east coast of India is also characterized by contemporaryGondwana rift valleys which are known as the Godavari, and the Mahanadi rift valleys of almost samelength (500–600 km). Prior to the breakup of India from Antarctica, the Lambert and the Mahanadi Riftbasins were located in line with each other. There are several hypotheses for the origin and evolution ofthese faulting dominated volcano sedimentary conjugate basins. Some workers argue a single – riftrelated evolution of these basins while others propose multiple-rift model. Further, it is still uncertainwhether the sedimentation occurred within a broad rift zone or in smaller channel like basins. Hence,the problem of origin of these rift basins and their volcanosedimentary evolution is still a conten iousissue. The gravity and the total intensity magnetic anomalies of the Lambert Glacier and the Amery iceshelf of Antarctica and that of the Mahanadi basin of India are compared constraining from availableseismic studies to delineate the shallow and the deep seated crustal structures. An integrated interpretationof geophysical and geological information is used to provide insight into the Phanerozoic history ofAntarctica and India by tackling the larger questions concerning the generation of the conjugatecontinental rifts.

Studies on heavy minerals in the sediments of Kayamkulam lake,Kerala -its implications on sediment sourcing

Reji Srinivas1* and K. Sajan2

1 Centre for Earth Science Studies, Thiruvananthapuram- 695031, India.2 Department of Marine Geology and Geophysics, School of Marine Sciences, Cochin University of

Science and Technology, Kochi- 682016, India.*Email: srinivasreji@gmail.com

The coastal belt of Kerala is endowed with an interlacing network of fluvial channels, lakes and otherbackwater bodies. Among these, Kayamkulam lake (Kayamkulam lagoon sensu stricto) is the least studiedsystem although it is third largest in aerial spread. The Kayamkulam estuary is a linear water body stretchingfrom Sankaramangalam in the south and Karthikapalli in the north for a length of about 24 km and widthvaries between a few tens of metres over a kilometre. Available reports shows that the lake is under threatdue to anthropogenic (encroachments) and natural (siltation) causes. Discrimination of these two oftenbecomes difficult, because of the lack of sufficient information on the natural sources of sediments.Therefore, in the present study, an attempt has been made to use information on mineralogical compositionof sediments as a tool to unravel the sources of sediment in the Kayamkulam lake.

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The content of total heavy minerals in the fine sand fraction is 12.38%. Based on the differencein the content of heavy minerals, the Kayamkulam lake can be divided into three sectors- Southern,Central and Northern sectors. The total heavy minerals exhibit an increasing trend from Northern sectorto the Southern sector. Analysis of the heavy mineral suite in the Kayamkulam estuary shows a spectrumof minerals, which include opaques, sillimanite, zircon, garnet and ionosilicates as the major and rutileand monazite as the minor constituents. Magnetic separation reveals that magnetite and ilmeniteconstitute the major members among the opaque minerals (79.17%). The sector wise studies showhigher opaque content in the Central sector. Most of the sillimanite exhibits prismatic character andthe Southern sector records the maximum content. Zircon is rounded to sub rounded and exhibitsovergrowths. The average number percentage of zircon is 4.88%. Among the garnet population Almandine(pink) is dominant type in Southern part. Hornblende is identified as the predominant amphibole in theheavy mineral assemblage. Hypersthene, enstatite and diopside are the predominant pyroxene membersidentified in the ionosilicate category. Rutile and Monazite occurs only in marginal amounts in the finesand fraction of the Kayamkulam lale.

The decrease of heavy mineral contents in the Northern and Central regions and increase in theSouthern region may be due to non-entrainment by low energy currents, subsequent deposition andprotection by the coarse, light minerals. The drainage basin of the Pallikkal river, one of the importantrivers draining into the Kayamkulam lake, consist mainly of khondalite, charnockite, garnetiferrousquartzo feldspethic gneiss as the common rock types. Of these the former two khondalite and charnockiteare widely spread out. These rocks might have acted as the provenance for the sediments in theKayamkulam lake, in addition to a substantial contribution from the polycyclic sediments brought fromthe innershelf region of the Lakshadweep Sea.

Mass movements triggered by subsurface pipe flow in the western ghatsG Sankar

Centre for Earth Science Studies, Thiruvananthapuram - 695 0031E-mail: gsankar@cessind.org

Mass movements in the form of landslides are common during the peak rainy periods of monsoonsin the Western Ghats region of Peninsular India. The studies conducted by CESS in the Western Ghatsindicate that these landslides are rain induced ones. So far no indications are there to conclude thatseismic tremors as the trigger to such incidences. Studies also have indicated that majority of theslides are confined to the topographic hollows. During the monsoon periods of 2006 and 2007 therewere a number of land disturbances in the form of landslides occurred in different localities in thehighland region of the state with different modes of failure such as slide type, flow type and creep type,topple type etc. An important factor observed was the free pipe flow of subsurface ground water movementas a triggering factor of such mass movements in many localities. Piping or subsurface tunnel erosion isthe main cause for developing such pipes in the overburden material. Such pipes will have an inlet andoutlet. Existence of such pipes will come to light only when a failure occurs when these pipes getexposed in the scarp where the slope failure has occurred. Recently pipe flow (or piping) inducedlandslides are observed in many localities in the state. Piping is the subsurface erosion of soil by percolatingwaters to produce pipe-like conduits underground. Piping phenomenon is not very common in Kerala.Piping was earlier reported from Palkkayam village and Agali of Mannaghat taluk of Palakkad district,Venniyanimala in the Thodupuazha taluk of Idukki district, Banasura sagar and Kunnamangalam vayal inthe Vythiri taluk, Wayanad district and Thirumeni village in Taliparamba taluk of Kannur. Even thoughpiping has been reported from many localities, piping triggered landslides are not reported from anywhere in Kerala.

Valamthodu landslide occurred in the Thondarnad village of Mananthavady taluk of Wayanad districtis a classic example of pipe flow induced landslide. This landslide in the form of debris flow (locallyknown as urul pottal) occurred during early hours of 23.06.2007 taking a toll of four human lives andcausing extensive damage to agricultural land. This incidence took place after prolonged rainfall associatedwith the SW monsoon. The region experienced pre-monsoon rains followed by heavy monsoon rains. It is

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also reported that high to very high velocity winds accompanied the rains uprooting a number of trees.The area has a general elevation of 835 meters from MSL at the middle of the affected slope. The slope ofthe failed slope is 30 degrees. The slope is dominated by mixed crops and coffee in the down slopes anddegraded forest on the up slopes and crown area. The relative relief of the area is high (+200 m) it alsohas considerable soil cover. The thickness of the soil cover is more than 3m. Silt rich loamy soil with lotof carbonaceous material constitutes the soil cover. The soil is fully saturated with water at the time ofinspection. Closer inspection of the failed slope revealed the existence of pipe. Pipe with a diameter ofabout 100 cm is found discharging ground water at the time of inspection few days after the failure.

Pipes generally form where the sediment thickness is very high in a clay rich soil. In Wayanaddistrict the sediment thickness is generally very high and sometimes exceeding more than 5 m. The clayand silt content are also high. The SW monsoon rains during the beginning of June the area receivedgood rainfall promoting high discharge through the pipes. About 150cm of rainfall occurred in the areaon the day of the incident. This has resulted in huge quantity of water discharging through the pipe.The pressure exerted by the water in these pipes on the overburden material which was sloping at anangle of 30degrees might have served as the trigger to this failure. Since pipe flow is free flow comparedto laminar flow through the soil the impact of high rainfall shall be instantaneous on the slope. After thefailure of the slope high discharge of water is taking place through the exposed pipe. This is good forthe overall stability of the remaining slope material as the build up of pore pressure is considerablyreduced by the free flow through the pipes.

Development of free and open source Web-GIS System for3D visualization for geospatial data

Sarawut Ninsawat, Venkatesh Raghavan, Shinji MasumotoOsaka City University, 3-3-138 Sugimoto-cho, Sumiyoshi-ku, Osaka 558-8585, Japan

E-mail: raghavan@media.osaka-cu.ac.jp

With increasing access to appropriate geospatial data, 3D visualization in Web-GIS application hasattracted wide interest. Most available solutions for 3D geospatial visualization still require standaloneapplications that offer little flexibility in accessing of dynamic data from Web Processing Service (WPS)as a “browser-only” (Firefox, Interner Explorer etc.) solution. In this study, a novel solution is implementedusing various open standards that enable 3D visualization of geospatial data as Virtual Reality ModelingLanguage (VRML) or X3D model. The system offers a “browser-only” Web-GIS solution, wherein the onlyrequirement on the client side being the ability to access in Internet/Intranet and use a Web-browser.Not only static geospatial data layers can be accessed as Web Feature Service (WFS) and Web CoverageService (WCS) but also dynamic results offered through Web Processing Service (WPS) can be visualized.The system was implemented based on a clearly demarcated Service Oriented Architecture (SOA) consistingof Data Provider, Data Processing and 3D Rendering Services.

Firstly, the Data Provider service creates a web-service that publishes various geospatial datasource both of grid-based (raster) and vector data set. These services add a level of abstraction to thedata that is extremely important in distributed computing environments. Secondly, the Data Processingservice is compliant with Web Processing Service (WPS) specification, which is also the Open GeospatialConsortium (OGC) proposed specification, is used to allow distributed geoprocessing. The WPS specificationdefines a mechanism and procedures by which geoprocessing task will be carried out on remote serversand processed result can be obtained over the network. Thirdly, the 3D Rendering service is componentto create dynamic 3D visualization from user-specified spatial datasets.

The system is entirely based on Free and Open Source Software (FOSS) at both client and server end.At the server side, the system is implemented on Linux using GRASS GIS, PostgreSQL and VisualizationToolKit (VTK) for geospatial analysis, management and rendering of 3D model. The client web-applicationwas developed using OpenLayers to facilitate user interaction and 2D/3D visualize output result. Thedata transmission protocol follow the WFS (vector) data or WCS (raster) Open Standards,. Spatial analysis

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of requested data is carried out using the WPS Open Standard and lastly, generation of VRML models isalso implemented as WPS using the FOSS Visualization ToolKit (VTK). Necessary input parameters for dataprocessing and visualization are be communicated to the Data Processing service over the Http protocol.AJAX, (Asynchronous JavaScript and XML) technology has been used to construct asynchronousconnection using the XMLHttpRequest to efficiently manage requests and communicate results as adistributed geoprocessing service.

Many simulation scenarios such as flood modeling, landslide and debris flow have successfullytested using the system. The present system, not only allows the virtual modeling of static datasets suchas sub-surface geology and bore-hole data, but also the 3D representation of dynamic simulation resultssuch as flood simulation and debris flows. As the system is independent of any proprietary softwarecomponent, further customization, enhancement and improvements to suit various educational andpractical needs can be incorporated with relative ease.

Distribution and geochemistry of platinum group of elements (PGE) fromMadawara Igneous Province, Lalitpur, Southern part of

Bundelkhand massifSatyanarayanan M1, Singh SP2, Balaram V1, Anjaiah KV1

1National Geophysical Research Institute, Uppal Road, Hyderabad 500606.2Department of Earth Sciences, Bundelkhand University, Jhansi – 284128

E-mail: msnarayanan@ngri.res.in

The recent discovery of platinum group of elements (PGE) enrichment from the Madawara IgneousProvince (MIP) has promoted the possibility of PGE deposit in Bundelkhand craton. The high concentrationof PGE is mainly confined in the ultramafic rocks in the MIP that occurs along the E-W trending shear/fracture zones developed throughout the southern part of Bundelkhand massif. Several bodies of maficand ultramafic rocks consisting of harzburgite, websterite, lherzolite, pyroxenites have been encounteredfrom the Archaean gneissic terrain that were intruded by diorite-gabbro-granite associated in subsequentevent. The mafic and ultramafic bodies of MIP are 500m - 2.5km in width and are 30km in lengthtrending in N70oE as detached hillocks.

Our present study is exclusively based on surface rock samples collected from Madawara, Tisgawan,Ikauna, Pindari and Bhikampur areas for the petrological interest of PGE distribution in the ultramaficbodies occurring in the northern part of MIP.

The geochemical history of 80 samples indicate that MgO in mildly altered to least altered rocks variesfrom 26.4 to 35.9% in the websterite, harzburgite, lherzolite and pyroxenites, while Cr (955 to 6319 µg/g) and Ni (1173 to 2290 µg/g) contents are also high in these rocks. The SiO2 content ranges from 42 to51 wt %. The incompatible large ion lithophile elements (LILE) and high-field strength elements (HFSE) arein general low. These rocks are also characterized by low total REE contents (åREE = 3.7 to 15.6 µg/g) aswell as PGE (SPGE = 52 to 382 ng/g; n = 15). The ultramafic rocks are characterized by negative Eu anomaly(Eu/Eu* = 0.89 to 2.16), slight LREE enrichment, especially cerium (La/SmN = 0.93 to 2.78) and almost flatHREE (Gd/YbN = 0.86 to 1.85). The Eu anomaly was found to be positive for the diorite and gabbro whileit is strongly negative for the websterite, harzburgite, lherzolite and pyroxenites. Cu/Pd vs. Ni/Cu suggestsS-under saturated magma in the initial stage. It was observed that the chrome spinel participated in thepartitioning of PGE in early stage of magmatic rock. The geochemical and field data reveal that thechromite and sulfide mineral are disseminated through out the ultramafic body but the high concentrationwas encountered at the late stage of evolution of komatiite magma.

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Pore water pressure as a trigger of shallow landslidesin the Western Ghats of Kerala, India: some preliminary

observations from an experimental catchmentSekhar L. Kuriakose, V.G. Jetten and C.J. van Westen

United Nations University-ITC School for Disaster Geo-Information Management,International Institute for Geo-information Science and Earth Observation (ITC),

Hengelosestraat 99, P.O Box 6, 7500AA, Enschede, The Netherlands.G. Sankar

Centre for Earth Science Studies, Thiruvananthapuram, Kerala, IndiaL.P.H van Beek, Department of Physical Geography, Utrecht University, The Netherlands

Email: sekhar.lk@gmail.com

The region of the Western Ghats in Kerala, India is prone to landslides mainly due to anthropogenicdisturbances and very high rainfall amounts, initiating many shallow landslides leading to debris flows.Here some initial observations on the apparent relationship amongst pore water pressure fluctuations,rainfall characteristics and landslide initiation are presented based on monitoring in an experimentalcatchment in the upper Tikovil River basin. On 21 and 22 June 2007, continuous rain fell over 15 hrswith a total precipitation of 194.8 mm; the storm caused high pore water pressures in 3 piezometers inhollows for over 9 hours contributing to several shallow landslides which evolved into debris flows.These initial results indicate that the transient response of pore water pressure in the hollows that didnot fail are representative of the pore water pressure pattern in the hollows which failed and thusenables such data to be used for the calibration of physically-based slope hydrology models coupledslope stability models.

Evolution and crustal growth of Bundelkhand craton viz-a-vizsouthern Indian cratons

K. K. Sharma(Retd. Scientist-G, Wadia Institute of Himalayan Geology)

Kesar Niwas, 1-Nehru Enclave, G.M.S. Road, Dehra Dun 248001E-mail: kkswadia@yahoo.com

Indian shield is one of the many significant regions of the Earth, which preserves the records ofthe evolution and the growth history of the early Archaean-Palaeoproterozoic crust. In the earlierrecognized list of three proto-continental nuclei (Dharwar, Singhbhum and Aravalli) in the Indian shield(Naqvi et al., 1974), another proto-continental nucleus-Bastar Craton, was added later (Yedekar et al.,1990). The bulk of the Indian shield now comprises of three southern cartons (Dharwar, Bastar andSinghbhum) separated by Godavari and Mahanadi grabens and lies to the south of the Narmada-Sonlineament, while the Aravalli craton (Gopalan et al., 1990 Sharma, 1990; Wiedenbeck et al., 1996) liesto the north of it. Radhakrishna (1989) proposed that a “Central Indian Tectonic Zone” (CITZ)encompassing the SONATA (Son-Narmada-Tapti) Belt, marks the junction of the Bundelkhand block in thenorth and the Peninsular block in the south, each block constituting an Early Proterozoic magmatic“Terrane”. Subsequently this idea was enlarged to propose two ancient nuclei, the Bundelkhand proto-continent in the north and the Deccan Proto-continent in the south separated in mid-to late Archaeantime by a narrow inter-cratonic basin of which no remnant is now seen, but whose only signature isrepresented by the Central Indian Shear (Yedeker et al., 1990).

A semicircular to triangular outcrop of Bundelkhand Granitoid Massif covering some 26,000 sq kmarea was known for a very long time as a monotonous granitic terrain comprising multi-phased granitoidintrusions of early Proterozoic age (Jhingran, 1958, Misra and Sharma, 1975, Sharma, 1982, Sarkar etal., 1984, Basu, 1986, Radhakrishna, 1989). It has now been established as Early-Archaean-Palaeoproterozoic (207Pb/206Pb zircon age of 3.3 Ga to 2.2 Ga) proto-continental crust representing thenorthern most craton of the Indian shield, preferably named as Bundelkhand Craton, which cratonizedaround 2.5 Ga (Sharma and Rahman, 1995, 2000; Mondal et al., 1997, 2002; Sharma, 1998). Three

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distinct, linearly exposed litho-tectonic units, (i) the highly deformed older gneisses-greenstonecomponents (peridotites, pyroxenites, gabbros, amphibolites closely associated with aranaceous-argilaceous-calcareous-ferruginous metasediments, intruded by tonalite-trondhjemite-granodiorite (TTG)gneisses of early- to late-Archaean (3.3 Ga-2.6 Ga) age; ii) undeformed multiphase granitoid (K-rich)plutons (hornblende-rich granodiorites, porphyritic granites, coarse grained biotite granites,leucogranites, porphyries) and the residual H2O, Si, Al, K-rich phase- Quartz Reefs (all emplaced in anarrow time span (2.5 Ga- 2.4 Ga), representing Archaean-Proterozoic Boundary Event, and (iii) NW-SEtrending mafic dykes swarms cutting cross the NE-SW trending Quartz Reefs, have been broadly recognizedin Bundelkhand Craton. The rift related chemistry of the Mafic Dykes intruding accreted proto-continentalcrust (Bundelkhand Craton) and mafic flows (Mg-rich tholeiites, Fe-rich tholeiites with minor basaltickomatiites), interbedded with the quartz dominated, ferruginous, phosphorous and calcareous (Meso-to Late- Proterozoic) sediments of the marginal basins of Gwalior and Bijawar, unconformable overlie onthe highly weathered and eroded surfaces of the Bundelkhand Granitoids. Tectonic elements, dispositionof various litho-tectonic units, pattern of extensional fractures later occupied by Quartz Reefs (some ofthem hundred of km long) and the rift-related mafic dyke swarms within the Bundelkhand Craton and theinterbedded tholeiitic flows in the quartz dominated sediments of the marginal basins, clearly suggestdoming up of the much more than presently exposed 26,000 sq km of Bundelkhand continental crust,on-setting of extensional regime, opening-up of large fractures, subsidence, development of basinslocated within the craton (Mauranipur basin) and along its margins (Gwalior-Bijawar basins). Such ascenario, in the opinion of the author, suggests a widespread plume activity associated with up-rise oftholeiitic magma in the northern part of the Indian shield (Sharma and Rehman, 2000).

Bundelkhand Craton Viz-a-Viz Other Cratons of Indian Shield: The evolution history and thenature of crustal growth of Bundelkhand Craton that lies to the north of the Narmada-Son Lineament, ismore or less similar to other three cratons (Singhbhum, Bastar, and Dharwar cratons) of the Indian shieldthat lie to the south of it. A comparative crustal growth history of all the four cratons of the Indianshield is given in Table-1. The author strongly feels that the Bundelkhand Craton, being least deformedafter late Archaean-Palaeoproterozoic Boundary Event, better preserves the records of the crustalgrowth and the accretion dynamics of the Late Archaeon-Palaeoproterozoic micro plates, than theother cratons of the Indian shield.References:

Basu, A.K., 1986. Geology of parts of Bundelkhand Granite massif Central India. Rec. Geol. Surv.India, 117: 61-624.Gopalan,K. Macdoughall, J.D., Roy, A.B. and Murli, A.V., 1990. Sm-Nd evidence of 3.3 Ga old rocksin Rajasthan, Northwestern India. Precambrian Research, 48, 287-297.Jhingran, A.G., 1858. The problem of Bundelkhand granite and gneisses: Presidential address, SectionGeology and Geography, 45th Indian Science Congress, Madras.Misra, R.C. and Sharma, R.P., 1975. New data on the Geology of the Bundelkhand complex of CentralIndia. Recent Researches in Geology, 2, 311-346. Hindustan Pub. Co., Delhi (India).Mondal, M.E.A., Sharma, K.K., Rahman, A., Goswami, J.N., 1998. Ion microprobe 207Pb/206Pb zirconages for the gneiss-granitoid rocks from Bundelkhand massif : evidence for the Archaean components.Curr. Sci., 74 , 70-75.Mondal, M.E.A, J.N.Goswami, M.P.Deomurari and K.K.Sharma (2002). Ion microprobe 207Pb/206Pb zirconages of the Bundelkhand massif, northern India shield: implications for crustal evolution of theBundelkhand-Aravalli protocontinent. Precambrian Research, 117, 85-100.Naqvi, S.M., Divakara Rao, V. and Harinarain, 1974. The Proto-Continental growth of the Indianshield and the antiquity of its rift valleys. Precamb. Res., 1, 345-389.Sarkar, A., Trivedi, J.R., Gopalan, K., Singh, P.N. Singh, B.K., Das, A.K. and Paul, D.K., 1984. Rb-SrGeochronology of the Bundelkhand granitic complex in the Jhansi-Babina-Talbehat sector, U.P.,India.Jour. Earth Sciences V. CEISM Seminar, 64-72.

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Sarkar, A., Paul, D.K. and Potts, P.J., 1995. Geochronolgy and geochemistry of the Mid-Archaean,trondhjemitic gneisses from the Bundelkhand craton, Central India. Recent Researches in Geologyand Geophysics of the Precambrians (RRG vol. 16: Ed. A.K.Saha),76-92.Sharma, R.P., 1982. Lithostratigraphy, structure and petrology of the Bundlekhand Group. In: K.S.Valdiya, B.S. Bhatia, and V.K. Gaur (Editors), Geology of Vindhyachal. Hindustan Pub. Co. India,30-46.Sharma, K.K. and Rahman, A., 1995. Occurrence and petrogenesis of the Loda Pahar trondhjemiticgneiss from Bundelkhand craton, central India: Remnant of an early crust. Curr. Sci., 69, 613-617.Sharma K.K. and Abdul Rahman, 2000. The early Archaean-Palaeoproterozoic Crustal Growth of theBundelkhand craton, Northern Indian Shield. In: (M. Deb Ed.) Crustal Evolution and Metallogeny inthe Northwestern Indian Shield”, Narosa Publishing House, New Delhi , 51-72.Sharma, K.K., 1998. Geological evolution and crustal growth of the Bundelkhand craton and itsrelicts in the surrounding regions, N. Indain shield. In: Editor B.S. Paliwal (Ed.) The Indian Precambrian(A.B. Roy Volume), Scientific Publishers (India) Jodhpur (India).Radhakrishna, B.P., 1989. Suspected tectono-straitigraphic terrane elements in the Indian Sub-continent. Geol. Soc. India, 34, 1-24.Wiedenbeck, M., Goswami, J.N. and Roy, A.B. 1996. Stabilization of the Aravalli craton of NorthwestIndia at 2.5 Ga: an ion microprobe zircon study. Chem. Geol., 129, 325-340.

Ganga plain foreland basinI.B. Singh

Geology Department, Lucknow University; Lucknow 226007indrabir@yahoo.com

The Ganga Plain is part of the Indo-Gangetic Plains, the active foreland basin of the Himalayas.The Indo-Gangetic Plains represents one of the largest alluvial plains of the world. The Ganga Plainforeland basin developed on an old, cold and rigid Indian lithosphere with many irregularities in theform of basement ridges and basement faults. The basement exhibits high variability in down flexingand thickness of foreland sediments above the basement. It seems, initially this foreland basin wasnarrow and deep, and become wide and shallow with time. These processes are related to the loading inthe Himalaya and rigidity of the down flexing Indian lithosphere. There is evidence that the Ganga Plainhas shifted more than 100 km over the craton during Late Quaternary. The sediments coming into theGanga Plain are derived from the Himalaya, some sediments come from the southern craton.The Himalayanderived sediments onlap over the craton derived sediments.

Present day Ganga Plain shows a large variety of fluvial features which have been formed under thechanging tectonic and climate conditions during Late Pleistocene-Holocene. The present-day fluvialsystem shows a strong control of active tectonics, as river channels show highly deformed meanders.Pattern and orientation of tectonics varies from Himalayan orogen towards craton margin in the form ofcompressional tectonics to extensional tectonics respectively. The craton margin shows many tectonicfeatures, namely tilted blocks, conjugate fractures, gravity faults and kilometer scale warping. The GangaPlain show distinct regional geomorphic feature namely Upland Interfluve Surface, Marginal Plain UplandSurface, Megafan Surface, River Valley Terrace Surface, Piedmont Fan Surface and Active Flood PlainSurface. All these Surfaces are depositional and possess a cover of Holocene sediments.

A tectonic event dated 8-5 kyrs disrupted many drainages of Ganga Plain., converting river channelsinto linear lakes, and produced kilometre scale warping. There are distinct zones of more intense warpingand cliff development in the Ganga Plain. Relationship between tectonics of the Ganga Plain, Himalayantectonics and response of basement are not yet clear.

There is evidence of human settlement of Ganga Plain already around 40 ka. The Ganga Plain was ofgrassland during Late Pleistocene-Holocene. Study of lake profiles has helped in reconstruction ofHolocene climate history. There is evidence of rice cultivation in Ganga Plain around 8500 years BP.

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Investigation on specific site response on ground motionin varied geological formations in and around Kochi city

using Microtremor data, Kerala StateH. N. Singh1, V. N. Neelakandan2 and V. Shravan Kumar2

1Department of Geophysics, Banaras Hindu University, Varanasi 221 005 2Centre for Earth ScienceStudies, P. B. No. 7250, Akkulam, Thiruvananthapuram 695 031

E-mail: hridaynarain.singh@gmail.com

Measurements of microtremor were performed by using a CityShrak seismic recorder and a tri-axial1 second seismometer in and around Kochi city and obtained a total of 942 records at different sites.Location of sites was obtained with the help of a Garmin make handheld GPS. The records were subjectedto spectral analysis using H/V technique, and resonance frequency and site amplification were estimatedat each site. The data thus obtained on site amplification and resonance frequency were processed inGIS environment and prepared a seismic microzonation map of the Kochi city.

It is observed that the estimated resonance frequency varies significantly within short distances inand around Kochi city. The resonance frequency is spatially distributed in three northwest-southeasttrending regions parallel to the coast which differ appreciably in their site response characteristics. Thelowest resonance frequency values (d” 1.0 Hz) coupled with high site amplification were observed incoastal and backwater areas covered with younger alluvial deposits, and high resonance frequency values(> 5 Hz) to charnockites and laterites in the hinterlands. Though the areas of low resonance frequencygenerally exhibit higher level of site amplification (H/V), certain scattered pockets with similarcharacteristics were observed in high frequency areas too in the hinterlands. The distribution pattern ofresonance frequency and site amplification along west-east trending four parallel profiles across thecoast show low resonance frequency and high site amplification (H/V) within the coastal belt andbackwater zones. Sudden jump in resonance frequency and reduction in site amplification was observedat the boundary of younger alluvium deposits and the charnockite-laterite formations along theseprofiles. On the other hand, no significant variation in site response characteristics was noticed alongthe profiles parallel to coastline (NW-SE) showing more or less similar geological setup.

Using the spatial distribution of resonance frequency and site amplification, three seismic zoneshaving appreciably distinct site response characteristics were identified as Microzones I, II and III. TheMicrozone I and Microznone III occupy the easternmost and westernmost part of the city whereasMicrozone II is sandwiched between them. Microzone III is characterized by lowest resonance frequency(d” 1.0 Hz), Microzone II with medium level of resonance frequency (1.1-5.0 Hz) and Microzone I withhighest level of resonance frequency more than 5 Hz. The Longest characteristic site periods more than6.3 sec. for Microzones III, medium period 1.2-6.3 sec. for Microzone II and minimum of less than 1.2sec. for Microzone I were estimated. This information suggests that buildings and structures in MicrozoneIII have the highest probability to achieve resonance as compared to Microzones II and I when thenatural frequency of ground motion resulting due to an earthquake matches with that of the naturalfrequency of structures.

Evolution of Proterozoic foldbelts of NW Indian craton :A plate tectonic- and asthenosphere-driven hybrid model

S. Sinha-RoyBirla Institute of Scientific Research, Statue Circle, Jaipur 302001

E-mail: ssinharoy@yahoo.com

Proterozoic continental crust has grown and evolved through accretion of mobile belts at differentstages around Archaean nucleii. This growth mechanism has created various tectonothermally distinctProterozoic terranes. Many such terranes as the product of Proterozoic crustal growth have been modeledin terms of modern-style plate tectonics, but alternative approach has been suggested for intraplate

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asthenosphere-driven models for lithosphere evolution and dynamics in which vertical rather than lateralaccretion was dominant. This paper considers these two end-member processes in the development ofProterozoic terranes to suggest a hybrid model for the evolution of the Aravalli and Delhi foldbelts of NWIndia in Rajasthan region.

The Aravalli and Delhi foldbelts define a distinct fold-thrust-belt terrane that stitches the Mewarterrane, a part of the Greater Bundelkhand block, in the east, and the Marwar terrane in the west, bothcontaining strongly reworked and reconstituted Archaean juvenile crustal elements. The older Aravallifoldbelt contains stratigraphic and magmatic records suggesting its development via an intracratonicrift and sag basin having multiple extensional history and spatial variability. The main Aravalli foldbeltcontains a basal mafic volcanic and sedimentary sequence (Delwara Group), dated at ca. 2.0 Ga, whoseequivalent sttratigraphy is the Raialo Group in the northern Delhi domain. The geochemistry of themafic volcanics suggests their derivation being related to mantle plume emplaced in hot lithosphere.These two sequences mark the first Aravalli rifting event in the Palaeoproterozoic. This event was closelyfollowed by the emplacement of ca. 1.8 Ga old I-type granitoids (Ahar, Bairat, Udaipurwati, Gotro, Seolietc.). The second Aravalli rifting event at ca. 1.6 Ga produced contrasting lithofacies in differentdomains such that in the main Aravalli foldbelt the rift shoulders comprised a platform sequence ofarenite-pelite-carbonate (Debari Group) in the east (present coordinates) and a carbonate-free turbiditesequence (Jharol Group) in the west. The axial fracture zone of the rift is marked by mafic-ultramafic-plagiogranite association (Rakhabdev lineament). This event also emplaced a number of 1.6-1.5 Ga oldgranitoid plutons (Tekan, Amet, Anjana, Darwal etc.). The second Aravalli extensional event producedintracratonic narrow rift system with triple junctions (Rajpura-Dariba, Pur-Banera, Agucha belts) withinthe Bhilwara belt of the Mewar terrane and Alwar-Ajabgarh fault-bound sag basins in the northern Delhibelt. The Aravalli multiple rift-related sequences collapsed and the rift system closed at ca. 1.5 Ga as aresult of cooling and contraction of the Aravalli lithosphere to give rise to the Aravalli foldbelt and itsequivalent foldbelts in the Bhilwara and north Delhi domains.

The Mesoproterozoic contraction of the eastern Mewar lithosphere in the Aravalli terrane wasaccompanied with extension of the rigid western Mewar lithosphere that opened the linear Delhi rift atca. 1.5 Ga where mafic volcanics and sedimentary prisms developed (Sendra and Devgarh Groups). Thisevent is marked by alkali magmatism (Kishangarh nepheline syenite, 1490 Ma). The rift propagated intoa Red Sea-type oceanic trough that was consumed by westward ensimatic subduction to produce bimodalvolcanics-dominant chain of immature island arcs (Deri-Ambaji, Birantiya etc.) at ca. 1.0 Ga and a back-arc basin. The south Delhi foldbelt formed when the back-arc basin closed by westward subduction. Anophiolite-melange tectonic zone (Phulad ophiolite) and a Cordilleran-type magmatic belt (Erinpuragranite) mark the south Delhi suture, formed at 0.9-0.8 Ga.

Seismic reflection data and their tectonic interpretation indicate the presence of crustal duplexstructures and mantle-reaching dislocation zones in the Marwar-Delhi-Mewar terrains. Beneath the Delhifoldbelt Moho gets deeper (45-50 km) and branches off to contain oppositely dipping double Mohotraces. The lower crust contains 8-12 km thick high velocity zone (7.2 km/sec). The variable thicknessof the high-velocity zone of the lower crust and the unstable Moho topography, including the doubleMoho, are interpreted to have formed diachronously by a combination of processes, including originalarc development and subsequent magmatic underplating in the Delhi foldbelt as a product of progressivelithosphere evolution.

The hybrid tectonic evolution model of the Proterozoic Aravalli and Delhi foldbelts, as constrainedby the above general features, involves the development first of the Aravalli foldbelt on a hot and weaklithosphere during ca. 2.0-1.5 Ga, and subsequent development of the Delhi foldbelt on a colder andstronger lithosphere by plate tectonic processes during Ca. 1.5-0.9 Ga. In lithospheric dynamics heatproduction distribution in the crust plays a crucial role in strength distribution. The Aravalli-Delhiterrains show high surface heat flow (62-74 mWm-2) which is higher than Proterozoic global average (49-54 mWm-2). The anomalous heat flow reflects crustal radiogenic sources within the felsic igneous rocks inthe upper 5-10 km of the crust. In Palaeoproterozoic and Mesoproterozoic the heat sources wereconcentrated in the deeper crust near the source regions of magmatic melts at the SCLM, thus contributingto long-term lithospheric weakening and thinning. Heat distribution was modified in Late Mesoproterozoic

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and Neoproterozoic with the transfer of heat sources to the upper crust thus making the lithosphererigid and thicker. The spatial and temporal variations in lithosphere strength are reflected in the disparateanatomy of the Aravalli and Delhi foldbelts.

The hybrid diachronous model assumes the Proterozoic foldbelt substrate to have developed byjuvenile crustal accretion at ca. 3.2 Ga in NW Indian craton, and by its restricted cratonisation andlimited vertical growth at ca. 2.5 Ga due to anomalously high heat producing felsic magmatism (Berachand equivalent granitoids). The Palaeoproterozoic lithosphere was thus hot, weak and thin. Far-fieldcrustal extension due to asthenospheric dynamics created the Aravalli rift and sag basins containingcontrasting shallow marine and turbiditic sediments and mafic volcanics (ca. 2.0 Ga), punctuated bygranitoid emplacements at ca. 1.8 Ga and 1.6 Ga. The rift-axial extension emplaced mafic and ulramaficbodies along SCLM-reaching fracture system (Rakhandev lineament) at the facies transition zone of theplatform and turbidite sequences. No ophiolites developed and the metamorphism of the sedimentsrecords HT-LP assemblages in the Aravalli foldbelt.

The Aravalli rift basins closed at ca. 1.5 Ga, and the lower and middle crust cooled as with high-level granite emplacement the heat sources migrated to the upper crust. The lithosphere became rigidand got set for Phanerozoic-style plate tectonics. Distension of the rigid lithosphere produced Red Sea-type ocean basin in the Delhi belt during ca. 1.5-1.0 Ga which was eventually closed via island arc andback-arc development to produce ophiolitic suture and a Cordillera-type magmatic belt during 0.9-0.8Ga. HP-LT metamorphism characterizes the Delhi foldbelt.

The evolution of the Aravalli and Delhi foldbelts brings out the contrasting styles of Proterozoiccrustal evolution and foldbelt development in NW India craton. It also highlights the changes that haveoccurred in the transition from asthenosphere-driven lithospheric dynamics during ca. 2-0-1.5 Ga thatdeveloped the Aravalli foldbelt on a hot and weak crust to plate tectonic-driven lithospheric dynamicsduring ca. 1.5-0.9 Ga that developed the Delhi foldbelt on a colder and rigid crust.

Bhavani shear extension in Kerala - a significant zone in thecrustal evolution of peninsular India

P. Soney KurienGeological Survey of India, Unit: Kerala

Dharani Bhavan, Manikanteswaram. P.O. Thiruvananthapuram

The Bhavani shear zone is a major tectonic zone in the south Indian granulite terrain and itgenerally trends in ENE-WSW direction. It is considered to merge with the Moyar shear in its easternextension in Tamil Nadu. This shear zone has a lot of significance as it hosts a good number of goldoccurrences, especially in the Attapady valley. The western extension of this shear zone has not beendelineated so far. In this work, an attempt has been made to study the nature of shearing in the westernextension of Bhavani shear zone in Mannarkkad and Perinthalmanna areas.

The various rock types delineated in the area are classified under the Wayanad Group, PeninsularGneissic Complex (PGC), Charnockite Group and later intrusives. The Wayanad Group comprising pyroxenite/metapyroxenite, hornblende granulite/amphibolite and banded iron formation (BIF)/magnetite quartzite,represents the oldest rock units. The PGC comprises biotite-rich gneiss, biotite gneiss, hornblendegneiss and foliated/sheared granite. Two phases of granite emplacements have been identified. Threephases of folding episodes chronologically designated as F1, F2 and F3 are decipherable in the area. TheF1 and F2 folds are co-axial and as such hook-shaped interference pattern between F1 and F2 folds arenoticed in the area. F2 axial planes show a change in trend from almost E-W in the eastern part to NW-SEbeyond Mannarkkad. Effects of shearing, as evinced by the presence of mylonite and pseudotachyliteveins are well recognized and dextral sense of shear is deciphered from mylonite zones. Trend of mylonitezones indicate that the trend of Bhavani shear zone changes from ENE-WSW to WNW-ESE beyondMannarkkad. Incidences of gold mineralization have been noticed for the first time in the westernextension of Bhavani shear zone.

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The Precambrian Redox evolution of atmosphere-hydrospheresystem: An Indian perspective

B. SreenivasNational Geophysical Research Institute, Hyderabad 500606, India

E-mail: bsreenivas@ngri.res.in

The redox evolution of atmosphere-hydrosphere system held key to the organic evolution at thesurface of the earth (Knoll, 2003). In fact, it is now considered that these to processes have coevolvedtogether (Hedges et al., 2001) and such a process may be unique to the surface of planet earth. It wasinitially believed that the earth surface remained predominantly anoxic during the entire Archean andoxygenation process initiated some time during the Paleoproteorzoic (2.5 to 1.8 Ga) (Cloud, 1968;Holland, 1994). Many geological, mineralogical and geochemical indicators such as banded iron formations(BIFs), red beds, detrital redox-sensitive heavy minerals (eg. Uraninite, pyrite, siderite), redox-sensitiveelement compositions in shales, iron concentrations in paleosols, stable isotope compositions of C, S, N,Fe – all seems to favor the model of oxygen rise during the Paleoproterozoic (Sreenivas and Murakami,2005; Holland, 2006), although it is debated that earth remained oxygenated from 4.0 Ga onwards(Ohmoto, 2004). The mass independent fractionation (MIF) in S isotopes (Farquhar et al., 2000) andretention of Fe in paleosols (Sreenivas and Murakami, 2005) authenticate the Paleoproterozoic rise ofatmospheric oxygen. These evidences are depicted in Fig. 1.

0.511.522.533.54

Age Ga

Decrease in ä56Fe rangesÄ33S – 0.1 to +0.5 ‰δδδδδ34Ssulfate – δδδδδ34Ssulfide > 20 ‰Positive ä13Ccarb excursionsFe retention in paleosolsMn, Ce retention in paleosolsPause in BIF deposition Ä33S > ±1‰ä34Ssulfate – ä34Ssulfide < 20 ‰Fe loss in paleosolsPresence of detrital heavy minerals

Figure 1. Summary of evidence for reducing (bottom half) and oxidizing (upper half) conditionsduring the Precambrian. Note polarization of all the reducing evidence to the Archean and vice versa(modified after Sreenivas and Murakami, 2005).

The biomarker evidences point out that oxygenic photosynthesis initiated much earlier (by about~2.7 Ga) in the geological history (Brocks et al., 1999) than the above pointed evidences for aPaleoproterozoic increase in oxygen. This makes the delayed appearance of these evidences by about300 to 700 Ma, a conundrum. However, recently accrued evidences of variations in Mo contents (Anbaret al., 2007) and MIF in S isotopes (Kaufman et al., 2007) suggest that oxygen was present although insmall quantities by ~ 2.55 Ga. This leads to a new perception of fluctuating oxygen concentrations priorto the onset of the Paleoproterozoic. Also there is a change in the understanding of the atmosphericoxygen increase from that of the increase in oxygen concentrations to the diminishing of high methaneconcentrations (Zahnle et al., 2006).

The causal processes for the increase in oxygen concentrations have also remained highly elusive.Several mechanisms have been invoked as the causal process of oxygenation of the Earth’s atmosphere.It was conventionally thought that increase in organic carbon burial might have led to the oxygenationof atmosphere-hydrosphere system. However, many other processes such as diminishing reductant fluxesin volcanic gases (Holland, 2002), biogenic methane and hydrogen escape (Catling et al., 2001), increasein subaerial volcanism (Kump and Barley, 2007), formation of supercontinents (Campbell and Allen,

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2008) have also been thought to be responsible for the oxygen enrichment. Deciphering the exactquantitative nature atmospheric oxygen levels may better constrain these causal processes. The retentionfractions of Fe and the application of oxidation kinetics led to a quantitative modeling suggesting agradual rise in atmospheric oxygen from 2.5 to 2.0 Ga onwards (Murakami et al., 2007). The Fe isotopecompositions of paleosols further corroborate such a conclusion (Sreenivas et al., 2008).

Recently, the transitions in the redox conditions of the Proterozoic ocean (especially those ofMesoproterozoic) have gained attention because of the possibility that deep oceans could representsulfidic conditions (Canfield, 1998). It has been suggested earlier that the Paleoproterozoic rise ofatmospheric oxygen has led to the oxidation of deep oceans as well. However, one of the importantconsequences of atmospheric oxygenation is the oxidation of pyrite and increase in the sulfateconcentrations of the oceans. As sulfate concentrations increase, the bacterial sulfate reduction willbecome dominant producing a large difference in the S isotope compositions of the sulfide and sulfate.Using this as a proxy Canfield (1998) suggested enhanced sulfide concentration might have removedthe iron from deep ocean water instead of oxygen at the end of Paleoproterozoic at ~ 1.85 Ga – the timeof disappearance of BIFs. Following these it is now proposed that the deep oceans have remained anoxicduring the entire Mesoproterozoic from 1.84 Ga onwards. Recent elemental and isotopic studies on thesedimentary rocks of < 1.84 Ga attest the dominance of sulfide-rich deep ocean (Arnold et al., 2004).This model being called ‘Canfield Ocean model’ indicative of prolonged euxinic deep ocean conditionsduring the Proterozoic has important bearing on the primary productivity and algal evolution of thisperiod (Anbar and Knoll, 2002).

The information available from the rocks of the Indian Precambrian sequences on the redox evolutionis scanty despite the fact that they present a fascinating range of geological framework. It is knownthat the Late Archean Chitradurga Group presents evidence for well developed columnar stromatolites aswell as one of the oldest Mn formations of the world. It may be interesting to verify the oxidation stateof Fe using Fe isotope compositions in this intriguing sequence as well as to study the Mo concentrations.Also the late Archean Dharwar sequence comprises barites, whose MIF compositions may yield importantinformation regarding redox conditions. Preliminary results on the Ghattihosahalli barites indicate alarge of MIF in S isotopes (Sreenivas and Bekker unpublished data) suggesting anoxic conditions. Thepaleosol of 2.4 to 2.2 Ga age at the base of the Paleoproterozoic Aravalli Supergroup show evidences fortheir development under anoxic conditions (Sreenivas et al., 2001a). Further, the phosphatic stromatolitebearing Jhamarkotra Formation of the Aravalli Supergroup preserve high d13C excursions in both carbonate(up to 12 ‰) and organic carbon (up to -11 ‰) serving as the Indian example of global 2.22 to 2.06Ga excursion event (Sreenivas et al., 2001b). Despite the presence of Purana Basins of India, the workto validate the euxinic deep ocean conditions during the Mesoproterozoic is yet to be initiated. Alsothe MIF in S isotope record of Indian Precambrian sequences is non-existent. The foregoing discussionbrings out the importance of carrying out researches on Indian Precambrian rock suites focusing onredox evolution especially considering the bearing of this process on organic evolution.

References:Anbar, A. D., Duan, Y., Lyons, T. W., Arnold, G. L., Kendall, B., Creaser, R. A., Kaufman, A. J., Gordon,G. W., Scott, C., Garvin, J., Buick, R., 2007. A Whiff of Oxygen Before the Great Oxidation Event?Science, 317, 1903–1906.Anbar, A.D., Knoll, A.H., 2002. Proterozoic ocean chemistry and evolution: A bioinorganic bridge?Science, 297, 1137–1142.Arnold, G.L., Anbar, A.D., Barling, J. and Lyons, T.W. (2004) Molybdenum isotope evidence forwidespread anoxia in mid-Proterozoic oceans. Science, 304, 87-90.Brocks, J.J., Logan, G.A., Buick, R. and Summons, R.E. (1999) Archean molecular fossils and the earlyrise of eukaryotes. Science, 285, 1033-1036.Campbell, I.H. and Allen, C.M. (2008) Formation of supercontinents linked to increases in atmosphericoxygen. Nature Geoscience, 1, 554-558.

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Canfield, D.E. (1998) A new model for Proterozoic ocean chemistry. Nature, 396, 450-453.Catling, D.C., Zhanle, K.J. and McKay, C.P. (2001) Biogenic methane, hydrogen escape and theirreversible oxidation of early earth. Science, 293, 839-843.Cloud, P. (1968) Atmospheric and hydrospheric evolution on the primitive earth. Science, 160, 729-736.Farquhar, J., Bao, T.H. and Thiemens, M.H. (2000) Atmospheric influence of earth’s earliest sulfurcycle. Science, 289, 756-759.Holland, H.D. (1994) Early Proterozoic atmospheric change. In Early Life on Earth: Nobel Symposium,84 (Bengtson, S. Ed.). pp. 630, Columbia University Press, New York, 237-244.Holland, H.D. (2002) Volcanic gases, black smokers, and the Great Oxidation Event. Geochim.Cosmochim. Acta, 66, 3811-3826.Holland, H. D., 2006. The oxygenation of the atmosphere and oceans. Phil. Trans. Royal Soc. Sect. B,doi:10.1098/rstb.2006.1838.Kaufman, A. J. Johnston, D.T., Farquhar, J., Masterson, A.L., Lyons, T.W., Bates, S., Anbar, A.D.,Arnold, G.L., Garvin, J. and Buick, R. (2007) Late Archean biospheric oxygenation and atmosphericevolution. Science, 317, 1900–1903.Knoll, A. (2003) The geological consequences of evolution. Geobiology, 1, 3-14.Kump, L. R. and Barley, M. E. (2007) Increased subaerial volcanism and the rise of atmosphericoxygen 2.5 billion years ago. Nature, 448, 1033–1036.Murakami, T., Sreenivas, B., Das Sharma, S. and Sugimori, H. (2007) Gradual rise of atmospheric oxygenbetween 2.5 and 2.0 Ga revealed by iron oxidation kinetics Geochim. Cosmochim. Acta, 71, A697.Ohmoto, H. (2004) The Archean atmosphere, hydrosphere and biosphere. In The Precambrian Earth:Tempos and Events (Eriksson, P.G., Altermann, W., Nelson, D.R., Mueller, W.U. and Catuneanu, O. Eds.),Elsevier B.V., Amsterdam, The Netherlands, pp. 361-388.Sreenivas, B., Murakami, T., 2005. Emerging views on the atmospheric oxygen evolution during thePrecambrian. J. Min. Pet. Sci., 100, 184–201.Sreenivas, B., Hirata, T. and Murakami, T. (2008) Fe isotope compositions of 2.45 Ga Cooper Lakepaleosol. Geochim. Cosmochim. Acta, 72, A890.Sreenivas, B., Roy, A. B. and Srinivasan, R. (2001a) Geochemistry of sericite deposits at the base ofthe Paleoproterozoic Aravalli Supergroup: Evidence for metamorphosed and metasomatised Precambrianpaleosol. Proc. Indian Acad. Sci. (Earth and Planet. Sci.), 110, 1-23.Sreenivas, B., Das Sharma, S., Kumar, B., Patil, D.J., Roy, A.B., and Srinivasan, R. (2001b) Positiveä13C excursions in carbonate and organic fractions from the Paleoproterozoic Aravalli Supergroup,Northwestern India. Precamb. Res., 106, 277-290.Zahnle, K.J., Claire, M.W., Catling, D.C., 2006. The loss of massindependent fractionation in sulfurdue to a Paleoproterozoic collapse of atmospheric methane. Geobiology 4, 271–283.

Progress relating to study of fluid inclusions inmetamorphic rocks and future direction of research

C. Srikantappa.Department of Geology, University of Mysore, Manasagangothri, Mysore 570006.

E-mail: srikantappa@googlemail.com

Presence of fluid inclusions have been reported from different types of metamorphic rockswhich suggest occurrence of a free fluid phase during metamorphism. Minute amounts of free fluidstrapped along grain boundaries or in fluid inclusion in metamorphic rocks, mostly remain trapped untildislodged by thermally induced hydro-fracturing, shearing, deformation or tectonic uplift. While studyingmetamorphic rocks and their evolution, apart from recording field relationship, types of deformation,mineral assemblages, micro-textural features and mineral P-T estimates, data on the nature and

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composition of fluids play a significant role in understanding various mineral reactions, mineralstability, heat flow, elemental transport, melting and deformation in metamorphic rocks.

Progress made relating to the study of fluid inclusions in different types of metamorphic rocksnotably in granulites and in shear zones with particular reference to rocks exposed in southern PeninsularIndia are reviewed, illustrated and discussed. Some of the problems and areas of future researchwork in the field of Fluid inclusion study is presented.

Fluid inclusions study in metamorphic rocks from southern Peninsular India has shown presence ofCO2, CO2-H2O, CO2-CH4-N2, CH4-N and H2-NaCl bearing fluids. Occurrences of different types of fluids inthese metamorphic rocks is dependent on lithology, protolith characters (ortho or Para) and type ofdeformation.

CO2 and CO2-H2O fluids appears to be the dominant fluids characteristic of massive granulites,derived from igneous precursors. In contrast, CO2, CH4-N2 and N2 bearing inclusions appear to becommon in granulites derived from sedimentary protoliths.

Fluid inclusions in metamorphic rocks indicate to their trapping conditions in a wide rangeof P-T conditions ( 650 to ~ 800oC and 5 to 10 kbars) and even in UHT rocks ( T > 1000oC). Thereare many instances where evidences of extensive changes after initial trapping of fluids have beendocumented. For these reasons, interpretation of fluid inclusions in metamorphic rocks requires athorough knowledge on the chronology of inclusion formation with respect to host mineral and anindependent mineral P-T estimate for a given rock. Establishment of fluid inclusion chronology is amust while studying fluids in metamorphic rocks and various concepts like GIS, IFI, TBFI, FIA areavailable in literature and may be used to characterise the fluid inclusion assemblage in metamorphicrocks. There is a need for a careful ‘fluid inclusion petrographic’ study in metamorphic rocks forproper evaluation of fluid inclusion data. Further, the concept of relative chronology betweendifferent types of fluid inclusions trapped in different metamorphic minerals, including relativechronology between different isochors obtained for inclusions is essential for proper interpretation offluid inclusion data in metamorphic rocks. In principle, only fluid inclusions which can be usedproperly can be measured and collecting data on large number of inclusions without propermicro-textural analyses in metamorphic rocks will be unrealistic. Many experimental and theoreticalstudies on PVTX properties of geologic fluids will help for accurate interpretation of microthermometricmeasurements and microanalytical data obtained from inclusions.

The need for systematic fluid inclusion study in high grade metamorphic rocks has beendemonstrated using data available on well exposed Deep crustal rocks (granulites) rocks from southernPeninsular India. Field evidences for fluid pathways, fluids present in different mineral like garnet,plagioclase, zircon, aluninosilicates and quartz ( in different generations of quartz) and theirrelation of micro-textures and P-T conditions of metamorphism is evaluated to asses “FluidPresent” vs “Fluid Absent” metamorphic process in high grade rocks. Partial melting of some of themeta-pelites show “Fluid Absent” metamorphism. A combination of fluid inclusion chronology andmineral P-T-t paths and have been used to evaluate IBC and ITD paths and related tectonicprocess in the origin and evolution of metamorphic rocks.

High density carbonic fluids(1.10 to 1.15 g/cc) occur in minerals like garnet, plagioclase andquartz in all the massive to banded charnockitic granulites in southern Peninsular India. CO2 fluids(0.97 to 1.02 g/cc) in quartz inclusions in garnet, garnet porphyroblasts and in some aluminoslicatesrepresent near-peak metamorphic pore fluids (syn-metamorphic). These fluids are responsible forstablising granulite facies mineral assemblages. Presence of moderate to high density CO2 fluids (090- 1.10 g/cc) in 2400 to 550 m.y. old garnets in granulites provide direct evidence for preservationof paleo-fluids in these metamorphic rocks which have been preserved for million of years. CO2 fluids(1.02 to 1.07 g/cc) in the deformed matrix quartz grains have been trapped at post peak metamorphicstage. The relatively low density CO2 fluids (0.95 to 0.90 g/cc) occur in incipient charnockites.

Although the exact nature and source for fluids in high grade metamorphic rocks is debatable,focussed fluid flow of fluids originating from sublithospheric magmas appears to be a viable modelto explain the transfer of heat and volatiles to lower to middle levels of the continental crust. Careful

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study on the types of fluids present in some of the syn-metamorphic mafic igneous rocks (basic granulites)could provide solution to unravel the source for deep crustal fluids.

Development of localised, incipient charnokite formation in southern Peninsular India isinterpreted to be a post- peak metamorphic phenomenon, probably related to the upliftment of thegranulite from deep to mid-crustal levels, along ductile and ductile/brittle shear zones. Shearing andupliftment of the granulites, probably aided by shear zones, triggers the release of CO2 fluids alreadystored in the deep crustal rocks causing development of incipient charnockites along late shears.

Fluids along major shear zones in southern Peninsular India is more complex and heterogeneousin nature. The high grade metamorphic rocks show evidence of ductile, ductile-brittle and brittledeformational features with the development of mylonitic to ultramylonitic fabrics. Followingfeatures have been recorded in shear zone:1. Presence of early high-density CO2 paleo-fluids in less deformed rocks in shear zones, indicating

existence of metamorphic “aquitards”.2. Removal of H2O from the CO2-H2O fluids and fluid-rock interaction during retrograde metamorphism

in shear zones.

3. Release of CO2 and their re-entrapment under low-P-T conditions and or complete removal fluids inhighly sheared rocks.

4. Addition of late low (5- 10 wt% NaCl) to high salinity( upto 30 wt% NaCl) aqueous fluids in shearzone from the syn to post tectonic intrusive granitoids.Several areas of research that needs to be studied in future programs are a flows:1. A comprehensive study including field, petrography and detailed fluid inclusion study is

essential on relatively smaller area (quarry scale) to understand the role of fluids duringmetamorphism.

2. Study mechanism of mobility of many economically important elements like Gold,Molybdenum, tin, tugnston etc., and to unravel ‘Fluid flow’ process in shear zones andcharaterization of Pan-African tectonothemal events.

3. Characterisation of fluids in many intrusive igneous rocks like carbonatites, syenites andalkali granites confined to shear zones and their role in addition of fluid in shear zones.

4. Study of fluids in migmatitic gneiss (Peninsular Gneiss) in the Dharwar craton - tounderstand the role of fluids in partial melting of rocks.

5. Fluids in Closepet granite and along shears which cross cut these granites. To find outgenetic link between fluids from granites and their role in providing necessary heat andtransportation of metals like gold, copper and U to the adjacent greenstone belts andin overlying Proterozoic sedimentary basins.

6. Various problems related to fluid inclusion study in metamorphic rocks needs to beaddressed and persons to be trained to carry out in this type of specialised and timeconsuming research work in India, by organising training programs.

7. Establishment of analytical facilities like micro-Laser Raman probe and Cathodeluminescence(CL) facility at labs. in India.

Inverted ferro-pigeonites from c-type charnockites, Dindigul, Tamil nadu.C.Srikantappa1 and M.N.Malathi2

1Department of Geology, Manasagangothri, University of Mysore, Mysore 570 006.2Department of Mines and Geology, Government of Karnataka, Chamarajnagar, 570 006,

E-mail: srikantappa@googlemail.com

C-type igneous charnockites occur extensively around Dindigul in Tamil Nadu, forming part of theMadurai Block (MB) in southern Peninsular India. Based field relations, petrography (igneous texture)and geochemical data (higher K2O, TiO2, P2O5 and CaO when compared to metamorphic charnockites), therock types exposed around Didigul are grouped under C-type Charnockites, a distinctive group ofigneous charnockites in south India. The C-type Charnockites are spatially associated with hornblende

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+ biotite bearing migmatitic gneiss. Numerous meta-sedimentary bands consisting of quartzites, pelitic(qtz+sill+plag+k-feldspar+gt+cord+bio), calc-granulites (cal+dol+diop+plag+bio) and banded magnetitequartzites (qtz+mag+opx) occurs as enclaves within the igneous charnockites. The various metasedimentaryrocks within the charnockites are interpreted to represent older supracrustal units (?).

The C-type Charnockites are medium to coarse grained, melanocratic rocks, exhibit sharp contactrelationship with the metasediments. They show porphyritic texture with phenocryst of alkali feldsparsand lesser amount of plagioclase. They show mineral assemblage of pyroxene-feldspar-quatz-amphibole-ilmenite. Alkali feldspar are commonly strongly perthitic, with compositions Or78-Or89. Plagioclasefeldspar are often strongly mesoperthitic. Early formed pyroxene of ferro-pigeonitic in composition(XMg = 30-35 with CaO = 11-11.38 wt.%) is characteristic of these charnockites. Ferro-pigeonites isoften surrounded by orthopyroxene (XMg=23-38), resulting in the formation of the of inverted pigeonites.They also show complex exsolution features with the formation of orthopyroxene and clinopyroxene.Rutile shows fine exsolution lamellae of magnetite. All these micro-textural features are attributed tothe original high temperature ( > 1000 oC) of crystallisation of C-type charnockites. Many UHT meta-pelitic rocks (900 to 950oC) have been reported in the Madurai Block. It is interpreted that thewidespread C-type magmatic charnockites may have provided the necessary heat for UHT metamorphismin the area. These high temperature charnockites appears to have intruded the SGT, probablyduring Neo-Proterozoic to Pan-African times.

The C-type charnockites from Dindigul in is much similar to Charnockite Magma Type (CMT) reportedfrom Antarctica and has a relevance to unravel the various process of continental fragments which formpart of the ancient Gondwana supercontinent

Metallogeny in relation to Archaean crustal evolution : A study from theDharwar craton of douthern India

R. SrinivasanGeomysore Services (India) Pvt. Ltd., #89/1, Raja Ikon Building, 4 th Floor,

Marath Halli Outer Ring Road, Bangalore 560 057.E -mail: srinivasan@geomysore.com

Archaean sedimentary tectonic environments in the Dharwar craton evolved from stable to mobilerealm between 3.3 to 2.5 Ga. The province was finally cratonized ca 2.5 Ga. >3 G a stable crust servedas milieu for emplacement of layered igneous complexes, which host chromite, titaniferous magnetiteand platinum group element mineralization. Unlike in younger layered complexes, these Archaean mineraldeposits are complexly deformed and metamorphosed along with the host rocks. At around 2.9 Ga theatmosphere must have been deficient in oxygen as indicated by the deposition of detrital pyrite anduraninite bearing quartz pebble conglomerates of Rand type, which are also known to contain gold.Stromatolites in the carbonate rocks deposited more than 2.7 Ga ago, mark the dawn of photosyntheticbacterial activity in the Dharwar sedimentary basins. Syngenetic coccoid and filamentous fossil bacteriapreserved at places in the iron formation, and carbon isotopic evidence from graphite (d13C= - 22 to 36‰ PDB) serve as additional evidences for Archaean palaeobiological activity. The oxygen produced bybiological activity, triggered precipitation of iron and manganese from the Archaean seawaters. Lanthanumspiking, negative cerium and positive europium anomalies in banded iron formations suggest that,hydrothermal activity associated with contemporary volcanism in the sedimentary troughs, may havesupplied iron and manganese into the depositional basin. The submarine hydrothermal activity (BlackSmoker type) also gave rise to copper, iron, arsenic, antimony, lead sulphide and gold mineralization.The Dharwar sedimentary and volcanic rocks were deformed and metamorphosed around 2.6 Ga in anoblique compressive regime. Strain was partitioned into compressional folding and thrusting, and sinistralstrike slip shearing in the Dharwar province. Deep burial of supracrustal rocks and earlier gneisses by

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folding, metamorphosed them from green schist to granulite facies and led to differentiation of thecrust into lower granulite and upper granite-greenstone layers. Remobilised basement gneisses as welljuvenile potassium rich granites, invaded the schist belts as well as the gneissic crust. These cratonisingprocesses were accompanied by transport of hydrothermal solutions that gave rise to gold and tungstenmineralization principally in brittle-ductile shear zones parallel to axial planes of folds in a variety ofhost rocks such as metamorphosed basalts, rhyodacites, tuffs, greywackes, iron formations and evengranitoids. Rare instances of molybdenum, columbium and tantalum mineralization occurred in pegmatitesemplaced during the cratonization.

Clay mineralogical records of the intra-volcanic bole horizonsfrom the eastern Deccan volcanic province: plaeoenvironmental

implications and Cretaceous/Palaeogene boundaryJ. P. Shrivastava1*, M. Ahmad2 and Mamta Kashyap1

1Department of Geology, University of Delhi, Delhi -1100072Geological Survey of India, Southern Region Hyderabad-500068

E-mail: jps1815@yahoo.com

Deccan volcanism occurred in c. 67- 63 Ma (straddling Cretaceous-Palaeogene boundary) andcoeval with the global environmental and climatic changes. Present study is focused on the intra-volcanic bole horizons of varied colours and thicknesses, formed during major hiatus between the twovolcanic episodes, occur within the 900 m thick lava pile of the eastern Deccan volcanic province. Therelative abundance of clay minerals group bole horizons of this area into seven distinctive groups suchas, (a) montmorillonite predominant (> 90% montmorillonite), (b) montmorillonite with sub-ordinateamount of halloysite,(c) montmorillonite < halloysite, (d)montmorillonite + illite/smectite + other clayminerals, (e) montmorillonite + chlorite/smectite + other mineral phases, (f) kaolinite ± montmorilloniteand (g) palygorskite predominant boles.

Clay minerals contain iron rich montmorillonite, halloysite and kaolinite, show distinct microstructuresand microaggregates. In kaolinite, Fe3+ ions substitute for Al3+ at octahedral sites. The smectite associatedwith these boles is rich in iron content. Most of these clays are dioctahedral type, show balance betweennet layer and interlayer charges. The interstratified illite - smectite (I/S) mixed layers containing variableproportions of montmorillonite. Illite contains sheet-like, well oriented microaggregates. The parallelstacks of chlorite sheets show chlorite/smectite (C/S) mixed layers. Progressive enrichment of Fe anddepletion of Al ions with the advancement of kaolinization process is observed. High order of structuraland compositional maturity observed in these bole clays, signify long hiatuses.

It is inferred that alternate cycles of climatic changes occurred during the volcanism. The lowersuccession dominated by four cycles of montmorillonite, formed under alkaline conditions with alternatewet and long spell of dry seasons, whereas, in the upper sequence (above 25th lava flows), the kaoliniteappeared dominantly, indicative of the existence of tropical or subtropical climate during waning stageof the eruption (Fig. 1). It is observed that the bole horizons suffered rigorous weathering, approximately5 fold higher than the respective parent lava flows, indicating alternate wet and dry spells of climaticchanges (Fig.2). Translating the production time estimates of clays associated with the 21 bole horizonsoccurring across the succession, it is assessed that the minimum time required for the formation isapproximately 7 my (Table.1). Clay minerals occur across the sequence show cyclic changes in the climateentail longer duration. Late Maastrichtian Lameta beds post-date Deccan volcanism to 70 Ma or earlierto this. Considering the formation time for bole clays, it is possible that the volcanic activity startedmuch earlier in the late Maastrichtian and continued even after 65 Ma.

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Fig. 6. Distribution of clay mineral assemblages with height through composite section of easternDeccan volcanic sequence (Pattanayak and Shrivastava, 1999) and three paleomagnetic chrons (30N,29R and 29N) of Vandamme et al. (1991). Abbreviations: CT = Chemical Types, C/S = Chlorite / Smectite,= intra-volcanic bole horizon sandwiched between two lava flows.

Fig.7 Bole horizons from the eastern Deccan volcanic province showing variations in the ChemicalIndex of Alteration (CIA), Chemical Index of Weathering (CIW), Plagioclase Index of alteration (PIA) andpalaeoprecipitation across the sequence.

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Table 5 Thickness of bole horizons, extent of weathering and hiatusesbetween lava flows across the volcano-sedimentary succession.

Lava Degree of weathering Palaeoprecipitation Thickness Hiatuses

Flows CIAb/CIAlf CIWb/CIWlf PIAb/PIAlf (mm/year) (m) ( m.y.)

35 5.304 5.527 6.392 1305 0.500 0.071

34 8.455 8.550 11.234 1313 0.300 0.043

29 5.662 5.951 6.811 1199 1.500 0.214

28 6.257 6.403 7.825 1131 4.000 0.571

27 4.841 5.078 5.497 1243 3.500 0.500

26 5.163 5.198 5.829 1369 0.400 0.057

25 8.277 9.211 9.747 1080 0.450 0.064

23 3.788 4.935 4.488 658 1.500 0.214

22 5.031 5.112 5.477 1430 1.000 0.143

21 3.972 4.719 4.958 1026 0.900 0.129

20 10.294 10.892 11.179 1230 0.600 0.086

17 4.800 4.964 5.308 1308 1.000 0.143

16 6.232 6.621 8.091 1429 1.000 0.143

15 6.762 6.659 8.170 752 4.000 0.571

8 5.205 5.221 5.608 1458 4.000 0.571

7 - - - - 0.850 0.121

5 5.296 5.558 6.061 1082 0.900 0.129

4 8.349 8.729 11.200 1291 0.600 0.086

3 4.416 5.343 5.880 994 0.350 0.050

2 5.440 5.536 5.995 1375 6.000 0.857

1 4.982 5.365 5.558 937 4.000 0.571

Total 37.350 5.340

Abbreviations: CIAb/CIAlf = Chemical Index of Alteration of bole / Chemical Index of Alteration ofunaltered lava flow, CIWb/CIWlf = Chemical Index of Weathering of bole / Chemical Index of Weathering ofunaltered lava flow and PIAb/PIAlf = Plagioclase Index of Alteration of bole / Plagioclase Index of Alterationof unaltered lava flow, - = Data not available

Synthesis of expected ground motion using semi-empirical Green’s functionapproach and its comparison with observed accelerations in Garhwal Himalaya

N. Subhadra, Simanchal Padhy, T. Sesunarayana and R. VijayaraghavanNational Geophysical Research Institute, Hyderabad – 500606

E-mail: padhys@rediffmail.com

We present results of ground motion attenuation relations in Garhwal Himalaya. A semi-empiricalGreen’s Function approach based on envelope summation technique of Midorikawa (1993) was used to

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model the ground motions. In this approach, the fault of the large earthquake is divided into a certainnumber of elements (sub-faults). Our model assumes each sub-fault as point source in uniform earthstructure. The acceleration envelope waveforms, instead of time histories, from such elements aredetermined using empirical relations. The envelope from each element are lagged and summed at thereceiver to get the resultant envelope of a large earthquake. The resultant envelope is multiplied withfiltered white Gaussian noise to synthesize the acceleration at a given site.

The methodology was applied to predict the strong motion records and to calculate the peakground acceleration (PGA) from the aftershocks of 1999 Chamoli earthquake. The results show a reasonablygood agreement between theoretical and recorded waveforms and their spectra at high frequencies.Significant discrepancies between the spectra at low frequencies may be attributed to the effects ofsource or medium in the simulation process. The PGA values are found to be ~ 3 m/s2 at 15 km anddecays to ~ 1.5 m/s2 at 80 km distance. Our result shows a rapid decay of ground motion amplitude withdistance, similar to that found in other tectonically active regions like Himalaya.

Probable and definitive events that sculpted southern IndiaK R Subrahmanya

1806/B, 7th Main, Kengeri Satellite Town, Bangalore 560060, India.E-mail: krsubrahmanya@rediffmail.com

The SGT is traversed by major shear zones which are within and also radiate from a circular depression.The surrounding hill ranges have a steep slope facing the depression and a gentle slope in the otherdirection. The region is also known for the presence of pseudotachylites. The Bouguer gravity high tothe east of Palghat is elliptical in nature and its major axis trends nearly E-W. The shallow seismicvelocity picture from Chennimalai to Palani indicates a graben structure. The velocity structure alsodepicts a 4-5 km Moho upwarp near Chennimalai. Aeromagnetic contours are elliptical, the major axistrends nearly E-W and indicate a down throw of about one km in the region east of Palghat, with respectto all the surrounding regions. These evidences taken together point that possibly an extra-terrestrialimpact created a complex crater (Kaveri crater), of approximately 120 km. in diameter. The ages of theyounger granite plutons (800 to 550Ma) point to Neoproterozoic age for the impact.

Rifting between India and Antarctica and drifting began around 120 Ma ago. This marks the birthof the East Coast of India. The oldest marine magnetic anomaly in the Arabian Sea is M 22 (~150 Ma),which represents the separation of Africa from Madagascar + India. The oldest anomaly between Indiaand Madagascar is A34 (120 to 80Ma). Based on other evidences available from the West Coast of India– WCI - (St. Mary’s island rhyodacites) and the east coast of Madagascar (Marion hotspot volcanics), itcan be stated that doming occurred around 93 Ma ago and rifting began around 88 Ma ago. This alsomarks the origin of the WCI and the Sahyadris (Western Ghats,).

The northern parts of the WCI and the Sahyadris experienced basaltic magmatism of exceptionalscale around 67 Ma ago. Subsequent to the Deccan Traps event, the WCI underwent another spell ofrifting (~62Ma), resulting in the break-up of Seychelles micro continent and the genesis of a new MOR– the Carlsberg ridge. This was followed by the subsidence of the region south of Saurashtra peninsula,under the influence of SONATA and Gulf of Cambay rifts/faults. About 40 Ma ago, a Mid Oceanic Ridge(MOR) which was close to the Madagascar became extinct and a new MOR originated close to India. Thenew MOR – Central Indian Ridge, resulted in the separation of Mascarene Plateau from the Lakshadweep-Chagos ridge.

Sea floor spreading in the Indian Ocean and the resistive forces in the Himalayan collision zone hasresulted in a compressional regime throughout the Indian plate. Under its influence the region closeto 13oN in the Indian Peninsula is getting deformed. The WCI is divided into two prominent units: theKonkan region which has characters of a submergent coast and the Malabar Coast has an emergentcharacter. The youngest submarine terraces occur at shallower depths in the southern offshore comparedto northern offshore. These features indicate that the WCI has a northerly tilt.

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Satellite Image of the area east of Palghat Gap

Slope map of the area east of Palghat gap. The circular depression has been named KAVERI CRATER

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Radiometric studies along the southern coastal Orissa, eastern IndiaN. Sulekha Rao*1, R.Guin2, S.K.Saha2 and D. Sengupta1

1Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur,West Bengal 721302, India

2Radiochemistry Laboratory, RCD, BARC, Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata– 700 064, West Bengal, India

E-mail: geo_sulekha@yahoo.com

The use of thorium in the Indian context is becoming significantly important due to its largethorium reserve along its long coast line. A major part of these deposits could be utilized as an energyresource. It is the fourth largest known resource in terms of the thorium placers available worldwide.India with its coastline of ~6000 km comprising of ten coastal states is reasonably well known for itsheavy mineral deposits of beach and dune placer origins. These minerals include monazite, zircon,ilmenite, rutile, garnet and sillimanite, of which former two are important sources for radioactive elements(232Th and 238U) and others are also important in terms of resources for REE, Y, Zr, Hf and Ti. In order todelineate new sources of thorium and rare earths, and add to the proven resources, a detail study wasundertaken under a research project sponsored by Department of Atomic Energy/Board of Research inNuclear Sciences (DAE/BRNS), Mumbai, India. The study area was the southern coastal Orissa along theGopalpur-Chhatrapur-Rushikulya region. The study comprised of field studies using Geiger Muller Countersand Radiation Survey Meters. For laboratory studies, around hundred samples of beach sands werecollected from the shore line, bar, berm and the dune zones. The gamma-ray spectrometric analysis wasundertaken at the Radiochemistry Division, Variable Energy Cyclotron Centre, BARC, Kolkata, using acoaxial HPGe detector (EG & G, ORTEC) having a 15% relative efficiency. This was primarily to estimatethe activity concentrations of 232Th, 238U and 40K, and obtain the absorbed gamma and annual effectivedose rates in this region. The mean activity of 232Th in Gopalpur and Rushikulya beach placer depositswere about 67 and 40 times higher than that of the world average,

respectively. The high concentration of 232Th and 238U were found in the samples from the dunezones which agree well with the field studies. The region studied could be considered to be a zone ofeconomic potential but further studies are necessary to quantify the results obtained. Cross plot of eTh/eU versus eTh/K suggested that the heavy mineral sands of this area were presumably deposited in aleached uranium and an oxidizing environment. Inhalation dose measurements due to indoor Rn-isotopes(222Rn and 220Rn) was undertaken in the dwellings of nine villages along Gopalpur-Chhatrapur-Rushikulyacoast. Data were collected using LR-115 type II cellulose nitrate films in bare, filter and membrane modeusing the twin chamber plastic 222Rn/220Rn dosimeter developed by Bhabha Atomic Research Centre(BARC), Mumbai. This was undertaken for one complete year (January-2007 to January-2008) at aninterval of three months. The concentration of thoron was observed to be higher than that of radon, inall the dwellings and for all the seasons. This could be attributed to the wide provenance of minerals likemonazite and zircons in the area under study. Seasonal variation of indoor radon and thoron exhibithigh values in winter and low values in the rainy season. However it was observed that the values arelower than the recommended action levels. Some of the relative high values may be due to poor ventilationduring winter and the low values in rainy season could be attributed to the low emanation of radon andthoron from grains due to excess water content.

K/T boundary extinctions and paleobiogeography of peninsular India: recentadvances from Deccan volcanic province

Sunil BajpaiDepartment of Earth Sciences

Indian Institute of Technology, Roorkee 247 667, IndiaE-mail: sunilbajpai2001@yahoo.com

During the past few years, paleontological data from the Deccan intertrappean deposits ofpeninsular India have led to major advances in our understanding of the i) timing of Deccan Traps

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volcanic eruptions relative to the Cretaceous-Tertiary boundary (KTB) event and ii) the biotic links ofthe Indian plate around the time of Deccan eruptions in a geodynamic perspective.

Biostratigraphic studies, based mainly on planktic foraminifera recovered from the quarry sectionsnear Rajahmundry in the Krishna–Godavari Basin of southeastern India, have shown that the intertrappeansediments in this area were deposited in the earliest Paleocene (early Danian zone P1a), which spans themagnetic polarity chron 29R above the KTB. The new data strongly suggest that the main phase of theDeccan volcanism ended near the KTB, thereby pointing to the critical role played by the Deccan eruptionsin the end- Cretaceous mass extinctions. Recent quantitative estimates of gas emissions also point tothe importance of Deccan volcanism in causing the catastrophic mass extinctions at the KTB.

The second major advancement comes from the recent recognition of extensive endemism amongthe latest Cretaceous freshwater ostracods found in the Deccan intertrappean beds. The endemism hasbeen documented on the basis of remarkably diverse ostracod assemblages from a number of intertrappeanlocalities across peninsular India including those in Gujarat, MP, Rajasthan, Maharashtra, GulbargaKarnataka, and Uttar Pradesh. Over 75 new taxa of ostracods have been recorded, some of which hadpreviously been attributed erroneously to Chinese and Mongolian forms. At the species level, theintertrappean ostracods are strongly endemic (“Indian”) in character. Overall, the intertrappean ostracoddata points to a significant degree of India’s physical isolation at the K/T boundary prior to its collisionwith Asia, consistent with the geophysical data for this interval.

Cretaceous – Tertiary boundary mass extinction dueto large bolide impact on Earth

V.C.TewariWadia Institute of Himalayan Geology, 33, General Mahadeo Singh Road, Dehradun- 248001,

Uttarakhand, E-mail : vtewari@wihg.res.in

The extraterrestrial bolide impact at the Cretaceous – Tertiary Boundary is the most widely acceptedreason for the catastrophic mass extinction on Earth about 65 million years ago. Recently this asteroidhas been recognized as Baptistina family asteroids. The dinosaurs were killed by broken up chunks of abigger asteroid estimated as 170 km wide. The Chicxulub crater , long thaught to be associated with theextinction of the dinosaurs is 180 km wide. The bolide impact theory is strongly supported by theimpact derived spherules , shocked quartz and the rich concentration of the rare earth element iridiumand other platinum group elements in the boundary clay layer from Yucatan Peninsula ( Mexico ) ,Sugarite section in New Mexico ( USA ) , Padriciano and Gubbio sections of Italy, Dolenja Vas section ofSlovenia and Um Sohryngkew section of Meghalaya , India. The mass extinction of dinosaurs and planktonicforaminifera at the K/ T Boundary is related to this impact. The benthic foraminifera show reorganizationand resulted from the drop in biotic productivity after the asteroid impact in the end Cretaceous. Thesedimentological , carbon isotopic and geochemical study of the carbonate rocks from the K / T boundaryto Palaeocene - Lower Eocene rocks in the Karst area of Italy and Slovenia in NW Adriatic platform ,western Tethys has been compared with the eastern Tethys in the Meghalaya plateau , NE India.

Teris of southern Tamil nadu: Holocene climate historyThrivikramji.K.P.1 , Joseph, S2 & Anirudhan, S3

1Center for Environment & Development, Trivandrum 695 013 and2Dept. of Environmental Science, & 3Dept. of Geology,

University of Kerala, Kariavttom Campus 695 583E-mail: thrivikramji@gmail.com

The ubiquitous Teri deposits (extent=500 km2 ) or red sands of semiarid-southern-Tamil Nadu,chiefly noticed to occur in the Kattabomman and Chidambaranar districts (carved out of former TirunelveliDist.), carry unique colours from yellowish red (5YR4.5/6) to dark reddish brown (2.5YR ¾) and dark red(10R 3/6).

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In aerial photos teris manifest in various morphological types, among which the commonest formsare sand dunes (shaped into barchans, barchanoids, and longitudinal dunes) and interdune sand sheets,sandy hummocks and sand sheets.

The teri sand fraction is easily divisible into frame work grains (allochthonous detritals like quartz ofdifferent types, subordinate feldspar altering to clay and a suite of heavy minerals) and a matrix of clay andquartz silt. Though cement, chiefly hematite, poorly manifests on grains due to partial induration, itappears on the negative relief features on the grains surfaces, like cracks, depressions, corrosion pits etc.

Further, the autochthonous-calcareous-rhizoliths, chiefly noticed in Sattankulam, Kudiramoli andSayarpuram teris and dominantly showing a discordant relationship with primary sedimentary structures andmorphologies (size, shape and sense of branching) reminiscent of calcified-roots, need a much warmerclimate (like the current climate) for their origin.

The red colour and matrix of authigenic clays (viz., kaolinite and illite in the fine fraction),products of pedogenic weathering, do strongly point to a wetter or humid climate which enables releaseof red pigment (or now hematite) by the chemical alteration of iron bearing heavy minerals like theopaque ilmenite, red almandine-garnet and pyroxenes of the heavy fraction as well as authigenic formationof clays from feldspar in the frame work grains and in the matrix.

A 14C date (3680+or- 110 BP) on a sample of rhizolith collected at a depth of 2.5 m, at Sattankulamsets a time line for the transition from a humid climate to the current semi-arid type when the calcareousrhizoliths originated. Hence, semi-arid conditions of the present day in the Teri land of southern Tamil Nadu,should have set in at least as late as 3680+/-110y B.P.

From the foregoing evidences, relating to the morphology of teris, sediment colour, intra-sedimentsolution features on metastable mineral particles, mineral composition of clay in the matrix, and presence ofauthigenic calcareous concretions ( actually rhizoliths), a cyclic-climate-transition, i.e., semiarid —> humidà semiarid is inescapable for the teri province of southern Tamil Nadu.

GPS Campaign in Palghat Gap Region – Preliminary ResultsUnnikrishnan K. R.

Centre for Earth Science StudiesCamp Office, Kochi – 682 026

Email: kr_u54@yahoo.com

In Southern Peninsular India, low-level seismic activity has been taking place near Shornur in thePalghat Gap region. A tremor of magnitude 4.3 that took place in 1994 in Wadakkancherri (TrichurDistrict, Kerala State) followed by low magnitude tremors prompted to take up studies to understand theseismogenic potential of the area. Five annual GPS campaigns beginning from May 2002 were conductedparticularly in the 1994 epicentral region. GPS Network consisted of four monumented stations situatedwithin 10 km of Shornur; which served as the Base. The GPS data was collected on dual frequency for aminimum of 48 hours and with a logging interval of 30 seconds. The data processing was carried out byBernese GPS Software to produce iono-free ambiguity-fixed geocentric and ellipsoidal co-ordinates forthe Shornur GPS Base in ITRF-2000 frame using IGS Stations of BAHR (Arabian Plate), LHAS, POL2(Eurasian Plate) and IISC (Indian Plate). Preliminary results point that the temporal changes in coordinatesobserved for the first three annual campaigns at Shornur is in conformation with that of the IISC IGSsite. The analysis of the local network is in progress.

Geochronological constraints, palaeomagnetic data, palaeogeography and thechaos in the neoproterozoic : examples from India

Vibhuti RaiCentre of Advanced Study in Geology

University of Lucknow, Lucknow -226007Email: vibhutirai@gmail.com

Palaeomagnetic signatures obtained from primitive magnetised rocks provide us an authentic toolto know the palaeo-position of the sequence with reference to the palaeo-equator and when corroborated

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with adjacent regions, such data also provides us the relative palaeo-longitudes as well. However, animportant constraint in all such study is the timing of the palaeomagnetism as being the most crucialfactor. A perfect situation is only possible when the same sample is used for palaeomagntism as well asfor geochronometric studies. Such a situation is a rare coincidence due to paucity of datable rocks. Toovercome such constraints, usually chronological data is derived from the other horizons of the successionsor are picked up with the correlative horizons of the same basin or even with other basins which aregeologically or stratigraphically “believed” to be of similar ages. Such a situation warrants a well focussedattention as many a times, the drawn out conclusions go haywire and results are absurd with probablyno bearing on the palaeo-positions of the continents ( Palaeogeographic reconstructions ).

A situation of that kind becomes most controversial when the sequences belong to Proterozoictime-span, particularly Neoproterozoic. Here the pristine data is rare, basins are large, ages are not wellconstrained and variables are wide. Although India has the distinction of preserving several of thePrecambrian basins including Achaean basins, the palaeogeographic reconstructions are very few. Eventhose which have been attempted for, the geochronological data is not very authentic. In the globalreconstructions of the Neoproterozoic time span, India has been placed differently by different workers,to the extent that it is just fit-in, in a jig-saw puzzle manner. The issue needs serious attention as moreauthentic dates are coming forward from Mesoproterozoic to Neoproterozoic basins particularly theChattisgarh, Vindhyans and the Marwar basins. We cannot keep the chaos going in the globalpalaeogeographical reconstructions as some of the world’s best preserved undeformed Proterozoicsuccessions are developed in India with many of them showing exceptionally well developed fossils andperhaps ash-beds. The only issue is that these needs to be identified, corroborated with regional dataand worked out in a dignified manner, instead of just fit-ins and fill-ins. Attempts should be made togenerate data from detailed sampling from wide-apart basins of India, collecting sedimentological,palaeontological, geomagnetic and geochronological information and to corroborate all such informationas a global reference. This is high time, we must all put our efforts for generating most authenticpalaeogeographical maps as these are going to help in locating important fossil fuel and economicmineral deposits, which being the need of the hour for our region’s growth and development.

Predicting disastersProf Dr Victor Jetten

Dept. of Earth Systems AnalysisITC - International Institute for Geo-Information Science and Earth Observation

Enschede, The NetherlandsE-mail: jetten@itc.nl

Among the natural processes that occur in mountainous areas such as the Western Ghats are thedegradation processes. Examples are mass wasting in various forms and erosion by water that are part ofour every day environment. The effects of these processes are threatening to the inhabitants of an area.Many casualties and damage to property and infrastructure occur each year because of landslides, flashfloods and erosion. The processes have become hazardous and lead to disasters. This has triggered a lotof response from the scientific community. Since the study of these processes is well established scientistshave attempted to predict the effects of natural hazards on the community, to assess the risk and aid indisaster management. Disaster statistics since 1900 are compiled by the Emergency Disasters Database(EM-DAT). Currently the idea is that these disasters are increasing because of climate change. This is notnecessarily true. An increasing population and urbanisation, that puts itself at risk because hazardousareas are occupied such as floodplains, steep slopes and marginal lands, cause the damage to risesubstantially over the last years. It appears to be difficult to unravel the causes from the effects indisaster management.

Nevertheless, hazard prediction, i.e. the statistical or deterministic simulation of the probabilityand magnitude of hazards, is one of the first steps in disaster management. The choice of methodologydepends on the temporal and spatial scale at which the risk is assessed, as well as the data requirements.Examples are given here of risk assessment for debris flows from very different scales: national and

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regional level in Cuba (by Castellanos et al., 2008). Furthermore, advances in the modelling of drivingforces (often climate and/or earthquakes) and effects of triggering factors (relief and land use) enableus to predict areas that are at risk with a given scenario. At these scales triggers and mitigating factorsare modelled statistically, to derive areas with a high hazard probability. These areas can then be combinedwith “elements at risk” (people, houses etc.) and their vulnerability. If the hazard is very particular andthe design ofr conservation measures is needed, a more detailed approach is called for. An example isgiven from detailed debris flow modelling in Kerala (Kuriakose et al., 2008). These rapid debris flows inthe Western Ghats originate from filled up depressions in upslope areas. The trigger is heavy Monsoonrainfall, and the rapid movement follows predefined flow paths. The research includes spatial groundwaterbalance to assess the period of risk in a year, and a subsequent spatial modelling of the movement, topredict the reach of a debris flow and potential damage that may occur.

In spite of these advances, the results are not necessarily clear cut. The models need a vast amountof detailed data that determine their outcome and both the uncertainty in the answers and the numberof possible scenarios can be very large. The scientists response to this is natural: we need more research.It is however unlikely that that will enable us to make better prediction, in view of these chaoticsystems. It would be better to get a dialog going between planners and decision makers and scientists,so that the first can make clear what kind of information is helpful, the second can then make sensiblescenarios based on these demands.

A plate tectonic appraisal of the eastern ghats belt, IndiaK. Vijaya Kumar1 and C. Leelanandam2-

1School of Earth Sciences, SRTM University, Nanded-431 606, Maharashtra, INDIA2House No. 12-13-205/1, Street No. 2, Tarnaka, Hyderabad- 500 017

Andhra Pradesh, IndiaE-mail: vijay_kumar92@hotmail.com1

E-mail: cleelanandam@rediffmail.com2

Ancient suture zones or belts within continents are complexly deformed regions, which containpossible indicators or remnants of former ocean basins. In collision zones between two Precambriancontinental blocks, it is utopian wish to expect all the customary characteristic evidences for the formerexistence and later demise of the intervening ocean. The nature and variety of rock packages found atdeep or lower structural levels of the eroded old orogenic systems are not strictly comparable to thosewitnessed at top or shallow levels of the young mountain belts, and rightly so! Yet, many Precambrianrock sequences, with considerable structural shuffling, exhibit trace element signatures almost identicalto those found in Phanerozoic plate tectonic environments, implying their formation in an analogoussetting. We are aware that petrotectonic settings must be cautiously viewed in conjunction with theregional geological setting, because dependence on a single line of evidence may not give the truepicture and could be even hazardous! Along the western fringe of the Eastern Ghats Belt (EGB), weprovide critical evidences for the presence of subduction-related magmatic arcs, arc-root complex,partial but “true” ophiolite complex and deformed alkaline rocks and carbonatites (DARCs) all of which,besides many others, collectively in concert, establish and define the suture zone. Furthermore, thetools employed here will additionally help us to gain a better appraisal of the plate tectonic perspectiveof the EGB, which in turn will be useful in proper understanding of the formation and break-up of threesupercontinents- Columbia, Rodinia and Gondwana.

The strongest arc signal for the mafic and felsic magmatism in the EGB comes from the NMORB-normalized extended incompatible element diagrams. The Kondapalli felsic granulites represent basalportions of the magmatic arc and correlate exceedingly well with the average continental arc magma.

Fe-rich pyroxenes, An-rich plagioclase and primary hornblende in the gabbro-anorthositecumulates of the Kondapalli Layered Complex (KLC) indicate the crystal fractionation of a hydrousbasaltic magma under lower crustal conditions. The Kondapalli spidergrams are extraordinarily similar tothose of other arc-related gabbronorites. We interpret the KLC as the plutonic core of an arc-rootexposed in the deeply eroded Eastern Ghats orogen.

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Unambiguous sheeted dykes with chilled margins on either side (100% dykes) and, veins and“immiscible droplets” of plagiogranite within the dykes typify the Kandra Ophiolite Complex.

DARCs straddling the western margin of the EGB represent products of two important segmentsof the Wilson cycle. A line of DARCs represents both a rifted continental margin and a suture marking thesite where an ocean closed. The Elchuru alkaline complex contains a solitary example of a deformedproven carbonatite in the entire EGB.

We postulate two distinct episodes of convergence, both being initiated by the onset of continentalrifting, to explain the tectno-thermal evolution of and lithological disposition within the EGB.

Evolution of the Western Ghats (Sahyadri), Western IndiaM. Widdowson

Department of Earth Sciences, Open UniversityMilton Keynes MK7 6AA.UK

E-mail: M.Widdowson@open.ac.uk

Rifted passive continental margins constitute about half of the overall length of present daycontinental coastlines, and represent the transition between the relatively simple tectonics of theoceans, and the more complex setting of continents. Passive margins, associated continental floodbasalt (CFB) volcanism, and their syn- and post-rift morphotectonic evolution have now become thefocus of considerable scientific interest.

Since the early Mesozoic, peninsular India has been involved in major rifting events related to thebreak up and dispersal of eastern Gondwana. This began during the latest Lower Jurassic (c. 180 Ma),and was followed at c. 130-120 Ma by the separation of a fragment incorporating India. However, theformation of the present western Indian margin was effected by the late Cretaceous detachment ofMadagascar (c. 88 Ma]) and, finally, by a ridge jump which detached India from the Seychelles Bank atthe time of the Deccan volcanism (c. 64 Ma).

One remarkable result of this continental break-up is that some of the margins of the Gondwana-derived continents display a spectacular landform that is intimately associated with, and forms a crucialpart of, their rift history : these are the so-called ‘great escarpments’, of which the Western Ghats(Sahyadri) of India is a prime example. Great escarpments are ‘continental scale’ landforms, and their sizeand extent is indicative of an origin resulting from the regional tectonic cycles that ultimately controlledand defined the global geographical distribution and morphology of the continental masses. Therecognition of a link between the essentially endogenetic processes of plate tectonic processes, and theevolution of major landform types such as the great escarpments has been termed ‘morphotectonics’.

The Ghats (Sahydri) escarpment itself exists as an immense, near continuous ‘cliff-like’ featurerunning the length of the rifted segment of the western Indian continental margin. It can be traced atotal length of c. 1500 km from northern Mahrashtra to southern Kerala States (c. 22° – 8°N), brokenonly by the Palghat gap (12°N). The Ghats are not only important because of their sheer extent, butbecause the feature exerts a fundamental influence upon post-rift regional geomorphological evolutionof western India. It confers a continental-scale topographic asymmetry which then controls the continentaldrainage divide, and the rates of geomorphological (erosional and sedimentological) processes. Theselatter differ significantly on either side of this continental divide, and serve to help perpetuate theescarpment as a long-lived geomorphological feature. Moreover, the presence of the escarpment is importantin the modern context since it creates a major topographic barrier to transport communications, exertsa profound influence on climate and rainfall, controls patterns of agriculture, and provides a keygeographical location for hydro-electric power generation.

In common with other passive margins associated with extensive CFB volcanism (e.g. Drakensbergescarpment in the Karoo of South Africa; Serra Geral in the Parana of Brazil), the coastal plain, escarpment,and inland plateau of western India appear to have undergone uplift. However, the timing and underlyingcauses of this phenomenon have remained a matter of some debate. Dynamic and thermal effects ofhotspot plume activity may be the cause of initial surface uplift along the flanks of newly-rifted continental

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margins, but it is evident that uplift has continued long after the plume effects have decayed. One clueto the mechanism driving this uplift has comes from the detailed chemostratigraphical studies of theDeccan lava succession. These demonstrate that the lavas have undergone considerable erosion duringthe 65Ma since their eruption with thicknesses of 1-1.5km having been removed from the western edgeof the rifted Deccan CFB province thus creating the coastal (Konkan) plain and forming the WesternGhats escarpment. Accordingly, regional uplift may be interpreted as a consequence of the isostaticresponse to this onshore denudational unloading and concommitant offshore sedimentary loading, andtheir combined effects have subsequently produced a lithospheric flexuring of the entire margin. Moreover,because denudational unloading is independent of plume effects, it provides a long-term mechanismwhich permits the generation of permanent and continuing uplift over geological time.

In terms of both thermo mechanical (i.e. lithospheric flexuring) and surface processes, the potentialcoupling between the onshore and offshore regions depends upon the lithospheric strength across themargin, and the relative contributions of offshore sedimentary loading and onshore denudationalunloading. In this context, the contribution of onshore denudational unloading is significant becausethe eroded material will be more dense than the porous sediment deposited. Since it is primarily thepost rift denudational history that regulates the nature and timing of sediment supply to the offshoremargin, an understanding of the long term onshore evolution of these margins is of fundamentalimportance to assessing competing passive margin models.

Recent studies have used apatite fission-track (AFT) data to quantify the degree, rate, and timinglong term denudation at the western Indian margin, and to infer the morphotectonic evolution of theWestern Ghats. The majority of the AFT ages are considerably older than the timing of break-up in theearliest Tertiary, and record a complex and protracted cooling and denudation history. Interestingly, theeruption of the Deccan CFB and rifting on the western margin of India does not appear as a major discreteevent in the inferred AFTA denudation chronologies. Rather, earlier rift events, such as the separation fromMadagascar, and the rifting from Antarctica, appear to be preferentially recorded in what is now thelowland coastal plain. The overall implication is that some proportion of the present-day morphology ofthe western Indian margin may be inherited from events pre-dating the Deccan CFB. These AFTA chronologiesalso indicate the beginning of a period of significant denudation during the Cenozoic.

Offshore, the Konkan and Kerala Basins constitute a major depocentre for sediment from the onshorehinterland of Western India. These provide a valuable record of the timing and magnitude of Cenozoicdenudation along the continental margin and indicate two major pulses in sedimentation: an earlyphase in the Palaeocene, and a second beginning in the Pliocene. The Palaeocene increase in sedimentationcan be interpreted in terms of a denudational response to the rifting between India and the Seychelles,whereas the mechanism responsible for the Pliocene pulse is more enigmatic. Analysis of sedimentationin the Konkan-Kerala Basin using mass balance studies and numerical modeling of flexural responses canalso be used to test competing conceptual models for the development of high-elevation passive margins.Study of the Konkan- Kerala Basin indicate large clastic sediment volumes which are difficult to reconcilewith a ‘downwarped rift flank model’, and appear more consistent with a denudationally-driven ‘elevatedrift flank’ model.

To summarize, the onshore erosional signature, and offshore depositional histories during passivemargin evolution is complex, but the broad similarities of the macromorphology of different margins ofdifferent ages clearly indicates a common pattern of evolution. Accordingly, the Indian continentalmargin should be viewed within the outlined framework of passive margin evolution and erosion. Comparisonwith other examples of similar VRM at later stages of their erosional development (e.g. Karoo, 190 Ma,and Paraná, 120 Ma) indicate that continuation of the current erosion processes in Western India willlead to further exhumation, associated isostatic uplift, and seismicity.

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