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Precambrian Research 99 ( 2000) 91111www.elsevier.com/locate/precamres

The Dharwar craton, southern India, interpreted as the resultof Late Archaean oblique convergence

B. Chadwick a,*, V.N. Vasudev b, G.V. Hegde caEarth Resources Centre, University, Exeter EX4 4QE, UK

b120/45(A) III Block, Thyagarajanagar, Bangalore 560 028, India

cDepartment of Mines and Geology, Government of Karnataka, 16/3-5 S. P. Complex, Lalbagh Road, Bangalore 560 027, India

Received 6 March 1999; accepted 2 July 1999

Abstract

The Dharwar craton comprises two distinct parts separated by a steep NS sinistral shear zone. In the western

part a pre-2900 Ma complex of orthogneisses, granodiorites and narrow tracts of supracrustal rocks (Sargur Group)

forms the basement to volcanic and sedimentary basins of the Dharwar Supergroup (ca. 28002550 Ma). Late

Archaean deformation is characterised by NESW crustal shortening and steep NS sinistral shear zones. The eastern

part is underlain by parallel, steep NS or NWSE linear belts of calc-alkaline, anatectic and juvenile granites and

granodiorites (Dharwar batholith, ca. 27502510 Ma) with intervening volcanic and sedimentary schist belts (ca.

28002550 Ma). The plutonic belts are 1525 km wide, up to 150 km long, and bounded by steep NWSE high-strain

zones up to 2 km wide with sinistral shear sense (except one which is dextral ). Magmatic-state fabrics and structures

in the plutonic rocks are parallel to solid-state sinistral shear fabrics in the high-strain zones, but diffuse magmatic

banding is commonly oblique to these zones and coincides with the plane of instantaneous shortening in sinistral

shear. Magmatic-state structures, swarms of vertical NWSE dykes of granite, and the vertical wedge shape of the

linear belts are consistent with emplacement of the batholith during sinistral shear when magma pressure exceeded

regional horizontal compressive stress. Upright folds and schistosity, steep reverse faults and effects of regional HT/LP

metamorphism show that deformation was partitioned into NESW shortening in the schist belts during emplacement

of the plutonic belts in the sinistral shear regime. The western part of the craton is interpreted as the foreland to an

accretionary arc represented by the batholith and schist belts (intra-arc basins) in the east. NESW shortening and

sinistral transcurrent displacements in the foreland and arc are consistent with arc-normal and arc-parallel displacements

during oblique convergence analogous to MesozoicCenozoic convergent settings. 2000 Elsevier Science B.V. All

rights reserved.

Keywords: Batholith emplacement; Dharwar craton; Foreland deformation; Late Archaean; Oblique convergence

1. Introduction ocean ridge lengths, are widely regarded as thetectonic environment of Archaean terrains(Windley, 1995; Condie and Sloan, 1998; de Wit,Convergent settings analogous to those of the1998). In contrast, a minority holds that non-Phanerozoic, but with smaller plates and longeruniformitarian processes related primarily to thethermal vigour of the Archaean Earth were pre-* Corresponding author. Tel.: +44-1392-263916;dominant. The conflict in views is exemplified byfax: +44-1392-263342.

E-mail address:[email protected] (B. Chadwick) a spirited attack on the plate tectonic consensus

0301-9268/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved.

PII: S 0 3 0 1 - 9 2 6 8 ( 9 9 ) 0 0 0 5 5 - 8

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92 B. Chadwick et al./Precambrian Research 99 (2000) 91111

by Hamilton (1998). The Dharwar craton in south- and anatectic granites, granodiorites, monzonites

and diorites. They are interspersed with schist beltsern India is a critical example in the current debate.

On the one hand, Choukroune et al. (1995, 1997) which are lithologically similar to the Dharwar

Supergroup in the west, but a lack of precise agesand Chardon et al. (1996, 1998) contend that its

evolution was controlled by non-uniformitarian precludes direct correlation (Chadwick et al., 1996;Nutman et al., 1996). The plutonic complex wassagduction (Goodwin and Smith, 1980), that is,

passive sinking of volcanic and sedimentary basins termed the Dharwar batholith by Chadwick et al.

(1996) on the grounds of the close lithologicalinto basement gneisses (softened lithosphere) with

no crustal shortening. In this paper we present similarity, structural coherence and emplacement

of its principal components in the period ca. 2750new evidence of magmatic- and solid-state struc-

tures and fabrics which point to control of the 2510 Ma (Table 1). High-grade metamorphism

leading to charnockites took place close toLate Archaean history of the Dharwar craton

(Fig. 1, Table 1) not by non-uniformitarian pro- 2500 Ma in the south of the batholith (Hansen

et al., 1997): lower grade metamorphic recrystalli-cesses but by emplacement of a calc-alkaline batho-

lith, NWSE shortening and NWSE sinistral sation of limestone in the Sandur belt took place

at about the same time [2475+

65 Ma; Russelltranscurrent displacements with close analogies inoblique convergent settings, for example, in the et al. (1996)].

The Dharwar batholith includes the so-calledEast Indies, the Andes and the Cordillera of west-

ern North America. Of the widely different propos- Closepet Granite, a term introduced in 1901

( Fig. 1; Smeeth, 1915; B.P. Radhakrishna, per-als for the Late Archaean plate tectonic setting of

the Dharwar craton (Chadwick et al., 1997), our sonal communication, 1994) for a narrow linear

tract of granites and gneisses trending NS ornew interpretation is closest to models of Hanson

et al. (1988) and Newton (1990) who envisaged NWSE close to the western boundary of the

batholith. The tract has figured prominently onCordilleran or Andean margin intrusion and NS

lateral shearing. published maps for many years. Allen et al. (1986)

and Jayananda et al. (1995) described it as the

Closepet batholith, but with no justification. We

regard the terms Closepet Granite and Closepet2. Geology of the Dharwar cratonbatholith as unsatisfactory because the belt is not

a single granite and, moreover, it is no more thanThe craton comprises a western domain

underlain by orthogneisses and granodiorites [ca. a small part of the much larger system of plutonic

rocks forming the Dharwar batholith. This larger29003300 Ma, collectively termed Peninsular

Gneiss: Beckinsale et al. (1980); Taylor et al. grouping is better described as a batholith (Pitcher,

1979; Bateman, 1992) in the sense that it is a(1984); Bhaskar Rao et al. (1991); Peucat et al.

(1993)] interspersed with older tracts of metasedi- cluster of plutons and plutonic belts whose magma

generation and intrusion were controlled by amentary and metamorphosed igneous suites

[Sargur Group, Swami Nath et al. ( 1976)]. This crustal scale event. Chadwick et al. (1996) attrib-

uted this event to Late Archaean oblique con-association forms the basement to mixed-mode

[sensu Gibbs (1987)], volcanic and sedimentary vergence that is addressed in this paper.The southern part of the batholith has been thebasins (schist belts) of the low-grade Late

Archaean Dharwar Supergroup [ca. 2900 prime target of petrogenetic studies. Early work

viewed metasomatism (granitisation) of older2600 Ma; Swami Nath et al. (1976); Chadwick

et al. (1991, 1992); Nutman et al. (1996); Kumar gneisses as the principal genetic mechanism

(Radhakrishna, 1956), but more recent studies inet al. (1996); Trendall et al. (1997a,b)]. The west-

ern domain is locally intruded by granite plutons the southwestern marginal zone revealed the preva-

lence of partial melting of older gneisses,[ca. 2600 Ma, Taylor et al. (1984); Rogers (1988)].

The eastern part of the craton is dominated by >2900 Ma (Friend, 1983; Friend and Nutman,

1991; Oak, 1990; Jayananda and Mahabaleshwar,a Late Archaean calc-alkaline complex of juvenile

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93B. Chadwick et al. /Precambrian Research 99 (2000) 91111

Fig. 1. (A) Regional map of the Dharwar batholith and part of the foreland in the Dharwar craton in Karnataka and southern

Andhra Pradesh, showing the principal schist belts and the sites of Figs. 2 and 4. (B) Position of the Dharwar craton in

southern Peninsular India.

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Table 1

Salient isotopic age data (with error bars) related to principal geological divisions and Late Archaean oblique convergence in the

Dharwar craton in Karnataka and Andhra Pradesha

a Notes: (a) Nutman et al. (1996): 1, acid volcanic rocks, Sandur schist belt; 2, Joga granite; 3, Belagallu Tanda gneiss; 4, acid

volcanic rocks, Daginkatte. (b) A.P. Nutman, personal communication (1998): 1, clast of granodiorite in polymict conglomerate,

Hutti schist belt; 2, Koppal syenite; 3, granodiorite west of Gooty. (c) Zacharaiah et al. (1995): metabasalts, Ramagiri schist belt;

(d) Balakrishnan et al. (1990): tholeiite, Kolar schist belt; (e) Peucat et al. (1993): granulite facies metamorphism, Krishnagiri, in

the extreme south of the Dharwar batholith; (f ) Friend and Nutman, 1991: 1, anatectic granite, Ramnagaram; 2, gneiss, Ramnagaram.

(g) Krogstad et al. (1991, 1995): 1, Dod Gneiss; 2, Dosa Gneiss; 3, Patna Granite; 4, Kambha Gneiss; all adjacent to the Kolar

schist belt. (h) Subba Rao et al. (1998): 1. Hampi granite; 2. Lepakshi granite. i. Taylor et al. (1984): 1, Chitradurga granite; 2, acidvolcanic rocks, Daginkatte, E of Honnali; ( j) Bhaskar Rao et al. ( 1992): 1, Chitradurga granite; 2, Volcanic suite, Shimoga district.

(k) Trendall et al. ( 1997a): acid volcanic rocks, Daginkatte, E of Honnali. ( l ) Trendall et al. ( 1997b): ash-fall tuffs, Bababudan. (m)

Kumar et al. (1996): volcanic suites, Bababudan. (n) Stroh et al. (1983): Halekote trondhjemite; (o) Monrad (1983); (p) Beckinsale

et al. (1980); (q) Nutman et al. (1992): 1, metamorphic zircon. (r) Peucat et al. (1995): rhyolite, Holenarsipur. (s) Ramakrishnan

et al. (1994): detrital zircon.

1991), which generated granitic melts that (Jayananda et al., 1995; Moyen et al., 1997). In

contrast, Krogstad et al. ( 1991, 1995), Peucat et al.interacted to various degrees with contemporane-

ous intermediate magmas of mantle origin (1993) and Hansen et al. (1995) identified major

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episodes of juvenile crustal accretion, ca. 2550 Granite (Table 1). Reverse faults and thrust

wedges of basement gneisses with top-to-SW SC2510 Ma, that took place in association with gran-

ulite facies metamorphism in the extreme south of fabrics, large-scale asymmetric folds with SW

vergence, lobe and cusp contacts between thethe batholith. These isotopic and geochemical data

point to the predominance of granites derived by Dharwar cover and its basement (Chadwick et al.,1991), and a previously unreported top-to-SWpartial melting of older gneisses (>2900 Ma) in

the western portion of the batholith in contrast thrust stack of mylonitised basement gneisses and

Dharwar cover rocks in the Gadag region (Figs. 2with juvenile granites and related suites which

predominate in the east (Chadwick et al., 1996). and 3) are all consistent with NESW crustal

shortening. Apart from zones of ductile mylonites,The eastern and western parts of the Dharwar

craton are separated by a steep sinistral shear zone brittle-ductile deformation of the bulk of the base-

ment gneisses on myriad fractures and small retro-which includes mylonitised batholith granites and

volcanic and sedimentary rocks of the Dharwar grade shear zones contrasts with the pervasive

ductile behaviour of the cover.Supergroup: the zone is up to 23 km wide and

extends for ca. 400 km along the eastern boundary Structures formed during NESW shortening

are deformed by N- or NE-trending folds andof the GadagChitradurga schist belt (Fig. 1;Chadwick et al., 1992 ). crenulation fabrics that are consistent with sinistral

displacements in the steep NS shear zones within

the foreland and along its eastern boundary

(Fig. 1; Chadwick et al., 1985b, 1988, 1989, 1991,3. Late Archaean basin development and

deformation in the western part of the craton 1992). The link between folding, schistosity and

transcurrent shear is evident in transitions from(foreland)

the mylonitised cover into mylonitised batholith

granites in the steep sinistral shear zone flankingFacies distributions and well-preserved volcanic

and sedimentary structures show that basin devel- the east of the Gadag-Chitradurga schist belt.

Calcite in veins in the basement and as porphyro-opment of the Dharwar Supergroup between

Chikmagalur and Ranibennur (Fig. 1) had much blasts in the cover suggests CO2

was an important

volatile phase during NESW shortening and Nin common with mixed-mode basins (Gibbs, 1987 )generated in transpression (Chadwick et al., 1989, S sinistral shearing.

Contrary to the widespread evidence of NE1992). Initial crustal extension led to shallow

marine+fluvial sedimentation (quartzpebble con- SW shortening, Chardon et al. (1996, 1998)

claimed that the Late Archaean structure in theglomerates, quartzites, argillites, banded iron for-

mations) and eruption of basalts with back-arc west of the craton resulted from passive sinking

of the Dharwar Supergroup into its basementaffinity ca. 29002700 Ma (Table 1; Bhaskar Rao

and Drury, 1982; Drury, 1983; Anantha Iyer and gneisses with no crustal shortening. They envisaged

two distinct episodes of diapirism, ca. 3000 andVasudev, 1985). Later fluvial and marine sedi-

mentation (greywackes, polymict conglomerates ca. 2600 Ma, under the influence of mantle plumes

and sagduction. They based their case for Latewith intra-basinal and basement clasts, banded

iron formations, stromatolithic limestones) was Archaean sagduction on structures at the base ofthe Dharwar Supergroup in the Kibbanahalli Armaccompanied by further basaltic and rhyolitic vol-

canism. Some of the later sequences are at least and the Bababudan schist belt (Fig. 1), namely,

mylonitic extensional structures at the boundary7000 m thick and reflect variable uplift and sub-

stantial syn-depositional subsidence of the older between the basement gneisses and the Dharwar

cover, cleavage more shallow than bedding inDharwar cover and basement gneisses (Chadwick

et al., 1985a, 1988, 1989, 1991). quartzpebble conglomerates at the base of the

supergroup, and patterns of fabric trajectories.Deformation took place at ca. 2600 Ma as

indicated by fabrics younger than rhyolites and However, cleavage steeper than bedding immedi-

ately above the basal contact, and the form andthe cross-cutting relationship of the Chitradurga

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Fig. 3. Shallow mylonitic basement gneiss showing top-to-SW

shear sense. Outcrop approximately midway between Lakkundi

and Dambal (Fig. 2).

that the reverse fault forming the northern bound-

ary of the Bababudan schist belt is a refolded

extensional structure, contrary to its overthrust

relationship with the underlying cover which is

consistent with a similar reverse fault north of the

Kaldurga syncline (Chadwick et al., 1985b). The

sagduction model implies that the Sirankatte dome

of basement gneisses NE of Kibbanahalli (Fig. 1)is also a diapiric structure, but we have found

abundant NW-trending, upright contractional

crenulations superimposed on migmatitic banding

which are consistent with ENEWSW shortening.

Although we agree with Naha et al. (1995) that

the dome is not a diapir, we do not share their

view that the basement was extensively remobi-

lised. On the basis of fabric trajectories, ChardonFig. 2. Map and NESW section across the north of the Gadag

et al. (1996) modelled the Kibbanahalli synclineschist belt showing thrust stacking of the Dharwar Supergroupas widening with depth and having a flat base, butand its basement gneisses.

neither of these characteristics are indicated by itssteep wedge shape at its NW extremity. There is

also no exposed evidence of a flat floor to theasymmetry of widespread folds older than those

generated by NS sinistral shear in the Bababudan basin (see Chardon et al., 1998).

The claim that the Dharwar Supergroup sankKibbanahalli and Bababudan belts are consistent

with NESW shortening. Moreover, in the south passively into its basement is thus open to question

because it neglects widespread evidence of NEof Bababudan the shallow cleavage at the base of

the supergroup is deformed by small-scale con- SW regional shortening. Moreover, the sagduction

model takes no account of the NS sinistral shear-tractional folds with SW vergence consistent with

NESW shortening. Chardon et al. (1998) claimed ing and refolding of regional folds developed

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during NESW shortening, for example, the main the interpretation of the growth of the Dharwar

batholith.Bababudan syncline, the Kaldurga syncline in NE

Bababudan and the Nidnegal anticline (Chadwick Based on the foregoing references, recognition

of magmatic-state fabrics in the batholith hingedet al., 1985b; Mukhopadhyay, 1986; Chadwick

et al., 1991). Substantial syn-depositional subsi- on preferred shape orientations of subhedral pla-gioclase, K-feldspar, biotite and hornblende, anddence and intra-basinal clasts with pre-depositional

schistose fabrics in the polymict conglomerates in interstitial aggregates of coarse-grained quartz

with minimal preferred orientation and few recrys-the upper part of the Dharwar stratigraphy

(Chadwick et al., 1991) point to the local exten- tallisation textures. In contrast, solid-state (crystal-

plastic) fabrics are indicated primarily by wingedsional structures at the base of parts of the

Dharwar Supergroup being effects not of sagduc- porphyroclasts of K-feldspar and ribbons of

fine-grained quartz. Magmatic-state fabrics aretion but basin subsidence that occurred during

accumulation of major thicknesses of younger widespread, but common transitions from

magmatic- to solid-state fabrics are indicated bysequences in the supergroup, for example, the

Kaldurga conglomerate (Chadwick et al., 1985a). shape modification and internal distortion of feld-

spars, biotite and quartz aggregates,Our evidence is drawn mainly from an area of

ca. 26 000 km2 in NE Karnataka and SW Andhra

Pradesh ( Fig. 4) where the batholith and schist4. The Dharwar batholith and its schist belts

belts crop out on a rolling plain with an altitude

of ca. 600 m. Exposure is extremely variable, butEmplacement of the Dharwar batholith coin-

cided with the transition from predominantly linear ranges of granite tors and numerous quarries

opened in the last 20 years for aggregate andtonalitetrondhjemitegranodiorite ( TTG) suites

in earlier periods of crustal evolution to greater dimensional stone provided abundant, previously

unreported data for structural analysis and classi-abundances of granite and granodiorite in new

additions to continental crust in the Palaeo- fication of the plutonic suites.

proterozoic and thereafter (Martin, 1994;

Sylvester, 1994) . This transition marked the begin-ning of a persistent uniformitarian pattern of 4.1. Plutonic belts

granitegranodiorite batholith construction at

convergent plate boundaries ( Windley, 1995). The batholith comprises a series of parallel,

steep elongate belts analogous to, but smaller than,Insight into the mechanisms of batholith develop-

ment has been revolutionised by recent radical the plutonic belts of subduction-related Mesozoic

granites in Sumatra (McCourt et al., 1996). Thechanges in ideas of granite generation, melt

transfer and emplacement (Brown, 1994; Pitcher, plutonic belts in the Dharwar batholith are elon-

gate vertical wedges ca. 1525 km wide, ca. 751997), based on numerous illustrations of magma

ascent and emplacement controlled by crustal 150 km long, trending NWSE, but swinging to

NS further south (Figs. 1 and 4). They taperscale, compressional and extensional shear zones

and fractures (Clemens and Mawer, 1992; Hutton, upward ( Fig. 5) and along strike into interdigitatedor rounded contacts with the schist belts. Outcrop1988, 1992, 1996, 1997; Ingram and Hutton, 1997;

Tikoff and Teyssier, 1992; Petford, 1996) . At the areas and steep magmatic fabrics suggest vertical

dimensions of at least a few kilometres, but mag-same time, the genesis of magmatic- and solid-

state fabrics featured prominently in new theoreti- netic and gravity data (Mahadevan, 1994) and a

deep seismic profile ( Kaila et al., 1979; Kaila andcal and field studies of granite rheology (Hutton,

1988; Paterson et al., 1989; Fernandez and Sain, 1997) provide no clues to the vertical form:

the seismic profile reveals only sub-horizontalBarbarin, 1991; Fernandez and Gasquet, 1994;

Saint Blanquet and Tikoff, 1997). In this paper reflectors of uncertain significance. Each belt is

bounded by steep contacts with schist belts orwe use these new developments as the basis for

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with an intense tectonic S fabric and coplanar

seams of pegmatite. It is cut by deformed mafic

dykes and includes xenoliths of quartzite and

amphibolite. Grey gneisses of Belagallu Tanda

type occur in other belts as xenoliths in granitesand as extensive tracts intersheeted with younger

granites. They also form a major part of the

batholith south of Anantapur and west of Kolar.

Similar orthogneisses east of Ramagiri are folded

with the schist belt in a large S-plunging antiform.

Appinite dykes (our unpublished data) cut theFig. 5. SWNE section across the central part of the Sandur migmatised gneisses, but were disrupted duringschist belt (Fig. 4) showing the saw-tooth boundary resulting partial melting of their host.from interdigitation of steep sheets of granite with metabasalts,

metagabbros and tremolite schists of the Sandur Group in the4.1.3. Dioritescrest of a plutonic wedge (after Chadwick et al., 1996).

Enclaves of diorite are common in the greygranodiorites described below, and a major body

of quartz monzonite to diorite composition, hereemplacement and granulite facies metamorphism

(Peucat et al., 1993; Hansen et al., 1995). called Kallur diorite, occurs SW of the Raichur

schist belt which defines part of its eastern bound-

ary. The western boundary of the Kallur diorite is4.1.1. Western margin of the batholith

Sub-horizontal migmatitic orthogneisses form a defined by a steep zone of mylonitised granites

and high-strain orthogneisses whose protolithsbelt ca. 25 km wide and extending NS for ca.

400 km immediately east of the shear zone separat- were a mixture of the diorite and younger inter-

sheeted granites. Diorite sensu lato in the SE ofing the two parts of the craton. On the grounds

of their TTG composition (our unpublished data) the belt grades into porphyritic hornblende gran-

ites s.l.: there appears to be a similar gradation inand limited isotopic ages ( Friend and Nutman,

1991), the gneisses are correlated with the the NW of the belt. The diorite is cut by steepNWSE dykes of aplogranite and pegmatite.pre-2900 Ma gneisses of the basement in the west

of the craton. In contrast with the gneisses immedi- At the type locality at Kallur the diorite is dark,

medium-grained with common ellipsoidal enclavesately west of the shear zone, they display variable

degrees of partial melting with transitions to pink of coarse-grained hornblende diorite and fine-

grained diorite with blue blebs of plagioclase: thegranites with partly digested remnants of the old

gneiss percursor. Swarms of criss-crossing pegma- enclaves and their host have an intense vertical S

fabric trending NW. Elsewhere the Kallur dioritetite dykes and steep NS wedges of granite with

linear and planar magmatic-state and crystal- is fine-grained with enclaves of mafic diorite up to

2 m in size. Hornblende and plagioclase (com-plastic fabrics intrude the belt of shallow gneisses.

For these reasons, the 25 km wide tract of sub- monly sericitised) have a magmatic-state preferred

orientation, but a superimposed disequilibriumhorizontal older gneisses and metatexites isincluded in the Dharwar batholith. texture appears to be of post-magmatic tectonic

origin.

4.1.2. Older orthogneiss with mafic dykes

Other older orthogneisses are found in a few of 4.1.4. Granodiorite

Grey hornblende granodiorite (including mon-the plutonic belts. They are similar to the high-

strain, granodioritic, Belagallu Tanda gneiss zonitic facies) with mafic enclaves of feldsparphyric

or even-grained, hornblende diorite equivalent to[2719+40 Ma; Nutman et al. (1996); Chadwick

et al. (1996)] which at the type locality west of themicrogranular mafic enclaves (MME)andpoly-

genic swarms of Barbarin and Didier (1991) pre-Bellary is a streaky, banded, biotitic migmatite

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dominates in the largest plutonic belt between grey, biotite- or hornblende-rich phases. Granites

Guntakal and the Hutti schist belt. Similar grano- NW and SE of the Sandur schist belt include

diorite is found W of the Hutti schist belt, NW of mixtures of homogeneous grey granite with largeRaichur, and S of Anantapur. Granodiorite W of enclaves of porphyritic granite and rounded immis-

Gooty has yielded a SHRIMP UPb zircon age of cible inclusions of quartz monzonite. This variety2580+31 Ma (Table 1; A.P. Nutman, personal of granite [ Toranagallu type, Chadwick et al.communication, 1998). Large tracts of hornblen- (1996)] has yielded a whole rock RbSr age ofdite, hornblende gabbro and gabbroic diorite are 2452+50 Ma (Bhaskar Rao et al., 1992) whichcommon in the granodiorites W of the Hutti belt, appears to be a cooling age on the grounds of theand appinite dykes displaying synmagmatic disrup- older SHRIMP age of the Joga granite describedtion, including the Sederholm effect, feature else- below (Table 1). Similar granites are found at leastwhere. West of Anantapur the older orthogneisses as far south as Kalyandurg. Although some gran-are cut by granodiorite with appinite dykes. ites include commingled immiscible dark phases,

Mafic enclaves in the granodiorites commonly mafic dioritic enclaves and synmagmatic dykes ofhave prolate ellipsoidal shapes with long axes the appinite and lamprophyre suites are less

coinciding with magmatic-state hornblende linea- common in the granites s.s. compared with thetions plunging gently NW or SE. Their relatively granodiorites. Most granites are younger than thesmooth, rounded forms and lobate boundaries are granodiorites (Table 1), but available isotopic ageconsistent with commingling of diorite and grano- data are limited to granites in the western part ofdiorite melts. Some with angular shapes appear to

the batholith.be disrupted synmagmatic dykes or detached frag-

Magmatic banding, manifest by variations inments of solid diorite. Solid-state deformation

biotite, feldspar and quartz abundances, is promi-superimposed on the magmatic fabrics in the

nent in granites in many plutonic belts (Fig. 6). Itgranodiorites is indicated by distortion and sericiti-

varies from almost imperceptible, through diffusesation of plagioclase. Chloritisation of hornblende

to sharply defined layering a few centimetres toand biotite appears to be most pronounced in the

ca. 1 m thick which persists along strike for manygranodiorite SE of the Hutti schist belt compared

metres. Some banding is enhanced by coplanarwith elsewhere.seams of pegmatite or is impersistent, with grada-

tions into diffuse, elongate schlieren. Outcrop evi-4.1.5. Granites

dence suggests the banding was the result ofGranites sensu stricto range from grey, throughdifferent processes that acted together or indepen-grey-pink to brick red, porphyritic and even-dently, including smearing of commingled palegrained types. Microcline megacrysts, zoned pla-and dark granite melts into layers and lensesgioclase and quartz with variable proportions ofduring magmatic flow; dispersion of enclaves andbiotite (commonly chloritised) and hornblendetheir mixing to yield schlieric lenses and wisps (cfoccur with accessory apatite, monazite, epidote,Blake and Koyaguchi, 1991); injections of succes-allanite, titanite, zircon, magnetite, pyrite andsive sheets of pale and dark granites yielding well-molybdenite: trace amounts of fluorite and carbon-

defined or diff

use, persistent or impersistent layer-ate are almost universal, but some granites are ing; injection or diatexis leading to banding definedrich in coarse-grained fluorite. Muscovite granitesby thin seams of pegmatite; concentration of crys-are rare. Tourmaline occurs in the groundmass oftals by mechanical or chemical effects associatedsome granites or in late pegmatites, and spodu-with magmatic flow s.l. which included sorting ofmene has been recorded in pegmatites NW of theminerals by magmatic currents, separation of min-Hutti schist belt (Devaraju et al., 1990) anderals and melt by filter pressing, and transpositionelsewhere.of pre-existing banding. Sporadic felsic ocelli withSteep NWSE wedges of uniform granite arecores of titanite are consistent with precipitationevident in some plutonic belts, but most granites

are multipulse mixtures of different pale and dark of specific minerals consequent on magma replen-

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Fig. 7. Magmatic-state NWSE shear zone with sinistral dis-

placement in diffusely banded grey granite; arrows highlight

displaced banding. Chandrabanda, 10 km E of Raichur.

(1997), are up to 1 m wide with displacements upFig. 6. Diffuse magmatic banding in grey granite trending NW to 6 m indicated by displaced banding and trainsSE, 40 km E of Raichur. of small-scale asymmetric folds. Shear zone trends

and displacement directions vary, but NWSE

zones with sinistral shear sense consistent with thatishment, mixing and other changes in PT condi-

tions ( Hibbard, 1995 ). in the steep border zones of mylonite predominate.Magmatic-state fabrics are of S, LS or L type.

Fabrics and banding commonly coincide, but mag- 4.1.6. Late plutons of granite and syenite

Sporadic small plutons form late componentsmatic-state fabrics were also impressed across

banding or other compositional boundaries such of the plutonic belts. The post-tectonic, porphyritic

Joga granite, with scattered rounded enclaves ofas occur in plutons in the Cascades Mountains,

Washington (Paterson et al., 1996). Magmatic- mafic syenite or monzonite rich in fluorite, cuts

schistosity in metabasalts with interbedded chertsstate S fabrics and banding in some belts trend

NWSE, although banding is also irregular at in the central NW of the Sandur schist belt

(Chadwick et al., 1996). The granite has aoutcrop scale as a result of magmatic-state folding.

Mafic enclaves have a shallow NWSE elongation SHRIMP UPb zircon age of 2570+62 Ma

( Table 1; Nutman et al., 1996).parallel to the magmatic linear fabric, for examplein the granite at Bellary. Banding and S fabrics The Koppal syenite with microcline, albitic pla-

gioclase, hornblende and pale green clinopyroxenealso dip steeply, with NESW strike oblique to

the NWSE trend of the belts (Fig. 4). Steep axial has an elliptical outcrop elongated NESW

(Fig. 4). Its SE boundary is concordant with steepsurfaces of magmatic-state, open to isoclinal folds

of banding with coplanar S fabrics trending NW banding in the host granites: boundary relation-

ships in the NW are not exposed. The uprightSE indicate NESW shortening, but others are

oblique to the regional NWSE trend. Steep mag- asymmetric wedge shape of the pluton is indicated

by variations in the orientation of magmatic band-matic shear zones ( Fig. 7) , equivalents of intra-

magmatic shear zones (isz) of Fernandez et al. ing and parallel S fabrics with lineated hornblende

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plunging down dip. The syenite has a SHRIMP relatively high temperatures. Accessory chlorite

replacing biotite may be the result of later ductileUPb zircon age of 2526+8 Ma (Table 1; A.P.

Nutman personal communication, 1998). movement or younger brittle fracturing that led to

NE joints with veneers of epidote and chlorite

which are common throughout the craton.4.2. High-strain orthogneisses and mylonitesMagmatic-state folds indicating NESW shorten-

ing, sinistral NWSE magmatic shear zones, NWThe steep NWSE high-strain zones between

the plutonic belts are characterised by ortho- SE magmatic-state L and S fabrics parallel to

solid-state fabrics in the shear zones, and trans-gneisses and mylonites derived from adjacent unde-

formed granites or granodiorites. Mylonitised itions from NESW magmatic-state S fabrics to

NWSE solid-state fabrics (Fig. 4) point to closegranites are common adjacent to the schist belts.

The high-strain zones are up to 2 km wide and links between emplacement in the plutonic belts

and solid-state sinistral shear.traceable along strike for up to 110 km: strike

lengths may be much longer, but exposure is

incomplete. Steep SC fabrics, winged porphyro- 4.3. Schist belts

clasts of microcline, shallow lineations (mainlyquartz), small-scale S-folds and extensional shear Volcanic and sedimentary rocks in the schist

belts (Fig. 4) comprise greywackes, polymict con-bands (Fig. 8) are consistent with sinistral shear

in all the high-strain zones apart from that east of glomerates, banded iron formations, subordinate

orthoquartzites and limestones (Chadwick et al.,the Kushtagi schist belt where the displacement

was dextral. The reason for the different shear 1996), and bimodal basaltrhyolite arc associa-

tions in which basalts predominate (Anantha Iyersense is uncertain.

Stable hornblende and biotite in the mylonites and Vasudev, 1979; Zacharaiah et al., 1996;

Hanuma Prasad et al., 1997). The schist belts wereand high-strain orthogneisses show that ductile

deformation in the shear zones took place at deformed and metamorphosed at greenschist to

amphibolite facies ( Roy, 1979; Roy and Biswas,

1979; Harris and Jayaram, 1982; Hanuma Prasad

et al., 1996). Lower grade assemblages characterisethe interiors of larger belts, whereas their margins

adjacent to the plutonic belts are at amphibolite

facies. Syntectonic minerals in the Sandur belt

include cordierite, gedrite, garnet, andalusite, stau-

rolite, biotite, muscovite and chlorite in pelites,

and hornblende, garnet and plagioclase in metaba-

salts. MetamorphicT550600C andP45.2 kbar

are correlated with granite emplacement (Hanuma

Prasad et al., 1996).

With a few exceptions (Roy, 1979; Roy

and Biswas, 1983; Mukhopadhyay, 1989;Mukhopadhyay and Matin, 1993), the detailed

structure of most schist belts is largely unknown.

Recent work in the Sandur belt has revealed

thickening of the stratigraphy on reverse faults

dipping steeply NE which are marked by narrow

zones of mylonite and low-angle discordances withFig. 8. Extensional shear band indicating sinistral shear in steep

stratigraphic markers such as banded iron forma-NWSE high-strain orthogneiss derived from banded granite;

tions (Chadwick et al., 1996). Orientations of La sub-horizontal mineral lineation lies on the gneiss banding.15 km NE of Adoni. and S fabrics show that faulting was broadly

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contemporaneous with large-scale, tight upright planar fabrics in common with those in the palefolds. Associated schistosity contains a steep finite grey granite host (Fig. 9) . These characteristicselongation lineation marked by the long axes of indicate emplacement while the host was hot andellipsoidal clasts and pillows. Outcrop patterns ductile [crystallinity >ca. 70%; Fernandez and

and curved hingelines suggest the folds are regional Barbarin (1991)], but with sufficient rigidity tosheath folds. fracture. The quarry also exposes vertical sheets

Magmatic- and solid-state fabrics in the granites of granite breccia trending NWSE, ca. 20 m wideimmediately adjacent to the Sandur schist belt with exposed lengths of ca. 500 m (Fig. 10). Thehave trends in common with those in the schist grey granite matrix with diffuse magmatic fabricsbelt, but shallow linear fabrics predominate in the is host to packed inclusions of pale granite a fewplutonic belts compared with steep lineations in metres in size. The form of thin apophyses ofthe schist belts. Since deformation and metamor- matrix granite along the sheet boundaries pointsphism in the schist belts were contemporaneous to emplacement during shear fracture of the hotwith emplacement of the plutonic belts, we attri- host: accessory fluorite and carbonate suggest thatbute the difference in lineation plunge to partition- fracturing was facilitated by high volatile pressure.ing of regional deformation into NESW

Vertical granite dykes elsewhere, for example, S ofshortening in the schist belts during sinistral Raichur, have pull-apart structures consistent withtranscurrent displacements in the plutonic rocks. sinistral shear during intrusion (Fig. 11).The shape of the Jonnagiri schist belt (Fig. 4) Vertical NWSE dykes of pale granite, darksuggests it was controlled by sinistral shear along

microgranite, aplite, pegmatite and commingledthe eastern boundary of the granodiorite between

granite and diorite with widths 0.3ca. 100 m wereGooty and the Hutti schist belt. Moreover,

also emplaced late in the growth of the plutonicZachariah et al. (1996) implied sinistral shearing

belts when the host rocks were cooler and moreto account for the collage of distinct blocks of

brittle. Some dykes occupy vertical conjugate shearamphibolites and intersheeted granites in the

fractures formed during EW shortening, but mostRamagiri schist belt. Every schist belt is intruded

were controlled by NWSE fractures. NWSEto different degrees by syn- and post-tectonic sheets

dykes have sharp boundaries and little internal

of granite and pegmatite. deformation: irregular lobate masses of immiscible

4.4. Emplacement of the plutonic belts

Magmatic-state planar fabrics and banding aresteep with either NWSE or NESW trends,whereas magmatic-state linear fabrics mostly haveshallow NW or SE plunges. Apart from localisedcurvature of mylonite fabrics adjacent to thecentral northern boundary of the Sandur schistbelt, the plutonic belts include neither radial pat-terns of magmatic-state lineations nor concentric

patterns of banding and magmatic-state planarfabrics consistent with diapirism or ballooning.

4.4.1. Inflation of plutonic belts by vertical NWSEdyking

Inflation by dyking is common in every plutonicbelt. For example, in the large quarries atSanganakallu, NE of Bellary, vertical NWSEdykes of dark grey granite, 12 m thick, have Fig. 9. Vertical NWSE dykes of dark facies of granite intruded

into hot host of pale granite, Sanganakallu, 4 km NE of Bellary.irregular boundaries and magmatic-state, NWSE

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dark facies show no distortion subsequent to their

magmatic disruption (Fig. 12). In contrast, some

dykes were mylonitised as a result of strike-parallel

shearing whose effects were restricted to individual

dykes within swarms.Granite dykes in the Dharwar batholith are

consistent with emplacement in fractures devel-

oped either during the magmatic consolidation of

the host (cf Clemens and Mawer, 1992) or post-

consolidation brittle fracturing (cf Petford et al.,

1994). Widths of dykes in hot and cool fracture

systems in the Dharwar plutonic belts are consis-

tent with the range quoted by Petford (1996) for

rapid magma ascent in dykes. Inflation of the

plutonic belts by granite dyking is also compatible

with the contention that magma pressure is anintegral part of the regional stress system ana-

logous to the effective stress concept of soilFig. 10. Part of a vertical NWSE sheet of granite breccia in mechanics (Hutton, 1997), that is, NWSE dykespale granite (scale: laundrywoman bottom right); the pale in the Dharwar batholith are consistent withblocks are similar to the host granite and the matrix is similar

emplacement into hot and cool plutonic host rocksto the dark dykes in Fig. 9. Sanganakallu, 4 km NE of Bellary.

in a sinistral strikeslip regime when magma pres-

sure was enhanced by high volatile content and

exceeded regional horizontal compressive stresses.

4.4.2. Magmatic banding and synmagmatic shear

zones

Magmatic banding in many belts trends NESW and has curving transitions into steep NW

SE high-strain zones (Fig. 4). This curvature is

common to S fabrics generated in ductile shear

Fig. 11. Pull-apart indicating sinistral shear contemporaneous Fig. 12. Vertical NWSE dyke of commingled, immiscible dark

facies (diorite?) in pale granite intruded into grey granite.with emplacement of NS, dark grey granite dyke into pale

granite host, ca. 10 km S of Raichur. Devinagara, 40 km N of Bellary.

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zones (Ramsay and Graham, 1970) and it implies granite with NWSE banding are consistent withHuttons (1992) model of emplacement broadlythat the magmatic- and crystal-plastic fabrics wereparallel to the trend of regional sinistral shearpart of a continuum of emplacement and deforma-planes with magma pressure exceeding regionaltion like that in more recent intrusions, for exam-

horizontal compressive stress (Hutton, 1997).ple, the Mono Creek Granite in the CretaceousSyntectonic HT/LP metamorphism, fabrics, foldsSierra Nevada batholith, California (Saintand reverse faults in the schist belts show thatBlanquet and Tikoff, 1997). Oblique relationshipsNESW shortening was intimately related tobetween magmatic phenomena and regional sheargrowth of the plutonic belts during regional sinis-zones led Tikoff and Teyssier (1992) to proposetral shear. The broadly contemporaneous NESWthat tensional bridges between en echelon P shearshortening and NWSE sinistral shear contrastsarrays facilitated emplacement in the Sierrawith the structural chronology in the west of theNevada batholith. However, the oblique trends incraton where NESW shortening preceded NSthe Dharwar plutonic belts bear no relationship tosinistral shearing. Intrusion of the ca. 2600 MaP shears. Instead they coincide with, or are nearlyChitradurga granite (Table 1) into deformed meta-parallel to, the plane of instantaneous shorteningbasalts low in the Dharwar Supergoup (Seshadriin sinistral simple shear and transtension based on

et al., 1981) suggests that NESW shorteningtheoretical analyses of extension, shortening andoccurred earlier in the west, but the lack of isotopicRiedel shears in strikeslip regimes (Sandersonage data precludes detailed correlation of the struc-and Marchini, 1984, Fig. 5).tural chronology in each part of the craton.The regular NESW trend of magmatic banding

indicates a lack of progressive rotation concomi-tant with increasing shear strain like that predicted

5. Plate tectonic setting of the Dharwar batholithby the theoretical analyses of Ramsay and Graham(1970) and Sanderson and Marchini (1984). This Apart from the gravity-driven diapiric modellack of rotation suggests relatively rapid develop- based on sagduction (Choukroune et al., 1995;ment of the banding prior to crystallinity exceeding 1997; Chardon et al., 1996, 1998), previous viewsca. 70% in accord with granites being relatively of the Late Archaean tectonic setting of the

short-lived geological events (Clemens and Mawer, Dharwar craton hinged on uniformitarian prin-1992; Hanson and Glazner, 1995; Saint Blanquet ciples (Chadwick et al., 1997). At least two of theand Tikoff, 1997). However, deformation of NE earlier proposals likened the setting to that of theSW banding by common magmatic-state shear North American Cordillera ( Krogstad et al., 1989)zones and folds trending NWSE shows that crys- and Andean margin and island arc magmatismtallinity

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described, for example, by DLemos et al. (1992), parallel transcurrent displacements (Condie and

Chomiak, 1996), large-scale relationships betweenHutton and Reavy ( 1992) and McCaffrey (1992).

With specific reference to Phanerozoic convergence emplacement and tectonism appear to be more

complex in the Andean and Cordilleran systemsin the East Indies, for example, the structure of

the Dharwar batholith compares closely with the compared with the Dharwar batholith.sub-parallel, NWSE belts in which emplacement

of subduction-related, mainly I-type, Late Triassic 5.1.2. Significance of polymict conglomerates with

plutonic clasts in schist belts within the Dharwarto Pliocene granites and granodiorites was focused

along deep faults acting as magma conduits batholith

Polymict conglomerates with mixtures of plu-(McCourt et al., 1996). The deeply rooted, strike

slip, dextral faults that controlled magmatism in tonic and intrabasinal clasts are common, but

clasts of plutonic rocks are not universal. They arethe Sumatran plutonic belts were a consequence

of partitioning of displacements during oblique intensely deformed, with steep schistosity and clast

elongation having moderate or steep plunge.convergence into arc-normal and arc-parallel com-

ponents (Malod and Kemal, 1996; McCaffrey, Zircons in a clast of gneiss from Kolar with ages

ca. 2800 Ma (Krogstad et al., 1991) suggest the1996).Similarities with the Dharwar batholith are also erosional provenance included either early phases

of the batholith or late phases of the forelandfound in the Andean mobile belt and North

American Cordillera where Mesozoic batholiths basement. In contrast, a SHRIMP UPb zircon

age of 2576+12 Ma from a deformed clast ofare steep linear arrays of plutons (Pitcher, 1997).

JurassicCretaceous magmatism and volcanism in hornblende granodiorite in the Palkanmardi con-

glomerate in the Hutti schist belt compares closelynorthern Chile, for example, took place during

five distinct episodes within ca. 100 Ma when with the SHRIMP UPb zircon age of

2580+31 Ma from similar granodiorite in the plu-extensional deformation in the foreland was

replaced by sinistral strikeslip displacement, tonic belt extending south of the schist belt (Fig. 4,

Table 1; A.P. Nutman personal communication,probably as a result of a change in the convergence

vector (Dallmeyer et al., 1996). However, although 1998). Granodiorite intrudes schistose metabasalts

in the south of the Hutti belt. The SHRIMP agesMesozoic to Early Tertiary Cordilleran plutonismas a whole was associated with significant arc- indicate rapid unroofing and erosion of granodio-

Fig. 13. Approximate NESW section across the Dharwar craton showing relationships between plutonic belts and schist belts in

the batholith terrain in the northeast and SW-vergence of structures in the Dharwar Supergroup and its basement in the foreland

in the southwest.

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rite after its emplacement as part of the growingbatholith. Deposition was closely followed by

deformation and further additions of granodiorite.These relationships are identical to those

of intra-arc and fore-arc basins within andadjacent to the calc-alkaline batholith in thePalaeoproterozoic Ketilidian orogen in SouthGreenland (Chadwick and Garde, 1996; Hamiltonet al., 1996). They reinforce our interpretation ofthe schist belts in the Dharwar batholith as intra-arc basins that were intimately involved with batho-lith accretion (Chadwick et al., 1996). The obliqueconvergent setting of the Ketilidian orogen has otheraspects in common with the Dharwar craton,namely, a batholith dominated by steep plutonicbelts of granite and granodiorite and a foreland

with an Archaean gneiss basement unconformably Fig. 14. Model of slip-partitioning in the Dharwar cratonoverlain by Palaeoproterozoic volcanic and sedi- during Late Archaean oblique convergence based on slip vectorsmentary basins which have much in common with in the East Indies (Malod and Kemal, 1996). Note reduction

of arc-normal compression and increase in sinistral arc-parallelthe Dharwar Supergroup. A salient difference is theshear from south to northwest. F, Foreland on the margin oflack of a fore-arc in the Dharwar craton, but onthe overriding continental plate of the Dharwar convergentthe grounds of composition and isotopic age data,system; DB, Dharwar batholith with juvenile plutonic suites in

albeit limited (Dasgupta, 1995), we suggest thatthe east and granites derived from partial melting of older conti-

psammitic and pelitic paragneisses (khondalites) in nental crust adjacent to the foreland; the bulk of the subductingthe Proterozoic Eastern Ghats Mobile Belt east of plate is presumed to have been oceanic.the craton are a likely candidate.

well known in Phanerozoic convergent boundary5.2. Late Archaean basin development and

systems (McCaffrey, 1996). McCaffrey showed,deformation in the forelandfor example, that slip-partitioning can occur on

relatively small spatial scales, and arc-parallel dis-Basin development of the Dharwar Supergroupplacements are evident even where subduction isand the pattern of ensuing Late Archaean defor-normal to an arc. Application of slip-partitioningmation, which was the result of NESW shorten-of the type seen in the East Indies to the Dharwaring and NS sinistral transpression on steep,craton accounts for the NESW shortening in thebrittle-ductile shear zones, compare closely withforeland and the intra-arc basins in the Dharwarbasin development and deformation in the schistbatholith as the result of arc-normal compressionbelts and batholith in the east of the craton

(Fig. 13). Whereas sinistral shear outlasted NE during oblique convergence of an oceanic plate

SW shortening in the west as indicated by refolded subducting towards the WNW (Fig. 14). Arc-

large-scale folds [e.g. NW of Shimoga, parallel displacements are manifest in the NWSEMukhopadhyay (1986); Chadwick et al. (1991)], and NS sinistral transcurrent shear zones in thethere appears to have been a closer link between foreland and batholith.NWSE sinistral shear and NESW shortening inthe east of the craton.

6. Conclusions

5.3. Late Archaean oblique convergence in theThe Late Archaean history of the DharwarDharwar craton

craton is interpreted as the consequence of:

1. accretion of the Dharwar batholith, ca. 2750Partitioning of convergence into two compo-nents, parallel and perpendicular to subduction, is 2510 Ma, in the east of the craton with close

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Balakrishnan, S., Hanson, G.N., Rajamani, V., 1990. Pb andstructural and geochemical similarities to calc-Nd isotope constraints on the origin of high Mg and tholei-alkaline batholiths in Proterozoic anditic amphibolites, Kolar Schist Belt, South India. Contrib.

Phanerozoic convergent settings;Miner. Petrol. 107, 279292.

2. control of batholith accretion by multipulse Barbarin, B., Didier, J., 1991. Macroscopic features of mafic

emplacement of steep plutonic belts during microgranular enclaves. In: Didier, J., Barbarin, B. (Eds.),Enclaves and Granite Petrology. Elsevier, Amsterdam,regional sinistral transcurrent displacements;pp. 253262.3. formation of schist belts in the east of the

Bateman, P.C., 1992. Plutonism in the central part of the Sierracraton as intra-arc basins during batholith

Nevada batholith, California. U.S.G.S. Prof. Paper 1483,accretion; 186.

4. overlap of arc accretion onto a foreland conti- Beckinsale, R.D., Drury, S.A., Holt, R.W., 1980. 3,360-Myrold gneisses from the South Indian Craton. Nature 283,nental margin and its incipient back-arc basins469470.in the west;

Bhaskar Rao, Y.J., Drury, S.A., 1982. Incompatible trace ele-5. WNW-directed convergence of oceanic litho-

ment geochemistry of Archaean metavolcanic rocks fromsphere oblique to an overriding continental the Bababudan VolcanicSedimentary Belt, Karnataka.lithospheric plate represented by the foreland J. Geol. Soc. India 23, 112.

Bhaskar Rao, Y.J., Naha, K., Srinivasan, R., Gopalan, K.,in the west; and1991. Geology, geochemistry and geochronology of the6. partitioning of the oblique convergence vectorArchaean Peninsular Gneiss around Gorur, Hassan District,into arc-parallel NWSE and NS sinistral dis-Karnataka, India. Ind. Acad. Sci. (Earth and Planet. Sci.)

placements and arc-normal NESW shortening. Proc. 100, 399412.Bhaskar Rao, Y.J., Sivaram, T.V., Pantulu, G.V.C., Gopalan,

K., Naqvi, S.M., 1992. RbSr ages of Late Archaean meta-Acknowledgementsvolcanics and granites, Dharwar craton, South India, and

evidence for Early Proterozoic thermotectonic event(s).The authors are deeply indebted to thePrecambrian Res. 59, 145170.

Department of Mines and Geology, GovernmentBlake, S., Koyaguchi, T., 1991. Insights on magma mixing

of Karnataka, Bangalore, for logistic facilities and model of volcanic rocks. In: Didier, J., Barbarin, B. (Eds.),steadfast support. BC gratefully acknowledges Enclaves and Granite Petrology. Elsevier, Amsterdam,

pp. 403413.funding from the Royal Society, London, the

Brown, M., 1994. The generation, segregation, ascent andIndian National Science Academy, New Delhi, emplacement of granite magma: the migmatite-to-crustally-and the University of Exeter. They are also grateful

derived granite connection in thickened orogens. Earth-Sci.to A. P. Nutman for SHRIMP age data, and Rev. 36, 83130.thank A. A. Garde, J. Grocott and K. McCaffrey Chadwick, B., Garde, A.A., 1996. Palaeoproterozoic oblique

plate convergence in South Greenland: a reappraisal of thefor their constructive comments on an early versionKetilidian Orogen. Geol. Soc. Spec. Publ. 112, 179196.of the paper and W.S. Pitcher for guidance through

Chadwick, B., Ramakrishnan, M., Vasudev, V.N., Viswanatha,the labyrinth of pluton and batholith terminology.

M.N., 1989. Facies distributions and structure of a DharwarThe authors also acknowledge an original idea of volcanosedimentary basin: evidence for late Archaean trans-M.A. Hamilton (Garde et al., 1998) for the con- pression in southern India? J. Geol. Soc. Lond. 146,

825834.struction of Table 1.Chadwick, B., Ramakrishnan, M., Viswanatha, M.N., 1985a.

Bababudan a Late Archaean intracratonic volcanosedi-

mentary basin, Karnataka, South India. Part I: StratigraphyReferences and Basin Development. J. Geol. Soc. India 26, 769801.Chadwick, B., Ramakrishnan, M., Viswanatha, M.N., 1985b.

Bababudan a Late Archaean intracratonic volcanosedi-Allen, P., Condie, K.C., Bowling, G.P., 1986. Geochemicalmentary basin, Karnataka, South India. Part II: Structure.characteristics and possible origins in the southern ClosepetJ. Geol. Soc. India 26, 802821.batholith, South India. J. Geol. 94, 283299.

Chadwick, B., Vasudev, V.N., Jayaram, S., 1988. StratigraphyAnantha Iyer, G.V., Vasudev, V.N., 1979. Geochemistry ofand structure of Late Archaean, Dharwar volcanic and sedi-Archaean metavolcanic rocks of Kolar and Hutti Gold

mentary rocks and their basement in a part of the ShimogaFields, Karnataka, India. J. Geol. Soc. India 20, 419432.

Basin east of Bhadravathi, Karnataka. J. Geol. Soc., IndiaAnantha Iyer, G.V., Vasudev, V.N., 1985. Copper metallogeny

32, 119.in the Jogimardi volcanics, Chitradurga greenstone belt.

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Archaean Basin Development and Regional Structure in the cess and shape and mineral fabrics of mafic microgranular

enclaves. In: Didier, J., Barbarin, B. (Eds.), Enclaves andWestern Part of Karnataka. J. Geol. Soc. India 38, 457484.

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22, 315. Stephens, W.E. (Eds.), Granite: From Segregation of Melt

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Fernandez, A.N., Gasquet, D.R., 1994. Relative rheologicalfor Late Archaean Crustal Evolution in Karnataka. J. Geol.

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