Geochemistry and Tectonic Significance of Basic Volcanics in … · 2018. 1. 4. · CERTIFICATE This to certify that the thesis entitled "Geochemistry and tectonic significance of

Geochemistry and Tectonic Significance of Basic Volcanics in Parts of Singhbhum Craton, Eastern India.

Shabber Habib Alvi

Thesis submitted for the award of the degree of DOCTOR OF PHILOSOPHY In GEOLOGY Aligarh Muslim University, Aligarh. 1 9 9 0

iwnui T4WJ

0 9 JUN 1993

D r . MAHSHAR RAZA y^^^^K DEPARTMENT OF GEOLOfY Reader / ^ S ^ m ALIGARH MUSLIM UNIVERSITY

' ^ A LI Q A R H — 2 0 2 002

PHONE : ( 0671 ) 6 6 1 5 TELEX : 664-230-AMU-IN

Oated..l5^Ql...ld9-0-

C E R T I F I C A T E

This to certify that the thesis entitled "Geochemistry and

tectonic significance of basic volcanics in parts of Singhbhum

Craton, Eastern India" is the record of bonafide research carried

out by Mr. Shabber Habib Alvi under my supervision. This work

is' an original contribution to the existing knowledge of the

subject.

I allow Mr. Alvi to submit the work for the Ph.D. degree of

the Aligarh Muslim University, Aligarh.

Dr. Mahshar Raza Research Guide

CONTENTS

ACKNOULEDGEMENTS

LIST OF FIGURES

LIST OF TABLES

INTRODUCTION

Crt PTER I GEOLOGICAL SETTING

XXX

V

xiv

1

9

CHAPTER II

CHAPTER III

CHAPTER IV

General Geology o-f Eastern Indian Shield.

Stratigraphic Framework And Field Uccurrence?

o-f Dhanjori and Jagannathpur Volcanics

PETROGRAPHY 32

MAJOR ELEMENT GEOCHEMISTRY 36

General Statement

Analytical Techniques

Major Element Distribution

Effect of Alteration on Rock Chemistry

General Geochemical Characteristirs

Major Element Variability

TRACE ELEMENT GEOCHEMISTRY 76

General Statement

Trace Element Distribution

(i)

CHAPTER V MAGMA CLASSIFICATION

General Statement

Magma Series Classification

Tectonic Setting Classification

120

CHAPTER VI

CHAPTEi? VII

CHAPTER VIII

TABLES I TO X)

REFERENCES

PETROGENESIS

TECTONIC IMPLICATIONS

SUMMARY AND CONCLUSIONS

142

160

171

175

205

(ii)

ACKNOULEDGEMENTS

This work is suggested and supervised by Dr. Mahshar

Raza. I -feel great pleasure to express my deep sense o-f

gratitude to him for the valuable guidance, encouragement and

cooperation in all stages of this work. I am also indebted

to Dr. S.M. Naqv;i, Scientist, NGRI , Hyderabad, for the

inspiration,' encouragement and help received during the

course of this work,

I am grateful to Prof. S.M. Casshyap, Chairman,

Department of Geology, A.M.U., Aligarh and Prof. D.

Guptasarma, Director, N.G.R.I., Hyderabad, for providing all

the necessary facilities for the completion of this work.

My sincere thanks are due to Drs. R. Sriniwasan, S.H.

Jafri and S.M. Ahmad, Scientists NGRI, Hyderabad for their

critical review and constructive suggestions and to Drs. P.K.

Govil and V. Balram, Scientists NGRI, Hyderabad for their

help in analytical work.

The help received from Drs. S. Farooq, S. Ra i s ,

Lecturers, Department of Geology, A.M.U. and Dr. R.A. Akhunji

in various stages of this work is thankfully acknowledged.

(iii)

Messers T. Gnaneshwara Rao, S.L. Ramesh, Mukesh A r o r a ,

Riyaz Mohd. Kamaruddin Khan a t NGRI , H y d e r a b a d , M r . Z a k i r

H u s a i n , Depar tmen t o f G e o l o g y , A . M . U . , M r . A k h t a r H.

S i d d i q u i , Department o-f S t a t i s t i c s , A . M . U . and my h o s t e l

mates Messers S a j i d Usmani, B i l a l Mashhood, Abdul Mumeet,

R i z w a n u l l a h and Mohd Noman a r e a c k n o w l e d g e d - for t h e i r

coopera t ion and he lp du r ing the coarse o-f t h i s work.

Ms. Nancy Ra jan and D r . M o h d . A s l a m a r e

acknowledged -for t y p i n g t h e m a n u s c r i p t and d r a - f t i n g t h e

i l 1 u s t r a t i o n s .

C o u n c i l o-f S c i e n t i f i c and I n d u s t r i a l R e s e a r c h i s

acknowledged f o r the f i n a n c i a l support which I rece ived as

Jun io r and Senior Research Fe l l ow .

S 4 ^ <Shabber Habib A1vi>

(iv)

LIST OF FISURES

F i g . 1 . S i m p l i f i e d geoloQical map of Extern Ind ian Shield

< a f t e r S a r k a r , 1982) i l l u s t r a t i n g t h e t h r e e

geo log ic p r o v i n c e * v i z . Chotanagpur g r a n i t e gneiss

complex, Singhbhum o r o g e n i c b e l t and Singhbhum

c r a t o n .

F i g . 2 . S i m p l i f i e d geo log ica l map of Dhanjor i v o l c a n i c s and

a d j o i n i n g area ( a f t e r Baner jee, 1982) .

F i g . 3 . S i m p l i f i e d geo log ica l map of Jagannathpur v o l c a n i c s

and ad jacent area ( a f t e r Baner jee, i 982> .

F i g . 4 . Na20 - CaO - K2O te rna ry v a r i a t i o n diagram showing

K2O enr iched nature of Jagannathpur v o l c a n i c s , as

compared to D h a n j o r i v o l c a n i c s .

F i g . 5 . K2O versus Na2^ b ina ry diagram showing s c a t t e r and

random d i s t r i b u t i o n of these elements in Dhanjor i

and Jagannathpur v o l c a n i c s .

F i g . 6, Na20/K20 versus Na20 + K2O b i n a r y diagram ( a f t e r

M i y a s h i r o , 1975) show ing t h a t t h e p o s t i g n e o u s

a l t e r a t i o n in Dhanjor i and Jagannathpur vo l can i cs

has no t e f f e c t e d t h e w h o l e r o c k a l k a l i

d i s t r i b u t i o n .

F i g . 7 , CaO/Al203 - MgO/10 - S i O j / I O O t e r n a r y v a r i a t i o n

diagram ( a f t e r Schweitzer and Kroner , 1985) showing

u n a l t e r e d n a t u r e o f D h a n j o r i v o l c a n i c s a n d

Jagannathpur v o l c a n i c s .

C' Q M 9 0 / T i 0 2 M#rf.u» C a 0 / T i 0 2 b i n a r y d i a g r a m -for

Dhanjori and Jaaannathpur voTcanics, i U u s t r a t i n g

the sympathetic r e l a t i o n s h i p , an i n d i c a t i o n f o r

t h e i r primary magmatic character-

FiQ. 9 . MgO yer^s various major elwnent oxides p lots for

D h a n j o r i and Jagannathpur v o l c a n i c s s h o w i n g

d i s t r i b u t i o n of various elements r e l a t i v e to MgO.

F i g . 10. Mg-numfaer versus « i02 binary diagram ( a f t e r Hickey

and Frey, 1982) f o r Dhan jo r i and Jagannathpur

volcanics showing enrichment of Si02 ir» comparison

to MORB and komat i i te .

F i g . l i . A<Na20 + K2O) - F<FeO)* ~ M<MgO> ternary diagram

showing iron enrichment trend in Dhanjori volcanics

and iron depletion trend In Jagannathpur vo lcanics .

F i g . 12. Normative Ne-01-Di -Hyp-Qt2 v a r i a t i o n diagram f o r

Dhanjori and Jagannathpur volcanics i l l u s t r a t i n g

the r e l a t i v e propor t ions of normat ive o l i v i n e ,

h y p e r s t h e n e , d i o p s i d e and q u a r t z . Both t h e

volcanics are predominantly quartz normative.

F i g . 13. FeO*/MgO versus various major element oxides p lots

for Dhanjori and Jagannathpur v o l c a n i c s showing

f rac t iona t ion trends of d i f f e r e n t elements.

F i g . 14. Mg-number versus Ti02 binary diagram ( a f t e r Dungah

and Rhodes, 1978> f o r D l tan jor i and Jagannathpur

volcanics showing r e l a t i v e o l i v i n e f rac t ionat ion in

these volcanics.

F i g . 15. Ti02. v»r4^l^|î^rAl 2 ° 3 v « r i a t i o n diagram ( a f t e r

Dungan and miod«*, 1978J. »howln9 r e l a t i v e o l i v i n e

and plagloclaste <<fpact ionat ion in D h a n j o r i and

Jfagannathpur vol cart i c s .

F i g . 16. MQO versus Ca0/Al203 binary diagram ( a f t e r Bence et

a l . , 1979) for Dhanjori a^d J^^nnathpur volcanics

exh ib i t ing posi t ive re lat ionships between them, an

i n d i c a t i t n of clinopyroxene fr»ctt'c«nation.

F i g . 17a. Ti02 versus Al203/Ti02 binary diagram and

b. Ti02 versus Ca0/Ti02 binary dîatâm for Dhanjori

and Jagannathpur vâlcaniCft indicat ing compatible

nature of TiO^ ^nd holding of ^ ^ 2 % " ^ ^ ' ^ ^^ *^*

residual source.

F i g . 18. K2O versus T i02 b i n a r y diagf'am ft>r Dha i ) jor i and

Jagannathpur v o l c a n i c s i n d i d a t i n g . a sympathet ic

re lat ionship between these e lements in D h a n j o r i

vo lcanics .

F i g . 19. T i 0 2 versus ^2^5 v a r i a t i o n d i a g r a m s h o w i n g

compatible (non'-cthondri t i c ) behaviour of these

elements in Dhanjori and Jagannathpur volcanics.

F i g . 20 . FeQ*, versus T i 0 2 b ina^y v a r i a t i o n d i a g r a m

, i l l u s t r a t i n g the sympathe t ic behav iour of these

elements in Dhanjc»ri ^m4 Jagannathpur volcanics.

F i g . 2 1 . FeO* versus Ftt2'^3^^*^ binary diagram for Dhanjori

and Jagannathpur v o l c a n i c s showing sympathet ic

re la t ionships between theo^ an indicat ion fo r t h e i r

g e n e r a t i o n in r e l a t i t v e l y h i g h e r o x i d a t i o n

conditions than tl*» .<ii|#^^4W»ic r idge basalt (MQRB) .

F i g , 22 . Ti02 ver»u» M^k0/Ti02 binary ^diagram -for Dhanjori

and Jagannathpur volcanlcs e«hib i t ing ant ipathet ic

r e l a t i o n s h i p , an indicat ion -for t i tano-magnet i te

and/or amphibole f r a c t i o n a t i o n .

F i g . 23. MgO versus Ni b i n a r y diagram f o r D h a n j o r i and

Jagannathpur v o l c a n l c s showing s y m p a t h e t i c

re la t ionsh ip in both of these elements.

F i g . 24a. Histograms showing Ni abundances in Dhanjori and

Jagannathpur volcanics and

b. Histograms showing FeO*/MgO r a t i o d is t r ibu t ion in

Dhanjori and Jagannathpur volcanics.

F i g . 25. Mg-number versus Ni binary diagram for Dhanjori and

Jagannathpur v o l c a n i c s showing s y m p a t h e t i c

re la t ionsh ips . «

Fig. 26. Ca0/Al2^ versus Ni binary diagram for Dhanjori and

Jagannathpur vo lcan ics i n d i c a t i n g c 1 inopyroxene

f r a c t i o n a t i o n .

F i g . 27. Ni versus Co b i n a r y diagrain f o r D h a n j o r i and

Jagannathpur v o l c a n i c s , e x h i b i t i n g decoup l ing

between these two elements.

F i g . 28. S i 0 2 versus N i / C o b i n a r y d i a g r a m s h o w i n g a

symplithetic re lat ionship in Dhanjori volcanics and

no re la t ionship in Jagannathpur volcanics. I t i s

an indicat ion for the amphibole f rac t iona t ion in

Dhanjori volcanics.

F i g , 29. MgO versus Cr b inary diagram f o r D h a n j o r i and

Jagannathpur vol c a n i c s . showing a s y m p a t h e t i c

r e l a t i o n between theB» fws elements.

F i g . 30 . Ni versus Cr b i n a r y diagram -for D h a n j o r i and

Jagannathpvr y o l c a n i c s e x h i b i t i n g d e c o u p l i n g


F i g . 3 1 . Mg-Number versus Cr binary diagram -for Dhanjori and

Jagannathpur volcanics, i l l u s t r a t i n g a sympathetic

r e l a t i o n .

F i g . 32. Ca0/Al203 versus Cr/Ni binary diagram for Dhanjori

and ^3agannathpu^ volcanics, i l l u s t r a t i n g a pos i t ive

r e l a t i o n between the two. This indicates tha t both

Ni and Cr are controlled by clinopyroxene.

Fig. 33. Ti versus V diagram showing non-c h on dr i t i c

behaviour of V relative to Ti in Dhanjori and

Jagannathpur vol can ics.

Fig. 34. Cu-Ni-Co triangular variation diagram for Dhanjori

and Jagannathpur volcancis illustrating the

behaviour of Cu relative to Ni and Co in both of

these suites.

Fig. 35. K versus Rb binary variation diagram showing Rb

enrichment in Dhanjori and Jagannathpur volcanics.

Fig. 36. K versus K/Rb binary variation diagram exhibiting

absence of any relationship between K and K/Rb in


Fig. 37. Ca0/Al203 versus Sr binary variation diagram for

Dhanjori and Jagannathpur volcanics exhibiting an

antipathetic relation between these elements. This

suggest control of c1inopyroxene rather than

piagioci ase.

Fig. 38a. K versus K/Sr variation diagram

b. Rb versus Rb/Sr gariation diagram and

c. K versus Ca/Sr variation diagram illustrating the

Sr depletion relative to K and Rb in Dhanjori and

Jagannathpur volcanics. In relation to Ca, Sr is

enriched in Jagannathpur volcanics.

Fig. 39a. Ba versus K binary diagram showing a sympathetic

relation in Dhanjori and Jagannathpur volcanics.

b. Ba versus Rb binary variation diagram and

c. Ba versus Sr diagrams illustrate the Ba depletion

in Dhanjori volcanics and Ba enrichment in

Jagannathpur vol canics.

Fig. 40. Zr versus Ti binary variation diaigram for Dhanjori

and Jagannathpur volcanics exhibiting non-chondrite

variations of Zr and Ti in both volcanic suites.

Fields -For island arc basalt, MORB and calc-

alkaline volcanics Are taken from Pearce and Cann

(1973).

Fig. 41. Zr versus Y binary variation diagram for Dhanjori

and Jagannathpur volcanics showing non-chondritic

distribution of these elements in both volcanic

suites.

Fig. 42. Chondrite normalized REE patterns of Dhanjori and

Jagannathpur volcanics. Normalization values are

those of tiasuda et al . (1973) .

Fig. 43. Total al kal i-si 1 i ca diagram for Dhanjori and

Jagannathpur volcanics.Classification boundaries are

those of Le Maitre (1984) and Le Bas et al., (iv86).

F i g . 44. NormatiM» |»^,ii|ôc 1 ase composition versus normative

colour index b inary d iagram ( a f t e r I r v i n e and

Baragar, 1971) indicat ing basa l t ic composition o-f

Dhanjori and Jagannathputf* volcanics.

F i g . 45a. FeO*/MgO versus SiOj binary diagram

b. FeO*/MgO versus FeO* binary diagram and

c. FeO*/MgO versus T i 0 2 b i n a r y diagram i l l u s t r a t i n g

natur® o-f Dhanjori and Jaganriathpur wolcacxtcs*

C lass i f ica t ion boundaries are those of Miyashiro

(1974) .

F i g . 46a. Ni versus Si02 binary diagram ( a f t e r Miyashiro and

Shido, 1976) and

b. Cr versus Si02 var ia t ion diagram ( a f t e r Miyashiro

and Shido, 1975) exh ib i t ing the nature of Dhanjori

and Jagannathpur volcanics.

F i g . 47. Y(Y + Zr) - T(Ti02J^) - C(Cr) diagram ( a f t e r Davies

e t a1 . 1979) f o r Dhan jor i and J a g a n n a t h p u r

v o l c a n i c s showing cat c - a l ka 1 i ne t r e n d of

d i f f e r e n t i a t i o n .

F i g . 48. Ti02 versus Zr b inary v a r i a t i o n diagram showing

absence of l inear re lat ionship between them, as a

character of c a l c - a l k a l i n e d i f f e r e n t i a t i o n .

F i g . 49. P l o t of screened samples of D h a n j o r i and

Jagannathpur volcanics in discrimant functions F]_

versus F2 diagram ( a f t e r P e a r c e , 1 9 7 6 ) ,

i l l u s t r a t i n g t h e i r volcanic arc tectonic s e t t i n g .

F i g . 50 . TiOo versus FeO /MgO r a t i o b ina ry diagram <a+ter

Mu11er , 1980) e x h i b i t i n g t h e i r a r c t e c t o n i c

s e t t i n g .

F i g . 5 1 . T i /1000 versus M b inary v a r i a t i o n diagram (a-f ter

Sherva is , 1982) -for D h a n j o r i and J a g a n n a t h p u r

v o l c a n i c s , i l l u s t r a t i n g t h e i r arc <or subduct ion

zone> s e t t i n g .

F i g . 52 . Zr versus T i v a r i a t i o n d i a g r a m f o r D h a n j o r i and

Jagannathpur vo l can i cs showing t h e i r arc t e c t o n i c

s e t t i n g . Tec ton ic s e t t i n g b o u n d a r i e s Are t aken

•from Pearce (1982) .

F ig . 53. MORB-normalized mu l t i -e lement diagram f o r Dhanjor i

and Jagannathpur v o l c a n i c s . No rma l i za t i on va lues

atire taken f rom Pearce (1982) .

F i g . 54 . N o r m a t i v e I l m e n i t e x 10 - Q u a r t z - E n s t a t i t e

t e rna ry diagram ( a f t e r M e i j e r , 1980) f o r Dhanjor i

and Jagannathpur v o l c a n i c s , i l l u s t r a t i n g t h e i r

c a l c - a l kal ine s e r i e s membership r a t h e r than t he

b o n i n i t e s e r i e s .

F i g . 55 . Mg-number versus d i f f e r e n t i a t i o n i ndex b i n a r y

v a r i a t i o n diagram i n d i c a t i n g hel^rogeneous mant le

sources f o r Dhan jor i and Jagannathpur v o l c a n i c s .

F i g . 56. A l203 /T i02 versus Ca0 /A l203 b i n a r y d i a g r a m f o r

Dhanjorî and Jagannathpur v o l c a n i c s i n d i c a t i n g

t h e i r d e r i v a t i o n f r o n non-depleted sources . F i e l d s

f o r MORB, arc basa l t and andes i te Are taken from

Crawford and Cameron (1985) .

F i g . 57 . Mg-Number versus C a 0 / A l 2 ^ 3 b i n a r y d i a g r a m -for

Dhan jo r i and Jagannathpur v o l c a n i c s , e x h i b i t i n g the

v a r i a t i o n s i n Mg-numbers and Ca0/Al203 - r a t i o s .

F i g . 58 . Histogram showing unimodal d i s t r i b u t i o n of Dhanjor i

and Jagannathpur v o l c a n i c s , i n d i c a t i n g convergent

zone t ec ton i c c o n d i t i o n s d u r i n g t h e e r u p t i o n o-f

these v o l c a n i c s .

F i g . 59 . K2O - T i02 - P2^5 ^sr'ri^'^y diagram <a-fter Pearce et

a l . , 1975) f o r Dhanjor i and Jagannathpur vo l can i cs

i l l u s t r a t i n g con t i nen ta l set up f o r t h e i r e r u p t i o n .

F i g . 60 . Zr versus Zr/Y o c e a n i c - c o n t i n e n t a l v o l c a n i c a r c

d i s c r i m i n a t i o n d i a g r a m ( a f t e r P e a r c e , 1983) f o r

Dhanjor i and Jagannathpur v o l c a n i c s , i n d i c a t i n g

t h e i r c o n t i n e n t a l arc s e t t i n g .

LIST OF TABLES

TABLE I

TABLE II

TABLE III

TABLE IV

TABLE V

TABLE VI

TABLE VII

TABLE VIII

TABLE IX

TABLE X

Various generalized strati graphic successions

of eastern Indian shelld.

Instrumental parameters used in major and

trace element analysis of Dhanjori and

Jagannathpur volcanics.

Major element abundances <in wt'/.') and CI PUI

n o r m a t i v e c o m p o s i t i o n s o f D h a n j o r i v o l c a n i c s .

Ma jo r e lement a b u n d a n c e s ( i n w t X ) a n d CIPW

n o r m a t i v e c o m p o s i t i o n s o f J a g a n n a t h p u r

v o l c a n i c s .

T r a c e e l e m e n t c o n c e n t r a t i o n s ( i n p p m ) o f

D h a n j o r i v o l c a n i c s .

T r a c e e l e m e n t c o n c e n t r a t i o n s ( i n p p m ) o f

Jaganna thpu r v o l c a n i c s .

Ranges o f v a r i a t i o n a n d a v e r a g e c h e m i c a l

c o m p o s i t i o n o f D h a n j o r i a n d J a g a n n a t h p u r

v o l c a n i c s .

Element ratio in Dhanjori volcanics.

Element ratio in Jagannathpur- volcanics.

Comparison of the average chemical composition

of Dhanjori and Jagannathpur volcanics with

the other volcanic rocks.

<Miv>

INTRODUCTION

Basalt, the widespread igneous rock on the earth sur-face

today appear to have been equally important in the geologic

past. Basaltic rocks are mostly partial melting products of

the upper mantle and thus they provide insights into crust

and mantle interaction in terms o-f both petrology and

tectonics. Geochemical and experimental studies on basaltic

rocks have revealed that the depth of magma formation, degree

of partial melting, physico-chemical conditions of the magma,

its differentiation, contamination and/or mixing, all these

factors leave their signatures on the end products (Yoder and

Til ley, 1962; Ringwood, 1975; Dungan and Rhodes, 1978; Sun et

al . , 1979; Yoder, 1979; Perfit et al ., 1980; Thompson et al .,

1984; Huppert and Sparks, 1985; Sparks, 1986; E1 1 am and

Hawkesworth, 1988). The compositional variations in

different basaltic rocks have been successfully used to

estimate the depth of magma genesis (Sagimura, 1968), the

rate of lithosphere subduction (Sugisaki, 1976), the mantle

heterogeneity <Langmuir and Hanson, 1980) and in

identification of tectonic environments in plate tectonic

parlance <Pearce and Cann, 1973; Pearce et al . , 1975, 1977;

Pearce, 1976, 1982; Rogers, 1V82; Mullen, 1983; Holm, 1985).

Our knowledge of modern plate tectonics, involving the

global motions and interactions of large, rigid lithospheric

plates greatly influences our interpretation of Precambrian

(Kroner, 1981). Numerous investigators revealed that

studied by many workers (e.g. Naqyi amd Hussain, 1973a, b;

Condie and Baragar, 1974; Naqvi et al., 1974; Naqyi, 1979;

Condie, 1985, 1989). Generally, these studies are based on

the data which vary in time and space.

The eastern part of Indian shield forms a coherent

crustal segment in which geological history can be traced

continuously throughout most of the iPrecambrian starting from

3400 Ma ago (Moorbath and Taylor, 1988>. It therefore

provides a classic area for the study of the different stages

of the Precambrian crustal evolution. This part of Indian

shield comprises the Chotanagpur granite-gneiss complex in

the north, the Singhbhum-Orissa Iron Ore craton (referred to

as Singhbhum craton in the present study) in the south and an

E-U) trending Singhbhum orogenic belt (SarUar, 1982) between

these two (Fig. 1). The terrain of Chotanagpur granite-

gneiss complex predominantly consists of granites and granite

gneisses with the enclaves and blankets of supracrustal

rocks. Singhbhum craton comprises of granites, banded iron

formations (BIF), several type of metasedimentary and basic

volcanic rocks. Singhbhum orogenic belt consists mainly of

metamorphosed sedimentary and basic volcanic rocks.

The Singhbhum craton occupying the southern part of

eastern Indian shield hosts fairly extensive occurrences of

basic volcanic rocks which are characteristically associated

with metasedimentary rocks flanking the granite massif (Fig.

1). In variety and extent these volcanic rocks appear to be

different from those of many Precambrian terrains of the

world as reviewed by Condie (1981, 1982a). However, these

volcanic rocks of Singhbhum craton have not been studied in

detail as yet.

The stratigraphic positions o-f these volcanics are still

not clear (Dunn, 1929, 1940, 1966; Dunn and Dey , 1942;

Iyengar and Anandalwar, 1965; Banerji, 1974; Sarkar and Saha,

1977, 1983; Banerjee, 1982; Iyengar and Murthy, 1982; Gupta

et al., 1985). Although the age given by Saha and Ray (1984)

and Saha et al . (l98S) is questionable, the earliest phase o-f

vol can ism in this region is evident from ortho-amphibolites

which occur as enclaves within the Older Metamorphic Group.

The next phase o-f volcanic activity is represented by

Gorumahisani-Ukampahar mafic and ultramafic rocks, whose

relationship with the associated metasediments (Badampahar

Group; Iyengar and Murthy, 1982) is not clear. Banerjee

(1982) suggested that this suite represents a sub volcanic

assemblage, intrusive into and extrusive on the Gorumahisani-

Badampahar BIF sequence.

The late Archaean-early Proterozoic volcanism is

represented by Bonai range metavol canics which consist mainly

of variable amount of mafic flows and tuff with minor silicic

volcaniclastic interbeds (Bose, 1982; Banerjee, 1982). The

basic volcanics of Dhanjori, Ongarbira and Jagannathpur areas

respectively occur on the north eastern, north western and

western margins of the granite massif (Fig. l^. Dhanjori and

Jagannathpur volcanic suites have been correlated with Dalma

metavolcanics of Singhbhum orogenic belt with a possible age

of 1600-1700 Ma (Sarkar et al., 1969; Sarkar and Saha, 1977,

1983). Howeyer, Banerjee <1982) on the basis o-f geochemical

characters and tectonic style placed the stratigraphic

position o-f Dal ma metavol canics above the Dhanjon , Ongarbira

and Jagannathpur vol canics. Iyengar and Anandalwar (1965'>,

Iyengar and Murthy (1982) and Sarkar and Saha a977, 1983)

have correlated the lavas o-f Dhanjon and Simlipal basins.

However, Rb-Sr isochron age o-f 2084 +. 70 Ma <Iyengar et al . ,

1981) for Simlipal basin and structural studies (Sarkar and

Saha, 1977, 1983; Mukhopadhyay, 1986) contradict this

correlat ion.

Ongarbira and Dhanjori volcanics have also been

correlated with the Dal ma metavolcanics of Singhbhum orogenic

belt (Dunn, 1929; De, 1964; Gupta et al . , 1980; Iyengar and

Murthy, 1982). Both of these volcanics, occurring in south

of Singhbhum thrust, are associated with molasse type

metasediments <Banerjee, 1982; Sarkar, 1982; Sarkar and

Chakraborti, 1982). Dalma metavol cam cs, on the other hand,

unconformably overlie the metasediments of Singhbhum orogenic

belt <De et al., 1963; Sarkar and Saha, 1977, 1983; Uerma et

al ., 1978). The metavolcanics, ranging m composition from

ultramafic to basaltic andesite, also contain fragments of

dolente, epidionte, serpen t in i te, gabbro and pyroxenite

<Sarkar, 1982) and have been considered as a greenstone belt

in an in tracraton i c rift (Gupta et al., 1980; Bose and

Chakraborti, 1981) and an ophiolite suite resulted by the

collision of Chotanagpur and Singhbhum microplates (Sarkar,

1982). Naha and Ghosh (1960) and Banerjee (1982) have

considered it as an island arc suite.

In order to achieve a better understanding of the

Proterozoic geologic events in Singhbhum craton, geochemical

investigations on the two most critical volcanic suites are

presented here in this thesis. The volcanic suite occurring

on the north eastern margin o-f carton is re-ferred to as

Dhanjon volcanics (Dunn and Dey, 1942; Banerjee, 1982^,

while the suite on the western margin is designated as

Jagannathpur volcanics (Saha, 1964). Major, minor and trace

elements including REE of various samples from these suites

have been determined. Based on the data certain important

aspects like comparability of these volcanic suites with

those from Archaean, Proterozoic and Phanerozoic eras, their

petrogenesis and tectonic implications are discussed.

Chapter I contains general geologic frame work of the

eastern Indian shield as well as the studied basic volcanic

suites. An account of the mineralogic and petrographic

characters of Dhanjori and Jagannathpur volcanics is given in

Chapter II. Major and trace element distributions and their

relationships are discussed in Chapter III and IKf

respectively. In Chapter M magma classification is

discussed. Under the head of petrogenesis in Chapter VI, the

origin of Dhanjori and Jagannathpur volcanics is discussed in

the light of geochemical data available in the literature.

This will provide insights into the tectonic processes

operating m the crust and upper mantle. Chapter UII

presents a discussion of the geochemical as well as the

geological data to interpret the tectonic settings o-f these

volcanics and associated tectonic events in the Singhbhum

craton. Summary and conclusions are provided in Chapter

VIII .

CHAPTER I

GEOLOGICAL SETTING

GENERAL GEOLOGY OF EASTERN INDIAN SHEILD

The eastern Indian shield is an ancient crustal block

that contains the rocks as old as 3400 Ma (Moorbath and

Taylor, 1988). It is bounded by Mahanadi Graben and SuUinda

thrust in the west and in the south by Charnockite-Khondalite

province o-f Eastern Shats and Recent coastal alluvium. In

the north and east it is masked by vast Bangetic alluvium and

Quarternafjr sedimen t s o-f Bengal basin (Fig. 1 ) . It has

received adequate attention o-f geosci en t i sts and almost all

aspects o-f its geology have been discussed (Mazumdar, 1978,

1988; Sarkar, 1902; Bhattacharyya and Sanyal , 1988; Saha et

al . , 1988). However, due to its complex structures and

geological history, the published maps and stratigraphic

sections -from di-fferent parts are inconsistent from each

other <Dunn, 1929, 1940, 1966; Dunn and Dey, 1942; Iyengar

and Anandalwar, 1965; Mukhopadhyay, 1976; Sarkar and Saha,

1977, 1983; Banerjee, 1982; Sarkar and Chakraborti, 1982;

Gupta et al . , 1985). The scarcity o-f radiometric dating and

isolated outcrops o-f various basins are the factors which

make the strat igraph i c correlation difficult (Naqvi and

Rogers, 1987).

lu

Sarkar <1982> has recognised three geologic provinces in

this part o-f the Indian shield i.e. Chotanagpur granite

gneiss complex -forming a plateau in the north, (ii) Singhbhum

erogenic belt in centre and <iii) Singhbhum craton in the

south. The tectonic and temporal relationship between these

provinces and the stratigraphy with in each province have

been subjects o-f debate since the early sixties <Sarkar and

Saha, 1962, 1963). Stratigraphic successions proposed by

various workers are given in Table I. These successions

indicate that there are wide differences of opinion regarding

the positions of various rocks of Singhbhum orogenic belt and

their relationships with the rocks of Singhbhum craton. For

example, Dunn (1929, 1940) and Dunn and Dey tl942) considered

the metasedimentary rocks underlying the Dalma metavolcanic

belt as the equivalent of 'Iron Ore Stage'. But Sarkar and

Saha (1977) and Saha et al., (1988) named these rocks as

'Dhalbhum Formation' and considered them younger than their

'Iron Ore Group'. Iyengar and Murthy (1982.) did not mention

these rocks in their stratigraphic succession and placed the

Dalma metavolcanics below the 'Koira Group' which has been

considered as older than the Dalma metavolcanics (Dunn, 1929,

1940; Dunn and Dey, 1942; Sarkar and Saha, 1977; Saha et al .,

1988). The general geological features of each of the above

geologic provinces are briefly discussed in the following

paragraphs.

12

CHOTANAGPUR GRANITE GNEISS COMPLEX

Chotanagpur granite gneiss complex is exposed between

latitudes 23°N to 25°N and longitudes 83°45'E to 87°45'E. It

IS a composite mass consisting mainly o-f granite gneiss,

migmatites and massive granite with enclaves o-f para and

orthometamorphics, dolerite dyt'es and innumerable veins of

pegmatite, aplite and quartz <Ghose, 1983). From the

structural patterns, worked out in di-f-ferent parts o-f the

Chotanagpur granite gneiss complex (Sen Gupta and Sarkar,

1964; Ghose, 1971; Chattopadhyay and Saha, 1974;

Bhattacharyya, 1976; Sarkar, 1977; Chatterjee and Sen Gupta,

1980), it IS clear that the area has undergone three phases

of deformation producing distinctive folds and related linear

fabrics. The available age data <Ghose, 1983; Sarkar, 1988)

indicate the metamorphism and granitic activity continued for

a period from 1500 to 635 Ma.

SINGHBHUM 0R06ENIC BELT

This is an arcuate tectonic belt, convex towards the

north and has distinctive sedimentary, deformationa1 and

thermal zones grossly parallel to the belt cFig. 1 ) .

Opinions differ regar-ding the age relationship between the

rocks of this belt and those occurring in the Singhbhum

craton lying to the south of this belt (Dunn, 1929, 1940,

1966; Dunn and Dey, 1942; Sarkar and Saha, 1959, 1962, 1963,

1977, 1983; Iyengar and Anandalwar, 1965; Banerji, 1975,

1984; Iyengar and Murthy, 1982; Sarkar and Chakraborti, 1982;

Saha et al . , 1988). This belt may be divided into four

12

l o n g i t u d i n a l t e c t o n i c s t r i p s as d i s c u s s e d be low :

The m e t a s e d i m e n t a r y sequence o c c u r r i n g t o t h e n o r t h o f

t h e Dal ma m e t a v o l c a n i c b e l t , c o n t a i n s p h y l l i t e , mica s c h i s t ,

t h i n and i m p e r s i s t e n t b a n d s o f q u a r t z i t e , q u a r t z s c h i s t ,

ca rbon p h y l l i t e , i m p u r e g r e y t o b l a c k c h e r t s a n d c a l c -

s i l i c a t e r o c k s < S a r k a r , 1 9 8 2 ) . Numerous l e n s o i d b o d i e s o f

metamorphosed m a f i c and u l t r a m a f i c r o c k s , i n d i c a t i n g b o t h

i n t r u s i v e and e x t r u s i v e c h a r a c t e r s , a l s o o c c u r as e p i d i o r i t e ,

h o r n b l e n d e s c h i s t , c h l o r i t e s c h i s t a n d t a l c s c h i s t . T h i s

m e t a s e d i m e n t a r y sequence has been v a r i o u s l y r e f e r r e d t o a s

' I r o n Ore S t a g e ' ( D u n n , 1 9 2 9 , 1 9 6 6 ; Dunn a n d D e y , 1 9 4 2 )

'Dhalbhum F o r m a t i o n ' (Sa rka r e t a l . , 1969 , S a r k a r and Saha ,

1977) and ' o u t e r w i l d f l y s c h b e l t ' ( S a r k a r , 1 9 8 2 ) .

Dal ma m e t a v o l c a n i c b e l t e x t e n d s o v e r a d i s t a n c e o f abou t

200 km and fo rms a number of f o l d c l o s u r e s i n eas t and west

S inghbhum. Though , p r e d o m i n a n t l y m e t a b a s a l t i c t hey c o n t a i n

abundant d a r k e r f r a g m e n t s , p o c k e t s and l e n s e s of p e r i d o t i t e ,

s e r p e n t i n i t e and g a b b r o - p y r o x e n i t e . T h r u s t p l a n e s a r e

r e c o g n i s a b l e on b o t h s i d e s of Dal ma m e t a v o l c a n i c b e l t (Dunn

and Dey, 1942; S a r k a r , 1 9 8 2 ) . The m e t a v o l c a n i c b e l t i t s e l f

i s a l s o sheared a t few p l a c e s ( S a r k a r , 1 9 8 2 ) . Dunn (1929)

and k/ierma e t a l . ( 1 9 7 8 ) o p i n e d t h a t t h e s e me t a v o l can i c s

m a i n l y r e p r e s e n t b a s a l t i c f l o w s , m ixed w i t h m ino r vo lumes of

p y r o c l a s t s and t u f f s , e r u p t e d under s u b - a e r i a l c o n d i t i o n s and

f o r m s t h e c o r e o f a s y n c l i n e . H o w e v e r , v a r i o u s

i n v e s t i g a t i o n s r e v e a l e d t h a t t h e s e m e t a v o 1 c a n i c s a r e l o w

p o t a s s i u m ocean f l o o r t h o l e i i t e s w i t h l o c a l p i l l o w s t r u c t u r e s

13

(Yellur, 1977; Bha t tac haryya and Dasgupta, 1979;

Bahattacharyya et al . , 1980), erupted in a r i-f t zone, either

in a marginal basin environment <Bose and Chakraborti, 1981;

Chakraborti and Bose, 1985) or on a thinned continental crust

(Gupta et al., 1980). An island arc origin o-f this

metavolcanic suite has also been proposed by Naha and Ghosh

<.i960> arid Banerjee <;i9e2>. SarUar <1982> cortsidered it as

an ophiolite suite. The age o-f emplacement o-f Dal ma

metavolcanics has been considered about 1600-1700 Ma <Sarkar

et al . , 1969; Sarkar and Saha, 1977, 1983; Saha et al.,

1988) .

The metasedimentary sequence occurring to the south o-f

the Dal ma metavolcanic belt and extending upto the 'Singhbhum

thrust zone' have variously been re-ferred to as 'Chaibasa

Stage' <Dunn, 1929, 1966; Dunn and Dey, 1942), 'Chaibasa

Formation' <Sarkar and Saha, 1977, 1983; Saha et al., 1988),

'Ghatshila Group' (Iyengar and Murthy, 1982) and 'central

metaflysch belt' (Sarkar, 1982). It comprises a thick

sequence o-f phyllites and mica schists with intercalated

bands and lenses of micaceous quartzite and gritty quartzite.

These rocks have generally preserved primary sedimentary

structures such as, cross bedding, convolute laminations,

graded bedding and current ripple laminations. The -flysch

character o-f the rocks o-f this belt have been emphasized by

many workers (e.g. Gobar Gaa 1 , 1964; Iyengar and

Anandal war,1965; Naha,1966; Sarkar, 1982).

14

Bes ides t hese - f l ysch t ype metasedimen t s , t h e r e a r e v a s t

t e r r a i n s o-f p l a t f o r m t y p e me t a s e d i men t s t o t h e s o u t h o f

S i n g h b h u m t h r u s t z o n e a s w e l l ( m o s t l y t o t h e w e s t o f

Singhbhum G r a n i t e ) . M a r k e d c o n t r a s t s b e t w e e n t h e two a r e

n o t i c e a b l e wh i ch l e a d t o d i v e r g e n t o p i n i o n s i n t h e r e g i o n a l

s t r a t i g r a p h i c and t e c t o n i c c l a s s i f i c a t i o n (Dunn, 1940; Dunn

and Dey, 1942; S a r k a r a n d S a h a , 1 9 5 9 , 1 9 6 2 , 1 9 6 3 , 1 9 7 7 ,

1983; I yenga r and M u r t h y , 1 9 8 2 ; S a r k a r , 1 9 8 2 ; S a r k a r a n d

C h a k r a b o r t i , 1982) .

An a r c u a t e b e l t , s t r e t c h i n g f o r a b o u t 200 km i n t h e

s o u t h e r n p a r t o f t h e Singhbhum o r o g e n i c b e l t i s w e l l known as

t h e ' 'Copper B e l t t h r u s f (Dunn, 1929; Dunn and Dey, 1942;

Sarkar and Saha, 1962, 1977, 1983) or 'S inghbhum t h r u s t ' o r

'S inghbhum s h e a r ' (Naha, 1965; B h a t t a c h a r y y a , 1966; B a n e r j i ,

1975; S a r k a r , 1 9 8 2 ) . I n t he west t he zone i s more than 25

km w i d e where t h r e e m a j o r t h r u s t s l i c e s a r e r e c o g n i s e d .

These s l i c e s a r e compressed i n t o a na r row zone o f abou t 1 km

i n t h e c e n t r e bu t w i d e n a g a i n t o m o r e t h a n 5 km. i n i t s

e a s t e r n e x t e n s i o n ( S a r k a r , 1 9 8 2 ) . The r o c k s o c c u r r i n g i n t h e

Singhbhum t h r u s t zone a r e m a i n l y p h y l l o n i t e , c h l o r i t e -

s e r i c i t e s c h i s t and sheared g r a n i t e - g n e i s s a l o n g w i t h some

l e n t i c u l a r b o d i e s of sheared c o n g l o m e r a t e and s a n d s t o n e . The

n o r t h e r n edge of t h e t h r u s t zone i s , however , marked by a

s t r i n g of k y a n i t e b e a r i n g q u a r t z i t e b o d i e s and o c c a s i o n a l

v e i n s of mass ive p o s t - t e c t o n i c k y a n i t e ( S a r k a r , 1 9 8 2 ) .

The g r a n i t e r o c k s o f S i n g h b h u m t h r u s t z o n e a r e

c l a s s i f i e d i n t o f o l l o w i n g f o u r g roups :

15

<1) Chakradharpur granite gneiss, containing two distinct

units, the older tonalite-trondhjemite gneiss intruded by the

pegmatitic granite and granodionte (Bandyopadhya/, 1981;

Sengupta et al ., 1983; Bhaumik and Basu, 1984; Ghose et al . ,

1984) .

(ii) Arkasani granophyres represent a group o-f lenticular

bodies containing massive cores o-f monso to syeno-granite and

margins of granodionte and tonal ite (Banerji et al . , 1978).

(ill) Soda granite comprising a group o-f lenticular bodies

o-f tonal ite which are commonly mylonitized and converted into

sencite or muscovite-quartz schist (Mukhopadhyay, 1986) and

<iv) Mayurbhanj granite consisting o-f three distinct

lithologic units yiz. -fine grained granophyric granite, a

coarse grained granite with biotite and ferrohastingsite and

small injections of biotite aplogranite (Saha, 1975) .

SINGHBHUM CRATON

The Singhbhum craton is an intensely studied region and

almost all the aspects of its geology are heatedly debated.

The most outstanding of all the controversies is perhaps the

dual concept regarding the stratigraphic and tectonic

classification of the rocks of this region. Sarkar and Saha

(1959, 1962, 1963, 1977, 1983) classified the rocts occurring

in north and south of Singhbhum thrust zone into two

stratigraphic and orogenic belts whereas, the others believe

that inspite of their apparent structural and metamorphic

contrast they belong to one broad stratigraphic unit (Dunn,

1929, 1V40; Dunn and Dey, l9^2; Iyengar and Anandalwar, 1965;

16

B a n e r j i , 1 9 7 4 ; I y e n g a r a n d M u r t h y , 1 9 8 2 ; S a r U a r a n d

C h a k r a b o r t i , 1 9 8 2 ) . V a r i o u s rock u n i t s i n t he s t r a t i g r a p h i c

sequence are d e s c r i b e d as f o l l o w s .

Older Metamorphic Group <OMG)

The O lder M e t a m o r p h i c Group < S a r k a r a n d S a h a , 1 9 7 7 ,

1983) o c c u p i e s an a r e a 0+ abou t 130 s q . km. a r o u n d Champua

< L a t . 22°04 ' 'N : Long . 8 5 ° 4 0 ' E ) . T h i s group i s r e p r e s e n t e d by

p e l i t i c s c h i s t , g a r n e t i - f e r o u s q u a r t z i t e , ca 1 c - m a g n e s i an

me tased imen ts and s i l l l i k e m a f i c r o c k s - now metamorphosed

t o o r t h o - a m p h i b o l i t e And h o r n b l e n d e s c h i s t s . T h e s e

s u p r a c r u s t a l s a r e p a r t i a l l y g r a n i t i s e d by a s u i t e o f b i o t i t e

( — h o r n b l e n d e ) - t o n a l i t e g n e i s s g r a d i n g i n t o t r o n d h j e m i t e ,

w h i c h o c c u p i e s abou t 1000 s q . km. a r e a i n t h e w e s t - c e n t r a l

p a r t o f Singhbhum G r a n i t e b a t h o l i t h i c complex (Saha and Ray,

1984 ; Saha e t a l . , 1 9 8 8 ) .

The s u p r a c r u s t a l s o f OMG as w e l l as t o n a l i t e g n e i s s have

been a f f e c t e d by two phases o f d e f o r m a t i o n . The Rb-Sr

i s o c h r o n s a n d K -A r d a t a i n d i c a t e t h e c l o s i n g d a t e o f

metamorphism o f b o t h OMG m e t a m o r p h i c s a s w e l l a s t o n a l i t e

g n e i s s a round 3200 Ma (Sa rka r and Sana, 1977 ; S a r k a r , e t a l . ,

1 9 7 9 ) . Sm-Nd i s o c h r o n of t he t o n a l i t e g n e i s s i n d i c a t e s an

a g e o f 3775 +. 89 Ma , w h i c h p r o b a b l y r e p r e s e n t s t h e

c r y s t a l l i s a t i o n age of t h e t o n a l i t e magma (Basu e t al . , 1 9 8 1 ;

Saha e t a l . , 1988) and i s s u p p o r t e d by Pb-Pb i s o c h r o n age of

3659 +. 34 Ma f o r Champua r o c k s (Saha e t a l . 1986, 1 9 8 8 ) .

R e c e n t l y M o o r b a t h a n d T a y l o r ( 1 9 8 8 ) p o i n t e d o u t t h e

1^

i n a c c u r a c y o-f t hese dates and o b t a i n e d Sm-Nd, TDM model ages

of 3 . 4 1 , 3 .39 and 3 . 3 5 Ba -for t o n a l i t e g n e i s s . i n s u p p o r t of

t h e i r r e s u l t s , t h e y ( o p . c i t . ) a l s o p r o v i d e d Pb-Pb who le r o c k

i s o c h r o n age of 3378 +_ 98 Ma and Rb-Sr who le rock i s o c h r o n

age of 3280 +. 130 Ma f o r t he t o n a l i t e g n e i s s .

Banded I ron Formation <BIF)

Banded I r o n F o r m a t i o n s < B I F ) a n d a s s o c i a t e d r o c k s o f

P recambr ian sequence a r e f o u n d i n t h e r e g i o n f l a n k i n g t h e

Singhbhum B r a n i t e b a t h o l i t h i c comp lex . A c c o r d i n g t o Verma

e t a l . , (1984) t h e s e r o c k s e x t e n d t o w a r d s t h e w e s t up t o

l o n g i t u d e a4°E ( F i g . 1 ) .

Dunn and Dey (1942) Sarkar and Saha < 1962, 1963, 1977,

1983 ) a n d Saha e t a l . , ( 1 9 8 8 ) c o n s i d e r N o a m u n d i ( La t .

2 2 ° 0 9 ' N : L o n g . 8 5 ° 3 l ' E ) - K o i r a ( L a t . 2 1 ° 5 4 ' N : L o n g . 8 5 ° 1 5 ' E )

sequence and Gorumahisan i ( L a t . 2 2 ° 1 8 ' ' 3 0 " N : Long . 8 6 ° 1 7 ' E ) -

Badampahar ( L a t . 2 2 ° 0 4 ' N : Long . 8 6 ° 0 7 ' ' E ) , sequence o f B IF

r o c k s t o be s t r a t i g r a p h i c a l 1y e q u i v a l e n t whereas Prasada Rao

e t a l . ( 1 9 6 4 ) , I y e n g a r a n d A n a n d a l w a r ( 1 9 6 5 ) , I y e n g a r a n d

Bane r j ee ( 1 9 7 1 ) , B a n e r j i ( 1 9 7 4 ) , Acharya (1984) and Acha rya

e t a l . , (1989) r e g a r d t h e s e two a s s e p a r a t e s t r a t i g r a p h i c

u n i t s .

I n Gorumahisan i - Badampahar s e c t o r t he BIF r e p r e s e n t s

t h e r o c k t y p e y i z . , c h e r t y q u a r t z a r e n i t e , f u c h s i t e

q u a r t z i t e , h o r n b l e n d e s c h i s t , t u f f and p h y l l i t e o v e r l a i n by

one or two d i s t i n c t h o r i z o n s o f BIF wh ich a r e s e p a r a t e d by a

z o n e o f c h e r t y q u a r t z i t e w i t h n u m e r o u s t h i n l a y e r s o f

i n t e r c a l a t e d c h e r t and a l t e r e d v o l c a n i c t u f f ( C h a k r a b o r t y and

18

Majumdar , 1 9 8 6 ) . B a n d e d - g r u n e r i t e - m a g n e t i t e - q u a r t z i t e ,

banded q u a r t z i t e and b a n d e d - m a g n e t i t e - q u a r t z i t e a r e usua l

v a r i a t i o n s i n d i c a t i n g a med ium h i g h g r a d e m e t a m o r p h i s m

( A c h a r y a , 1984; A c h a r y a e t a l . , 1 9 8 9 ) . T h e s e r o c k s a r e

d i s t i n c t l y i n t r u d e d by e p i d i o r i t e s , Newer d o l e r i t e s a n d

u l t r a m a f i c dykes of younger age ( B a n e r j e e , 1982) .

In t h e Noamund i -Ko i r a s e c t o r BIF r o c k s a r e made up o-f

s h a l e , p h y l l i t e , t h e m i d d l e f o r m a t i o n o f b a n d e d h e m a t i t e

j a s p e r and an upper f o r m a t i o n of m a n g a n i f e r o u s s h a l e , c h e r t ,

i r o n f o r m a t i o n and s h a l e (Prasada Rao e t a l . , 1964; Sa rang i

and A c h a r y a , 1975; ttcharya, 1984; Acharya e t a l . , 1 9 8 9 ) .

The o c c u r r e n c e of BIF i n a b e l t a round Singhbhum G r a n i t e

i s s i g n i f i c a n t as t h e i r p o s i t i o n i n s p a c e a n d t i m e i s

c o n t r o v e r s i a l . Dunn, ( 1 9 4 0 ) ; Dunn and Dey <1942) and Sarka r

and Saha ( 1 9 7 7 , 1983) have p roposed Singhbhum G r a n i t e t o be

younger t h a n 6 i F . B u t , B a n e r j i ( 1 9 7 4 ) , Mukhopadhyay (1976)

and I yenga r and M u r t h y ( 1 9 8 2 ) h a v e o p i n e d t h a t S i n g h b h u m

G r a n i t e i s t h e o l d e s t c r a t o n i c b l o c k on w h i c h BIF were l a i d

down.

Seve ra l l a r g e v o l c a n i c b l a n k e t s o c c u r a s s o c i a t e d w i t h

B I F . These a r e :

Bonai 'v'olcanic S u i t e

B e l o w t h e B I F o f N o a m u n d i - K o i r a b a s i n o c c u r a n

e x t e n s i v e v o l c a n i c s u i t e i n d i c a t i n g s u b - a e r i a l c h a r a c t e r i n

19

the west and submarine in the east (Banerjee, 1982). The

volcanics consist o-f variable amount of tholeiitic ^ ava and

tui-f with minor silicic yol cani c 1 ast i c interbeds which are

metamorphosed under green schist -facies. In the eastern part

picritic lava exhibits pillow structures (Sarangi and

Acharya, 1975; Bose, 1982). Banerjee (1982) regarded the

suite as an island arc basalt.

Jagannathpur Volcanic Suite

Along t h e e a s t e r n l imb o-f Noamundi -Koi ra sync l I n - o r i u m ,

a tho l e i i t e - a n d e s i t e s u i t e uncon-f o r m a b l y o v e r l i e t h e BIF

r o c k s ( S a h a , 1 9 6 4 ) . In c o m p a r i s o n t o B o n a i s u i t e t h i s

v o l c a n i c s u i t e i s r e m a r k a b l y -fresh and u n a l t e r e d ( B a n e r j e e ,

1 9 8 2 ) . No i n t r u s i o n s a r e s e e n t o h a v e a - f - f ec t ed t h e s e

v o l c a n i c r o c k s . T h i s s u i t e , h a s been d a t e d a t a b o u t 1629 +.

30 Ma by K-Ar method ( S a r k a r e t a l . , 1969) and i s c o n s i d e r e d

t o be e q u i v a l e n t o-f Dalma and Dhan jo r i b a s i c v o l c a n i c s u i t e s

( S a r k a r and S a h a , 1977 , 1983 ; I y e n g a r and Mur thy , 1982) .

Ongarbira 'v'olcanic Suite

The O n g a r b i r a V o l c a n i c s u i t e h a s a g e n e r a l ENE-UJSW t r e n d

and o c c u r s d i s c o r d a n t t o t h e r e g i o n a l NNE-SSE s t r i k e o-f t h e

m e t a s e d i m e n t s ( S a r k a r a n d C h a k r a b o r t i , 1 9 8 2 ) . T h e

ul trama-f i c s , b a s a l t s and g a b b r o - p y r o x e n i t e w i t h s u b o r d i n a t e

tu - f faceous members show i n t r i c a t e i n t er-f i n g e r i ng among

t h e m s e l v e s and a l s o w i t h t h e under - ly ing metased imen t s w i t h

which they a r e co—folded (Gupta e t a l . , 1 9 8 1 ) . S u b a e r i a l

v o l c a n i s m i s i n d i c a t e d in a major p a r t o-f t h i s v o l c a n i c s u i t e

20

(Banerjee, 1982). Howeyer, presence o-f pillow structures at

several places suggest subaquous volcanism in parts of this

volcanic suite (Gupta et al ., 1981, Sarkar and Saha, 19B3) .

Dhanjori Uolcanic Suite

The m e t a y o l c a n i c s o c c u r r i n g t o t h e sou th and sou thwes t

o f Singhbhum t h r u s t zone are i n t e r l a y e r e d w i t h o r t h o q u a r t z i t e

and p h y l l i t e , u n d e r l a i n by quar t z i t e - c o n g l omera te and -form a

group of r o c k s named D h a n j o r i Group <Dunn and Dey, 1 9 4 2 ) .

A b o u t 30 km s o u t h w a r d s , t h e r o c k s o f S i m l i p a l b a s i n ,

c o n s i s t i n g o f a b o u t 1 0 , 0 0 0 m t h i c k s e q u e n c e o f t h r e e

q u a r t z i t e h o r i z o n s a l t e r n a t i n g w i t h t h o l e i i t i c l a v a f l o w s

have g e n e r a l l y been c o r r e l a t e d w i t h t h e D h a n j o r i G r o u p

( I y e n g a r and Ananda lwa r , 1965; S a r k a r and Saha, 1977 ; I y e n g a r

and M u r t h y , 1 9 8 2 ) . But s t r u c t u r a l l y t hese two b a s i n s i . e .

D h a n j o r i and S i m l i p a l a r e q u i t e d i s t i n c t (Naqv i and R o g e r s ,

1 9 8 7 ) . The r o c k s of D h a n j o r i b a s i n a r e i n v o l v e d i n two phase

superposed f o l d i n g - an e a r l i e r NNUI t o NW t r e n d i n g d o u b l y

p l u n g i n g i s o c l i n a l s y n c l i n e , o v e r t u r n e d t o w a r d s SW a n d a

l a t e r ENE t r e n d i n g s e t of f o l d s - t o f o r m a canoe l i k e f o l d

s t r u c t u r e ( S a r k a r , 1982) S i m l i p a l b a s i n however e x h i b i t s a

s i m p l e s y n c l i n a l s t r u c t u r e w i t h l o w d i p p i n g l i m b s a n d

c i r c u l a r o u t c r o p p a t t e r n ( S a r k a r and Saha, 1 9 7 7 ) . The Rb-Sr

i s o c h r o n s of t h e m a r g i n a l l y i n t r u d e d g a b b r o - a n o r t h o s i t e and

f e r r o h e d e n b u r g i t e - g r a n i t e g r a n o p h y r e o f S i m l i p a l b a s i n ,

i n d i c a t i n g t h e age o f t h e s e r o c k s a t a b o u t 2084 ± 70 Ma

( I y e n g a r e t a l . , 1981) a l s o c o n t r a d i c t s t h i s c o r r e l a t i o n .

21

Gorumahisani Volcanic Suite

Along the eastern border oi Singhbhum Granite,

C-iorumahisani volcanic suite is associated with mica schists,

cherty quartzite and BIF. The relationship between the

associated metasediments and the volcanic suite is obscure.

They consist of both mafic and ultramafic types, and some of

them have garnet peridotite inclusions (Banerjee, 1982), Dunn

and Dey (1942) and Banerjee (.1982) are of the opinion that

this suite IS partly volcanic but primarily intrusive. The

rocks of this volcanic suite are intruded by f-umhardubi (Lat .

22°17'N: Long. a6°19'30") - Dublabera (Lat. 22°29'30"N: Long,

86°17'E) gabbro-anorthosite, Rangamatia (Lat. 22°29'15"N:

Long. 86°19'E) 1 eucotonal i te, Katupith (Lat. 22°18''N: Long.

86' " 17'30"E; leucogranite and Newer Dolerite dyke swarm.

Singhbhum Granite Batholithic Complex

The huge g r a n i t i c body ex tends over more than 150 km i n

N-S d i r e c t i o n and 70 \ m i n E-W d i r e c t i o n between l a t i t u d e 2 1 °

and 2 2 ° 4 5 ' N and be tween l o n g i t u d e 8 5 ° 3 0 ' a n d 8 6 ° 3 0 ' E a n d

f o rms a ma jo r p a r t o f t h e S i n g h b h u m c r a t o n . S i n g h b h u m

G r a n i t e b a t h o l i t h i c complex i s made up of a t l e a s t t w e l v e

s e p a r a t e magmatic b o d i e s , wh ich a r e c o n s i d e r e d t o have been

emplaced i n t h r e e s u c r e b s i v e phases ( S a r k a r and Saha, 1977 ,

1983; S a r k a r , e t a l . , 1979; Saha, 1979; Saha e t a l . , 1 9 8 8 ) .

The p e t r o l o g i c a l and geochemica l s t u d i e s on most o f t h e u n i t s

o f Singhbhum G r a n i t e i n d i c a t e t h r e e d i s t i n c t p h a s e s o f

g r a n i t e a c t i v i t y . The f i r s t phase r o c k s a r e r e l a t i v e l y k -

poor g r a n o d i o n t e s and t r o n d h j e m i t e s w h i l e t hose of second

^2

and third phases are granodiorites grading into adamellitic

granites (Saha, 197V; Saha et a1 . , 1988), Trace element data

(Roonwal, 1972; Saha et a1., 1973a) provided clear support to

the idea o-f three distinct phases o-f emplacement, each phase

of the magma being derived independently.

The strat igraphic position o-f Singhbhum Granite and its

relation with OMG and BIF has been discussed by many workers

(e.g. Iyengar and Anandalwar, 1965; Banerji, 1974;

Mul--hopadhyay, 1976; Iyengar and Murthy, 1982) who opined that

Singhbhum Granite is the oldest cratonic block on which BIF

were laid down. On the other hand Sarkar and Saha '.1962,

1963, 1977, 1983) -following Dunn (1940) and Dunn and Dey

(1942) proposed a later phase of granite intrusion, younger

than BIF, especially in the eastern part of main massif.

However, in subsequent studies Saha et al. (1988) concluded

that first and second phase Singhbhum Granite forms the

basement whereas phase three are intrusive into the BIF

rocks. Here it is noteworthy that geochr on ol ogi ca 1 data

(Sarkar and Saha, 1977; Sarkar et al . , 1979; Saha et al , ,

1986, 1988) for Singhbhum Granite is less precisely defined

than OMG tonalite gneiss. Rb-Sr whole rock isochron age and

Pb-Pb whole rock isochron age for two sets of samples

indicate that at least parts of Singhbhum Granite were

emplaced around 2900-3000 Ma (Sarkar, et al . , 1979, Saha et

al., 1986). The reported ^^Sr/^^sr ratio indicate so large

spread that no conclusion can be drawn (Naqvi and Rogers,

1987) .

2S

Newer Dolerite Dyke Swarm

A dolerite dyke swarm known as the Newer Dolerite

traverse the Singhbhum Granite in some regular sets; of

these, the sets NNE-SSW and NW-SE are most common and invoke

the presence of a conjugate fracture system disposed at 75

(Saha et al . , 1973b). According to Sarkar and Saha <'1977,

1983), the intrusions of these dykes continued intermittently

from 1600 Ma to 950 Ma ago. Some minor ultramafic

intrusions, mostly serpentinised poikilitic harzburgite are

spatially associated with the Newer Dolerite dykes <Bose and

Boles, 1970; Saha et al., 1973b).

Kolhan Group

The Kolhan Group is the youngest Precambnan sequence

within the Singhbhum craton. The sequence starts with a

basal conglomerate, purple sandstone, shale and limestone.

The conglomerate contains pebbles of Singhbhum Granite,

banded hematite jasper and iron ores (Sarkar, 1982^. These

rocks overlie the Singhbhum Granite and BIF of the south-west

Singhbhum with a marked structural discontinuity <Sarkar and

Saha, 1977, 1983) and are less deformed and unmetamorphosed,

thus has no comparable suite in the region <Sarkar, 1982;.

De (1964) suggested that kolhan Group is a product of

sedimentation on a marginal flat lying stable land surface in

shallow marine shelf environment.

24

STRATI GRAPHIC FRAMEWORK AND FIELD OCCURRENCE OF DHANJORI

AND JA6ANNATHPUR VOLCANlCS

Dnanjori and Jagannathpur yolcanics represent middle

Proterozoic volcanism in Singhbhum craton (Sarkar et a1 . ,

1969; Sarkar and Saha, 1977, 1983; Banerjee, 1982; Iyengar

and Murthy, 1982; Saha et al., 1988). In various

stratigraphic successions <Tab1e 1> these volcanics are

considered as contemporary (Banerji, 1974; Sarkar and Saha,

1977; Banerjee, 1982; Iyengar and Murthy, 1982; Saha et al.,

1983) however, their stratigraphic positions still need some

clari-f ication. In -foregoing pages the stratigraphic -frame

-work and field occurrence o-f these volcanics are discussed.

Dhanjori Volcanics

The Dhanjori volcanics -form a part o-f Dhanjori basin,

exposed between latitude 22°30' and 22°45'N and between

longitude 86°15' and 86°30'E, in the northeastern part o-f the

Singhbhum craton <Fig. 2). Dunn and Dey <:i942) described

this volcanic suite as an epidiorite suite underlain by

quartzite-conglomerate and metapelites resting unconformably

over 'Iron Ore Series'. Subsequently Iyengar and Anandalwar

(l965) clubbed Dhanjori and simlipal basins and described the

entire suite to be uni-formly spilitic in composition. Sarkar

and Saha (1977, 1983) in their stratigraphic succession, also

correlated Dhanjori and Simlipal basins but placed it over

'Dhalbhum Formation' o-f 'Singhbhum Group'. Iyengar and

Murthy <1982) contended that the rocks o-f Dhanjori basin

uncon-formably overlie the 'Ghatshila Group' and thus they are

zs

I ' J Mbile draimc

" Juiiunjon Volciinics

'H l ih i in jo i 1 Q u i i i l / i t i (iiK) '( onglomoiiito

I Undiffcicntiatcd Hockb

^3Schis ts und Quiirl/ite

IV Ncwci Dolor ilc

[%] lault

S I race ol \xial Plane of nhaiijoi I Reclined I old

^ llirust

2,|f'^âduguda

/rj, ;. 0 '^ ' ' Z^ ^ v.*«Vv • • Musabani

«6°20' 86'2 5'

Fig.2 . Simplified geological map of Dhanjori

volcanics and adjoining area (af ter Banerjee, 1982).

26

o l d e r t h a n ' K o i r a G r o u p ' .

Gupta e t A], < 1 9 8 5 ) w h i l e d e a l i n g w i t h t h e s t r a t i g r a p h y

o-f D h a n j o r i b a s i n , c o u l d no t d i f f e r e n t i a t e t h e D h a n j o n and

Gorumahisan i v o l c a n i c sequences and d e s c r i b e d them t o g e t h e r

a s a p a r t o f t h e same b a s i n . The s t r a t i g r ap h i c

i n t e r p r e t a t i o n g i v e n by Bane r j ee (1982) seems t o be i n b e t t e r

a c c o r d w i t h t h e f i e l d d a t a .

The 'Newer D o l e r i t e ' dyke swarms wh i ch c u t a c r o s s t h e

S i n g h b h u m G r a n i t e , B I F me t a s e d i m e n t s a n d a s s o c i a t e d

metavo l c a n i c s o f Gorumah i san i - B a d a m p a h a r a r e a a s w e l l a s

KumarUocha < 2 2 ° 2 7 ' 3 0 " N : 86°16E) - Rangamat ia < 22°29- '15"N:

8 6 ° 1 9 ' E ) - Bo rumah isan i 1 e u c o t o n a l i t e do n o t a t even a s i n g l e

p o i n t c u t a c r o s s t h e D h a n j o r i v o l c a n i c s o r t h e D h a n j o r i

q u a r t z i t e a t i t s base . T h e r e f o r e , t he Newer D o l e n t e dykes

and y o l c a n i s m i . e . G o r u m a h i s a n i g r e e n s t o n e s o f t h i s a r e a

seems t o be o l d e r than D h a n j o r i s e d i m e n t a t i o n and v o l c a n i s m .

D h a n j o r i v o l c a n i c s u i t e i s u n d e r l a i n by c r o s s l a m i n a t e d

q u a r t z i t e and g r i t . A v e r y d i s t i n c t i v e dark g rey t o

o p a l e s c e n t q u a r t z i s an i m p o r t a n t c o n s t i t u e n t of D h a n j o r i

g r i t . A c c o r d i n g t o Bane r j ee (1982) t h i s o p a l e s c e n t c o l o u r i s

v e r y common i n t h e q u a r t z v e i n s t r a v e r s i n g t h e n e i g h b o u r i n g

B I F m e t a s e d i m e n t s a n d a s s o c i a t e d m e t a v o l c a n i c s i . e .

Badampahar - G o r u m a h i s a n i g r e e n s t o n e s e q u e n c e i n t h e

Dub labera ( 2 2 ° 2 9 ' 3 0 "N : 8 6 ° 1 7 ' E ) - K u n d a r k o c h a < 2 2 ° 2 8 ' N :

86 14 '30 "E ) a r e a . C o n c i e v a b l y , Badampahar-Gorumahi san i a r e a

c o u l d have been t h e p r o v e n a n c e o f t h e D h a n j o r i c l a s t i c

s e d i m e n t a t i o n .

27

The l e u c o t o n a l x t e , e x t e n d i n g -fronn K u m a r k o c h a a n d

Rangamat ia t o t he eas t o-f Gorumahisan i c u t s a c r o s s the B IF

m e t a s e d i m e n t s a n d G o r u m a h i s a n i g r e e n s t o n e s a s w e l l a s

Dub labe ra and Kumhardubi < 2 2 ° 1 7 ' N ; 8 6 ° 1 9 ' 3 0 " E ) yanad i - f e rous

g a b b r o - a n o r t h o s i t e . T h i s i s o v e r l a i n by D h a n j o n q u a r t z i t e

and t h e r e i s no s i g n o f i n t r u s i o n o-f t h e q u a r t z i t e by

1euco tona l i t e .

These v o l c a n i c s a r e b r o a d l y a l i k e i n t h e i r megascopic

c h a r a c t e r s and c o n s i s t o-f p r e d o m i n a n t l y mass i ve and compact

v a r i e t i e s , somet ime t h e y show p o r p h y n t i c n a t u r e . They a r e

g e n e r a l l y d u l l g r e e n t o b l a c k i n c o l o u r a n d a t p l a c e s

b rown ish g rey c o l o u r has a l s o been n o t i c e d . The basa l and

c e n t r a l p a r t o-f t he f l o w s a r e g e n e r a l l y f i n e t o m e d i u m

g r a i n e d a n d o c c a s i o n a l l y t h e y g r a d e t o w a r d s t o p i n t o

v e s i c u l a r v a r i e t i e s . The v e s i c l e s a r e p r e d o m i n a n t l y a n g u l a r

t o s u b - a n g u l a r i n shape . They are m o s t l y f i l l e d by seconda ry

m i n e r a l s l i k e c a l c i t e , q u a r t n and z e o l i t e .

B a s a l t i c l a v a f l o w s have been c l a s s i f i e d as pahoehoe,

aa-aa t y p e and b l o c k y l a v a depend ing on c e r t a i n d i s t i n c t i v e

c h a r a c t e r i s t i c s wh ich have been s t u d i e d m a i n l y m t h e f l o w s

of Hawai ian t ype o f v o l can i s m ( M a c d o n a l d , 1 9 6 7 ; . Some

f e a t u r e s such as smooth b i l l o w i n g o r r o l l i n g a n d g e n t l y

u n d u l a t i n g s u r f a c e s t y p i c a l t o pahoehoe t ype l a v a s a r e no t

n o t i c e d i n t hese b a s i c v o l c a n i c s . O t h e r t y p i c a l f e a t u r e s

a l s o of pahoehoe t y p e l a v a s such as r o p y , d raped o r f e s t o o n e d

s u r f a c e s , b u l b o u s t o e s e t c . a r e n o t n o t i c e d i n t h e s e

28

y o l c a n i c s . In absence of t hese c h a r a c t e r i s t i c f e a t u r e s of

pahoehoe l a v a and t h e p resence of c l i n k e r y top and i r r e g u l a r

t o subangu la r v e s i c l e s t y p i c a l o f a a - a a l a v a t h e D h a n j o r i

v o l c a n i c s may be grouped as aa -aa t y p e of f l o w s .

Jagannathpur tv*o1canics

There i s a r e c t a n g u l a r p a t c h o f b a s i c l a v a s e x p o s e d

between l a t i t u t d e 22° and 22°15' ' N and between l o n g i t u d e

SS^SO' and 85°45 ' 'E , c o v e r i n g an a r e a of abou t 200 square km

( F i g . 3 ) . Jones <1934) i n t e r p r e t e d t hese v o l c a n i c s as s i l l s

and c o r r e l a t e d them w i t h t h e m e t a v o l c a n i c s o f t h e e a s t e r n

l i m b o f ' I r o n Ore Sync 1 i n o r l u m ' i . e . Bonai m e t a v o l c a n i c s a s

w e l l a s Newer D o l e r i t e d y k e s w a r m s . D u n n ( 1 9 4 0 )

s u b s e q u e n t l y , r e c o g n i s e d t h e i r e f f u s i v e n a t u r e and p roposed

t h r e e p o s s i b l e r e l a t i o n s h i p s b e t w e e n t h e s e v o l c a n i c s a n d

banded i r o n f o r m a t i o n <BIF) sequence of Noamund i -Ko i r a a r e a .

I n t he f i r s t p o s s i b i l i t y t h e v o l c a n i c s a r e c o n s i d e r e d a s

r e s t i n g on t i l t e d and d e n u d e d e d g e s o f N o a m u n d i - K o i r a B I F

sequence. In t h e s e c o n d a l t e r n a t i v e t h e a p p a r e n t l y o l d e r

r e l a t i o n s h i p o f t hese v o l c a n i c s w i t h t he N o a m u n d i - K o i r a B IF

sequence i s c o n s i d e r e d due t o t h e p r o b a b l e o v e r f o l d i n g . I n

the t h i r d a l t e r n a t i v e these v o l c a n i c s a r e c o n s i d e r e d t o be

a c t u a l l y o l d e r t h a n t h e Noamundi-H'o i ra BIF sequence .

Saha < 1 9 6 4 ) on t h e b a s i s o f c a r e f u l f i e l d a n d

l a b o r a t o r y s t u d i e s c o n c l u d e d t h a t t h e s e v o l c a n i c s ^re younger

than Singhbhum G r a n i t e and o l d e r than Koihan Group o f r o c k s .

H o w e v e r , B a n e r j i < 1 9 7 4 ) a n d I y e n g a r a n d M u r t h y ( 1 9 8 2 )

29

I ' l '

I ' l ' i ' I ' l ' l ' i ' P l | i ! ' . .'I I

c CO



O

a o E a

3 = 5 H w O

II ll

++

^ 1

I i §

41 •a c

s s

to o

•H C (0

o H O >

u 3

4-1 (0 c c 03 cn c (0 ID

4-1

o

a

(0

u •H O) O H O (U cn

0) •H 4-1 •H H Qt E

•H CO • •

01 •H b

fN 00

^ (D

4 - 1

c 0) o (0

• n T3 ID

TJ C 10

30

c o n s i d e r e d t hese M o l c a n i c s o l d e r t h a n Noamund i - K o i r a B I F

sequence .

Bane r j ee (1982) p o i n t e d o u t t h a t n o r t h e r n , e a s t e r n ,

s o u t h e a s t e r n and w e s t e r n c o n t a c t s o f Jagannathpur v o l c a n i c s

a r e c o n t i n u o u s l y - f a u l t e d a g a i n s t K o l h a n s , Singhbhum G r a n i t e ,

a g a i n t he Ko lhans and Noamundi -Ko i r a BIF sequence o-f r o c k s

r e s p e c t i v e l y . I t i s a l s o i n t e r e s t i n g t o n o t e t h a t s i m i l a r t o

D h a n j o r i v o l c a n i c s , no t a s i n g l e dyt e o-f Newer D o l e n t e s u i t e

c u t s a c r o s s t h e s e v o l c a n i c s , e i t h e r near Dangoaposi ( 2 2 ° 1 0 ' N :

B5'^36'E) o r Horomutu ( 2 2 ° 0 3 ' N : B5°18 'E ) .

A l t h o u g h t h e c o n t a c t s between Jaganna thpur v o l c a n i c s and

ko l han Group a r e a l w a y s f a u l t e d , t h e d i r e c t i o n and amount o f

d i p of t h e ^ o l h a n beds near t h e f a u l t g e n e r a l l y i n d i c a t e t h a t

K o l h a n b e d s a r e down t h r o w n a g a i n s t t h e v o l c a n i c s .

T h e r e f o r e , t hese v o l c a n i c s a r e l i k e l y t o be o l d e r than t h e

Kolhan Group. An i n d i r e c t c o n f o r m a t i o n o f t h i s v i e w i s

o b t a i n e d f r om the a b s e n c e o f t h e l a v a f e e d e r s a c r o s s t h e

Ko lhan o u t c r o p s near Bara Nanda ( 2 2 ° 1 3 ' N : 8 5 ° 3 6 ' 3 0 " E ) .

I n t h e NE of S i ngabe ra < 2 2 ° 1 0 ' 4 5 " N ! 85°39 'E> a l o n g t h e

r a i l w a y c u t t i n g , an e x t r e m e l y w e a t h e r e d d y k e p o s s i b l y

c o r r e l a t i v e w i t h J a g a n n a t h p u r v o l c a n i s m c u t s a c r o s s t h e

Singhbhum G r a n i t e and t h u s t h e s e v o l c a n i c s a r e younger t h a n

t h e Singhbhum B r a n i t e .

Jaganna thpur v o l c a n i c s a r e m o s t l y p r o p h y n t i c i n n a t u r e

and a t p l a c e s i t may be g r o u p e d a s h i g h l y p o r p h y n t i c ,

m o d e r a t e l y p o r p h y n t i c and s p a r s e l y p o r p h y n t i c . Some o f t h e

f l o w s a r e c h a r a c t e r i z e d by h a v i n g v e s i c l e s o f v a r y i n g

31

degrees. The vesicles are mostly subangular in shape and are

•filled in by secondary minerals like calcite, silica and

zeolite etc. Empty vesicles are also present. The primary

linear and swirling -flow layers are well developed and

can be seen at many places. The typical characteristics o-f

AA-AA type lava is abundant in north eastern area whereas

pahoehoe type swirls of lava are noticed in the south eastern

area. In absence of pillow lavas and hyaloc1astites these

eruptions are considered as sub-aerial .

Judged from the cyclical abundance in north-eastern part

of the area this lava pile appears to be made up of large

number of flows. In the road section from N ot Buruhatu

<22°11'30"N: 85°36'30"E) to Dangoaposi individual flow sets

which are massive at the lower part with amygdule abundance

increasing towards the top, have a plan width of 100-2U0 m.

According to Banerjee <1982) the minimum number of flows in

the Buruhatu-Dangoaposi sequence would be 25 to 30. Roy

(1969) has identified "about 24 flows of block lava having an

average dip of 15°" in eastern part of the Jagannathpur

volcanics.

CHAPTER II

PETROGRAPHY

The -field characteristics o-f Dhanjon and Jagannathpur

Molcanics have been discussed in the preceding chapter.

Eihanjori volcanics have been affected by low grade regional

metamorphism as well as shear movements. On the other hand,

Jagannathpur volcanics are essentially unme tamor phosed

(Banerjee, 1982">. The petrographic and mi neral ogi c features

of these volcanics are discussed below :

Dhanjori Volcanics

These volcanics are pervasively altered. Mostly they are

fine to coarse grained and Are dark grey to greenish grey in

colour. Their primary mineralogy and texture are not

observed in majority of the rocU samples microscopically

studied. These volcanics are generally contain actinolitic

amphibole, 201 si te-ep idote+. chlorite, sodic plagioclase ±

quartz with accessory ilmenite and or sphene. A significant

feature is the abundance of amygdul ar facies - the am^ygdul es

being mostly composed of quartz, frequently with the rims of

epidote and/or chlorite and rarely associated with calcite.

These basic volcanics can broadly be divided into two

distinct types. The most widespread type is largely massive

and preserves rel let porphyritic and intergranul ar teiitures.

usually plagioclase phenocrysts retain their original lath

shape and are set in a groundmass of fine grained matted

amphibole aggregate (Plate 1).

PLATE 1

(a)

(b)

PLATE - 2

(a) Plagioclase, chlorite and epidote showing schistosity in Dhanjori

volcanics (crossed nicols x 90).

(b) Schistose rock with unaltered plagioclase laths in Dhanjori volcanics

(crossed nicols x 90).

PLATE-2

(b)

33

The second t ype i s f i n e g r a i n e d s c h i s t o s e rocU w i t h a

s i g n i f i c a n t c o n c e n t r a t i o n o f e l l i p t i c a l t o na r row e l o n g a t e

amygdu les . M i n e r a l 0 9 1 c a l l y these r o c k s a r e c h a r a c t e r i z e d by

an abundance o f a c t i n o l i t e a n d e p i d o t e a n d t h e f a b r i c i s

e s s e n t i a l l y d e f i n e d by i n t i m a t e l y a g g r e g a t e d assemblage of

t m y amph ibo le and e p i d o t e g r a n u l e s ( P l a t e 2 ) .

A c t i n o l i t e , t h e most e v e n l y d i s t r i b u t e d c o n s t i t u e n t , i s

p l e o c h r o i c f r om p a l e g r e e n i s h y e l l o w t o g r e e n i s h b l u e w i t h

the e x t i n c t i o n a n g l e o f 1 5 ° t o 16°. The p l a g i o c l a s e 1=

l a r g e l y a l b i t i c and o c c u r s a s l a t h s , g r a n u l e s a n d s t u m p y

g r a i n s w i t h i n c l u s i o n s o f e p i d o t e and a c t i n o l i t e . E p i d o t e -

z o i s i t e I S a common c o n s t i t u e n t a n d h a s s i g n i f i c a n t

p rominance i n many s c h i s t o s e v a r i e t i e s .

C h l o r i t e o c c u r s as f i n e f l a k e s and i r r e g u l a r p a t c h e s i n

a s s o c i a t i o n w i t h a c t i n o l i t e . I n m a s s i v e t / p e , c o a r s e

r e c t a n g u l a r b l a d e s ( 0 . 5 mm) and f l a k e s a r e more common w i t h

some t m y n e e d l e s .

Jagannathpur volcanics

Jagannathpur volcanics are mostly medium to fine grained

and are dark grey to greenish grey in colour.

Mineralogical1y, these rocks are predominantly consist of

plagioclase and pyro;;ene which show both porphyritic and non-

porphyntic varieties cPlate 3 and 4). Plagioclase ranges

from microlites to laths, commonly sausser111 zed with the

outline of individual sample blurred. Pyroxenes are

PLATE-3

(a)

34

d o m i n a n t l y d i o p s i d i c a u g i t e , - f r e q u e n t l y i n t he f o rm o-f s t o u t

e u h e d r a .

T e x t u r a l l y , t h e r o c k s show w ide v a r i e t y -from t r a c h / t i c

•flow t e x t u r e m some f i n e g r a i n e d p l a g i o c l a s e r i c h v a r i a n t s

t o r e l i c t i n t e r g r a n u l a r , g r a p h i c and o p h i t i c t o s u b - o p h i t i c

t e v t u r e s , p o s s i b l y r e p r e s e n t i n g t h e f e e d e r d v k e s o+ t h e

y o l c a n i s m ( B a n e r j e e , 1982 ) . In the p r e s e n t s t u d y , bes ides

t h e i n t e r g r a n u l a r , o p h i t i c t o s u b - o p h i t i c t e x t u r e ,

p l a g i o c l a s e quench t e x t u r e i s a l s o f o u n d .

Many of t h e s e r o d s are amygdul a r . L o c a l l y , amygdul es

a r e zoned w i t h q u a r t z and c a l c i t e a t t he c o r e and e p i d o t e a t

t h e m a r g i n .

P l a g i o c l a s e p h y n o c r y s t s w h i c h a r e o f a n d e s i n e a n d

L a b r a d o r i t e v a r i e t y , occu r i n many of t h e roci- samples „ They

a r e u s u a l l y s u b - h e d r a l t o e u h e d r a l i n s h a p e and c o m m o n l y

tw inned on a l b i t e and car 1sbad l a w s . The p l a g i o c l a s e a r e

somet imes s a u s s e r i t i z e d and have g i v e n r i s e t o c h l o r i t e and

e p i d o t e . C I i n o p y r o x e n e s a r e u s u a l l y d i o p s i d i c a u g i t e and

e x h i b i t o p h i t i c t o s u b - o p h i t i c t e x t u r e . They a r e s u b - h e d r a l

t o a n h e d r a l and e x h i b i t e x t i n c t a n g l e 35° t o 4 5 ° . L o c a l l y ,

c l i n o p y r o x e n e i s a l t e r e d t o h o r n b l e n d e , u r a l i t e a n d / o r

c h l o r i t e . P i g e o n i t e r a r e l y o c c u r s a= p h e n o c r / s t s o n l y i n

some r a p i d l y c o o l e d v o l c a n i c s .

Groundmass of t h e s e b a s i c v o l c a n i c s a r e e s s e n t i a l l y

composed o f p l a g i o c l a s e m i c r o l i t e s , py roxene g r a i n s and i r o n

o r e wh ich show h y a l o p i l i t i c t e x t u r e ^ P l a t e 4 ) . Py ro :<ene

PLATE-ii

(a)

o c c u r s a s g r a n u l a r a g g r e g a t e s a n d o c c u p i e s m o s t l / t h e

i n t e r s t i t i a l space between t h e p l a g i o c l a s e l a t h s . I n some o-f

t h e samples g l a s s i s p r e s e n t w h i c h h a s been c o n v e r t e d t o

s i de rome l a n e . I t o c c u r s as i n f i l l i n g s i n t he i n t e r s t i c e s o-f

g r a i n c o n s t i t u e n t s o-f t h e g r o u n d m a s s . O u a r t z i n m i n o r

amounts o c c u r s as sma l l ; !enomorphic rounded g r a i n s , w i t h v e r y

f i n e n e e d l e s o-f a c t m o l i t e i n c l u d e d i n some o-f t hem.

Sphene o c c u r s s p o r a d i c a l l y bu t i s absen t i n man v o-f t he

mass ive t y p e s where opaque o j d d e s a r e most common.

CHAPTER I I I

rVtJOR ELEMENT GEOCHEMISTRY

GENERAL STATEMENT

Among t h e man/ p e t r o c h e m i c a l i n d i c e s , S i , M , F e , Hq ,

Ca , \-\B., K , Ti , P a n d Mn a r e c o m m o n l y i n c l u d e d i n m a j o r

e l e m e n t 9 n a l > = e s . In i g n e o u s = u i t e s , t h e s e e l em en t= =houi

s y s t e m a t i c v a r i a t i o n s and -form t h e bull- roci- c h e m i s t r y . T h u s

t h e y p l a^ ' an i m p o r t a n t r o l e in d e t e r m i n i n g t h e c o m p o i i t i o n

a n d c l a s s i f i c a t i o n o+ v a r i o u s r o c k t y p e s . Among t h e s e

e l e m e n t s , S x , Al and Ca a r e e s s e n t i a l s t r u c t u r a l c o n s t i t u e n t s

( e . s . c s - ) m b a s a l t s b e c a u s e t h e y a l m o s t f u l l y o c c u p y H i t e s i n

o l i v i n e , p y r o x e n e , p1 a g i o c 1 a s e a n d g a r n e t . T h e r e + o r e ,

d i s t r i b u t i o n of t h e s e e l e m e n t s b e t i ^ j e e n = o l i d a n d m e l t i s

i n d e p e n d e n t of b o t h t h e a b u n d a n c e of t h e e l e m e n t i n t h e

s / s t e m 9nd p r o p o r t i o n of t h e p h a s e s p r e s e n t ' L a n g m u i r a n d

H a n s o n , 1980,^. Mg a n d F e a r e i n t e r m e d i a t e e l e m e n t s i n

b a s a l t i c roc l ' = a s t h e / r e m a i n in t h e s o l i d s o l u t i o n e n d do

n o t c o m p l e t e l y o c c u p y any o n e s i t e i n a n y m i n e r a l i n t h e m e l t

s -' s t em b u t a r e a b u n d a n t e n o u g h t o b e s t o i c h i m e t r i c a 1 1 -

i m p o r t a n t . The a b u n d a n c e o t t h e s e e l e m e n t s a p p e a r t o be a

f u n c t i o n of t h e p a r e n t c o m p o s i t i o n a s w e l l a s t h e e / t e n t of

m e l t i n g a n d p r o p o r t i o n of m i n e r a l s p r e s e n t i n t h e = ,> s t em

" [ L a n g m u i r a n d H a n s o n , 1 9 8 0 J . Na , k , T i , p a n d Mn

c o n c e n t r a t i o n s in b a s a l t i c r o c k s a r e g e n e r a l l y low a n d t h e r e

ArB no s t o i c h i m e t r i c c o n s t r a i n t s on t h e i r a b u n d a n c e s m ariy

o f t h e p h a s e s i n t h e s y s t e m . U n l e s s a m i n e r a l c o n t a i n s t h e s e

e lemen ts A= the ms jo r c o m p o n e n t i n a m i n e r a l - m f i t H- =+em ,

t h e / may be t r e a t e d as t r a c e e lements <Lan9muir and Hanson,

19BU).

The r e l a t i o n s h i p s between the major e lements ha','e been

u t i l i z e d M a r i o u s l / t o d i s t i n g u i s h the e M o l u t i o n a r > t r e n d s o-f

t he magmas (Kuno, 1 9 6 0 , 1 9 6 8 ; M u r a t a , I 9 6 0 ; P o 1 d e r ^ a a r t ,

1964; M i y a s h i r o , 1V74, 1 9 7 5 ) , t h e i r t e c t o n i c s e t t i n g s (Pearce

e t a l . , 1977; Rogers , 1982; H u I I en , 1983) c r u s t a l t h i c k n e s s

<. C o n d 1 e a n d P o t t s , 1 9 6 9 ; f | a q M i a n d H u s s a i n , 1 9 7 3 a , b ;

D i c k i n s o n , 1975; P e a r c e e t a l . , 1 9 7 5 ; a n d t h e d e g r e e o-f

p a r t i a l m e l t i n g as w e l l as p h y s i c o - c h e m i c a l c o n d i t i o n s d u r i n g

p a r t i a l m e l t i n g (Hanson and Langmtn r , 1978; Sun e t a l . , 1979;

Lsngmuir and Hanson, 1930; F r a n c i s ei" B\ ,, l 9 8 3 K I n t h e

p r e s e n t chap te r t h e major e lement d i s t r i b u t i o n s O'f D h a n j o r i

and Jagsinns thpur ' ^ o l c a n i c s a re tsit en i n t o c o n s i d e r a t i o n t o

• f ind out t he r e l a t i o n s h i p s beti-'ieen " a r i o u s ms or e i eT ien t s .

These r e l a t i o n s h i p s i^ji 1 1 enab le t o ssses i"he d i i t e r en 11 a 11 on

t r e n d s o-f these M o l c a n i c s w h i c h i n t u r n c 1 5 s s i-f ' them i n

t e r m s o-f t h e i r magma c o m p o s i t i o n s . ^ eep ing an e y on t r i e aqe

o f these MO I can i c s a t t e m p t s have a l s o been made to e , amine

t h e e f - f ec t and e ; ; t en t of a l t e r a t i o n on t h e c h e m i s t r y ot the'ê

vo I c a n i c s .

ANALYTICAL TECWMlQUES

A+ te r p e t r o g r a p h i c s t u d i e s most f r e s h rock samples ê r e

s e l e c t e d f o r c h e m i c a l a n a l y s i s . Roc I- s a m p l e s h a v i n g

amvgdu les , s e c o n d a r y q u a r t z , c a l c i t e a n d c h l o r i t e u.er e

36

r e j e c t e d . A f t e r c r u s h i n g t h e r o c I- t o 30 me = h , a l l t h e

• f ragments f r e e f rom secondary a s s o c i a t i o n were hand p i c k e d

a n d i . iere d r i e d i n t h e oven a t 100°C t o e l i m i n a t e t h e

h y g r o s c o p i c m o i s t u r e .

These 30 me=h f r a g m e n t ^ were powdered t o minu= I'OO me = h

s i z e and the samples f o r chemica l a n a l / s i = were tg i en b /

c o n i n g and q u a r t e r i n g .

S o l u t i o n s were p r e p a r e d u s i n g p r o c e d u r e s u g g e s t e d by

S h a p i r o (197 '?) . Two t y p o s of s o l u t i o n s t o r t h e e s t i m a t i o n n f

m a j o r , m inor and t r a c e e lemen ts were p r e p a r e d .

S o l u t i o n ' p\' 0 .1 gram of the f i n e l y poi'Jdered samples i s

f u s e d w i t h 15-20 p e l l e t s o f S o d i u m h j -d r o x i d e i n a n i c k I e

c r u c i b l e . T h i s i s d i s s o ^ l e d i n 20 ml o f 1:1 HC1 and hea ted

f o r abou t h a l f an hour t i l l c l e a r s o l u t i o n i s o b t a i n e d and

made t o 1 l i t r e a f t e r comp l e te c o o l i n g .

Sol u t i on ''B' 0 . 5 gram sample i s taken i n a t e f l o n bea te r of

100 ml c a p a c i t y w i t h 15 ml o f HF i 48'/.'• =ind 25 t o 30 ml o f

c o n c e n t r a t e d H-iSO^. The bealver i s hea ted on water ba th t o

a lmos t d r / n e s s . About 10 ml o+ HNOO I S added a t t h i s s tage

and the c o n t e n t s a r e hea ted a g a i n t i l l a c l e a r s o l u t i o n I E

o b t a i n e d . T h i s i s t h e n made t o 250 ml f o r ma jo r and minor

e lemen ts and u p t o bO ml f o r t r a c e e l e m e n t s .

S i l i c a and a l u m i n a a r e d e t e r m i n e d f r o m s o l u t i o n A

u s i n g d o u b l e beam U M - v i s i b l e s p e c t r o p h o t o m e t e r ' . M o d e l

Shimatzu UV'-190). S1O2 1= d e t e r m i n e d b^ mo l , . bdenum b l u e

3.

m e t h o d w h i l e A 1 o 0 3 i s d e t e r m i n e d b / c a l c i u m a l u m i n i u m

a l i z a r i n r e d - S complex me thod . MgO, CaO, ^â-.0, K-,n and nnO

a^rB e s t i m a t e d by a tom ic a b s o r p t i o n s p e c t r o p h o t o m e t e r (.nodeI :

P a r i a n i^H6-D) u s i n g s o l u t i o n ' B ' . L 9 n t h a n u m s o l u t i o n i s

added f o r MgO and CaO e s t i m a t i o n , 5S t he r e l e ^ ^ i n g 5gent -for

these e l e m e n t s . T o t a l i r o n "^FeoO^ / , T1O2 -and F-jOc; a r e

d e t e r m i n e d -from s o l u t i o n B u s i n g U'v-'-sp ec t r op h o t ome t er .

Fe-iOo IS d e t e r m i n e d on t h e o r a n g e c o l o u r de' , 'e l oped "i 1 t h

o r t h o p h e n a n L h r o l i n e . ^ i ^ ^ ' ^^ d e t e r m i n e d on a y e l l o w c u l o u r

p roduced w i t h t i r o n w h i l e P^:'-''^ ^ =• d e t e r m i n e d b/ - e l 1 OIM

mal yddovanadophosphor i c (Vanadomol ybda te ) ac i r t c o m p l e ; u s i n g

UV-spec t r ophotorr ieter . FeO i s d e t e r m i n e d b> t i t r a t i o n i - j i th a

s t a n d a r d po tass i um d i c h r o m a t e s o l u t i o n u s i n g d i p h e n - 1 amine

s u l p h o n a t e i n d i c a t o r . Lo=s on i g n i t i o n •LOI^ of t he samples

I S d e t e r m i n e d by h e a t i n g of t h e sample powder i n a g l a s s t u b e

a t a h i g h t e m p e r a t u r e .

A l l t h e a v a i l a b l e d a t a u ie re s t a n d a r d i z e d a q a i n s t

r e f e r e n c e rock s t a n d a r d s BCP-1 , SY-2 , SY-3 and EM. To a v o i d

a n / e r r o r i n tne d e t e r m i n a t i o n s doub le and t r i p l e runs I'lere

made t a k i n g d i f f e r e n t samples f rom the same specimen poiîder .

Pock s t a n d a r d s were a l s o ana l>=ed a l o n g 1*11 th t he samples tr,

c h e c k t h e p r o b a b l e e r r o r . I n s t r u m e n t a l p a r a m e t e r s a n d

o p e r a t i n g c o n d i t i o n s a r e g i v e n i n Tab le l l .

40

MAJOR ELEMEr^T DISTRIBUTION

The major e lement c o m p o s i t i o n = o-f t i ' )en t> ' =ample-= o t

D h s n j o r i " o l c a n i c = and t h i r t y -fxve samples of Jaganro thpur

v o l c a n i c s a l o n g w i t h t h e C . I . P . W . norms a r e g i v e n i n Tab le I I I

and I'-'' r espec 11 " e l / . SiO-n wh ich pla>'= ari i m p o r t a n t r o l e i n

de te rm ] n a t i o n o-f v a r i o u s rocl- t y p e s , shows w ide v a r i a t i o n s i n

bo t h s u i t e s . In Dhan j or i v o l c a n i c s i t r an ge = + r om 45 .4 2'/. t o

58.50"-: w i t h the a v e r a g e o-f 5 2 . 0 3V: w h e r e a s i n J a g a n n s t h p u r

v o l c a n i c s i t v a r i e s -from 47.2'?'/. t o 57.''OV. w i t h sn 5 "e r3ge o-f

54.06>'.. TiO-T i s s l i g h t l > h i g h e r i n I ^ h a n j o r i v o l c a n i c s ,

r a n g i n g f rom 0.59"/. t o 1.56'-. w i t h an a v e r a g e o f 0. ' 'v ' ' ' . as

compared t o Jagannathpur v o l c a n i c s where i t v a r i e s f r o m 0.4'>7:

t o 1 .A-9'/. w i t h t h e average o f 0.76"/..

AI ' iO^ i n bo th Dhan J or 1 and Jagannathpur ' Jo l can i c= =hoi'i5

c o n s i d e r a b l e v a r i a t i o n s . I n D h a n j o r i v o l c a n i c s , i t r anges i n

between i> .36'/. and 1 2 . 3 8'/. , a v e r a g i n g a t 1 1 . 4 1 / . w h e r e a s i n

Jaganna thpur v o l c a n i c s , i t v a r i e s •< rom V.U77. t o 16. l4" ' i w i t h

an ave rage of 1 2 . 0 9 / i .

D h a n j o r i v o l c a n i c s c o n t a i n h i g h e r i r o n c o n t e n t ( t o t a l he

as Fe203 > , var x i n g w i d e l y f r o m 1 1 . 0 0 / : t o 1 v . i 0". > 11 t h an

ave rage of 14.75'/ . , t h a n t h e Jaganna thpur v o l c a n i c s wherp at

ranges f r om 3.267. t o 13.80 p e r c e n t w i t h an average o f 1 1 . 5 J .

FeO c o n t e n t of D h a n j o r i v o l c a n i c s v a r i e s f r o m 7.207. t o 12.607,

w i t h an ave rage of 9.69% whereas i n Jagannathpur v o l c a n i c s i t

ranges i n between 5.08^'. and 9 .08/ . and a v e r a g i n g a t 7.137..

The Fe .03 -content (Fe.Og = Fe203* -FeO X 1.1) of Jaganna thpur

Mo l can i cs v a n e s w i d e l y ^ 0.44X to 7 .19-0 w i t h a low ave raqe

41

C 3 . * 1 "•'.) a s c ompar ed t o D h a n j o r i i,' o l c 5 n i c = i j h e r e i t - a n g e =

f rom 2 .437 . t o 6,47"/i w i t h a h i g h e r a v e r a g e (.4.0Q7.) c o n t e n t .

MQO, uar>' ir iQ -from 3.29"' . t o 21.33;-': ' a ' ^ ' e r a g e S.BO"-.', i =

m o r e and CaO r a n g i n g in beti^-ieen 3 . SO''; a n d 1 3 . 7 6 " . f 9 " e r 9 q e

7 . 3 BV. > 1 = ] ess in J a g a n n a t h p u r ' o 1 c a n i c = a s c o m p a r e d t o

D h a n j o n y o l c a n i c s w h e r e t h e / 'i-B.r / f r o m 4 . 3 4 V . t o 11 .14"/.

( a v e r a g e 7 . 1 2;'-. > a n d 7 . 4 7:; t o 1 2 , 4 7": ' a - ' e r s g e 1 0 . l 2"'. •

r e s p e c t i v e I y .

Am o n g a l k a l i s , Na o 0 c o n t e n t i n b o t h C h a n i o r i a n d

J a g a n n a t h p u r u o l c a n i c s s e e m s t o be s i m i l a r a s i t ' , ' a r i e s f rom

0.80 ' / . t o 4.44'-'. and 0 .82 ' / . t o 3 .33 ' / . i-'Ji th t h e a v e r a g e = of 2 . 3 3 ' ' ;

a n d 2.C)8X r e s p e c t i v e l y . H o w e v e r , t h e i r 1^0 c o n t e n t s d i f f e r

c o n s i d e r a b l y . In D h a n j o n v o l c a n i c s i t y a r i e = f rom 0 . 15"'. t o

1.28' ' ; w i t h t h e a v e r a g e of 0.60'/. w h e r e a s i n J a g a n n a t h p u r

M o 1 c a n1c = i t a p p ea r s r e1 a t i M e1 / e n r i c h e d a n d r a n g e s f r o m

0.04"/. t o 3.177. w i t h t h e a v e r a g e of 1.18"/,.

P-iOc; c on t en t i n Dh a n j o r i 'J o 1 c a n i c = r a n g e s f r om

0.05"'-. t o 0.25*/. i â i ' e rage 0 .15 ' ' ; ) a n d a p p e a r s h i g h e r t h a n t h e

J a g a n n a t h p u r v o l c a n i c s w h e r e i t v a r i e s i^ i ide l - i n b e t K i e e n

0 , 0 3 ' ^ and o .407. w i t h a low a v e r a g e of O.i.07..

Mn 0 , in b o t h Dh an j o r i a n d J a g a n n a t h p u r v o 1 c a n i c s i s

q u i t e c ompar a b l e , r a n g i n g f r om 0 . 0 •^:. t o 0 . 25"-'. a n d 0 . 1 0'-'. t o

0.207. w i t h t h e a v e r a g e s of 0.137. and 0.167. r e s p e c t i v e l y .

42 EFFECT OF ALTERATION ON ROCK CHEMISTRY

Most o f t h e a n c i e n t v o l c a n i c roc i - s have undergone some

deqree oi a l t e r a t i o n , so t h a t t h e i r o r i g i n a l n a t u r e ma/ be

o b s c u r e . The mo = t c ommon t / p e = o-f a l t e r a t i o n i n c l u d e

a l b i t i z a t i o n , e p i d o t i z a t i o n , s i l i c 3 + i c a t i o n c a r b o n a t i o n and

ch 1 or 1 11 z a t 1 on . M i n e r a l a = sembl age= -formed b ' such t / p e s of

a l t e r a t i o n a r e s i m i l a r t o low grade metamorph ic a==emblage=

( J o l l / and S m i t h , 1972; Condi e e t a l . , I '???; S t r o n g et a l . ,

1979.''. In some i n s t a n c e s , these a l t e r a t i o n s occur pur e l - as

response t o p r o g r e s s i v e l o w - g r a d e r e g i o n a l metamorphism w h i l e

i n o t h e r cases secondary m i n e r a l s such as c a r b o n a t e , q u a r t r

and s e r i c i t e ma/ r e p l a c e low grade assemblage= and c r o s s c u t

f c D l i a t a o n , i n d i c a t i n g p o s t - metamorph ic a l t e r a t i o n ( Lond ie e t

a l . , 1977; C o n d i e , 1 9 8 2 b ) .

In i n t e r p r e t a t i o n s ba=ed on chemica l c h a r a c t e r i s t i c s of

a n c i e n t r o c U s , the most c r i t i c a l q u e s t i o n a r i s e s 5= t o what

was t h e i r o r i g i n a l c o m p o s i t i o n a n d t o iîhst e / t e n t t h e i r

chemica l c o n s t i t u e n t s haue been a f f e c t e d bv the a l t e r a t i o n

p r o c e s s e s . Numerous s t u d i e s document t h e m o b i l i t y o f / a r i o u s

e lements d u r i n g a l t e r a t i o n p rocesses Ce .g . L / s i t s ^ n a , 1 9 * 8 ;

Cann , 1 9 * 9 ; Babcoc l ' , 1 9 7 3 ; H a r t e t a l . , I 9 7 4 ; S c o t t and

H a j a s n , 1976; Condie e t a l . , 1977; BeswicI- and S o u c i e , i 9 7 S ) .

Ml t hough , t h e r e i s a gene ra l agreement i n these s t u d i e s t h a t

major e l emen ts such a s N a , K, Ca and Si a r e a p p r e c i a b l y

m o b i l e d u r i n g a l t e r a t i o n , t h e r e a r e c o n f l i c t i n g r e s u l t s of

m o b i l i t i e s o f many o t h e r e l e m e n t s • Jo I 1 / a n d S m i t h , 1 9 7 2 ;

Cond ie e t a l . , 1977; Hurr,phr 1 s and Thorr.pson, I ' - r Q . . Other

43

major e l emen ts such as ft 1203* M9O, FeO, T i 0 2 ) '^'z'-'f. ^'""^ ''^'''-

were c o n s i d e r e d e i t h e r l e s s m o b i l e or immob i l e and thu= hs' e

been used ' . ' a r i o u s l / i n p e t r o g e n e t i c i n te r pr e t a t 1 on = ^ e . g .

P e a r c e , 1970; M i / s s h i r o , 1 9 7 4 , 1 9 7 5 ; P e s r c e e t a l . , 197 ' ^ ;

M u l l e n , 1 9 8 3 ) . I t , t h e r e + o r e , seems a p p r o p r i a t e t o det t^ rmine

the e x t e n t and e + f e c t oi pos t igneous a l t e r a t i o n on the TDCI

c h em 1 s t r V b e -f o r e u s i n g t h e d a t a -for p e t r o g e n e t i c

i n t e r p r e t a t i o n s . S i g n i + i c a n t l y , D h a n j o n v o l c a n i i " 3 havp been

a-f- fected b> 1 011 g r a d e r e g i o n a l rrie tamor p h 1 =m as w e l l 3 =

s h e a r i n g movements t h e r e f o r e major c o m p o s i t i o n a l changes ms-/

be e x p e c t e d i n t h i s s u i t e . I n c o n t r a s t , J a g a n n a t h p u r

v o l c a n i c s a r e e s s e n t i a l 1 / u nmet amor p hosed ( .Baner jee , I 9 S 2 J

thus any major c o m p o s i t i o n a l change i s u n l i U e l - . Hoi/ie','er ,

some e 1 emen t mob1 1 1 t / due t o o t h e r a l t e r a t i o n p r o c e s s e s

cannot be r u l e d o u t . In the p r e s e n t s t u d / ' . ' s r ious d iagrams

and chemica l c r i t e r i a a r e used to i n v e s t i g a t e the p o s s i b l e

e x t e n t and e f - fec t o f a l t e r a t i o n on t h e c h e r r n c a l d a t a o f

D h a n j o n and Jagannathpur v o l c a n i c s .

A l k a l i e l emen t s a r e t h e p r i m e s u s p e c t o f a l t e r a t i o n .

Both D h a n j o n and Jagannathpur v o l c a n i c s show c o n s i d e r a b l e

v a r i a t i o n s i n t h e i r Na-.O and K-,0 c o n t e n t ( T a b l e ' ' l l l ^ . I n

Na'^0 - CaO - V-'-.Q t e r n a r y d i a g r a m ' F i g . 4 ' p l o t s o f

Jagannathpur •••olcanics shoiAi i n c l i n a t i o n to i - ia rd i ['••^0 a p e \ ,

s u gges t i n g t h e i r rrio r e p o t a s s i u m e n r i c h e d n a t u r e t h a r t h e

D h a n j o r i v o l c a n i c s . F u r t h e r , i n t^-,0 v e r s u s fla-nO d i a g r a m

^ F i g . 5 ; samples of bo th D h a n j o r i and Jagannathpur " o i c a n i c s

show w ide s c a t t e r . Thus, i n o rde r t o c l a r i f / t he n a t u r e and

e ; ; t en t o f m i g r a t i o n of t h e s e a l l - a l l e l e m e n t s , a i l t h e samples

44

Fig. 4. Na20 - CaO - K2O ternary variation diagram showing

KÔ enriched nature of Jagannathpur volcanics, as compared

to Dhanjori volcanics.

45

u

3

;^

O 2 id

1

0

-

••

t

0

• • •1

•

•

• • o

h •

1

•

•

• • • •

• •

: • > • • • • »

0 * "

° 1

oDHANJORI VOLCANICS

• JAGANNATHPUR VOLCANICS

•

0 0 0 0

) • e

1 1 2 3 A

Na20 %

Fig. 5. K-O versus ^^n^ binary diagram

showing scatter and random distribution of

these elements in Dhanjori and Jagannathpur

volcanics.

46

o-f D h a n j o r i a n d J a g a n n a t t i p u r v o l c a n i c s a r e p l o t t e d i n

Na':>0/KoO v e r s u s Na20 + K2O d i a g r a m ( F i g . 6) 0+ M i y a s h i r o

( 1 9 7 5 ) . As e v i d e n t from t h e f i g u r e a l l t h e a n a l y s e s , e x c e p t

o n e s a m p l e o-f Dhan jor 'x v o l c a n i c s , p l o t b e l o w t h e W'-M

d i s c r i m i n a t i o n c u r v e , t h u s s u g g e s t t h a t t h e i r bulk chemica l

c o m p o s i t i o n s h a s r e m a i n e d m o r e or l e s s u n a l t e r e d . The

p r o c e s s of s a u s s e r i t i z a t i o n a p p e a r s t o be a low t e m p e r a t u r e -

p r e s s u r e m i n e r a l og i c a l c h a n g e , n o t a + t e c t i n g t h e m a j o r

e lement c o m p o s i t i o n . As f a r a s e x t e n t 0+ m i g r a t i o n o-f Na20

and KoO i s c o n c e r n e d , i t a p p e a r s t h a t b a r r i n g some e r r a t i c

p l o t s w i th h igh Na20/K20 r a t i o , Na20 and K2O c o n t e n t s of

both Dhanjor i and J a g a n n a t h p u r v o l c a n i c s p r o b a b l y r e p r e s e n t

t h e i r p r i m a r y c h a r a c t e r . T h e p l o t s s h o w i n g h i g h N a 2 0 / K 2 0

r a t i o a r e p r o b a b l y c a u s e d by t h e d e c r e a s e of K2O c o n t e n t s a s

t h e i r NaÔ + K- O remain l ow . JIU. X..

S c h w e i t z e r and K r o n e r il9Q5) h a v e u s e d C a 0 / A l 2 0 3 -

MgO/lO - SiO.->/100 t e r n a r y d iagram t o r e c o g n i z e t h e a l t e r e d

v o l c a n i c r o c k s . In t h i s d i ag ram ( F i g . 7) most o-f t h e s a m p l e s

of Dhanjor i and J a g a n n a t h p u r v o l c a n i c s p l o t in t h e f i e l d of

u n a l t e r e d b a s a l t . Some of t h e s a m p l e s of J a g a n n a t h p u r

v o l c a n i c s show t h e i r i n c l i n a t i o n t o w a r d s t h e Mg-apex. T h i s

p r o b a b l y r e f l e c t t h e i r o r i g i n a l l y h igh MgO c o n t e n t s .

Al though b o t h Dhanjor i and J a g a n n a t h p u r v o l c a n i c s show

d i s t i n c t mgO and CaO c o n t e n t s , t h e i r T i 0 2 < a b u n d a n c e s a r e

q u i t e comparab l e ( T a b l e V I O . I t h a s been p o i n t e d ou t ( e . g .

Cann, 1970; P e a r c e a n d Cann , 1 9 7 3 ; P e a r c e e t a l . , 1 9 7 5 ;

W i n c h e s t e r anfl F l o y d , l 9 7 6 , i 9 7 7 ; M u l l e n , 1983) t h a t Ti and a

47

o CM

O CM

O z

200

100

50

10

5

1

0-5

\ ^

• A

• \

• \

\r% I' ° / •••

\ o • • \ 0° •

\ 0

1 1

—

0

\ . 0

0 s 0

• •

t . 4* •

* * — • •

0

•

1

Iceland tho len te

- Hawai ian t h o l e i i t e Abyssa l tho l i zd te

0 OHANJORI VOLCANICS • JAGANNATHPUR VOLCANICS

^"^---~,__^ Altered - V

\ Unoltered

. 1 ,,,. , 1 L

6 8 10

Na20 + K2O

12

Na-O/KpO v e r s u s Na20+K20 b i n a r y Fig.6,

diagram (after Miyashiro, 1975) showing

that the post igneous alteration in Dhanjori

and Jagannathpur volcanics has not effected

the whole rock alkali distribution.

48

CaO/AljOa

MgO/10 50 SiO2/100

Fig. 7. CaO/Al202 - MgO/10 - SiO2/100 ternary variation

diagram (after Schweitzer and Kroner, 1985) showing

unaltered nature of Dhanjori volcanics. All the samples

of Jagannathpur volcanics plotting towards MgO apex

have LOI less than 3.0%. Therefore high MgO in Jagannath.

pur volcanics is their primary magmatic chacater.

49

•

u z

z o < >

o z 5 z 1 S I < a -. o •

1 1

0 0

• • 0

• _ 0 •

• 0

• • •% • • • V .

• • o o 0

:l% ^ ^%

\ oc \

• • -<

• -• •

1 1 1

o

I 00

J «>

J«»

o

o u

H 00

-\ *o

•H U O •r-i C (0 J3 Q

M O 4-1

E (0 U 01 10

•H T3

> i U 10 c •H

o •H •P 0) X! •P (0

e CO

0)

4J

cn c

•H + j fO U •M (0 3

u • H •P (0 E D1 03 E

> i U (0 E

•H

•H 0) X!

O •H H

0 (0

u CO 3 CO

u (1) >

rM O EH

o

• 00 •

W •H b

H H • H

CO O

• H

c (0 o H 0 >

3 x: •M (0 C

c (0 D1 10 r-i

-a c ro

M 0

( P

c 0

• H 4-> (0 u • H TJ C •H

C (0

•H £1 CO

c 0 •H 4J 10 H CU U

• 0) •P U ro M (0 £ O

o o o m

^ O j i / O B W

o

0 OHANJORI VOICANICS • MOANNATHPUR VOLCANICS

<.r

O N

0

0 i»0

in

'^ 0-20

• • • •o •

•8 ,

2r

1 h •. •r'sc;* ••'•

0

20 -

15 -

10 -

o u.

0

20

18

16

14

12

10

'A',

oo o

• o

• o /

H V

J I

-1 I 10 16 20 25

MgO V.

0 20

0 10

9»« t •

O fM

O

o

15

13

11 h

O o o

1

58

56

54

i? 52

est

o Ji

50

oO . . oo o o .

0 . « „

0«

' o

48

46

'" o •/

• o .

Fig.9. MgO versus variou

plots for Dhanjori and J

J 1

10 15 20

MgO •/. 25

Du

s major element oxides (in wt%)

fagannathpur volcanics showing

distribution Of various elements relative to MgO.

51

number o-f other elements a.re not mobile during various

alteration processes including low grade metamorphism. Thus

in order to check the validity o-f MgO and CaO contents o-f

Dhanjori and Jagannathpur volcanics, their MgO/Ti02 <=ind

CaO/TiO' j ratios are plotted against each other (Fig. 8 ) . The

sympathetic relationships between these two ratios do not

indicate any impact o-f secondary alteration on these two

elements.

The above considerations do not show any marked

depletion or enrichment in the suspected mobile elements such

as Na20, K2O, CaO and Si02. Further more, the systematic

variations and good correlations of various elements with ngO

(Fig. 9) in both Dhanjori and Jagannathpur volcanics suggest

that their abundances are controlled by magmatic processes.

GENERAL GEOCHEmCAL CHARACTERISTICS

The major element analyses o-f Dhanjori and Jagannathpur

volcanics indicate large variations in most o-f the elements

within each rock suite (Table ^^11). Their average chemical

compositions when compared show noticeable di-f-f erences in

FeO* (total iron as FeO* = FeO - Fe203 X 0.9;», CaO, Ti02 and

P2O5 contents. Dhanjori volcanics contain high FeO*, CaO,

TiOj and PgOg contents and low Si02, MgO and K2O contents as

compared to Jagannathpur volcanics (Table VIIJ .

Variations in basalt chemistry are generally examined

with respect to MgO content or Mg-number (lOO MgO/MgO + FeO*

52

mole '/. w i t h Fe203/Fe0 r a t i o , 0 .15 ) s i n c e decreas i r iQ v a l u e s

r e f l e c t - f r a c t i o n a t i o n o-f l i q u i d u s o r n e a r l i q u i d u s

f e r r o m a g n e s i a n phases (Bowen, 1 9 2 8 ) . I t i s i n t e r e s t i n g t o

n o t e t h a t b o t h D h a n j o r i a n d J a g a n n a t h p u r v o l c a n i c s h a v e

d i f f e r e n t Mg-numbers a t s i m i l a r MgO c o n t e n t s and v i c e v e r s a .

I n D h a n j o r i v o l c a n i c s Mg-numbers range f r om 6 7 . 0 8 t o 42 .18

and most o f t he samples (abou t 857.) have Mg-numbers < 6 0 . 0 .

On t h e o t h e r hand , Mg-numbers i n Jaganna thpur v o l c a n i c s v a r y

f r om 82.4<6 t o 38 .39 a n d m o s t o f t h e s a m p l e s c a b o u t 697.)

c o n t a i n M g - n u m b e r s > 6 0 . 0 . The S i 0 2 c o n t e n t s o f t h e s e

v o l c a n i c s u i t e s a r e h i g h e r than t h a t o f t h e e x p e c t e d v a l u e s

a t s i m i l a r Mg-numbers i n mid ocean i c r i d g e b a s a l t s (MORE) and

K o m a t i i t e s ( F i g . 1 0 ) . The a n a l y t i c a l d a t a of D h a n j o r i and

Jaganna thpu r v o l c a n i c s i n d i c a t e t h a t t h e y can be g rouped as

b a s a l t s , b a s a l t i c a n d e s i t e s a n d a n d e s i t e s on t h e b a s i s o f

t h e i r SiO-> c o n t e n t s s i n c e t h e u p p e r l i m i t o f b a s a l t a n d

a n d e s i t e have been t a k e n a r b i t r a r i l y a t 5 2 . 0 7 , 5 7 . 0 7 a n d

63 .07 S i02 r e s p e c t i v e l y ( M i d d l e m o s t , 1980; Le M a i t r e , 1984;

Le Bas e t a l . , 1 9 8 6 ) . T h e i r l ow a l u m i n a a n d h i g h FeO*

c o n t e n t s o f h i g n SiU2 samples do not p e r m i t t o c l a s s i f y them

s t r i c t l y as a n d e s i t e s . A c c o r d i n g t o I r v i n e a n d B a r a o a r

(1971) and B a i l e y <.l981) Al 2O3 and FeO* c o n t e n t s of a n d e s i t e

s h o u l d r a n g e +rom 1 6 . 0 7 t o 2 1 . 0 7 a n d 5 . 0 7 t o 8 . 5 7

r e s p e c t i v e l y and t h e i r A l 2 0 3 / F e 0 * r a t i o s h o u l d be g r e a t e r

t h a n 2 . 0 ( M i d d l e m o s t , 1 9 8 0 ) . I n b o t h D h a n j o r i a n d

Jagannathpur v o l c a n i c s AI2O3 c o n t e n t a l w a y s t end t o be lower

than 16 .07 and FeO* g r e a t e r t h a n 9 . 0 7 . M o r e o v e r , t h e i r

A l 2 0 3 / F e 0 * r a t i o s a r e a l w a y s l e s s than 2 .0 and t hus they do

53

75

70

65

, - 60

O

to 55

5 0 H

(,S

0.30

O DHANJORI VOLCANICS


Bonin Islands ond CapeVogel volconics

o%°MOR Komatiites

0.90 O.AO 0.50 0,60 0.70 0.80

Mg-Number (osMg/Mg + I Fe )

Fig.10. Mg-number versus SiO^ binary diagram (after

Hickey and Frey, 1982) for Dhanjori and Jagannathpur

volcanics showing enrichment of SiO^ in comparison to

MORE and komatiite.

54

Fig. 11. A(Na20 + K_0)-F(FeO) - M(MgO) ternary diagram

showing iron enrichment trend in Dhanjori volcanics

and iron depletion trend in Jagannathpur volcanics.

55

not support their andesi te character. As far as MgO and

total alkali <Na20 + K2O) contents are concern, Dhanjori

volcanics contain similar values to that o-f basalts and

alongwith the high FeO , show their tholeiitic basalt nature

(Fig. 11). On the otherhand, Jagannathpur volcanics, showing

wide variations in their MgO and total alkalis and alongwith

relatively lower FeD* contents appear to be o-f transitional

nature (Fig. 11). It there-fore leads to conclude that both

volcanic suites probably have distinct basaltic compositions.

Glikson (1983) has used MgO content and MgO/Al2O3 ratio

to distinguish the high-Mg basalts and tholeiitic basalts.

He (op.cit) placed the boundary between these two at about

lO.OVi or above 8.07. MgO and Mg0/Al203 ratio higher than 0.6.

According to this criteria, 40"/; samples ot Dhanjori volcanics

and 51% samples o-f Jagannathpur volcanics Are -found to be

high-Mg basalts while the rest 0+ the samples of Dhanjori and

Jagannathpur volcanics are considered as tholeiite basalts.

Among the high -Mg basalts, the terms basaltic

komatiite and boninite have attracted considerable attention

during the last decade (Brooks and Hart, 1974; Kuroda et al .,

1978; Cameron et al , 1979; Nesbitt et a I., 1979; Hickey and

Frey, 1982). Chemically the basaltic komatiites are

characterized by MgO > 9.0/.; Ca0/Al203 > 1; K2O and Ti02 <

0.9"/. and SiO^, 45/. to 53.0% (Brooks and Hart, l97^> . It is

interesting to note that not a single sample of Dhanjori and

Jagannathpur volcanics is found to obey the above criteria.

Therefore, samples containing high MgO contents in both

56

volcanic suites cannot be considered as basaltic komatiites .

In terms o-f n o r m a t i y e c o m p o s i t i o n , excep t one sample o-f

D h a n j o r i v o l c a n i c s a n d t h r e e s a m p l e s O'f J a g a n n a t h p u r

v o l c a n i c s , a l l o t h e r rock samples c o n t a i n n o r m a t i v e q u a r t z .

The r e m a i n i n g + o u r s a m p l e s b e l o n g i n g t o D h a n j o r i a n d

Jaganna thpur v o l c a n i c s u i t e s c o n t a i n n o r m a t i v e o l i v i n e (Tab le

I I I and IK>) . A l t h o u g h , i d e n t i c a l p l o t s o f bo th s u i t e s a r e

obse rved i n n o r m a t i v e N e - 0 1 - D i - H y p - Q t z c o m p o s i t i o n a l d iag ram

< F i g . 1 2 ) , marked d i f f e r e n c e s e x i s t m n o r m a t i v e c o m p o s i t i o n s

o+ t hese v o l c a n i c s u i t e s . Except one , a l l t he o t h e r rock

samples of D h a n j o r i v o l c a n i c s u i t e c o n t a i n h i g h e r d i o p s i d e

c o n t e n t than h y p e r s t h e n e c o n t e n t ( T a b l e I I T ^ . On tne o t h e r

h a n d , i n Jaganna thpu r v o l c a n i c s , e x c e p t f i v e s a m p l e s , a l l t h e

o t h e r rock samples c o n t a i n more h y p e r s t h e n e than d i o p s i d e

( T a b l e IV) wh i ch has been c o n s i d e r e d as a c h a r a c t e r i s t i c o f

m a f i c c a l c - a l k a l i n e e x t r u s i v e s ( W i l k i n s o n , 1 9 8 6 ) . I n

c o n t r a s t t o D h a n j o r i v o l c a n i c s , a b o u t 6 2'/. s a m p l e s o f

Jagannathpur v o l c a n i c s have n o r m a t i v e d i o p s i d e c o n t e n t l e s s

than 15.OX. Among these samp les , abou t 24>i samples c o n t a i n

v e r y 1 ow no rma t i v e d i o p s i d e ( l e s s t h a n l O . O v : ) , w h i c h

a c c o r d i n g t o Kuroda e t a l . , w 9 7 8 ) i s a c h a r a c t e r i s t i c

f e a t u r e of b o n i n i t e .

Among the q u a r t z n o r m a t i v e s a m p l e s o f t h e s e v o l c a n i c

s u i t e s , 58y. samples o f D h a n j o r i v o l c a n i c s and 22X samples o f

Jagannathpur v o l c a n i c s c o n t a i n n o r m a t i v e q u a r t z l e s s than

S.O'A whereas abou t 42'/. samples o f D h a n j o r i v o l c a n i c s and 787.

samples of J a g a n n a t h p u r v o l c a n i c s g r e a t e r t h a n 5.07. n o r m a t i v e

u 3 a JC 4J

<o c c (0 en ID <r>

n c <a •H M 0

c ITJ

x: Q

M 0 tM

E ro M CD (0 •H T3

c 0 •H -P (0

•H M <0 > N •P

o 1 CI > 1

1 •H Q 1

H O 1 (U

z 0) >

•H •P (0 E M 0 2

• fM iH

• 0)

•H h

0) C <D £ •P CO M Q) 0. > i

x; k

(D C •H >

•H H 0

0) >

•H •P (0 p

p 0 c

4-1 0

(0 c 0

•H +J M 0 o< 0 U d

0) >

•H •P (0 H 0) M

0) i 3 •P

c •H •P 10 u •p (0 D

H H •H

(0 O

•H C ID O H 0 >

• (U >

•H •P ID E U 0 c N -P ^l ID D CT

> i

H -P C ID C

•H E 0 T3 0) V

a <D u ID

CO

u •H

c ID U H 0 >

d)

-p

£ +j 0 CQ

• N •P u (0 3 cr

T3 c ID

0) T3 •H CO a 0

•H T3

58

q u a r t z . T h e r e f o r e , a c c o r d i n g t o W i l k i n s o n '.1986) t h e s e

samples may be c l a s s i - f i e d as t h o l e l i t e s and q u a r t s t h o l e l i t e s

r e s p e c t i v e I y .

Di-f-f e ren t i a t i on index ( T h o r n t o n and T u t t l e , I960) i s a

numer i ca l e x p r e s s i o n o-f t h e e x t e n t t o w h i c h a magma h a s

di-f-f e ren t i a t e d . I t r e p r e s e n t s t h e sum of w e i g h t p e r c e n t a g e s

of n o r m a t i v e q u a r t z , o r t h o c l a s e , a l b i t e , n e p h e l i n e , l e u c i t e

and k a l s i l i t e ( D . I . = Qtz + Or + ab + Ne + 1 eu + Rs) , t h u s I t

measures t h e r o c k s ' s b a s i c i t y . The upper l i m i t o f u l t r a m a f i c

d i f f e r e n t i a t e s i s 10 where~as e a r l y s t a g e , m i d d l e s t a g e and

l a t e s t a g e b a s a l t i c d i f f e r e n t i a t e s l i m i t a t 1 6 , 3 0 a n d 50

r e s p e c t i v e l y . The r o c k s c o n t a i n i n g D . I . >50 are d e s i g n a t e d

a s f e l s i c d i f f e r e n t i a t e s ( T h o r n t o n a n d T u t t l e , l 9 6 0 ; > . i n

D h a n j o r i v o l c a n i c s about 75/i samples a r e m i d d l e s t a g e b a s a l t s

as t h e i r D . I . r anges f rom 16 t o 30 and t h e r e s t 25X samples

appear as l a t e s t a g e b a s a l t s because t h e i r D . I . v a n e s i n

between 30 and 50 ( T a b l e K>lll). On t h e o t h e r h a n d , i n

Jaganna thpu r v o l c a n i c s , 6"/. sample a r e e a r l y s t a g e ( D . I . >10 <.

li>) , lyy. samples a r e m i d d l e s t a g e ( D . T . >\6 < 3 0 ) , and 717.

s a m p l e s a r e l a t e s t a g e ( D . I . >30 < 5 0 ; b a s a l t i c

d i f f e r e n t i a t e s . A b o u t 6'/. s a m p l e s a p p e a r a s f e l s i c

d i t + e r e n t i a t e s w i t h D . I . >50 ( T a b l e I X ) . I t t h e r e f o r e

appears t h a t D h a n j o r i v o l c a n i c s a r e l e s s d i f f e r e n t i a t e d than

t h e Jaganna thpu r vo l cane i s .

MAJOR ELEMENT V A R l A B l L l T r

Chemical d i f f e r e n c e s b e t w e e n v o l c a n i c r o c k s can be

u n d e r s t o o d l a r g e l y i n t e r m s o+ c r y s t a l l i z a t i o n

59

d i - f - f e r e n t i a t i o n a n d q u a ! i t a t i l T v e l y can be r e l a t e d t o t h e

c r y s t a l l i z a t i o n o f common i g n e o u s m i n e r a l s . C h e m i c a l

v a r i a t i o n d i ag rams show t h e r e l a t i o n s h i p between t h e e l e m e n t s

and g i v e an i n d i c a t i o n o f t he s t a t e o f d i f f e r e n t i a t i o n . I n

t h e p r e s e n t s e c t i o n m a j o r e l e m e n t o x i d e s o f D h a n j o r i a n d

J a g a n n a t h p u r y o l c a n i c s a r e p l o t t e d a g a i n s t d i f f e r e n t

p a r a m e t e r s t o see t h e c h e m i c a l d i f f e r e n c e s b e t w e e n t h e s e

s u i t e s . These d i f f e r e n c e s w i l l be u s e f u l t o f i n d o u t t h e

o r i g i n and e v o l u t i o n o f t h e s e r o c k s .

In F i g . 13 v a r i o u s m a j o r e l e m e n t s o+ D h a n j o r i a n d

Jagannathpur v o l c a n i c s a r e p l o t t e d a g a i n s t t h e i r FeO*/MgO

r a t i o wh ich has been c o n s i d e r e d a s a m e a s u r e o f a d v a n c e d

f r a c t i o n a l c r y s t a l l i z a t i o n ( M i y a s h i r o , 1974, 1 9 7 5 ) . I t i s

e v i d e n t f r om the F i g . 13 t h a t some of ma jo r e lement o x i d e

( e . g . MgO, CaO, T iOo and FeO + Fe203> show t r e n d c o n s i s t e n t

w i t h the e v o l v i n g magma? the o t h e r e l emen ts show s c a t t e r e d

p l o t s . Decrease of MgO and CaO and an i n c r e a s e of S1O2 w i t h

i n c r e a s i n g FeO*/MgO r a t i o i n bo th v o l c a n i c s u i t e s p r o b a b l y

i n d i c a t e p a r t i t i o n i n g o f c 1 i n op y r o x en e r a t h e r t h a n t h e

o l i v i n e . C o n t r a r y t o D h a n j o r i v o l c a n i c s , t r e n d s of FeO* and

TiOo i n Jaganna thpur v o l c a n i c s remain a l m o s t p a r a l l e l and

show l i t t l e i n c r e a s e . T h i s s u g g e s t s t h a t t h e i r d i s t r i b u t i o n

may h a v e been m o r e c o n t r o l l e d by m a g n e t i t e o r t i t a n o -

m a g n e t i t e s e p a r a t i o n . I n D h a n j o r i v o l c a n i c s FeO* and T iO^ do

not have a p a r a l l e l t r e n d and moreover FeO* shows a l a r g e

i n c r e a s e w i t h i n c r e a s i n g FeO*/hgO r a t i o , t h e r e f o r e m a g n e t i t e

o r t i t a n o - m a g n e t i t e s e p a r a t i o n i s u n l i k e l y . The i n c r e a s e of

60

0'25

c 0-15

0-05

01

0 00 .»„ 0 •

o

O rsi

O.

1

c

0-6

0-4

0-2

» , •» • • •

0 » °0 0 0,

V t

J

o z 't .• 08.V.V

0

0 • 0 ,

0

25

20

I" 15

• I

• • • • »*.o

r o OHANJORI VOLCANICS • JAGANNATHPUR VOLCANICS

0

18

o «; 15

10

i ; ^ * ^

' 2 3

P«0VMg0

0 fiS ••/•'' \ ?%'•.-•

u o 0 10

5h

o« 6 0 ogo '

O

60

55

50

• t

0 9 , 0

o <

45

20

15

10

. » • ?

• - . r* '?^: o''

J - _L ' 2 3

PeO* / MgO

Fig.13. FeO*/MgO versus

plots for Dhanjori and Jagannathpur volcani fractionation trends of different elements.

various major element oxides

cs showing

61

Al-nOo and a decrease o+ CaO with increasing FeO / H Q O m

Jagannathpur volcanics probably re-flects the absence o-f

a large degree of plagioclase fractionation. On the other

hand, in Dhanjon volcanics decreasing CaO content with

somewhat constant ^1203 content with increasing FeO /MgO may

be suggestive of plagioclase fractionation.

According to Hanson and Langmuir (1978), Mg-number is

sensitive to olivine fractionation and since T1O2 acts as a

relatively magmaphile element (olivine or plagioclase Kd =

0.01, Dungan and Rhodes, 1978>, the relationship between

these two would clearly indicate olivine fractionation in

Dhanjori and Jagannathpur volcanics. In Fig. 14, T102

contents of Dhanjon and Jagannathpur volcanics are plotted

against their Mg-numbers alongwith the olivine fractionation

path calculated by Dungan and Rhodes 11978). It appears that

samples of Dhanjon volcanics have undergone more than 1 OX

olivine fractionation whereas in Jagannathpur volcanics,

majority of the samples fractionated less than 107. olivine.

Ca0/Al203 ratio has been considered as one of the most

important characteristic of the basic volcanic roci-s since in

the primary melts it reflects the ratio of their mantle

source (Cawthorn and Strong, 1974; Perfit et al., 1980;'. In

Dhanjon and Jagannathpur volcanics CaO/Al2O3 ratio varies

from 0.53 to 1.65 and 0.28 to 1.22 with the averages 0.90 and

0.59 respectively. About 55% samples of Dhanjori volcanics

and 92'/. samples of Jagannathpur volcanics contain Ca0/Al203

ratio lower than chondnte or primitive upper mantle value

62

3

^

o 2 H

1

O

— •

DHANJORI VOLCANICS

JAGANNATHPUR VOLCANICS

Olivine fractionation path from primit ive,parental composition

° •

• •

1 1 1 1 1

30 40 50 60 70 M9- Number

80 90

Fig.14. Mg-number versus Ti02 binary diagram

(after Dungan and Rohdes, 1978) for Dhanjori

and Jagannathpur volcanics showing relative

olivine fractionation in these volcanics.

63

(0.9; Clauge and Frey, 1982). The lower Ca0/Al203 ratio,

alongwith the intermediate S1O2 content and high Mg-numbers,

as -found in these yolcanics, has been considered as the

characteristic •feature o-f low Ti-ophiol 11 ic and boninitic

lavas (Beccaluva and Serri, 1988).

TiOo contents o-f both Dhanjon and Jagannathpur

Molcanics are however higher <Table Vl1> than boninite and

low Ti-ophiolite lavas U0.5"/; Meijer, 1980; HicWey and Frey,

1982; Cameron et al . , 1983; Craw-ford and Cameron, 1985;

Bloomer and Hawkins, 1937; Beccaluva and Serri, l988>. Fig.

15 illustrates the relationship between Ca0/Al203 ratio and

TiQ.- contents o-f Dhanjon and Jagannathpur volcanics. During

plagioclase removal Ca0/Al203 ratio will increase whereas it

will be constant during olivine -fractionation <;Dungan and

Rhodes, 1978). It there-fore seems reasonable that all the

samples which have high Ca0/Al203 ratio (.greater than 0.9)

might have undergone plagioclase fractionation.

Per-fit et al., <1980) have noted that increasing

Ca0/Al203 ratio with decreasing MgO as observed in MORB can

be attributed to the fractional crystallization of olivine

and plagioclase whereas a positive correlation of CaO/AI-nO^

ratio with MgO is suggestive of c11nopyroxene fractionation.

In order to evaluate the role of c 1 i nop y r ox en e and/or

plagioclase during magmatic differentiation of Dhanjon and

Jagannathpur volcanics their MgO contents are plotted against

their CaO/AlgOg ratio (Fig. 16). The observed sympathetic

relationships indicate that plagioclase could not be a major

64

1.8 -

1.6

1.4

1.2

o 0.8 o

0.6

O.A -

0.2 -

"a

E

- «

-1 a

—

o

•

Olivine Removal

0

** o

•

o •

• • •

•• t • •

DHANJORI VOLCANICS

JAGANNATHPUR VOLCANICS o

o

•

• • •

. • • •

I 1 1

•

o

o o 0

o •

o • • o

• • •

•

•

1 1 1

0.2 OA 0.6 0.8

Ti02 % 1.0 1.2 1.4 1.6

Fig.15. Ti02 versus CaO/Al-O^variation diagram

(after Dungan and Rhodes, 1978) showing relative

olivine and plagioclase fractionation in Dhanjori


66

2.0

0

O OHANJORI VOLCANICS


<») o S^ < 1.0 o 0 (J

•

• • •

o°.

.%. V

_L X 8 12 16

MgO V. 20 2A

Fig.16. MgO versus CaO/Al-O^ binary diagram

(After Bence et al. , 1979) for Dhanjbri and

Jagannathpur volcanics exhibiting positive

relationships between them, an indication of

clinopyroxene fractionation.

66

• f r a c t i o n a t i n g phase in these v o l c a n i c s u i t e s . I n absence o f

l a r g e s c a l e p l a g i o c l a s e - f r a c t i o n a t i o n , i t appea rs t h a t low

a l u m i n a c o n t e n t s o-f D h a n j o r i and Jaganna thpur v o l c a n i c s may

r e - f l e c t e i t h e r f r a c t i o n a t i o n or t he p resence of a r e s i d u a l

a l u m i n o u s phase i . e . g a r n e t or s p i n e l ( N e s b i t t e t a l . , 1979).

The low AI2O3 c o n t e n t o f t h e m e l t i n e q u i l i b r i u m w i t h g a r n e t

c o n t a i n i n g 2Z/. AI2O3 i s f i x e d t o abou t 11"/. as a l u m i n a i s an

e s s e n t i a l s t r u c t u r a l c o n s t i t u e n t i n g a r n e t a n d t h e Kd f o r

Al/^jOg between g a r n e t a n d m e l t i s a b o u t 2 < L a n g m u i r a n d

Hanson, 1980) .

A loOo/T iOo and CaO/TiOo r a t i o of t he b a s a l t i c r o c k s has

been v a r i o u s l y i n t e r p r e t e d < e . g . Sun a n d N e s b i t t , 1 9 7 8 ;

N e s b i t t e t a l . , l 9 7 9 ; Sun e t a l . , 1 9 7 9 ; H i c U e y a n d F r e y ,

l9Q2) . A l 2 0 3 / T i 0 2 a n d C a O / T i 0 2 r a t i o s o f D h a n j o r i a n d

J a g a n n a t h p u r v o l c a n i c s a r e p l o t t e d a g a i n s t t h e i r T i 0 2

c o n t e n t s i n F i g . 17 . A l 2 0 3 / T i 0 2 r a t i o s o f t hese v o l c a n i c s

p l o t t h rough a l m o s t t h e w h o l e f i e l d o f m i d - o c e a n i c r i d g e

b a s a l t < MORE J and beyond towards lower TiO-p c o n t e n t s < F i g .

17a.). Ca0 /T i02 r a t i o s p l o t s r e m a r k a b l y be low t h e f i e l d o f

MORE and beyond , s h o w i n g s i m i l a r g r a d u a l i n c r e a s e w i t h

d e c r e a s i n g T i 0 2 c o n t e n t s t F i g . 1 7 b ) . S i n c e b o t h Al 203 /7102

and CaO/TiO-^ r a t i o s i n t hese v o l c a n i c s u i t e s a r e below t h e i r

r e s p e c t i v e c h o n d r i t i c v a l u e (20 and 17 r e s p e c t i v e l y ) i t l e a d s

t o i n f e r t h a t T i i s c o m p a t i b l e and Al and Ca a r e h e l d i n t h e

r e s i d u a l phases such as p y r o x e n e , g a r n e t , p l a g i o c l a s e and

spinel (Sun e t a l . , l 9 7 9 ) .

67

60

4 0

O

20

O O H A N J O n i V 0 L C A N I C 5

• JA G A N M A T H P U R V O L C A N I C S

. A r c h s Q n PK a n d h igh Mg b a s a l t s

B a r b e r t o n K o m a t n t e s

J I I L X

( a )

C H O N D R r T E

0 4 0 8 1.2

ri02*/«

1.6 2.0

4 0

O

o rJ o

20 z . A r c h o f i n PK nnd

high Mg b a s a l t s

M >^

^

-L X I

( b )

CHONDRITE

0 4 0,0 1 2

T1O2V.

1 6 2 0

Fig. 17. (a) Ti02 ^^^ûs Al_0.,/Ti02 binary diagram and

(b) TiO^ versus CaO/TiO^ binary diagram for Dhanjori

and Jaqannathpur volcanics indicating compatible nature

of Ti02 and holding of M-0, and CaO by the residual source.

6S

It is considered that K2O ncl Ti02 îre mainly

concentrated into the liquid through partial melting

processes, because the -former has a large ion radius and the

latter has large charge. There-fore, the K20/Ti02 ratio in a

magma remains nearly equal to that of the source material and

it is an indicator o-f the chemical character o-f the source

mantle material until a KÔ rich or TiOo rich phase begins to

crystallize (.Tatsumi and Ishizkd, 1982J. The K2O and Ti02

contents o-f Dhanjori volcanics (0.157. to 1.28'/: and 0.597. to

1.56'/:) show a sympathetic relationship <Fig. 18) and their

K^0/Ti02 ratios are low ^ 0 .20 to l.l2). This probably

indicates that K2O and Ti02 are occurring in the same mineral

phase. In contrast, K2O and Ti02 contents in Jagannathpur

volcanics (0.047. to 3.177. and 0.407. to 1.497. respectively) do

not show any relationship with each other and their K2O

contents are high in relation to Ti02 <Fig. 18). It,

there-fore, appears that high K-pO/Ti02 ratios o-f Jagannathpur

yolcanics (.0.04 to 5.46) indicate the -f rac t'lonat i on 0+ a Ti-

rich phase probably magnetite or titano-magnetite.

In Fig. 19 P2O5 contents- o-f Dhanjori and Jagannathpur

yolcanics are plotted against their T1O2 contents^ alongwith

the chondrite ratio and -field o-f mid-oceanic ridge basalt

(MORB) . Although, the data -from both volcanic suites show

sympathetic relationships, the absence o-f col linearity

between these elements and inconsistancy with chondrite ratio

is noteworthy. Since the abundance ot P2O5 seems related to

the degree o-f partial melting and initial composition o-f the

melt rather than the -trac t i ona t i on o-f any phase (Mullen,

69

3.5

O 20

1.0 -

-

-

•

•

•

•

•

• •

• •

• o

• i •^ oo

o

0

c

•

0 DHANJORI VOLCANICS

• JAGANNATHPUR VOLCANIM

• •

• • •

• •

O

° o 0 o o

o

O Chondfîl___-

1 1

0.5 1.0

Ti02 •/•

1 5 2.0

Fig.18. K2O versus Ti02 binary diagram

for Dhanjori and Jagannathpur volcanics

indicating a sympathetic relationship

between these elements in Dhanjori

volcanics.

7o

0 0

O OMANJORI VOLCANICS

• JAOANNATHPUR VOLCANICS

OO

• O

•• o

05 1 0

T1O2 V.

1.5 2.0

Fig.19. Ti02 versus P2O5 variation diagram showing

compatible (non-chondritic) behaviour of these elements

in Dhanjori and Jagannathpur volcanics.

1 9 8 3 ) , i t a p p e a r s t h a t d u r i n g m a g m a t i c e v o l u t i o n o-f t h e s e

v o l c a n i c s T i behaved as a c o m p a t i b l e e l e m e n t .

M i y a s h i r o (1974) obse rved t h a t v a r i a t i o n o-f TiOo c o n t e n t

i n c a l c - a l k a l i n e and t h o l e i i t e magma s e r i e s a r e more or l e s s

s i m i l a r t o t hose o-f FeO* ( t o t a l i r o n as FeO = FeO + FeOg a.

0 . 9 ) c o n t e n t and sugges ted t h a t v a r i a t i o n s i n T1O2 and FeO

c o n t e n t s o-f the magma a r e l a r g e l y c o n t r o l l e d b / t h e same

• f a c t o r - p o s s i b l y t h e o x y g e n - f u g a c i t y . Unde r h i g h o x y g e n

• f u g a c i t y , i n c a l c - a l k a l i n e s e r i e s , m a g n e t i t e w o u l d

c r y s t a l l i z e a t a r e l a t i v e l y e a r l y s t a g e , l e a d i n g t o d e p l e t i o n

o-f r e s i d u a l magma i n T i and Fe and compl imen t a r - ' e n r i c h m e n t

i n S1O2 whereas under low oxygen - f u g a c i t y as i n t h o l e i i t e

s e r i e s , e a r l y c r y s t a l l i z a t i o n w o u l d be domina ted by o l i v i n e

and c l i n o p y r o x e n e and hence T i and Fe a r e not so s t r o n g l y

removed -from the magma. When T1O-, c o n t e n t s o-f D h a n j o r i and

Jagannathpur v o l c a n i c s p l o t t e d a g a i n s t t h e i r FeO c o n t e n t s ,

s y m p a t h e t i c r e l a t i o n s h i p s a r e obse rved < F i g . 20) i n d i c a t i n g

gene ra l coherance o-f T i a n d Fe i n b o t h v o l c a n i c s u i t e s .

However , t h e i r d i s t i n c t t r e n d s Bre n o t e w o r t h y .

S ince m a g n e t i t e or t 1 t a n o - m a g n e t i t e c r y s t a l l i z a t i o n i s

c o n t r o l l e d by the o x y g e n p r e s s u r e o-f t h e magma a n d t h e

^^2°3^ '^®° r a t i o i s a measure o-f oxygen p r e s s u r e o-f t h e magma,

Fe203/Fe0 r a t i o s o f D h a n j o n <0.24 t o 0 .64 ) and Jaganna thpur

( 0 . 2 3 t o 1.32) v o l c a n i c s a r e p l o t t e d a g a i n s t t h e i r F e O *

c o n t e n t s ( F i g . 2 1 ) . A l t h o u g h , s y m p a t h e t i c r e l a t i o n s h i p s a r e

observed i n b o t h v o l c a n i c s u i t e s , t h e low Fe2a3/Fe0 r a t i o and

h i g h i r o n c o n c e n t r a t i o n o f D h a n j o n v o l c a n i c s a r e i n a c c o r d

n

20

15

iL 10 o it u.

O u.

o o

oo • ' • °

• • o

O O H A N J O R I V O L C A N I C S

• J A O A N N A T H P U R VOLCANICS

X 0.5 1.0

T1O2V.

1.5

Fig.20. FeO versus Ti02 binary variation

diagram illustrating the sympathetic behaviour

of these elements in Dhanjori and

Jagannathpur volcanics.

73

1-0

0-8

o »> u.

o fsi *>

0.6

Oi,

0-2

O DHANJORl VOLCANICS •


t (1.32)

o ^

•o o o (?

o

10 12 U re FeO'=(FeO*Fe203 xO-9)Vo

18 20

Fig. 21. FeO versus Fe202/FeO binary diagram for

Dhanjori and Jagannathpur volcanics showing

sympathetic relationships between them, an indication

for their generation in relatively higher oxidation

conditions than the mid-oceanic ridge basalt (MORB).

74

w i t h the o b s e r v a t i o n s o-f Walker and P o l d e r v a a r t a 9 4 9 ; ' and

Kuno a 9 6 5 ) , who f o u n d t h a t Fe203/Fe0 r a t i o s t end t o be low

i n h i g h i r o n c o n c e n t r a t i o n t y p e of f r a c t i o n a t i o n . The h i g h

Fe-jOo/Feo r a t i o s and l o w FeO* c o n t e n t s o f J a g a n n a t h p u r

v o l c a n i c s , p r o b a b l y i m p l y h i g h oxygen p r e s s u r e of t he magma,

wh ich i n t u r n i n d u c e d e a r l i e r s e p a r a t i o n o f m a g n e t i t e o r

t i t a n o - m a g n e t i t e .

M u l l e n <1983> has p o i n t e d o u t t h a t u n d e r h i g h o x y g e n

f u g a c i t y , as i n a r c magmas , e a r l y m a g n e t i t e o r t i t a n o -

m a g n e t i t e f r a c t i o n a t i o n d e p l e t e s the magma i n T i O j r e l a t i v e

t o MnO a b u n d a n c e s w h i l e u n d e r r e l a t i v e l y l o w e r o x y g e n

•Fugaci ty a m p h i b o l e f r a c t i o n a t i o n a l s o d e p l e t e s the magma i n

TiOo bu t w i t h r e l a t i v e e n r i c h m e n t o f MnO c o n t e n t . I n

c o n t r a s t , under v e r y l ow o x y g e n f u g a c i t y , i n m i d - o c e a n i c

r i d g e and ocean i s l a n d t h o l e i i t e s , e a r l y f r a c t i o n a t i o n o f

o l i v i n e and c l i n o p y r o x e n e d e p l e t e s t h e magma i n MnO r e l a t i v e

t o T i O o a b u n d a n c e s . MnO/TiO/p r a t i o s o f D h a n j o r i a n d

Jagannathpur v o l c a n i c s when p l o t t e d a g a i n s t t h e i r T i 0 2

c o n t e n t s show a n t i p a t h e t i c r e l a t i o n s h i p s ( . F i g . 2 2 ) . An

i n c r e a s i n g t r e n d of M n O / T i 0 2 r a t i o w i t h d e c r e a s i n g T i 0 2

c o n t e n t s i n D h a n j o r i v o l c a n i c s , a l o n g w i t h t h e e a r l i e r

c o n s i d e r a t i o n s v i s . s y m p a t h e t i c r e l a t i o n s h i p s between KÔ and

T i 0 2 , ^2^5 ^"^ T i 0 2 ' P ^ ° * ^^^ ' ' " i ° 2 ' ^ " ^ ^^'3^ Fe2D3/FeO r a t i o

and i t s s y m p a t h e t i c r e l a t i o n s h i p w i t h FeO* s h o u l d sugges t

a m p h i b o l e f r a c t i o n a t i o n whereas i n Jaganna thpur v o l c a n i c s i t

i n d i c a t e s m a g n e t i t e o r t i n a t o - m a g n e t i t e f r a c t i o n a t i o n .

75

o •si U

0 (M

E (0

u (0

•H -o >1

10

c •H

(N O

O <M ~^

-• .° o •- c s (0 3 (0 U

>

CM

o •H H

• fM f^

• 0) •H

fa

01

c •H •M •H

•H

X 0)

to u •H

c It) o H 0

>

M 3 0 .

J3 -P It] C c •0 en It} T)

c 10

•H M 0 •n C ITJ J3 Q

U 0

m

c o •H +J (0

•H •0 c

•H

C ItJ

^ a •H X! CO c 0

•H 4J ItJ H 0)

O •H •P 4) J3 •P It]

a •H + j

c 10

• c 0

•H •P 10

c o •H •P U 10

u (p

0) H 0

xs OJ

E 10

O

C 10

0)

•H •P

c 01 10 E 1 0 c 10 +J •H •p

o ^0! i /OUM

CHAPTER IV

TRACE ELEMENT GEOCHEMISTRY

GENERAL STATEMENT

Trace elements, having several distinct advantages over

the major elements, provide power-ful tools -for tracing or

modeling the igneous fractionation processes (e.g. Neumann et

al., 1954; Gast, 1968; Greenland, 1970; Paster et a1 ., 1974;

Allgere et al . , 1977; Hanson, 1980; Carr and Fardy, 1984).

The trace element concentration of a melt is dependent on the

trace element concentration o-f the parent, the extent of

melting, the process of melting involved, the solid phases

remaining at the time of removal of the melt, any

differentiation prior to complete crystallization and any

possible interaction with rocks, melts or fluids <Hanson,

1980> .

Tne trace element data on Dhanjori and Jagannathpur

volcanics are lacking. The contributions of Banerjee <1982)

and Santra (1982) containing some selected trace elements

were made to asses the mineralization potential of these

volcanics, thus Are inadequate to trace the fractionation

trends as well as tectonic environment of eruption of these

volcanics. In the present study, selected trace elements

including the rare earth elements <REEs) are discussed to

find out the magmatic evolution of Dhanjori and Jagannathpur

volcanics.

77

Trace elements N i , Co, C r , Cu, Pb, Z n , L i , Rb and Sr a re

es t imated by atomic absorp t ion spectrophotometer <AAS). Rb,

L i and Sr a r e e s t i m a t e d by a d d i n g K and L a - s o l u t i o n s a s

suppressing and r e l e a s i n g a g e n t s . A l l the a v a i l a b l e data a r e

s t a n d a r d i z e d aga ins t the r e f e r e n c e rock standards BCR-1, SY-

2 , SY-3 and BM. To a v o i d any e r r o r i n t h e d e t e r m i n a t i o n s

double and t r i p l e r u n s w e r e made t a k i n g d i f f e r e n t s a m p l e s

from the same specimen p o w d e r . Rock s t a n d a r d s w e r e a l s o

a n a l y s e d t o check t h e p r o b a b l e e r r o r . D e t a i l s o f

instrumenta l parameters and s e n s t i v i t y l e v e l s of d i f f e r e n t

elements a r e given in Tab le I I . P r e c i s i o n and accuracy of

t n i s method i s b e t t e r than +. 2 percent t o r most ot the t r a c e

elements except f o r few el ements^^l»\p--<af^"'-|wr«fiM^^t in ijery

small q u a n t i t y . / / * r MCCNO. ' \\

Trace elements V , Ba, Zr an<T T/^^re deter^rorijsed by X - r a y

Flourescence ( P h i l l i p s PW-1400 m i c r o p r o c e s s o r c o n t r o l l e d

sequent ia l X - ray f lourescence spectrometer w i th 100 KVA X- ray

generator and 72 p o s i t i o n a u t o m a t i c sample c h a n g e r ) a t

N a t i o n a l Geophysical Research I n s t i t u t e , Hyderabad, using t h e

procedure suggested by G o v i i C i 9 8 5 ) . For t h i s p u r p o s e

pressed p e l l e t s of the sample powders w i t h bor ic a c i d as

backing m a t e r i a l have been used. The r e p r o d u c i b i l i t y of the

data i s w i t h i n the range of +.2/'. f o r tnese e lements .

REE data were d e t e r m i n e d by INAA a t Bhabha A t o m i c

Research C e n t r e , Trombay, Bombay. For t h i s lOO mg of the

sample a l o n g w i t h t h e US6S s t a n d a r d B C R - 1 w e r e w e i g h e d

a c c u r a t e l y and s e a l e d i n s u i t a b l e p o l y t h e n e p a c k e t s t o be

78

irradiated for 24 hour in the Apsara reactor, at a neutron

•flux between lO^^n cm"^ S~ . The samples were cooled -for a

week be-fore counting -for La, Sm, Yb and Lu and -for three

weeks to count the rest o-f the REE. A Ge (Li) detector was

used along with a Canberra mut1ichannel analyser 1020.

Estimated errors due to counting statistics <L lr- i imi ts) are +.

1.5% -for La, Ce, Sm, Yb and Lu and 5 to 157. -For Eu and Tb.

Details o-f accuracy and procedure are given in Mural i et al .

(1979) .

The chemical data Are presented in Tables <J and KH .

The ranges of variation and average trace element

concentrations of Dhanjori and Jagannathpur volcanics are

given in Table V/*!!. For comparison average trace element

concentrations of these volcanics along with the different

volcanic suites are given in Table x. The distribution and

behaviour of various trace elements are discussed in the

following paragraphs.

TRACE ELEMENT DISTRIBUTION

Nickel in Dhanjori volcanics ranges from 48 ppm to 331 ppm

with an average of 110 ppm whereas in Jagannathpur volcanics

it shows a wide range of variation, ranging from 55 ppm to

900 ppm with an average of 195 ppm. In comparison to

different volcanics suites enlisted in Table X, the average

Ni values of Dhanjori volcanics Are comparable with depleted

Archaean tholelites (125 ppm) whereas Jagannathpur volcanics

have a higher Ni value than enriched Archaean tholelite (140

ppm). In relation to Si02 and MgO values (Table VII) Ni

79

abundances of Jagannathpur y o l c a n i c s a r e h i g h and show a

resemblance w i th b o n i n i t e s (Hickey and F r e y , 1982; Cameron e t

a 1 . , 1983; Crawford and Cameron, 1985; Bloomer and Hawkins,

1987; Beccaluva and S e r r i , 1 9 8 8 ) .

There i s a general t e n d e n c y of N i t o p r e f e r e n t i a l l y

enter i n t o the l a t t i c e of o l i v i n e and pyroxenes dur ing the

e a r l y s tage of magmatic d i f f e r e n t i a t i o n and upto middle s tage

i t i s almost c o m p l e t e l y removed f r o m t h e m e l t <Wager and

M i t c h e l l , 1 9 5 l j Storm and H o l l a n d , 1 9 5 7 ; T u r e k i a n , 1 9 6 3 ;

Burns and F y f e , 1966; P r i n z , 1 9 4 7 ) . Due to t h i s tendency of

N i t o become e n r i c h e d i n t h e e a r l y p r o d u c t s o f

d i f f e r e n t i a t i o n a p a r a l l e l i n c r e a s e o f N i a n d MgO i s

expected . The Ni c o n t e n t s of D h a n j o r i and J a g a n n a t h p u r

v o l c a n i c s when p l o t t e d aga ins t t h e i r MgO content? ( F i g . 23)

i n d i c a t e sympathet ic r e l a t i o n s h i p s between these two elements

of both v o l c a n i c s s u i t e s as t h e i r Ni contents r i s e s p a r a l l e l

t o t h a t of MgO.

I t has been considered t h a t Ni abundances and FeO^/MgO

r a t i o of b a s a l t i c m e l t s a r e no t s t r o n g l y a f f e c t e d by t h e

d e g r e e of p a r t i a l m e l t i n g a s c o m p a r e d t o f r a c t i o n a l

c r y s t a l l i z a t i o n < e . g . C a s t , 1 9 6 8 ; S a t o , 1 9 7 7 ; Hanson a n d

Langmuir, 1 9 7 8 ) . S i n c e most of t h e b a s a l t s have o l i v i n e

and /or cl inopyroxene a s l i q u i d u s or n e a r l i q u i d u s p h a s e ,

decrease of Ni abundances w i t h i n c r e a s i n g FeO*/MgO r a t i o may

be considered as a good f i r s t order q u a l i t a t i v e r e f l e c t i o n of

t h e d e g r e e of f r a c t i o n a t i o n . I t i s e v i d e n t f r o m t h e

histograms shown in F i g . 24 tha t Ni abundances of Dhanjor i

80

1000 h

800

600



E o. wiiOO

200 • 0

X 20 25 0 5 10 15

MgO */o

Fig.23. MgO versus Ni binary diagram for Dhanjori

and Jagannathpur volcanics showing sympathetic

relaionship in both of these elements.

o z u

UJ

81

[[] DHANJORI VOLCANICS


( a )

900 1000

Ni ( p p m )

> o z UJ z> a UJ QC U .

80

60

( b )

FeOVMgO

Fig.24. (a) Histogram showing Ni

abundances an Dhanjori and Jagannathpur

volcanics and (b) Histogram showing *

FeO /MgO ratio distribution in Dhanjori

and Jagannathpur volcanics. Both

histograms are not coinciding with

each other.

82

and Jagannathpur v o l c a n i c s Are n o t c o i n c i d i n g w i t h t h e i r

FeO*/MgO r a t i o .

Mg-numbers versus Ni p l o t s of Dhanjor i and Jagannathpur

v o l c a n i c s ( F i g . 25) a l though show a decreas ing t rend of N i

w i t h t h e decrease of Mg-numbers in both s u i t e s , i n d i c a t e t h a t

r o c k s a m p l e s w i t h s i m i l a r M g - n u m b e r s h a v e v a r i a b l e N i

contents and conversely samples w i t h d i f f e r e n t Mg-numbers

have s i m i l a r Ni c o n t e n t s . Thus i n a c c o r d w i t h W i l k i n s o n

< 1 9 8 i ) , i t i s suggested t h a t D h a n j o r i and J a g a n n a t h p u r

v o l c a n i c s were generated by d i f f e r e n t e x t e n t s of me l t ing of

m a n t l e s o u r c e s w i t h d i f f e r e n t c h e m i s t r y i . e . o f a

heôgeneous mant le w i t h each phase having undergone very

l i m i t e d f r a c t i o n a t i o n .

I t has been shown t h a t C a 0 / A l 2 0 3 r a t i o i n a magma

increases w i t h the f r a c t i o n a t i o n of g a r n e t <Cawthorn a n d

S t r o n g , 1974; N e s b i t t e t a l . , 1 9 7 9 ; B e s w i c k , 1 9 8 2 ) and

O l i v i n e <6ence e t a l . , 1979) whereas i t decreases w i t h the

f r a c t i o n a t i o n of c 1 i n o p y r o x e n e ( P e r f i t e t a l . , 1 9 8 0 ;

Beccaluva and S e r r i , 1 9 8 8 ) . N i c o n t e n t s of D h a n j o r i a n d

Jagannathpur v o l c a n i c s a re p l o t t e d a g a i n s t t h e i r Ca0 /A l203

r a t i o s in F i g . 26 . A p o s i t i v e c o r r e l a t i o n between Ni and

Ca0/Al203 r a t i o of Jagannathpur v o l c a n i c s suggest that Ni

c o n t e n t i n t h e s e v o l c a n i c s a r e c o n t r o l l e d by t h e

f r a c t i o n a t i o n of c l inopyroxene r a t h e r than t h e O l i v i n e . On

t h e o ther hand, Ni contents in Dhan jor i v o l c a n i c s do not show

any r e l a t i o n w i t h t h e i r Ca0/Al203 r a t i o s .

83

O DHAMJORI VOLCANICS

# JAGANNATHPUR VOLCANICS

£ Q .

w 100

10

t • •

^ (XT O „^0 00-0 •

0 • 0

90 80 70 60 50 40 30

Mg-Number

Fig.25. Mg-Number versus Ni binary diagram

for Dhanjori and Jagannathpur volcanics showing

sympathetic r e l a t ionsh ips .

84

1 6 -

1 U

1.2

1.0

O

5 0.8 o d u

06

0.4

0.2

O DHAN JORI V O L C A N I C S

• J A G A N N A T H P U R V O L C A N I C S

• • • • ,

X 100 2 00

Ni (ppm)

3 00 4 00 Hh-

900

Fig.26. CaO/AlÔ^ versus Ni binary

diagram for Dhanjori and Jagannathpur

volcanics indicating clinopyroxene

fractionation.

85

Cobalt in Dhanjori volcanics shows a wide range o-f

variation from 37 ppm to 126 ppm with an average o-f 69 ppm

whereas in Jagannathpur volcanics, its range o-f variation is

somewhat restricted, varying -from 26 ppm to 86 ppm with an

average of 55 ppm. Generally, in basaltic rocks, Co like Ni

also preferentially occupies the octahedral coordination

sites in a mineral (Burns and Fyfe, 1964). It is also found

that Co enters in the same mineral as Ni but comparatively in

lesser amount <e.g. tJager and Mitchell, 1951; Cornwall and

Rose, 1957; Wilkinson, 1959; Carr and Turekian, l96l; Burns

and Fyfe, 1964). Therefore, they should exhibit similar

geochemical behaviour during magmatic differentiation.

Fig. 27 illustrates the variation of Co and Ni contents

of Dhanjori and Jagannathpur volcanics. The data points in

both suites do not show crude linear correlation. Moreover,

Ni contents of both suites are high in comparison to their Co

contents. This leads to suggest that in both suites Ni and

Co are decoupled, i.e. occurring in two different mineral

phases.

Kogarko (1973) has pointed out that Ni/Co ratios of

various primary magmas arising at different depth during

partial melting of the mantle range from 2.2 to 7.6^ and the

melts produced by the fractional crystallization of these

primary magmas would have Ni/Co ratio around 1, on account of

the fractionation of olivine and pyroxene. If the

observation of Kogarko (op. cit) is correct, then Ni/Co

ratios of Dhanjori cO.75 to 4.86) and Jagannathpur (1.07 to

86

900

350

300

?so -

S200H

150

100

O OHANJOKt VOLCANICS

• MCANNATHPUR VOLCANICS

50 100 150

C o (pp m )

Fig.27. Ni versus Co binary diagram

for Dhanjori and Jagannathpur volcanics,

exhibiting decoupling between these two

elements.

87

13.04) v o l c a n i c s i n d i c * t » t h a t both s u i t e s have undergone

some - f r a c t i o n a t i o n . The h i gh N i / C o r a t i o a r e h o w e v e r

problemat ica l .

Burns and Fy-Fe kl964) nave proposed t ha t an i n c r e a s e in

Si02 aind a l k a l i s in the melt would lead to an i n c r e a s e o-f

t e t r a h e d r a l s i t e s r e l a t i v e t o o c t a h e d r a l s i t e s . B o t h

Dhanjori and Jagannathpur v o l c a n i c s have wide r anges o-f Si02

and a l k a l i s ( T a b l e V I I ) t h e r e - f o r e , i n c o m p a r i s o n t o

oc tahedra l s i t e s , t e t r a h e d r a l s i t e s would nave been abundant

in t h e i r r e s p e c t i v e m e l t s . Since Ni and Co pre-fer oc tahedra l

coord ina t ion s i t e s and abundance o-f such s i t e s wi l l be in

cl inopyroxene and hornblende , the Ni and Co would tend to

en te r in these m i n e r a l s , c r y s t a l l i z i n g -from t h e magma.

C I i n o p y r o x e n e c r y s t a l l i z a t i o n wou ld c a u s e a n e g a t i v e

c o r r e l a t i o n between Ni/Co r a t i o and Si02 whereas a p o s i t i v e

c o r r e l a t i o n wil l be obta ined by hornblende c r y s t a l l i z a t i o n

( B i l l , 1978).

In F ig . 28 Ni/Co r a t i o s o-f D h a n j o r i and J a g a n n a t h p u r

v o l c a n i c s a r e p l o t t e d a g a i n s t t h e i r Si02 c o n t e n t s . Ni/Co

r a t i o in Dhanjori v o l c a n i c s , showing a p o s i t i v e r e l a t i o n s h i p

with Si02 i n d i c a t e s t h a t in t h e s e v o l c a n i c s Ni and Co c o n t e n t s

a r e c o n t r o l l e d by h o r n b l e n d e c r y s t a l l i z a t i o n r a t h e r t han

c 1 i n o p y r o x e n e c r y s t a l l i z a t i o n . On t h e o t h e r h a n d , i n

Jagannathpur v o l c a n i c s a n e g a t i v e r e l a t i o n o-f Ni/Co r a t i o and

Si02 sugges t s t ha t Ni and Co c o n t e n t s in these v o l c a n i c s Are

probably c o n t r o l l e d by t h e c l inopyroxene c r y s t a l l i z a t i o n .

85

14,

12

10

o

^5

o DHANJORI VOLCANICS


••

• ••

O o oo o

•9

o o / •

50 55 60

Si'02 •/.

Fig. 28. Si02 versus Ni/Co binary diagram

showing a sympathetic relationship in Dhanjori

volcanics and no relationship in Jagannathpur

volcanics. It is an indication for the

amphibole fractionation in Dhanjori volcanics.

89

Chromium in Dhanjori volcanics ranges -from 12 ppm to

1491 ppm with an average of 242 ppm whereas in Jagannathpur

MOlcanics it varies more widely -from 38 ppm to 5400 ppm with

an average of 537 ppm. The average Cr values when compared

with the different volcanic suites listed in Table X, it

appears that Dhanjori volcanics are comparable with depleted

Archaean tholeiites <:250 ppm) whereas Jagannathpur volcanics

have a higher value than enriched Archaean tholeiite (490

ppm). The Cr abundances in Jagannathpur volcanics are also

high in relation to their S1O2 and MgO contents (Table VII)

and thus they resemble with the boninites <Hickey and Frey,

1982; Cameron et al . , 1983j Crawford and Cameron, 1985;

Bloomer and Hawkins, 1987; Beccaluva and Serri, 1988).

Cr initially enters the chrome spinels especially

Chromite and picotite (Prinz, 1967). Due to valency

difficulties, it prefers pyroxenes and enters olivine only in

a limited amount (Mc Dougal1 and Lovering, 1963; Turekian,

1963; Burns and Fyfe, 1964; Prinz, 1967). Thus, in order to

examine its genetic significance the Cr contents of Dhanjori

and Jagannathpur volcanics are plotted against their MgO

contents in Fig. 29. The observed sympathetic relations

indicate general coherence of Cr and MgO during magmatic

differentiation of both the suites. Similar trends of Ni

with MgO (Fig. 23) lead to infer the coherence o-f botn Ni and

Cr with MgO during magmatic differentiation of both suites.

However, the plots of Cr against Ni do not show crude linear

correlation (Fig. 30) between the two and thus indicate

decoupled behaviour of Ni and Cr in these volcanics.

9u

10000

1000

E a a

o

100

10

OL


• JAGANNATHPUR VOLCANICS 0

• •

MgOVo

Fig. 29. MgO versus Or binary diagram for


a sympathetic relation between these two elements.

91

5000

1000

E a a i_ u

100



10 1000 100

Ni { ppm )

Fig.30. Ni versus Cr binary diagram

for Dhanjori and Jagannathpur

volcanics exhibiting decoupling


92

Turekian <1963) observed that Cr/Ni ratio is not much

affected by fractional crystallization indicating that the

ratio is pro'bably derived from the mantle rather than

generated by the process in the crust. Contrarily, Prinz

<\967> found a general coherence between Cr and Ni in

basaltic rocks and a range of Cr/Ni ratios from 0.6 to 3.9.

Cr/Ni ratio in Dhanjori and Jagannathpur volcanics vary

from 0.13 to 4.50 and 0.34 to 6.00 with the averages of 1.73

and 2.16 respectively. These values are inconsistant with

MORB and komatiites in which Cr/Ni ratio generally ranges

Detween 1 and 3 <Kay and Hubbard, 1978; Nesbitt et al., 1979,

Sun et al ., 1979).

In Fig. 31,Cr contents of Dhanjori and Jagannathpur

volcanics Are plotted against their Mg-numbers. As compared

to Ni versus Mg-number plot <Fig. 25) Cr contents of these

volcanics show a steeper decrease with decreasing Mg numbers.

It therefore appears that Cr contents in these volcanics AVB

more modi-Fied Oy the fractionation than their Ni contents.

The distribution of Cr in these volcanics may be

modified by several processes involved in the genesis of

these rocks, the effects of which are superimposed. In order

to diminish the influence of some of the processes, Cr/Ni

ratios of Dhanjori and Jagannathpur volcanics are plotted

against their Ca0/Al203 ratios in Fig. 32. The observed

positive relationships between these two ratios indicate that

CIinopyroxene crystallization controls the Cr abundances in

these volcanics and c 1 i nopyroxene fractionation is

93

8000

1000

E o. Q.

O

O O M A N J O H I V 0 L C A N I C 5

• J A G A N H A T M P U R V O L C A N I C S

100 h

10

0 • % 0 .

••' o 0

0

t t

0

O 0

0

>s

90 80 70 60 50 AO 30

Mg-Number

Fig. 31. Mg-Number versus Cr binary diagram

for Dhanjori and Jagannathpur volcanics,

illustrating a sympathetic relation.

94

Ul o z 

cc o —» z < X

tn o z < o _ l

o > ££ D Q. I »-< 2 Z < vT) <

o* o

9> oo)

• • • M

o

• o • -

o

ir>

CO O

9 ^ — o n u

i n

o

•H M O

•1-1 C 10 ja o

u o

E

01 ro

•H

> i M 10 C

•H J3

•H 2 ^» U U

(0 9 (0 u 0)

n (N

i n

O 10 U

t

01

c o

•rl

to H 0) M

> •H +J •H (0 o a

10

01

c •H +J (0 H •P (0 3

H •H

(0 U

•H C (0

u H O >

u 3 Oi J3 •P 10 c c (0 Oi (0 •-i

-o c 10

10

M U

•O c 10

•H

z

o J3

10

• p

0) 0)

•p

u •H •O

c • H CO

• H X! EH

0)

•P

0)

c 0) X o M > i Si o. o c

•H

> i

0)

C H

a> o ? -p +J C 0) O

!N/JO

95

r e s p o n s i b l e for the o b s e r v e d v a r i a t i o n s o+ Cr c o n t e n t s in

both s u i t e s .

Manadium l i k e chromium di - f - fers -from o t h e r t r a c e

t r a n s i t i o n m e t a l s , in h a v i n g t h r e e common v a l e n c e s t a t e s

undar t e r r e s t e r i a l c o n d i t i o n s t h a t e x h i b i t s t r o n g l y

c o n t r a s t i n g g e o c h e m i c a l b e h a v i o u r . K/ h a s i o n i c

c h a r a c t e r i s t i c s s i m i l a r t o compat ib l e t r a c e t r a n s i t i o n m e t a l s

and commonly s u b s t i t u t e s f o r o t h e r t r i v a l e n t c a t i o n s in

s p i n e l s and p y r o x e n e s . The more o x i d i z e d s p e c i e s (M , V )

behave a s high f i e l d s t r e n g t h c a t i o n s wi th high charges and

low r a d i u s / c h a r g e r a t i o s C<. 0 . 1 7 ) s i m i l a r t o t i t a n i u m

( S h e r v a i s , 1 9 8 2 ) . V, in Dhanjori v o l c a n i c s v a r i e s from 251

ppm t o 3 2 5 ppm w i t h an a v e r a g e o f 3 0 2 ppm w h e r e a s i n

Jagannathpur v o l c a n i c s , i t v a r i e s from 263 ppm to 302 ppm

with an average of 281 ppm.

F i g . 33 i l l u s t r a t e s t h e v a r i a t i o n s b e t w e e n V and Ti

c o n t e n t s of Dhanjori and Jagannathpur v o l c a n i c s . All the

data a r e p l o t t e d to the r i g h t of c h o n d r i t e l i n e s u g g e s t i n g

that V has been d e p l e t e d r e l a t i v e to Ti . The d e p l e t i o n of V

r e l a t i v e to Ti in terms of Chondr i t i c abundances i n d i c a t e s an

i n h e r i t e d n o n - c h o n d r i t i c f e a t u r e in t h e upper m a n t l e .

S h e r v a i s <1982) has p o i n t e d out that the c r y s t a l / l i q u i d

p a r t i t i o n c o e f f i c i e n t s f o r M K/Ary f r o m >1 t o <1 w i t h

i n c r e a s i n g oxygen f u g a c i t y . The d e p l e t i o n of V r e l a t i v e to

Ti i s a measure o-f t h i s v a r i a t i o n and the r e l a t i v e oxygen

f u g a c i t y of the magma. The primary m e l t s produced by 20-30>I

98

E a. a.

u 3 0

•H > (0 X! (U

X)

O •H -P •H ^

' 0 c 0

n o 1 c 0

c en C

•H

0 Si (0

Dl

> M 3 CO u 0)

> •H EH

t

n

&)

• CO

u •H c (0 o

H 0 >

u 3 a x: •p (D c c ID t31 ID 1-3

C ID

•H

0 •n C 10

Q

C

-H H

0 +J

0) >

•H 4-) (0

H

>

4-1 0

0 » 4J

c •H

0) M (0

CO +J

c <u 6 (U

H CU

0) CO

X!

4 - 1 O

J3 -P

o JQ

4J ID

JG 4-J

CO • P CO

Cn 01 3 CO

CO

x: EH

• CO Q) CO ID

J3 04

H ID M 0) C

•H

E

c 0)

0) (p •H

-a

( U J d d ) A

97

p a r t i a l m e l t i n g under r l e a t i v e l y reduc ing c o n d i t i o n s l i k e

MORB w i l l have i n i t i a l T i / V r a t i o s o f about 20-50 and s i m i l a r

me l t s produced under more o x i d i z i n g c o n d i t i o n s such as the

mant le wedge o v e r l y i n g t h e d e v o l a t i z i n g , s u b d u c t e d s l a b

should have i n i t i a l Ti/ 'v ' r a t i o s o-f around 10-20 ^Sherva is ,

1982 ; Hodder , 1 9 8 5 ) . T i / V r a t i o s i n D h a n j o r i a n d

Jagannathpur v o l c a n i c s , rang ing f rom 13.60 t o 27.23 and 8.94

to 32.01 w i t h the averages o-f 18.71 and 16.42 r e s p e c t i v e l y ,

t h e r e f o r e sugges t t h e i r d e r i v a t i o n i n m o r e o x i d i z i n g

c o n d i t i o n s than t h a t o-f MORB.

I n an e x p e r i m e n t a l s t u d y r e l a t e d t o b a s a l t l i q u i d

f r a c t i o n a t i o n , Duke (1976) f o u n d t h a t v e x h i b i t e d a

p re fe rence f o r 1 i q u i d i n t he h igher temperature range and f o r

c l inopyroxene a t lower temperatures ^D^cpx <2) . Thus, f o r

rocks c r y s t a l l i z e d a t lower temperatures, namely, those w i t h

lower MgO c o n t e n t s , c 1 i nopyr oxene may h a v e p l a y e d an

important r o l e in m o d i + y i n g t h e V c o n c e n t r a t i o n s i n t h e

e v o l v i n g magmas. The f l a t t e n i n g of Kf ^ i n D n a n j o r i and

Jagannathpur v o l c a n i c s , c ross ing the constant T i / v r a t i o l i n e

( F i g . 33) may be i n d i c a t i v e o f t h e s i g n i f i c a n t r o l e of

c l inopyroxene <Jahn et a i . , i 9 8 0 ) . However, due to la rge D^

value of magnet i te and Cr s p i n e l , a minute amount of these

phases c o u l d a l s o i n d u c e t h e d e p l e t i o n o f V i n t h e s e

v o l c a n i c s .

Al though Rankama and Sahama (1950 ) c o n s i d e r e d t h a t

m a j o r i t y ot Cu in i gneous r o c k s i s c o n f i n e d t o s u l p h i d e

phase, subsequent s tud ies ( e . g . Wager and M i t c h e l l , i 9 5 i } MC

98

UougalI and Lovering, 1963; Prinz , 1967) indicate tnat Cu may

also be present in silicate and oxide phases. Because of

similar ionic radius Cu"*" may accompany Na in late

crystallizing phases whereas Cu""*" will be camouflaged by Fe*-"*"

in the early ferromagnesian silicates <Ringwood, 1955). But

high oxygen fugacity appears to be essential for Cu in

divalent state (Seward, 1971).

Cu in Dhanjori volcanics varies from 15 ppm to 179 ppm

with an average of 86 ppm whereas in Jagannathpur volcanics

it ranges from 29 ppm to 196 ppm with an average of 94 ppm.

In comparison to the volcanic suites listed in Table X,

Dhanjori volcanics containing lower Cu values than Archaean

andesites match with the modern island arc tholelites. On

the other hand, Jagannathpur volcanics appear to have Cu

values similar to Archaean enriched tholeiites as well as

modern continental tholeiites.

Burns and Fyfe <1964) showed that transition metals

enter into both octahedral and tetrahedral coordination sites

and proportion of tetrahedral co-ordination sites increases

with increasing amount of alkali and silica. In presence of

Cu in monovalent state, it is expected that Cu*** partitioning

would not be affected by the change in relative abundances of

octahedral or tetrahedral sites because it has zero

octahedral site preference energy (Seward, 1971). Therefore,

Cu would behave as an inccmpatibl e element in the ma^na.

Such character of Cu is a unique feature of continental

tholeiites (Dupuy and Dostai , i984) . On the other hand, Cu "

99

Fig. 34. Cu-Ni-Co triangular variation diagram for

Dhanjori and Jagannathpur volcanics illustrating

the behaviour of Cu relative to Ni and Co in both

of these suites.

100

2+ having octahedral site preference energy greater than Co

<Seward, 1971) will preferential 1y enter into ferromagnesian

silicates.

Fig. 34, illustrates the behaviour of Cu in Dhanjori and

Jagannathpur volcanics, Cu in both suites does not show any

enrichment with the decrease of Ni and Co contents. It

therefore appears that Cu in these volcanics, alongwith the

Ni and Co, is partitioned into ferromagnesian silicates.

This is in accord with the observation of Rajamani and

Neldrett (1978) that sulphophile character of Cu decreases

with decreasing basicity of the magma.

Rubidium is normally regarded as substituting for K in

mineral structures. In Dhanjori volcanics Rb content varies

from 7 ppm to 73 ppm with an average of 29 ppm. It is much

lower than that of Jagannathpur volcanics which shows a large

variation from 12 ppm to 120 ppm with an average of 52 ppm.

Rb contents of these volcanics when plotted against their K

concentrations (Fig. 35; indicate that there is no

relationship between K and Rb contents of these volcanics.

Moreover, in both suites Rb is enriched relative to K

concentrations.

Oxburgh (1964) suggested that K and Rb are not dispersed

through the major upper mantle phases but are more likely

concentrated in K-rich minor phases such as amphiboles and

mica. Experimental studies have indicated that amphibole is

protMibly stable in the upper mantle to depth of 75 or

possibly 100 km whilst phlogopite may well be stable to depth

10.



100 200 Rb(ppm)

Fig.35. K versus Rb binary variation

diagram showing Rb enrichment in Dhanjori


102

of upto 200 km (e.g. Kushiro tt al ., 1967; Yoder and Kushiro,

1969; Modreski and Boettcher, 1972; Forbes and Flower, 1974;

Beswick, 1976). Continental tholeiites, transitional MORE

(T-MURB) and normal MORB (N-MORB) are characterized dy K/Rb

ratio of 150-400, 200-250 and 1000 respectively (e.g. Sun et

al . , 1979; Barberi et al., 1982; Le Roex et al., 1983;

Collerson and Sheraton, 1986; Sevigny, 1988>. In Dhanjori

volcanics, K/Rb ratios vary from 40.00 to 1017.14 and about

65">i samples have K/Rb ratio less than 400 while the remaining

35% samples have K/Rb ratio higher than 400. On the other

hand, in Jagannathpur volcanics 94% samples have K/Rb ratio

less than 400 and the remaining 6'/, have K/Rb ratio higher

than 400. It has been pointed out (e.g. Besuiick, 1976) that

amphiboles strongly discrimate against Rb relative to K and

usually have K/Rb ratios greater than 1000 ranging from 400

to 4000 whereas phlogopites and biotites usually have K/Rb

ratios less than 250, ranging between 40 and 400. It

therefore appears reasonable that amphibole and mica both may

be involved in the magmatic evolution of these volcanics.

In oceanic basalts, Gast (l96U, 1965) and Engel et al .

(1965) have shown a strong correlation of decreasing K/Rb

ratio with increasing K content of the rocks from 1ow-k

tholeiites to alkali basalts. On the other hand, Jakes and

White tl971> observed that K increases across island arcs and

there is a corresponding decrease in K/Rb ratio from

tholeiites through calc-alkaline to shoshonite.

£1

a

103

1200

1000

800

600

400

200

n

~

-

-

—

—

o •

1

DHANJORI VOLCANICS JAGANNATHPUR

• 1 1 1 1 1 0

1

VOLCANICS

0

• 0

0

0

•

• • • o

h».\ • • • 1 1 • 1 1 1 1 1 1 1 1 _ 1 1 1 1 1 1

001 0-1 2 3 10

K 'U

Fig,36. K versus K/Rb binary variation diagram

exhibiting absence of any relationship between

K and K/Rb in Dhanjori and Jagannathpur

volcanics.

104

I n o r d e r t o d i s t i n g u i s h O h a n j o r i a n d J a g a n n a t h p u r

Molcan ics , t h e i r K/Rb r a t i o s a r e p l o t t e d a g a i n s t t h e i r K

contents in F i g . 3 6 . A l though, Dhan jor i v o l c a n i c s have low K

and comparat ive ly high K/Rb r a t i o s , s c a t t e r of data p o i n t s

i n d i c a t e s t h a t t h e s u i t e has undergone some - f r a c t i o n a t i o n of

amphibole (Kd^*'"P^''^ > Kd^j^^'^P^'^^ ; P h i l p o t t s and S c h n e t z l e r ,

1970^. On the other hand, in Jagannathpur v o l c a n i c s K/Rb

r a t i o s show an i n c r e a s e w i t h i n c r e a s i n g K c o n t e n t , w h i c h

probably suggest t h a t m e l t i n g was d o m i n a n t c o n t r o l l i n g

process in the e v o l u t i o n of t h i s s u i t e . Since Kd|^*"'P >

Kdptj^'"P^'^^ ( P h i i p o t t s and S c h n e t z l e r , 1970; the presence of

amphibole in the mant le Mould ac t as a b u f f e r f o r K. As soon

as the melt were f o r m e d , Rb w o u l d be r a p i d l y t r a n s p o r t e d

upward and e n t e r t h e c r u s t . The low K / R b r a t i o s o f

J a g a n n a t h p u r v o l c a n i c s a r e t h e r e f o r e , d u e t o l a c k o f

r e t e n t i o n of Rb in t h e m a n t l e .

S t ront ium in Dhanjor i and Jagannathpur v o l c a n i c s v a r i e s

from 54 ppm to 281 ppm and 47 ppm t o 613 ppm w i t h t h e

averages of 153 ppm and 273 ppm r e s p e c t i v e l y . In comparison

to the e n l i s t e d vo lcan ic s u i t e s of Tab le X , these v o l c a n i c s

conta in more Sr than t h e A r c h a e a n b a s a l t i c k o m a t i i t e s ,

Archaean dep le ted t h o l e l i t e s and mid-oceanic r i d g e b a s a l t

(MORS).

In b a s a l t i c rocks Sr tends to concent ra te in Ca r i c h

m i n e r a l s such as p l a g i o c l a s e , p y r o x e n e and a p a t i t e and i n

high temperature K - b e a r i n g m i n e r a l s such a s K - f e l d s p a r s

( P r i n z , 1 9 6 7 ) . In order t o see t h e r o l e of Sr in D h a n j o r i

1U5

800

700

600

500

E

5 400

10

300

200

100 -

O OHANJORI VOLCANICS • JACANNATHPUR VOLCANICS

• • •

o • • o o •O

O O

o

0 2 Oi, 0.6 1.4 1.6 1.8 0.8 1.0 1.2 CaO/A(2 03

Fig.37. CaO/Al20^ versus Sr binary variation

diagram for Dhanjori and Jagannathpur volcanics

exhibiting an antipathetic relation between

these elements. This suggests control of

clinopyroxene rather than plagioclase.

106

and JagannAthpur volcanics, their Sr contents are plotted

against their Ca0/Al203 ratio (Fig. 37). In both yolcanics

suites Sr decreases with increasing Ca0/Al203 ratio. It

there-fore appears that in both suites Sr is not controlled by

plagioclase crystallization rather it is controlled by

clihopyroxene.

The studies o-f Brooks (1968) and Schnetzler and

Phil potts (1968) indicate- that plagioclase concentrates more

Sr relative to K, Rb, Ca and Ba and K and Ba relative to Rb.

Therefore, separation of significant amount o-f plagioclase

•from the magma would cause Rb/Sr and K/Sr ratios to increase

more rapidly and Ca/Sr ratio to decrease less rapioiy during

•fractionation. K/Sr, Rb/Sr and Ca/Sr ratios of Dhanjori and

Jagannathpur volcanics are plotted againstK(or Rb) which

serves as an index of differentiation in Fig. 38. It is

evident that in both volcanic suites Sr is depleted relative

to K and Rb. This depletion is rapid in Pnanjori volcanics

as compared to Jagannathpur volcanics <:Fig. 38a,b). In

relation to Ca, Sr is enriched in Jagannathpur volcanics

whereas Dhanjori volcancis do not show any enrichment or

depletion trend (Fig. 38c).

The slightly differring fractionation trends of Sr in

Dhanjori and Jagannathpur volcanics may be attributed to the

presence or absence of plagioclase in the mantle source rocks

of partial melts or in the mineral assemblages involved in

crystal fractionation processes and the temperature at which

such differentiation processes took place. According to Sun

•

o

•

• o

o

o • • • o

o <x> • •

o

• » . • •

• • • t • •

o

•

••

•

• •

u

5-o o o

U

^ o 107 o

"^ I 0

"i /oa

C O

• H 4-> (0 -rl

u (0 > U

w • ^ ^

K (0 3 to

>

e (0 M Dl 10

•H T3

C O

•H 4-1 (0

• H )-l (0 >

U CO

5 ^

(/}

CO U

>

(0

00

•rl

T) C (0

e (0

>-( 01 10

• H -d

n c

•H

Q (T

T3 C (0

M

> •H +J (0 r-l 0) ^ c o

•H +J •H H

a -o M

CO

Q) - C

E (0 u en (0

-H ^3

c o • p (0 •H M (0 >

H CO ^ (0

u CO

(0

0)

>

to u

•H C (0 CJ

o >

D a x: +j (0 c c (0 01 (0 1-5

c •H

-o Q) £3 U

•H ^ C 0)

CO • H

M CO

O)

c •H -P (0

u * J CO 3

ID U

0 -P

c 0

•H P (0

0) 1

(0

u • H C (C3 O

H O > u a p ID C c (0 01 ID

c 10

'% /^

108

et a l . , <1974) and Drake and We i l l (1975) a t r e l a t i M e l y low

temperatures p l a g i o c l a s e l i q u i d e q u i l i b r i a w i l l ac t to leave

a l a r g e - f rac t i on o-f Sr o-f tne t-otal system l a p l a g i o c l a s e bu t

i n t h e absence o f p l a g i o c l a s e <or i n t h e p r e s e n c e o f

p l a g i o c l a s e a t r e l a t i v e l y h i g h t e m p e r a t u r e ) Sr w o u l d

f r a c t i o n a t e i n t o the l i q u i d .

Barium i s normal ly regarded as s u b s t i t u t i n g K i n mineral

s t r u c t u r e s . In Dhan jor i and Jagannathpur v o l c a n i c s i t ranges

from 30 ppm to 218 ppm and 12 ppm t o 986 ppm w i t h t h e

averages ot 83 ppm and 317 ppm r e s p e c t i v e l y . Ave rage Ba

v a l u e s o f t h e s e v o l c a n i c s a r e compared w i t h d i f f e r e n t

vo lcan ic s u i t e s in T a b l e X. I t a p p e a r s t h a t D h a n j o r i

v o l c a n i c s , c o n t a i n s h i g h e r Ba t han A r c h a e a n b a s a l t i c

k o m a t i i t e s , liORB and i s l and arc t h o l e i i t e s and are comparable

w i t h Archaean d e p l e t e d t h o l e i i t e s . On t h e o t h e r h a n d

Jagannathpur vo l can i cs are more ak in in to the Archaean as

we l l as modern a n d e s i t e s .

In F i g . 39 Ba c o n t e n t s of D h a n j o r i and J a g a n n a t h p u r

vo l can i cs a re p l o t t e d aga ins t t h e i r K, Rb and Sr c o n t e n t s .

I n both s u i t e s Ba increases w i t h i nc reas ing K ( F i g . 39a ) . I t

t h e r e f o r e appears tha t there i s a general coherence o+ K and

Ba in minera l s t r u c t u r e s . In D h a n j o r i v o l c a n i c s , Ba i s

dep le ted r e l a t i v e t o Rb and Sr whereas i n J a g a n n a t h p u r

v o l c a n i c s i t i s enr iched as compared to Rb and Sr ( F i g . 39b,

c ) . Drake and We i l l ( 1975 ) have shown t h a t p a r t i t i o n

c o e f f i c i e n t s f o r Sr and Ba a r e s t r o n g l y dependent upon

temperature. Since Dg^ > 1 a t temperature less than 1450°C

(uidd) j ;

(u jdd ) Dg

U

a Si 4J to c c (0 O) (0 >r>

c (0

(0 H a> (-1

u •rl +j-(U J3 +J (0 ft e (0

to

C •rl ? O

en E (0 n D1 (0

•rH

> i M (0 C

• H JQ

ui:

W

m VH

> to

•H

0) 4-1 to U •P CO 3

(0

e (0 M Cn to

103

•H 1 O • n C to Xi a c

•H

c 0

•r-l

TJ

U U)

m D CO u (U >

•a c

e (0 M O) ID

•H •D

C O

•H +J to

•H U

to >

u to c •H X)

<0 QQ

CO 3 to U

>

XI

CO

u • H C

to CJ

H O >

CO

o • H C

to O

H O >

3 a -p to c c to en to

• -3

c • H

- p c (U

E u

• H

c

to m

- o c to

CO

o • H C

to O

H O >

• H M O

• n C to

Q

C • H C O

• H •P (U

H

- a

to m

0) X3 •p

110 and Dg^ < 1 at temperature greater than 1060°C (Drake and

Weill, 1975) the plagioclase crystallization in some o-f the

samples of Jagannathpur volcanics perhaps impoverish Sr

content and enrich the Ba content. In Dhanjori volcanics, Rd

is enriched relative to Ba and Ba/Sr ratios are low (0.16 to

1.68). Since amphiboles contain Dg^ > Dp j (Gill, 1978) and

low Ba/Sr ratio (0.15 to 0.58; Basu, 1978), it seems that

amphibole -fractionation caused the observed Ba variation in

Dhanjori volcanics.

Elements having small ionic radii and low radius/charge

ratios are called high -field strength elements (HFSE). They

tend to be strongly incompatible, having very small bulk

partition coef-ficient in most situations and Are considered

immobile during low temperature alteration (Pearce and Norry,

1979; Saunders et al., 1980; Shervais, 1982). This property,

together with their systematic variation in -fresh lavas, has

meant that these elements can be used as the sensitive

indicators o-f their sources region (Eriank and Kable, 1976;

Pearce and Norry, 1979; Sun et al ., 1979, Pearce, 1982). Ti ,

Zr, H-f, Nb and Y are the elements which are included in the

group o-f high field strength elements. The abundances of

these elements in basaltic magmas show a general increase

from island arc through ocean floor to within plate magma

types (Pearce and Cann, 1973; Pearce and Gale, 1977; Pearce,

1982, 1983) .

Zirconium contents of Dhanjori and Jagannathpur

volcanics vary from 189 ppm to 236 ppm and 131 ppm to 238

I l l ppm with the average* o-f 204 ppm and 189 ppm respectively.

These values appears to be very high when compared with

di-f-ferent volcanic suites enlisted in Table X. The average

Zr contents of these volcanics however resemble with those o-f

continental ri-ft tholeiite <200 ppm) and Archaean andesite

type II <190 ppm). Continental tholeiites contain higher

contents o-f LILE <K, Rb, Sr , Ba) than MORB while the

abundance of HFSE <Ti , Zr, Y, P etc.) and corresponding

ratios are with in the range of oceanic tholeiites (Dupuy and

Dostal , 1984). Dhanjori and Jagannathpur volcanics have

higher concentration of LILE as compared to MORB but the

abundance of their HFSE, except Zr, are lower than oceanic

tholeiites (Table X). Moreover, the variation ranges of Zr

contents in these volcanics (Table VII) Are similar to that

found in modern orogenic andesites <35 ppm to 250 ppm;

Bailey, 1981) .

Since the relative incompatibility (i.e. the relative

preference of each element for liquid phase) of Zr is greater

than Ti which in turn is greater than Y <Sun et a1 . , 1979),

it is desirable to compare the trends of Zr and Ti in

Dhanjori and Jagannathpur volcanics. The variation of these

elements will be a signature of the processes operating

during their magmatic evolution. Fig. 40 illustrates the

relationships between Zr and Ti contents of Dhanjori and

Jagannathpur volcanics. In both suites Zr is enriched

relative to Ti. Lack of linear relationships between Zr and

Ti in these volcanics indicate that Zr and Ti are decoupled.

Such decoupl ing has been considered as a diagnostic feature

112

V

</) o

z. <

o >

o - z < X o 0

\ N

</) o z < o - J o >

a 3

I

< Z Z < < -) •

1

\

CD

c

*• Q

V )

*«

1%

.Ck

o

c

u o

\

(0

c

< 1 1

— «« o

3

« - •

o.

s _J

en

c 4

O

1 4-'

*« lA

*» . a

»« 1 U

<v O

•

(s)

\ \ \ ' \ \

1

•

\ \

O

•

•

\

w

•

o • o

1 •

@

\ s

\ \ s

\®

•

* • •

o

• •

• •

•

• •

\ \ s ^

\

m

\ \

\

\ \

\

'

N

\

o in

O o

o

o o o

o o o o

• H U 0

• n C

Q

U O

E flj U 01 (D

•H •O

C

o •H 4-1 (0

•H

> E a a

^ > i «- M N (0

C •H J3

•H H

to 3 to M 0) >

U N

t O

t

•H

(0 C o

• p

•H

ID >

0) 4-1

•H M

C o X! o c o c

01

c •H 4J •H i 3 •H

x: a) (0

o •H C (0

o H O > u 3

x: 4J

c c <0 01 (0 '^

T3 C 10

u 10

0) o u (0

c (0 H CO •H

V4 n

•4-1

CO T3 H 0) •H

k 0 M

M-l

C a; X (0

4J

u (0

CO

v 4-1 • H 3 CO

o •H c fO o H O >

Si 4-) 0 J3

C •H

•H EH

-O C 10

M

CO

o • H C «3 O

H O >

c •H H (0

Ji<

H 10 I

O H 10 O

T3 C (0

en DC

10 i 3

4-) H (0 CO "O

C (0

( u j d d ) ! i

113

o f c a l c - a l k a l ine v o l c a n i c * (Donnel ly and Rogers, 1980).

T i / 2 r r a t i o s in D h a n j o r i and J a g a n n a t h p u r y o l c a n i c s

range -from 21.53 t o 3 2 . 4 4 and 1 0 . 3 3 t o 3 7 . 5 2 w i t h t h e

averages of 27.48 and 24.19 r e s p e c t i v e l y . These values a re

ve ry low as compared t o the c h o n d r i t e va lue ( l l O ; Nesb i t t and

Sun, 1976). A number of workers ( e . g . Hickey and F rey , 1982;

Cameron et a1 . , 1983; Crawford and Cameron, 1985. Bloomer

and Hawkins, 1987; Beccaluva and S e r r i , 1988) have suggested

tha t T i / Z r r a t i o s d i s t i n c t l y less than the chond r i t e va lue

are a d i s t i n g u i s h i n g f e a t u r e of b o n i n i t e . Since T i and Zr

con ten t s of the b a s a l t i c mel ts are not s i g n i f i c a n t l y a f f e c t e d

by dominant c r y s t a l l i z i n g phases such as o l i v i n e , pyroxene

and f e l d s p a r , i t appears t h a t con t ro l of T i bear ing phases i n

these v o l c a n i c s may be respons ib le f o r t h e i r low T i / Z r r a t i o s

(Pearce and Nor ry , 1979).

y t t r i u m shows la rge v a r i a t i o n s in both Dhanjor i <3 ppm

to 41 ppm) and Jagannathpur (3 ppm to 45 ppm) vo l can i cs w i t h

the averages of 14 ppm to 26 ppm r e s p e c t i v e l y . Al though the

ranges of v a r i a t i o n in both s u i t e s Are s i m i l a r , Jagannathpur

vo l can i cs appear to be more enr iched as compared to Dhanjor i

v o l c a n i c s . In comparison w i t h the d i f f e r e n t vo l can ic s u i t e s

g iven in Table X, these vo l can i cs con ta in low Y values than

Archaean t h o l e i i t e s , m id o c e a n i c r i d g e b a s a l t s a n d

c o n t i n e n t a l r i f t t h o l e i i t e s .

Pearce (1982) has p o i n t e d ou t t h a t Y behaves as an

incompat ib le element throughout the t h o l e i i t i c s e r i e s but

114

O DHANJHORI VOLCANICS • JAGANNATHPUR VOLCANICS

1 1 1 1 500 10 50 100

Zr (ppm)

Fig.41. Zr versus Y binary variation diagram for


non-chondritic distribution of these elements in both

volcanic suites.

115 remains constant or decreases with the -fractionation in calc-

alkaline series. In Fig. 41 Y contents o+ Ohanjori and

Jagannathpur vo^canics are plotted aqainst their Zr contents.

The scattered data points of both volcanic suites below the

chondrite line indicate no relationship between their Y and

Zr contents. In both suites Y contents are much lower than

the expected value at particular Zr content.

Zr/Y ratios in Dhanjori and Jagannathpur wolcanics vary

from 5.76 to 63.0 and 5.29 to 43.67 with the averages of

11.57 and 7.27 respectively. These values are much higher

than the chondrite ratio (2.5; Nesbitt and Sun, 1976) and are

similar to those found in continental basalts (Pearce and

Cann, 1973), orogenic andesites (Bailey, 1981) and boninites

(Hickey and Frey, 1982). The high Zr/Y ratio may result from

the residual garnet and clinopyroxene since these minerals

have higher mineral/melt partition coefficients for Y than Zr

(Pearce and Norry, 1979).

The REE has been proved very useful particularly in

petrogenetic studies of basaltic rocks because their

geochemical behaviour changes gradually from the lightest

lanthanide La to the heaviest Lu . Thus a given REE has

geochemical characters very similar to those of its nearest

atomic neighbour but differing systematically from those of

REE with greater or smaller atomic numbers (Hanson, 1980).

But for the work of Wood et al. (1976), Ludden and

Thompson (1978) and Hellman et al. <1979) which indicate the

mobility of some of the REE in certain situations, the REE

lis

have g e n e r a l l y been c o n s i d e r e d as i m m o b i l e d u r i n g t h e

processes of post igneous a l t e r a t i o n and metamorphism. They

a r e t h e r e - f o r e b e l i e v e d t o be f r a c t i o n a t e d by m a g m a t i c

processes and t h e i r r e l a t i v e abundances appear t o r e c o r d

r e l i a b l y the e f f e c t of pr imary d i f f e r e n t i a t i o n processes in

igneous geochemis t ry .

T i l l date REE data on the vo l can ic rocks of Singhbhum

cra ton i s l a c k i n g . I n t h e p r e s e n t s t u d y two samples o f

D h a n j o r i v o l c a n i c s and t h r e e samp les o f J a g a n n a t h p u r

vo l can i cs have been analysed f o r seven se lec ted REE, v i z . L a ,

Ce, Sm, Eu, Tb, Yb and Lu . The chond r i t e normal ized REE

p a t t e r n s of these vo l can i cs are g iven in F i g . 42. The REE

data i s normal ized by us ing the c h o n d r i t e va lues of Masuda e t

a l . (1973) .

I t IS ev ident f rom t h e F i g . 42 t n a t b o t h of t h e s e

vo l can i cs are s i g n i f i c a n t l y LREE enr iched and show almost

p a r a l l e l t r e n d s . In c o m p a r i s o n t o D h a n j o r i v o l c a n i c s

C(La/Yb>p = 2 . 1 1 to 4 .25] Jagannathpur v o l c a n i c s appear to

be more enr iched C<La/Yb)^ = 2 . 9 t o 5 . 5 1 1 . One o f t h e

samples of Dhanjor i vo l can i cs con ta in p o s i t i v e Eu ancwnaly in

Chondr i te normal ized curve ( F i g . 42)« One of the samples i n

J a g a n n a t h p u r v o l c a n i c s c o n t a i n n e g a t i v e Ce a n o m a l y i n

chond r i t e normal ized curve <F ig . 4 2 ) . Such type of anomaly

may be i n h e r i t e d f rom the s o u r c e s i n c e no phase wh i ch

abnormal ly concentratesCe r e l a t i v e to REE have been found in

minera l separates from the t h o l e i i t e s and andes i tes (Dixon

and B a t i z a , 1979; Cul1ar and Gra f , 1984a, b ) .

117

lOOr OHANJORI VOLCANICS

La Ce 5m Eu Tb Vb Lu

< in

JAGANNATHPUR VOLCANICS

La Ce J L Sm E u Tb

J I Yb Lu

Fig.42. Chondrite normalized REE patterns of


Normalization values are those of Masuda et.al.,

(1973).

118 Both Dhanjori and J«gannathpur volcanics contain low to

moderate REE content* (Table V and VI) and their LREE/HREE

ratios C<La/Lu)^3 range -from 1.37 to 3.28 and 1.79 to 4.94

respectively. The Eu/Sm ratio in Dhanjori volcanics (0.74 to

1.07) indicates Eu anomaly in one of the sample. On the

other hand, Eu/Sm ratio in Jagannathpur volcanics (0.71 to

0.93) indicating the absence of Eu anomaly. These ratios are

however within the range of andesites, rather than the

tnolelites (Culler and Graf, 1984 a, b) . (La/Sm)p ratios in

Dhanjori <L1.82 to 2.33) and Jagannathpur (2.06 to 2.33) Are

also higher tnan N-type MORE and E-type MORB (0.40 to 0.70

and 0.83 to 1.97 respectively; Sun et ai . , 1979). However,

due to significant LREE enrichments in E-type MORB, their REE

patterns are indistinguishable frc»n any island arc basalts

and intraplate basalts (Perfit et al . , 1980). Tnere is an

enrichment of LILE relative to REE that distinguishes island

arc basalts from MORB and intraplate basalts (Kay, l977; Sun,

et al., 1979, Perfit et al . , 1980). In island arc basalts,

enrichment in Ba relative to LREE (Ba/La) characteristically

increases with decreasing LREE enrichment (Kay, 1980; Perfit

et al ., 1980). N-type MORB with depleted LREE patterns have

(Ba/La>pj (1.5 whereas this ratio increases to a maximum of 2

with increasing LREE fractionation, characteristic of E-type

nORB and alkalic intraplate basalts (Perfit et al . , 1980).

(Ba/La)^ values in Dhanjori (0.16 to 0.55) and Jagannathpur

(0.26 to 1.13) are low and showing a decrease with increasing

LREE this trend resembles with the boninites (Hickey and

Frey, 1982).

119 <Ce/Yb>j^ r a t i o s o-f Dhanjor i and Jagannathpur Molcanics

range -from 2 .05 to 3 . 1 7 and 1 . 7 3 t o 4 . 2 5 r e s p e c t i v e l y .

According to Saunders t l984> the magmatic processes tha t can

produce s i g n i f i c a n t v a r i a t i o n s in (Ce/YD)^^ r a t i o s a r e the

high pressure - f r a c t i o n a l c r y s t a l l i z a t i o n and e q u i l i b r i u m

p a r t i a l m e l t i n g ( i . e . batch m e l t i n g and cont inuous m e l t i n g ) .

High pressure - f rac t iona l c r y s t a l l i z a t i o n i n v o l v i n g garnet

( i . e . e c l o g i t e - f r a c t i o n a t i o n , O ' H a r a , 1 9 7 5 ) may a l t e r

( C e / Y b ) p r a t i o s i g n i f i c a n t l y b e c a u s e g a r n e t h a s h i g h

p a r t i t i o n coe-f-f i c i en t -for HREE ( '~4, Shimuzu and K u s h i r o ,

1 9 7 5 ) . In c o n t r a s t , low pressure f r a c t i o n a l c r y s t a l l i z a t i o n

i n v o l v i n g p l a g i o c l a s e , o l i v i n e and c1inopyroxene e i t h e r in

c lose or open system magma chamber M i l l r e s u l t in i n c r e a s i n g

REE w i t h constant ( C e / Y b ) ^ r a t i o and a l s o ( C e / S m ) ^ r a t i o

(Saunders, 1984>. The v a r i a t i o n s i n ( C e / Y o ; ^ r a t i o o f

D h a n j o r i and J a g a n n a t h p u r v o l c a n i c s may t h e r e f o r e b e

a t t r i b u t e d to the i n v o l v e m e n t of g a r n e t e i t h e r d u r i n g t h e

process o-f m e l t i n g or f r a c t i o n a l c r y s t a l l i z a t i o n . The

involvement of res idua l garnet dur ing the process of m e l t i n g

i s supported by low abundances of Al2O3 in these v o l c a n i c s .

CHAPTER V

MMt¥H CLASSIFICATION

GENERAL STATEMENT

in past, there was considerable ambiguity in the concept

o-f igneous rock series because intrinsic and more casual

characteristics of the series were not clearly distinguished.

Subsequently, the characteristics of various volcanic rocks

•from different tectonic settings were determined and as a

result of such studies a close relationship between tectonic

environment and chemical composition of volcanic rocks has

been revealed by many workers (e.g. Kuno, 1959, 1960, 1966,

1968; Chayes, 1964; Macdonald and Katasura, 1964; Engel et

al., 1965; Dickinson and Hatherton, 1967; Dickinson, 1968;

Gast, 1968; Jakes and White, 1972). In the meantime, the

plate tectonic concept (Le Pichon, 1968, Dewey and Horsfield,

1970; Dickinson, l97lJ caused a revolution in geologic

thinking and as a result three principal magma series have

been recognized, each composed of a group of closely related

maâ types that are emplaced in or on the earth crust.

These are tholeiite, cal c-al kal i ne and alkali series.

Tholeiite and alkaline series occur in almost all types of

tectonic environments whereas ,calc-alkaline series occur

characteristically in island arcs and continental margins.

At present there are two approaches to the problem of

the classification of volcanic rocks. They are either

cons idered to belong a s p e c i f i c rock a s s o c i a t i o n or they a r e l Z l

regarded as having e v o l v e d i n a s p e c i f i c t e c t o n i c a n d / o r

t h e r m a l e n v i r o n m e n t . These d i f f e r e n t m e t h o d s o f

c l a s s i f i c a t i o n do not a l w a y s comp lemen t one a n o t h e r

(Middlemost , 1985). Because one of the o b j e c t i v e s of t h i s

work i s to u t i l i z e the geochemical c r i t e r i a to c l a s s i f y the

magma types and t o i n v e s t i g a t e the e rup t i ona l environments of

Dhanjor i and Jagannathpur v o l c a n i c s , i t i s n e c e s s a r y t o

i d e n t i f y the magma type both in terms of rock a s s o c i a t i o n as

we l l as t e c t o n i c s e t t i n g . I n t h e p r e s e n t c h a p t e r ma jo r

e lement, t race element and REE c o n c e n t r a t i o n s of t h e s e

vo l can i cs are used, and w i t h the help of va r i ous d i s c r i m i n a n t

d iagrams, at tempt i s made t o achieve the above o b j e c t i v e .

tlfUQhA SERIES CLASSIFICATION

Ml kal i - s i I i ca (Na20 ••• K2O versus Si02> diagram has been

the most commonly used method t o d i s t i n g u i s h t h e v o l c a n i c

rock s e r i e s ( e . g . Macdonald and Ka tasura , 1964; Kuno, 1968;

I r v i n e and Barager, 1971). In recent yea rs , va r i ous workers

m o d i f i e d t h i s d i a g r a m and used i t a s an i n i t i a l

c l a s s i f i c a t i o n of the abundant types of vo l can ic rocks ( e . g .

Cox et a l . , 1979; Middlemost, 1980; Le M a i t r e , 1984; Le Bas

et a l . , 1986). In o rde r t o c l a s s i f y t h e magma t y p e s of

Dhan jor i and Jagannathpur vo l can i cs t h e i r Na20 + K2O and Si02

conten ts a re p l o t t e d i n t h i s d i a g r a m a l o n g w i t h

t h e boundar ies suggested by Le Ma i t r e (1984) and

Le Bas et a l . (.1986). I t i s ev ident from the F i g . 43 tha t

samples of both Dhanjor i and Jagannathpur v o l c a n i c s , p l o t in

122

o

O rg

O Z

O OHAN JORl VOLCANICS

• JACANNATHPUR VOLCANICS

AA

O o o o oO

oO

Basalt

1__

• •

• o

o , •

Basaltic andesite

Andesite

48 52 56 60

Fig. 43. Total alkali-silica diagram for Dhanjori

and Jagannathpur volcanics. Classification

boundaries are those of Le Maitre (1984) and

Le Bas et al., (1986).

t h e f i e l d s o f b a s a l t , b a s a l t i c a n d e s i t e a n d a n d e s i t e

HoMever, most of the p lots of Dhan jor i v o l c a n i c s f a l l i n the

f i e l d of b a s a l t s and those of Jagannathpur vo l can i cs l i e i n

t h e f i e l d of b a s a l t i c a n d e s i t e .

I r v i n e and Baragar <1971) have p r o p o s e d n o r m a t i v e

p l a g i o c l a s e composi t ion versus normat ive co lou r index diagram

t o d i s t i n g u i s h b a s a l t , a n d e s i t e , d a c i t e and R h y o l i t e . In t h i s

d iagram, except two samples of Dhanjor i v o l c a n i c s and one of

the Jagannathpur v o l c a n i c s , a l l t h e samples p l o t i n t h e

basa l t f i e l d , the remain ing three samples f a l l in the f i e l d

of andes i te ( F i g . 4 4 ) .

The AFM (A = Na20 + K2O; F = FeO*; M = MgO> te rna ry

diagram has been w ide l y used as a d i s c r i m i n a n t diagram f o r

the igneous rocks . Samples of D h a n j o r i and J a g a n n a t h p u r

v o l c a n i c s , when p l o t t e d i n t h i s d i a g r a m , show a c l e a r

d i s t i n c t i o n between t h e s e s u i t e s ( F i g . 1 1 ) . D h a n j o r i

v o l c a n i c s , showing a moderate i r o n enrichment t r e n d , p l o t i n

t h o l e i i t e f i e l d . On the other hand, samples of Jagannathpur

vo l can i cs do not show d i s t i n c t i v e v a r i a t i o n probably due t o

t h e i r h igh magnesium c o n t e n t s . Samples o f t h i s s u i t e p l o t on

both s ides of the b o u n d a r y , t h e r e f o r e , i n d i c a t i n g t h e i r

t r a n s i t i o n a l na ture between t h o l e i i t e and ca l c - a l ka l i ne

s e r i e s .

M iyash i ro (1974) used the p l o t s 0+ S i02 , FeO* and T i02

con ten ts aga ins t FeO*/MgO r a t i o t o d i s t i n g u i s h the t h o l e i i t i c

and c a l c - a l k a l i n e magma s e r i e s . He <op. c i t ) found tha t i n

t h o l e i i t i c s e r i e s Si02 content shows a slow increase whereas

124

80

6 0

•o c

£ 40

0/

> o E

20

0 D H A N J O R I V O L C A N I C S

• J A G A N N A T H P U R V O L C A N I C S

BosQlt

80 50 40 20 (

Normative Plagioclase composition

Fig.44. Normative plagioclase composition versus

normative colour index binary diagram (after

Irvine and Baragar, 1971) indicating basaltic

composition of Dhanjori and Jagannathpur

volcanics.

IZb

3

2

? 0.5

fM O

• o

• •

I-. I

5

(c)

1 1

c IJHANJORI VOLCANICS


18

16

14

12

o o o

og o o o

X J- X 1 2 3

FeO*/MgO

Fig.45. (a) FeO /MgO versus Si02 binary diagram

(b) FeO /MgO versus FeO binary diagram and

(c) FeO /MgO versus TiOj binary diagram

illustrating nature of Dhanjori and

Jagannathpur volcanics. Classification

boundaries are those of Miyashiro (1974).

12o

i n c a l c - a l k a l i n e s e r i e s i t increases r a p i d l y w i t h i nc reas ing

Fe0*/M90 r a t i o s . FeO* and Ti02 conten ts o-f t h o l e i i t e s e r i e s

• f i r s t show an enrichment and then decrease w i t h i nc reas ing

FeO*/MgO r a t i o w h i l e the cal c - a l k a l i n e s e r i e s shows monotonic

decreases of FeO* and Ti02 w i t h i nc reas ing FeO*/MgO r a t i o .

Fo l low ing the same approach the Si02» FeO* and T i02 conten ts

of Dhanjor i and Jagannathpur vo l can i cs a re p l o t t e d aga ins t

t h e i r FeO*/MgO r a t i o i n F i g . 45 . In Fe0*/Mg0-Si02 p l o t ( F i g .

45a) , m a j o r i t y of the samples of Dhanjor i vo l can i cs p l o t i n

t h o l e i i t i c f i e l d and those of Jagannathpur vo lcan ic l i e in

c a l c - a l k a l i n e f i e l d . In Fe0*/M90-Fe0* diagram ( F i g . 45b)

Dhanjor i vo l can i cs showing an i r on enrichment t r e n d , p l o t i n

t h o l e i i t e f i e l d whereas Jagannathpur vo l can i cs do not show

FeO* enrichment and p l o t in both t h o l e i i t e and c a l c - a l k a l i n e

f i e l d . In FB0*/ l ig0-Ti02 p l o t ( F i g . 45c; both vo l can i c s u i t e s

f i r s t show Ti02 increase and then decrease w i t h i nc reas ing

FeO*/MgO r a t i o w h i c h i s a c h a r a c t e r i s t i c f e a t u r e o f

t h o l e i i t i c s e r i e s . However , t h e samp les f a l l i n c a l c -

a l kal i ne f i e l d .

M iyash i ro and Shido (1975, 1976) observed tha t rocks of

c l a c - a l kal ine s e r i e s tend to have low Cr and Ni va lues than

the rocks of t h o l e i i t i c s e r i e s and suggested tha t the Cr and

Ni v a r i a t i o n s may r e f l e c t d i f f e r e n c e s between s u i t e s i n

degree of d i f f e r e n t i a t i o n r e l a t i v e t o s i l i c a c o n t e n t s .

A l t h o u g h , Cr and Ni c o n t e n t s of b o t h D h a n j o r i a n d

Jagannathpur s u i t e s Are w ide l y v a r i a b l e , they con ta in many

samples w i t h h igh Ni and Cr con ten t . In F i g . 46, Cr and Ni

127

bO

55

50

45

0 DllANJOni VOICAMICS

• JACANNATHPUR VOICANICS

-O

•

•

• / Q/ ft

/ l

. . : o / • /

I * / • • • / *

• / °° / • o

0 ( a )

f

60

55

50

45

10000

1000 100

Ni {ppm)

1000 too

Cr ( p p i i i )

10

10

Fig.46. (a) Ni versus Si02 binary diagram (after Miyashirb

and Shido, 1976) and

(b) Cr versus ^^'ô variation diagram (after

Miyashiro and Shido, 1975) exhibiting the

nature of Dhanjori and Jagannathpur volcanics.

128

contents o-f Dhanjori and Jagannathpur volcanics are plotted

against their Si02 contents. Except seven, all the samples

o-f Dhanjori volcanics contain low S1O2 at particular Ni

content and plot in thoeliite -field, the remaining seven

samples plot in cal c-al kal ine -field (Fig. 46a > . Similarly,

all except five samples of Dhanjori volcanics having low Si02

at particular Cr content, plot in tholeiite -field and rest of

the samples fall in calc-alkaline field (Fig. 46b). On the

other hand, samples of Jagannathpur volcanics have relatively

high Si02 at particular Ni and Cr contents and plot in calc-

al kal ine f iel d.

Trace elements appear to be better discriminant than the

major elements because instead of showing differences in

primary composition they are very sensitive to crystal

fractionation. YTC CY = Y + Zr <ppm), Ti = Ti02>'. X 100, C =

Cr <ppm)] ternary diagram (Davies et al . 1979) may thus be

considered to show the original differentiation trend of a

magmatic suite because Y and Zr are enriched progressively

during fractionation like Na20 and K2O, Ti02 behaves very

much like iron content being enriched in tholeiite suites and

decreasing systematically in both calc-alkaline and magnesian

suites and Cr follows MgO. On YTC diagram samples of

Dhanjori and Jagannathpur volcanics follow a common trend as

their plots fall on the line representing the cal c-al kal ine

trend and beyond towards Cr apex <Fig. 47). This diagram

which is predominantly based on trace elements suggests that

the Dhanjori and Jagannathpur volcanics have evolved along a

trend very similar to that followed by calc-alkalxne rocks.

12S

T1O2X100

Y . Z r

Fig. 47. Y(y + Zr) - T(Ti02%) - C(Cr) diagram

(after Davies et al., 1979) for Dhanjori and

Jagannathpur volcanics showing their calc-alkaline

trend of differentiation.

130

900

200

E a a

100

• • • • o o

• 0

o «o ^ o » " o , o » o


• JACANNATHPUR VOLCANICS

X _L J_ _L 0.2 0.4 0.6 O.ft U 1.6 1.8 2.0

TiO^ versus Zr binary variation diagram

1.0 1.2

Ti02V.

Fig.48.

showing absence of linear relationship between them.

It is a character of calc-alkaline trend of

differentiation.

131

Garcia ^1978) has demonstrated tha t in con t ras t to m i d -

oceanic r i d g e t h o l e i i t i c basa l t t r e n d , vo l can ic arc basa l t s

do not show a systemat ic increase of T i02 w i t h i nc reas ing Zr

c o n t e n t . The T i 0 2 and Zr c o n t e n t s o f O h a n j o r i a n d

Jagannathpur v o l c a n i c s , when p l o t t e d aga ins t each o t h e r , do

not show any r e l a t i o n s h i p ^ F i g . 4 8 ) . The l a c k o-f l i n e a r

r e l a t i o n s h i p between Zr and T1O2 has a l s o been used by

Donel ly and Rogers ^1980) and Rogers e t a 1 . <1984) as a

d i a g n o s t i c -feature o-f c a l c - a l kal ine b a s a l t s .

Most of the d i s c r i m i n a n t diagrams based on v a r i o u s major

e l e m e n t s < F i g . 43 t o 46) i n d i c a t e t h a t D h a n j o r i a n d

Jagannathpur v o l c a n i c s a r e t h o l e i i t e s w i t h ca l c - a l k a l i ne

a f f i n i t y . However, t h e t r a c e e lemen t r e l a t i o n s h i p s as

ev ident in F i g . 47 and 48 suggest tha t both of the vo lcan ic

s u i t e s have been evolved along a common t rend Nhich resembles

t o t h a t o f ca l c - a l k a l i ne s u i t e s . The r o c k s o f t h e s e

c h a r a c t e r i s t i c s have been f o u n d i n o r o g e n i c v o l c a n i c

a s s o c i a t i o n of modern i s l a n d a r c and c o n t i n e n t a l m a r g i n s

where they range in c o m p o s i t i o n f r o m t h o l e i i t i c s e r i e s i n

immature arc to c a l c - a l k a l i n e s e r i e s assoc ia ted w i t h mature

a r c , c o n t i n e n t a l margins and con t i nen ta l c o l l i s i o n zones. In

these areas which l i e along convergent p l a t e boundar ies t he

t h o l e i i t e and c a l c - a l ka l i ne s e r i e s o f r o c k s o c c u r

i n t e r r e l a t e d w i t h each o t h e r . These s e r i e s h a v e been

considered as the two end members between which the g rada t ion

may e x i s t (Baker, 1968; Hakesworth e t al . , 1977) . Caul on and

Thorpe <1981) has c la imed tha t i n na ture there i s no c lea r

132

distinction between the thoeliites and cal c-al kaline rocks

and the rocUs of one series may grade into the other. Magma

compositions can evolve -from tholeiitic to cal c-al Ual ine as

in central Japan (Yanagi and IshizaUa, 1978; or more rarely

•from cal c-al kal i ne to tholeiitic e.g. El Salvador

(Fairbrothers et al . 1978).

An important characteristic of Jagannathpur volcanics is

that there are many samples which have high MgO, Cr and Ni

accompanied by intermediate Si02i LiLE and low HFSE except

Zr. In YTC diagram <Fig. 47), these samples plot towards Cr

apex showing a continuum with calc-alkaline trend. In this

diagram they appear as cal c-al kal i ne analogue of high Mg-

basalts or komatiites of komatiite-tholeiite series. These

are the characteristics which possibly correspond closely to

those of modern boninites (Mickey and Prey, 1982; Cameron et

al ., 1983; Bloomer and Hawkins, 19S7;.

The chondrite normalized REE patterns o+ Dhanjori and

Jagannathpur volcanics show their LREE enriched nature and

almost flat patterns in HREE (Fig. 42). These trends are

clearly distinguishable from basaltic komatiite, liORB and are

closely similar to Archaean as well as modern andesites

(Condie, 1981) and boninite (Hickey and Frey, 1982).

Although the major element compositions of Dhanjori and

Jagannathpur volcanics distinguish them as tholeiites with

calc-alkaline tendency the trace elements and REE patterns

indicate their evolution along^-l^ji cal c-al ka 1 i ne trend.

134

- 1 - 2

- 1 - 3

- 1 - A -

-1-5

-1-6

-1-7 O OHANJORI VOLCANICS • JAGANNATHPUR VOLCANICS

Fig.49. Plot of screened samples of Dhanjori

and Jagannathpur volcanics in discrimant

functions F,versus F_ diagram (after Pearce,

1976), illustrating their volcanic arc tectonic

setting. (WBP = With in plate Basalt;

SHO = Shoshonite; CAB and LKT=Cale-alkaline

basalt and low potassium tholeiite OFB=Ocean

floor basalt.

135

o 0^

« O U.

oDHANJORI VOLCANICS


ISLAND h ARC ( 4 / RIDGE ISLAND

- 4P ^ >

•/ OCEAN \ ' RIDGE

' I

\ OCEAN ISLAND

1 2 3 A

Ti02' /»

Fig.50. Ti02 versus FeO /MgO ratio

binary diagram (after Muller , 1980)

for Dhanjori and Jagannathpur volcanics

exhibiting their arc tectonic setting.

136

(CAB + LKT) .

The Fe0*/M90 - T i 0 2 p l o t ( M u l l e r , 1980) a l s o prov ides a

c l u e to d i s t i n g u i s h t h e b a s a l t s o-f v a r i o u s t e c t o n i c

environments. T h i s diagram a l s o d i s c r i m i n a t e s the Dhanjor i

and Jagannathpur v o l c a n i c s a s i s l a n d a r c b a s a l t a s t h e

ana lyses o-f these v o l c a n i c s have a d i s t i n c t l i n e a r t r e n d

w i t h i n corresponding - f i e ld ( F i g . 5 0 ) .

Sherva is ( 1 9 8 2 ) , on the bas is o-f T i versus "v* p l o t s o-f

many modern v o l c a n i c r o c k a s s o c i a t i o n s , p o i n t e d o u t a

systemat ic increase in T i / V r a t i o s from i s l a n d arc t h o l e i i t i c

b a s a l t s to mid-oceanic r i d g e b a s a l t s t o i n t r a p l a t e v o l c a n i c s .

T i / V r a t i o s in mid-oceanic r i d g e b a s a l t s (MORS) vary -from 20

to 50 whereas in c o n t i n e n t a l r i - f t s and ocean i s l a n d b a s a l t s ,

i t goes upto 100. I s l a n d arc v o l c a n i c s have Ti/'v' r a t i o s o-f

about <20, except f o r c a l c - a l k a l i n e v o l c a n i c s i n w h i c h

magnet i te f r a c t i o n a t i o n causes T i / V r a t i o t o increase so t h a t

they have T i / V r a t i o 2. 15 <*nd over lap MORB f i e l d . Though

T i / V r a t i o s in Dhanjor i and Jagannathpur v o l c a n i c s vAry from

13.60 to 27 .22 and 8 . 9 4 t o 3 2 . 0 1 r e s p e c t i v e l y , most of

samples have t h i s r a t i o l ess than 2 0 . The data p l o t on T i

versus V diagram ( F i g . 51) c l e a r l y d i s t i n g u i s h both of them

as arc r e l a t e d v o l c a n i c s .

P e a r c e ( 1 9 8 2 ) has used T i v e r s u s Z r d i a g r a m t o

d i s c r i m i n a t e the mid-oceanic r i d g e b a s a l t s (MORBs) and a rc

vo lcan ic s u i t e s from the w i t h i n p l a t e vo lcan ic s u i t e s . In

t h i s d i a g r a m ( F i g . 5 2 ) t h e D h a n j o r i a n d J a g a n n a t h p u r

137

600

500

4 0 0

300

200

too -



too

J. 12 t; 16 ia 6 6 to

Ti (ppm ) / 1000

Fig.51. Ti/1000 versus V binary variation

diagram (after Shervais, 1982) for Dhanjori

and Jagannathpur volcanics, illustrating their

arc (or subduction zone) setting.

138

E a. a.

r>—' 'O

5.0

1.0

Q5

0.1


• JAGANNATHPUR VOLCANICS y ^ X

-«» • "^ ' N y ^

• y\^ 1 hy Y'^ i \ / \ V • 'O \

\. ^ ^ / - vT . / ^ 1 \

/ 'N ' ^ / 1 \

/ 1 N

—^ \ L 10 100

Zr(ppm) 1000

Fig.52. Zr versus Ti variation diagram for Dhanjori

and Jagannathpur volcanics showing their arc tectonic

setting. Tectonic setting boundaries are taken from

Pearce (1982).

139

yo l can i cs can c l e a r l y be c l a s s i f i e d as v o l c a n i c a r c i n

cha rac te r . However, t h e r e a r e some sample i n b o t h t h e

vo l can ic s u i t e which p l o t in the area o-f w i t h i n p l a t e lavas

but very near to the - f i e l d o-f arc l avas . Ma t te rs and Pearce

(1987) po in ted out tha t w i t h i n p l a t e charac ter o-f i s l a n d arc

vo l can i cs may be due to the involvement of sub c o n t i n e n t a l

1 i thosphere i n magma genes is .

I n o rder t o determine the t e c t o n i c s e t t i n g of Dhan jor i

and J a g a n n a t h p u r v o l c a n i c s more o b j e c t i v e l y i t seems

a p p r o p r i a t e to compare t h e i r geochemica l c h a r a c t e r s w i t h

those of modern vo l can ic s u i t e s of known t e c t o n i c s e t t i n g .

MORB-normal ized m u l t i - e l e m e n t d i a g r a m s a r e p a r t i c u l a r l y

usefu l f o r comparing a n c i e n t and modern v o l c a n i c s u i t e s

<Pearce, 1982, 1983; Pharaoh and Pearce, 1984) and in recent

years t h i s method has been w i d e l y used t o d e t e r m i n e t h e

t ec ton i c environment of anc ien t b a s a l t s . MORB-normalized

geochemical p a t t e r n s f o r Dhanjor i and Jagannathpur v o l c a n i c s

a re shown in F i g . 53. N o r m a l i z i n g v a l u e s and o r d e r i n g o f

e l e m e n t s a r e t aken f r o m Pearce < ; i 9 8 2 ) . P e a r c e ( 1 9 8 3 )

cons iders tha t w i t h the except ion of Sr , and p o s s i b l y Ti02» r

most of the elements used in the plot are incompatible and

hence the shape of diagram should be largely independent of

the degree of partial melting or crystal fractionation that

the rocks have experienced. Such processes affect only the

absolute concentrations of these elements.

Geochemical patterns of Dhanjori and Jagannathpur

volcanics are almost similar and closely resemble with those

140

100

OHANJORI VOLCANICS

001 - 1 — J J I I I I I I Sr K Hb Ou Ce P Zr Sm Ti Y Yta Cr

Fig.53. MORB-normalized multi

element diagram for Dhanjori and

Jagannathpur volcanics. Normali

zation values are taken from

Pearce (1982).

1 4 1

of cal c-al Ual ine series volcanics. They exhibit se1ecti<ê

enrichment in LILE <Rb, Sr, K and Ba) . Except Zr, Sm, Ti, Y

and Yb show typically low abundances (Fig. 53). This type of

pattern has been reported from the boninite tHickey and Frey,

1982) which has been considered to be a product of subduction

related melting. The high LILE/HFS element ratios the

characteristic of modern calc-alkaline volcanics erupted at

destructive plate margins are thought to be fundamentally

source related (Saunders et al . 1980^. Similar to boninite

LILE enriched HFSE depleted patterns are duplicated by

Dhanjori and Jagannathpur volcanics and therefore they Are

assigned to convergent zone tectonic setting.

CHAPTER VI

PETR06ENESIS

In the preceding chapters the geochemical characters of

Dhanjori and Jagannathpur volcanics, in terms of major and

trace elements have been discussed in detail. The behaviour

and relationship of various elements have brought certain

significant and interesting features concerning their origin.

In the present chapter attempt has been made to elucidate

such features within the limited scope of this work.

Dhanjori and Jagannathpur volcanics, occurring on the

north eastern and western extremities of Singhbhum Granite

have been considered as contemporary (Sarkar and Saha, 1977,

1983; Banerjee, 1982; Iyengar and Murthy, 1982; Saha et al.,

1988). Although various differences exist in the

composition of these volcanics, their plots in different

variation diagrams follow a common trend. This would suggest

that atleast the processes that controlled the abundances and

ratios of various elements in these volcanics remained the

same during the magmatism. In order to understand the

tectonomagmatic evolution of these volcanics, it seems

necessary to account for the differences in the chemical

composition of these volcanics. From these differences the

evolution could possibly be interpreted as either due to

changing conditions of magma generation or to differing

evQlutionaly paths of the magmas. The latter possibility may

be ruled out as both of these volcanics are evolved along the

calc-alkal ine trend.

143

CIPW n o r m a t i v e m i n e r a l o g y o-f D h a n j o r i and Jaganna thpur

w o l c a n i c s show t h a t b o t h o-f t h e s e y o l c a n i c s r a n g e - f rom

o l i v i n e t h o l e i i t e t o q u a r t z t h o l e i i t e < F i g . 1 2 ) . Both of

t h e s e v o l c a n i c s have h i g h e r l e v e l s o f f e r r o m a g n e s i a n e l e m e n t s

wh i ch a r e no t e x p l i c a b l e -from t h e i r n o r m a t i v e c o m p o s i t i o n s .

M g - n u m b e r s o-f D h a n j o r i v o l c a n i c s < 4 2 . 1 8 t o 6 7 . 0 8 ) a r e

accompanied by l o w e r N i (48 ppm t o 331 ppm) and Cr (12 ppm t o

1491 ppm) c o n t e n t s a s c o m p a r e d t o J a g a n n a t h p u r v o l c a n i c s

where Mg-numbers ( 38 .39 t o 82 .46 ) a l o n g w i t h t h e N i (55 ppm t o

900 ppm) and Cr (38 ppm t o 5400 ppm) c o n t e n t s v a r y w i d e l y .

However, bo th o f t hese v o l c a n i c s c o n t a i n some o f t h e samples

i n w h i c h N i and Cr v a l u e s approach those e s t i m a t e d f o r t h e

l i q u i d s i n e q u i l i b r i u m w i t h m a n t l e p e r i d o t i t e ( S a t o , 1 9 7 7 ) .

Mg-numbers i n some of t h e samples i n J a g a n n a t h p u r v o l c a n i c s

a r e a l s o h i g h e r than t h e v a l u e of 7 0 , s u g g e s t e d by Green e t

a l . , ( 1 9 7 4 ) f o r t h e m e l t s i n e q u i l i b r i u m w i t h m a n t l e

p e r i d o t i t e .

The d e c o u p l i n g of v a r i o u s ma jo r and t r a c e e l emen ts i n

D h a n j o r i a n d J a g a n n a t h p u r v o l c a n i c s a s s i g n s t h e m t o

s u b d u c t i o n r e l a t e d m a ^ a t i s m wh i ch i s g e n e r a l l y t h o u g h t t o

r e s u l t f r o m t h e h y d r o u s m e l t i n g o f p e r i d o t i t e m a n t l e

( G r e e n , 1 9 8 2 ; Mysen , 1 9 8 2 ; W y l l i e , 1 9 8 2 ) . B o t h o f t h e s e

v o l c a n i c s u i t e s c o n t a i n samp les , showing v a r i o u s chemica l

c h a r a c t e r s , s i m i l a r t o modern b o n i n i t i c r o c k s . However, due

t o t h e i r h i g h e r T i 0 2 c o n t e n t s t h a n t h e b o n i n i t e s OO.S'/i TiOo)

these samples do no t f o l l o w t h e d e f i n i t i o n o f b o n i n i t i c

s e r i e s r o c k s , ( F i g . 54) as p roposed by M e i j e r ( 1 9 8 0 ) . S i n c e

ma jo r and t r a c e e l e m e n t s i n b o t h o f t h e s e v o l c a n i c s a r e

144

oDMANJORI VOLCANICS

• JAGANNA7HPUR VOLCANICS

Fig.54. Normative Ilmenite x 10 - Quartz - Enstatite

ternary diagram (after Meijer , 1980) for Dhanjori

and Jagannathpur volcanics, illustrating their calc-

alkaline series membership rather than the boninite

series.

145

w i d e l y v a r i a b l e ( T a b l e Vll) and show i s l a n d a r c t h o l e l i t e as

w e l l as c a l c - a l k a l i n e c h a r a c t e r s , t hey a r e a t t r i b u t a b l e t o

t h e key r o l e o f w a t e r wh ich c o n t r o l l e d t h e m e l t i n g and phase

r e l a t i o n s h i p s i n t h e i r m a n t l e s o u r c e s ( B e c c a l u v a and S e r r i ,

1988) .

One o-f t h e geochemica l c h a r a c t e r t h a t d e s e r v e s comment

c o n c e r n s t h e c o n c e n t r a t i o n o f r e f r a c t o r y e l e m e n t s Ni and C r

( T a b l e K>, '^l and V I I ) . Both of t hese v o l c a n i c s on one hand

c o n t a i n samples w h i c h h a v e h i g h N i a n d Cr c o n c e n t r a t i o n s

s i m i l a r t o t hose f o u n d i n m i d - o c e a n i c r i d g e b a s a l t s (Sun e t

a l . , 1 9 7 9 ) b u t on t h e o t h e r h a n d , s a m p l e s a l s o s h o w

s i g n i f i c a n t l y l o w e r t h a n t y p i c a l v a l u e s f o u n d i n i s l a n d a r c

v o l c a n i c s (Jakes and W h i t e , l 9 7 2 ; Ewar t e t a l . , 1 9 7 7 ) . Based

on t h e u n d e r s t a n d i n g o f p e t r o g e n e t i c a s p e c t s o f b a s a l t s

(R ingwood , 1975) i t a p p e a r s t h a t m o r e e v o l v e d members o f

t h e s e v o l c a n i c s w i t h low Mg-numbers ( l e s s t h a n 60) c o u l d have

been g e n e r a t e d t h r o u g h f r a c t i o n a l c r y s t a l l i z a t i o n by removal

o f M g - r i c h phases such as o l i v i n e a n d / o r p y r o x e n e . However,

bo th o f t h e s e v o l c a n i c s c o n t a i n d i f f e r e n t N i and Cr v a l u e s a t

s i m i l a r Mg-numbers a n d v i c e v e r s a ( F i g . 25 a n d 3 1 ) . I n

D h a n j o r i v o l c a n i c s N i and Cr v a l u e s a r e g e n e r a l l y low wh i ch

may be a t t r i b u t e d t o c r y s t a l f r a c t i o n a t i o n . On the o t h e r

h a n d , N i a n d Cr v a l u e s o f J a g a n n a t h p u r v o l c a n i c s a r e

i n d i c a t i v e o f t h e i r p r i m a r y n a t u r e a n d show m i n o r c r y s t a l

f r a c t i o n a t i o n .

Hanson a n d L a n g m u i r ( 1 9 7 8 ) a n d U i l k i n s o n ( 1 9 8 1 )

sugges ted t h a t Mg-number r e l a t e s t o t h e d e g r e e o f p a r t i a l

146

m e l t i n g and m a n t l e h e t r o g e n e i t y . I-f Mg-number i s assumed as

a - f u n c t i o n o-f t e m p e r a t u r e and e x t e n t o-f m e l t i n g (Hanson and

L a n g m u i r , 1 9 7 8 ; , i t s h o u l d be r e f l e c t e d i n t n e t r a c e e l emen ts

and t h e r e l a t i o n s h i p s b e t w e e n v a r i o u s m a j o r e l e m e n t s a n d

t r a c e e l e m e n t s s h o u l d be c l e a r . V a r i o u s e lemen t abundances

and e lement r a t i o i n D h a n j o r i and Jaganna thpu r v o l c a n i c s a r e

no t a d e q u a t e l y e x p l a i n e d by t h e p r o c e s s e s o f f r a c t i o n a l

c r y s t a l l i z a t i o n , p a r t i a l m e l t i n g t o d i f f e r e n t d e g r e e s o f

m a n t l e s o u r c e s o r v a r i a t i o n s i n p r o p o r t i o n s o f ma jo r m a n t l e

p h a s e s .

Mg-numbers o f t h e s e v o l c a n i c s when p l o t t e d a g a i n s t t h e i r

d i f f e r e n t i a t i o n i n d i c e s show t h a t bo th o f t hese v o l c a n i c s

have d i f f e r e n t Mg-numbers a t s i m i l a r d i f f e r e n t i a t i o n i n d i c e s

and v i c e v e r s a ( F i g . 5 5 ) . D h a n j o r i v o l c a n i c s h a v i n g low Mg -

numbers and low d i f f e r e n t i a t i o n i n d i c e s a p p e a r a s m i d d l e

s t a g e b a s a l t s whereas Jaganna thpu r v o l c a n i c s c o n t a i n h i g h Mg-

numbers and h i g h d i f f e r e n t i a t i o n i n d i c e s and a r e g e n e r a l l y

l a t e s t a g e b a s a l t s . However , v a r i a t i o n s i n s i l i c a c o n t e n t s

o f t h e s e v o l c a n i c s a r e somewha t s i m i l a r ( T a b l e 'v'I I ) .

A l t h o u g h , t hese v o l c a n i c s have s i m i l a r s i l i c a c o n t e n t s a t

d i f f e r e n t Mg-numbers a n d v i c e v e r s a , t h e r e l a t i o n s h i p s

between Si02 ^ n d M g - n u m b e r s ( F i g . 10) i n d i c a t e t h a t t h e i r

S i 0 2 c o n t e n t s a r e h i g h e r t h a n t h a t e x p e c t e d a t p a r t i c u l a r Mg-

numbers i n MORE and k o m a t i i t e . I t t h e r e f o r e seems r e a s o n a b l e

t h a t Mg-numbers a r e l a r g e l y c o n t r o l l e d by m a n t l e h e t r o g e n e i t y

and f r a c t i o n a l c r y s t a l l i z a t i o n p l a y e d an i m p o r t a n t r o l e i n

t h e i r m o d i f i c a t i o n .

147

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Sun and N e s b i t t ( 1 9 7 8 ) a n d N e s b i t t e t a 1 . , < 1 9 7 9 )

i n d i c a t e d t h a t A l 2 0 3 / T i 0 2 and Ca0 /T i02 r a t i o s oHF p r i m i t i v e

MORBs and k o m a t i i t e s i n c r e a s e a l o n g w i t h t h e d e g r e e o-f

p a r t i a l m e l t i n g u p t o t h e r a t i o i n c h o n d r i t e s ( 2 0 a n d 17

r e s p e c t i v e l y ) and sugges ted t h a t MORBs and k o m a t i i t e s a r e

d e r i v e d f r o m t h e n o n - d e p l e t e d m a n t l e m a t e r i a l s . F u r t h e r m o r e ,

t hey a r g u e d t h a t t h e r o c k s w i t h h i g h A l 2 0 3 / T i 0 2 And Ca0 /T i02

r a t i o s were fo rmed by t h e m e l t i n g o f a d e p l e t e d sou rce wh i ch

had e x p e r i e n c e d a p r e v i o u s e p i s o d e o f magma e x t r a c t i o n .

A l 2 0 3 / T i 0 2 a n d C a 0 / T i 0 2 r a t i o s o f D h a n j o r i a n d

Jaganna thpur v o l c a n i c s do n o t show l a r g e v a r i a t i o n s . T h e

A l 2 0 3 / ^ 1 0 2 r a t i o s of D h a n j o r i and Jaganna thpu r v o l c a n i c s v a r y

frcMn 7 .23 t o 17 .92 and 8 .32 t o 31 .50 r e s p e c t i v e l y whereas

Ca0 /T i02 r a t i o s range f r om 5 .71 t o 18 .07 and 2 . 8 7 t o 17 .88

r e s p e c t i v e l y . S i n c e m a j o r i t y o f t h e samples i n b o t h of t h e s e

s u i t e s c o n t a i n A l 2 0 3 / T i 0 2 a n d C a 0 / T i O 2 r a t i o s l e s s t h a n

c h o n d r i t e (20 and 17 r e s p e c t i v e l y ) , i t a p p e a r s t h a t b o t h o f

t h e s e v o l c a n i c s a r e d e r i v e d f r o m n o n - d e p l e t e d s o u r c e s

p r o b a b l y s i m i l a r t o MORB wh ich have no t undergone an e a r l i e r

e p i s o d e o f m e l t i n g <Sun and N e s b i t t , 1978; N e s b i t t e t a l . ,

1979 ; Sun e t a l . , 1 9 7 9 ) .

C a 0 / A l 2 0 3 r a t i o s o f v o l c a n i c r o c k s h a s a l s o b e e n

c o n s i d e r e d as an i m p o r t a n t t o o l i n p e t r o g e n e t i c s t u d i e s ( e . g .

Cawthorn and S t r o n g , 1974; N e s b i t t and Sun, 1976; N e s b i t t e t

a l . , 1979; P e r f i t e t a l . , 1980; C r a w f o r d and Cameron, 1985;

Becca luva and S e r r i , 1 9 8 8 ) . Most o f t h e samples of D h a n j o r i

v o l c a n i c s have CaO/Al 2O3 r a t i o g r e a t e r t h a n c h o n d r i t e o r

149

p r i m i t i v e upper m a n t l e v a l u e < 0 . 9 , C l a u g e a n d F r e y , 1982 )

whereas i n Jaganna thpur w o l c a n i c s , m a j o r i t y o f t he samples

show CaO/Al 2O3 r a t i o l e s s t h a n c h o n d r i t e o r p r i m i t i v e upper

m a n t l e v a l u e . F i g . 56 i l l u s t r a t e s t h e r e l a t i o n s h i p s between

Ca0 /A l203 and A l 2 0 3 / T i 0 2 r a t i o s o f t h e s e v o l c a n i c s . A l t h o u g h

Ca0 /A l203 r a t i o s o f D h a n j o r i v o l c a n i c s < 0 . 5 3 t o 1 . 6 5 ) a n d

Jaganna thpu r v o l c a n i c s ( 0 . 2 8 t o 1.22) a r e w i d e l y v a r i a b l e ,

t h e i r A l 2 0 3 / 1 1 0 2 r a t i o s a r e s i m i l a r t o t h a t f ound i n MORE and

k o m a t i i t e . I t t h e r e f o r e a p p e a r s t h a t C a 0 / A l 2 0 3 r a t i o s o f

t h e s e v o l c a n i c s p r o b a b l y r e f l e c t v a r i a t i o n s i n t h e

c r y s t a l l i z a t i o n h i s t o r i e s .

I n F i g . 5 7 , C a 0 / A l 2 0 3 r a t i o s o f D h a n j o r i a n d

Jaganna thpur v o l c a n i c s a r e p l o t t e d a g a i n s t t h e i r Mg-numbers.

Both of t hese v o l c a n i c s c o n t a i n d i f f e r e n t Ca0 /A l203 r a t i o a t

s i m i l a r Mg-numbers and v i c e - v e r s a . However, t h e dec rease o f

Ca0/A l203 r a t i o i n bo th of t hese v o l c a n i c s w i t h d e c r e a s i n g

Mg-numbers r e f l e c t t h e f r a c t i o n a t i o n of c l i n o p y r o x e n e ( P e r f i t

e t a l . , 1 9 8 0 ) . N i and Cr v a l u e s o f b o t h of t hese v o l c a n i c s

behave i n a s i m i l a r manner w i t h Mg-numbers < F i g . 25 and 31)

i t i s t h e r e f o r e sugges ted t h a t c l i n o p y r o x e n e f r a c t i o n a t i o n

c o n t r o l s t h e a b u n d a n c e s o f N i a n d Cr i n b o t h o f t h e s e

vo l c a n i c s .

C l i n o p y r o x e n e becomes a s i g n i f i c a n t f r a c t i o n a t i n g phase

o n l y i n more e v o l v e d MORB, o r a b o v e 1 0 . 5 K b a r w h e r e i t

r e p l a c e s o l i v i n e as a 1 i q u i d u s phase ( K u h s i r o , 1973 ; Bender

e t a l . , 1978 ; Walker e t a l . , 1979; W i l k i n s o n , 1982) or when

magma-mix ing o c c u r s i n open-sys tem magma chambers (Dungan and

150

1.8

1.6

1 U

12

1.0

O

<

o

"0.6l-

0.

—/



MORB FIELD

0.2

0.0

Chondrrtt

10 20 30 40

Fig.56. Al-Oo/TiO- versus CaO/Al-O^ binary diagram

for Dhanjori and Jagannathpur volcanics indicating

their derivation from non-depleted sources. Fields

for MORB, arc basalt and andesite are taken from

Crawford and Cameron (1985).

151

1.65

1.5 O OHANJORI V0LCANIC5 • JACANNATHPUR VOLCANIC S

01 I 1 I 1 U K)0, 80 60 40 20 0

Mg Number

Fig.57. Mg-Number versus CaO/AlÔ^ binary diagram

for Dhanjori and Jagannathpur voxcanics, exhibiting

the variations in Mg-Numbers and CaO/AlÔ., ratios.

Fields of high magnesiam MORE and island arc basalts

arc taken from Beccaluva and Serri (1988).

152

Rhodes, 1978; Walker e t a l . , 1 9 7 9 ) . A c c o r d i n g t o U l i l U i n s o n

<1982 ) , t h e c r y s t a l l i z a t i o n s e q u e n c e o f m a g n e s i a n MORB

i n d i c a t e s t h a t a t low p r e s s u r e s (<5 Kbars) c l i n o p y r o x e n e does

no t c r y s t a l l i z e u n t i l t he s e p a r a t i o n of s i g n i f i c a n t o l i v i n e

a n d p l a g i o c l a s e ( s o m e t i m e s a f t e r a p p r o x i m a t e l y 50'/.

c r y s t a l 1 i z a t i o n ) .

Sun e t a l . (1979) s u g g e s t e d t h a t MORB w i t h l ow T i 0 2

<~0.?•/.>, h i g h AI2O3 ( ~ 1 6 . 0 X ) a n d CaO ( ~ 1 2 . 0 X ; ) , a n d h i g h

A l 2 0 3 / 1 1 0 2 ( ~ 2 0 ) , Ca0 /T i02 (~17) r a t i o s a r e g e n e r a t e d by a

l a r g e degree of p a r t i a l m e l t i n g (~25' / i ) w h e r e a s h i g h T i 0 2

(~1 .5Z> , and low A l 2 0 3 / T i 0 2 (~10) , CaO/T i02 <""/> r a t i o s a r e

d e r i v e d by a s m a l l e r degree (^15%) o f p a r t i a l m e l t i n g of a

s i m i l a r s o u r c e . The p o s i t i o n s o f D h a n j o r i and J a g a n n a t h p u r

v o l c a n i c s r e l a t i v e t o k o m a t i i t e and MORB a r e i l l u s t r a t e d i n

F i g . 17 w h i c h e m p h a s i z e s t h e i r T i 0 2 c o n t e n t s . A l 2 0 3 / T i 0 2

r a t i o s o f t h e s e v o l c a n i c s p l o t t h r o u g h a l m o s t t h e who le f i e l d

o f MORB and beyond towards lower T i 0 2 ( F i g . 1 7 a ) . C a 0 / T i 0 2

r a t i o s p l o t r e m a r k a b l y below t h e f i e l d o f MORB and b e y o n d ,

s h o w i n g s i m i l a r g r a d u a l i n c r e a s e w i t h d e c r e a s i n g T i 0 2

c o n t e n t s ( F i g . 17b> . T h e s e r e l a t i o n s h i p s l e a d t o s u g g e s t

t h a t T i i s c o m p a t i b l e and A! and Ca a r e h e l d i n r e s i d u a l

p h a s e s , such as p y r o x e n e , g a r n e t , p l a g i o c l a s e and s p i n e l (Sun

e t a l . , 1 9 7 9 ) . The c o m p l e t e s p e c t r u m o f A l 2 0 3 / T i 0 2 a n d

Ca0 /T i02 v a l u e s o f t hese v o l c a n i c s , a l l l y i n g a l o n g the same

t r e n d c o u l d a l s o be i n t e r p r e t e d a s r e s u l t i n g f r o m t h e

con t i nuum o f magmatism w i t h h i g h T i 0 2 samples b e i n g t h e l e a s t

h y d r o u s l y f r a c t i o n a t e d magmas a n d l o w e r T i 0 2 s a m p l e s

r e p r e s e n t i n g r e l a t i v e l y more h y d r o u s l y f r a c t i o n a t e d magmas

15,

<KdTj^^^ ~ 1 . 5 and K d j i * " ^ ~ 7 . 5 , Pearce and N o r r y , 1 9 7 9 ) .

Ti02/P20>=i rai t i OS i n D h a n j o r i and Jaganna thpur y o l c a n i c s

v a r y -from 3 . 6 8 t o 13 .80 and 1.07 t o 2 1 . 0 r e s p e c t i v e l y whereas

t h i s r a t i o i n MORS and k o m a t i i t e i s c l o s e t o 10 ^ N e s b i t t and

Sun, 1976; Sun e t a1 . , 1 9 7 9 ) . About 85'/. samples o f D h a n j o r i

and 23% samples o-f Jaganna thpur v o l c a n i c s , showing T i 0 2 / P 2 0 5

r a t i o l e s s than c h o n d r i t e r a t i o , i n d i c a t e P2O5 e n r i c h m e n t

r e l a t i v e t o T i 0 2 . On t h e o t h e r h a n d , 10% samples of D h a n j o r i

and 37'/. samples of J a g a n n a t h p u r v o l c a n i c s h a v e T i 0 2 / P 2 0 5

r a t i o h i g h e r t h a n c h o n d r i t e r a t i o and t h u s i n d i c a t e d e p l e t i o n

o f P2O5 r e l a t i v e t o T i 0 2 a b u n d a n c e s . T h e r e m a i n i n g 5%

samp les of D h a n j o r i and 40><; samples o f Jaganna thpu r v o l c a n c i s

c o n t a i n T i 0 2 / P 2 0 5 r a t i o s i m i l a r o r c l o s e t o c h o n d r i t e r a t i o

( T a b l e Vlll and IX> . S i n c e t h e a b u n d a n c e o f P2'^5 s t e n t s

r e l a t e d t o t h e d e g r e e o f p a r t i a l m e l t i n g a n d i n i t i a l

c o m p o s i t i o n of t h e m e l t r a t h e r than t h e f r a c t i o n a t i o n o f any

p h a s e ( M u l l e n , 1 9 8 3 ) , i t a p p e a r s t h a t d u r i n g m a g m a t i c

e v o l u t i o n o f t hese v o l c a n i c s T i b e h a v e d a s a c o m p a t i b l e

e l e m e n t .

T i 0 2 / P 2 0 5 r a t i o o f t h e magma i s d e p e n d e n t on t h e

p e r c e n t a g e o f w a t e r i n t h e o r i g i n a l m e l t , a m o u n t o f

f r a c t i o n a t i o n of s i l i c a t e p h a s e s a n d d e p t h . I f OH" i s

p r e s e n t i n t h e m a n t l e , t h e n w i t h t h e d e p t h of p a r t i a l m e l t i n g

t h e c o n c e n t r a t i o n of T i and P bo th w i l l i n c r e a s e i n the m e l t

(Chazen and V o g e l , 1 9 7 4 ) . T h i » w o u l d i m p l y i n t h e p r e s e n t

cases t h a t magmas o f D h a n j o r i and J a ^ i i ^ a t h p u r v o l c a n i c s were

*ormed ¥nth variable water contents.

154

Th'e i n c r e a s i n g t r e n d s o-f T i 0 2 w i t h d e c r e a s i n g MgO

c o n t e n t i n bo th o-f t hese v o l c a n i c s u i t e s a r e c o n s i s t a n t w i t h

t h e - f r a c t i o n a l c r y s t a l l i z a t i o n of o l i v i n e +_ p l a g i o c l a s e +.

c l i n o p y r o x e n e ( P e r f i t e t a l . , 1980) and a r e c o m p a t i b l e w i t h

t h e p e t r o g e n e s i s i n v o l v i n g T i b e a r i n g phases ( e . g . p h i o g o p i t e ,

a m p h i b o l e , F e - T i o x i d e ) as 1 i q u i d u s o r near 1 i q u i d u s p h a s e .

D h a n j o r i v o l c a n i c s show a s y m p a t h e t i c r e l a t i o n s h i p between

KÔ and T i 0 2 < F i g . 18) and t h e i r Mn0 /T i02 r a t i o i n c r e a s e s

w i t h d e c r e a s i n g TiOo c o n t e n t < F i g . 2 2 ) . F u r t h e r m o r e , t h e i r

i r o n e n r i c h m e n t t r e n d < F i g . 11) and Fe203/Fe0 r a t i o <0.24 t o

0 . 6 4 ) a r e i n a c c o r d w i t h h i g h i r o n t y p e o f f r a c t i o n a t i o n

(Wa lke r and P o l d e r v a a r t , 1 9 4 9 } K u n o , 1 9 6 8 ) . A l l t h e s e

f e a t u r e s a r e i n d i c a t i v e of amph ibo le f r a c t i o n a t i o n . On t h e

o t h e r h a n d , i n Jaganna thpu r v o l c a n i c s K2O has no r e l a t i o n s h i p

w i t h T i 0 2 < F i g . 18) and t h e i r K 2 0 / T i 0 2 r a t i o s a r e h i g h ( 0 . 0 4

t o 5 . 4 6 ) . M o r e o v e r , t h e i r Mn0 /T i02 r a t i o show a dec rease

w i t h i n c r e a s i n g T i 0 2 t F i g . 2 2 ) , r e l a t i v e l y h i g h S i O j , l a c k o f

i r o n e n r i c h m e n t ( F i g . 11) and h i g h Fe203/Fe0 r a t i o ( 0 . 2 3 t o

1.32) a r e s u g g e s t i v e o f t i t a n o - m a g n e t i t e f r a c t i o n a t i o n .

F r a c t i o n a t i o n o f a m p h i b o l e a n d / o r m a g n e t i t e h a v e b e e n

sugges ted as t h e mechanism f o r t he o r i g i n o f a n d e s i t e f r om

t h e b a s a l t i c magmas i n c a l c - a l k a l i n e s e r i e s ( O s b o r n , 1959,

1 9 6 2 , 1 9 6 9 ; C a w t h o r n a n d O ' H a r a , 1 9 7 6 ) . H e n c e , t h e

a s s o c i a t i o n of i s l a n d a r c r e l a t e d b a s a l t i c rocUs of D h a n j o r i

and Jaganna thpur v o l c a n i c s wh i ch deve lop a l o n g c a l c - a l k a l i n e

t r e n d s w i t h t he f r a c t i o n a t i o n o f a m p h i b o l e a n d m a g n e t i t e

r e s p e c t i v e l y a r e p l a u s i b l e .

155

I n a t t e m p t t o r e p r e s e n t t h e m a g m a t i c c h a r a c t e r o f

v o l c a n i c r o c k s n u m e r i c a l l y , Sagimura (1968) d e v i s e d t h e t a (8)

i n d e x , wh ich i s c a l c u l a t e d as - f o l l o w s

Na20 + K2O

SiOo - 47 JS. - — — — — — _ — — — — — — —

where S i02 i s i n w e i g h t p e r c e n t a n d o t h e r s u b s t a n c e s i n

m o l e c u l a r p r o p o r t i o n s . A c c o r d i n g t o S a g i m u r a < o p . c i t . )

v o l c a n i c r o c k s w i t h l a r g e Q v a l u e s may h a v e been

g e n e r a t e d f r o m s i l i c a r i c h t h o l e i i t e whereas t hose -for wh ich

v a l u e i s sma l l may h a v e been d e r i v e d - f rom a l k a l i b a s a l t

magma. S u g i s a k i < 1 9 7 6 ) s u g g e s t e d t h a t © i n d i c e s o f

v o l c a n i c r o c k s a l o n g t h e o c e a n r i d g e s Are a p p r o x i m a t e l y

c o n s t a n t , v a r y i n g i n between 34 and 3 7 . S i n c e © i n d i c e s of

D h a n j o r i and Jaganna thpu r vo l c a n i c s v a r y f r o m 2 1 . 0 8 t o 4 8 . 4 9

and 2 7 . 2 1 t o 4 9 . 9 7 i t appea rs bo th a l k a l i b a s a l t magma and

s i l i c a r i c h t h o l e i i t e were i n v o l v e d i n t h e e v o l u t i o n o f t h e s e

v o l c a n i c s . I t has been shown e x p e r i m e n t a l l y ( G r e e n , 1969,

1973) t h a t a t lower p a r t i a l p r e s s u r e s of w a t e r t h e magma may

be e i t h e r n e p h e l i n i t i c o r t h o l e i i t i c d e p e n d i n g upon t h e

degree o f p a r t i a l m e l t i n g . Y o d e r a n d T i l l e y ( 1 9 6 2 ) h a v e

d e m o n s t r a t e d t h a t t h e d i f f e r e n t i a t i o n of a b a s a l t i c magma a t

h i g h p r e s s u r e (20 K b a r s ) w i l l be c o n t r o l l e d by f r a c t i o n a l

c r y s t a l l i z a t i o n of g a r n e t and c l i n o p y r o x e n e . The f r a c t i o n a l

c r y s t a l l i z a t i o n o f g a r n e t f r o m t h o l e i i t i c l i q u i d s m i g h t

p roduce a l k a l i b a s a l t w h i l e f r a c t i o n a t i o n o f c l i n o p y r o x e n e

f r o m a l k a l i b a s a l t w o u l d c a u s e t h e r e s i d u a l l i q u i d t o

d i f f e r e n t i a t e t owards t h o l e i i t e . The d i s c r i p a n c i e s between

156

SiOo c o n t e n t s and t h e t a i n d i c e s o f D h a n j o r i and Jaganna thpur

v o l c a n i c s may t h e r e f o r e be e x p l a i n e d as r e s u l t i n g -from t h e

con t i nuum o f magmatism f r o m t h e h e t r o g e n e o u s s o u r c e s w i t h

h i g h Q v a l u e s a m p l e s b e i n g t h e l e a s t c1 i n o p y r o x e n e

f r a c t i o n a t e d a n d l o w Q s a m p l e s r e p r e s e n t i n g m o r e

c l i n o p y r o x e n e f r a c t i o n a t e d s a m p l e s . N i and Cr v a l u e s i n b o t h

o f t h e s e v o l c a n i c s s u p p o r t t h i s o b s e r v a t i o n .

Most of t h e model f o r t h e g e n e r a t i o n o f a l k a l i b a s a l t o r

s i l i c a u n d e r s a t u r a t e d b a s a l t sugges t t h a t i t t a k e s p l a c e a t

d e p t h s where g a r n e t i s s t a b l e (Hakeswor th and P o w e l l , 1 9 8 0 ) .

The A I 2 O 3 c o n t e n t o f m e l t i n e q u i l i b r i u m w i t h g a r n e t

c o n t a i n i n g abou t 22Vi Al 2O3 i s f i x e d t o abou t 11% as a l u m i n a

i s an e s s e n t i a l s t r u c t u r a l c o n s t i t u e n t i n g a r n e t and Kd f o r

AI2O3 between g a r n e t a n d m e l t i s a b o u t 2 < L a n g m u i r a n d

Hanson, 1 9 8 0 ) . Both D h a n j o r i a n d J a g a n n a t h p u r v o l c a n i c s

c o n t a i n low A1203, d e p l e t e d HREE p a t t e r n s , h i g h (Ce/Yb)^^ and

Z r / Y r a t i o s wh i ch s u g g e s t t h e p r e s e n c e o f g a r n e t as a

r e s i d u a l p h a s e i n t h e i r m a n t l e s o u r c e s b e f o r e m e l t

s e p a r a t i o n .

Both D h a n j o r i and J a g a n n a t h p u r v o l c a n i c s h a v e h i g h

c o n c e n t r a t i o n s L I L e l emen ts v i s , K, Rb , Sr and Ba r e l a t i v e t o

MORB ( F i g . 5 3 ) . A l t h o u g h t h e e n r i c h m e n t o f t hese e lemen ts

a r e c h a r a c t e r i t i s t i c f e a t u r e of c o n t i n e n t a l c r u s t ( R o g e r s ,

1982; Dupuy and D o s t a l , 1 9 8 4 ) , c r u s t a l c o n t a m i n a t i o n cannot

be assumed as the cause f o r t h e obse rved abundances of t hese

e l e m e n t s . C o n t a m i n a t e d b a s a l t s e x h i b i t a p o s i t i v e

c o r r e l a t i o n between f e r r o m a g n e s i a n t r a c e e l e m e n t s i (Huppe r t

157

and S p a r k s , 1985) wh i ch i s no t obse rved i n t hese v o l c a n i c s

The f e r r o m a g n e s i a n t r a c e e l e m e n t s a l s o s h o w p o o r

r e l a t i o n s h i p s w i t h S i 0 2 < F i 9 . 4 6 ) . Hence t h e s e may be

•fundamental 1 y s o u r c e r e l a ted .

Due t o t h e i r low i o n i c p o t e n t i a l < c h a r g e / r a d i u s r a t i o )

L ILE have a g r e a t e r tendency t o be m o b i l i z e d by t h e - f l u i d

phase (Saunders e t a l . , 1980; P e a r c e , 1982; 1983) and -for

t h i s reason L ILE e n r i c h m e n t i n D h a n j o r i a n d J a g a n n a t h p u r

v o l c a n i c s may be a t t r i b u t e d t o t h e m e t a s o m a t i s m o-f m a n t l e

s o u r c e r e g i o n s by h y d r o u s - f l u i d s .

The d i s t r i b u t i o n o f h i g h - f i e l d s t r e n g t h e l e m e n t s namely

P, T i , Zr and Y i n b o t h o-f t h e s e v o l c a n i c s u i t e s are c o m p l e x ,

a s compared t o MORE ( F i g . 5 3 ) . The most p u z z l i n g a s p e c t o-f

t h e HFSE abundances i n D h a n j o r i and Jaganna thpu r v o l c a n i c s

are t h e o r i g i n o-f Zr e n r i c h m e n t . Both of t h e s e v o l c a n i c s show

an e n r i c h m e n t o f Zr and a c o r r e s p o n d i n g dec rease i n T i . Low

T i / Z r r a t i o s l i k e those f o u n d i n D h a n j o r i and Jaganna thpur

v o l c a n i c s <21.53 t o 32 .44 and 10 .33 t o 3 7 . 5 2 r e s p e c t i v e l y )

a r e c h a r a c t e r i s t i c o f h i g h l y d i f f e r e n t i a t e d r o c k s ( g r a n i t e s

a n d r h y o l i t e s ; P e a r c e a n d N o r r y , 1 9 7 9 ) w h i c h h a v e

f r a c t i o n a t e d F e - T i o x i d e s . Low T i / Z r r a t i o s a r e a l s o f o u n d

i n some k i m b e r l i t e s ( K a b l e e t a l . , 1975; Fesq e t a l . , 1 9 7 5 ) ,

and may r e s u l t f r o m r e s i d u a l g a r n e t and c l i n o p y r o x e n e s i n c e

t h e s e m i n e r a l s h a v e h i g h e r m i n e r a l / m e l t p a r t i t i o n

c o e f f i c i e n t s f o r T i and Zr (Shimuzu and A l 1 e g r e , 1978; Pearce

and N o r r y , 1 9 7 9 ) . S i n c e b o t h D h a n j o r i a n d J a g a n n a t h p u r

v o l c a n i c s have r e s i d u a l g a r n e t and c l i n o p y r o x e n e i n t h e i r

15.

mantle sources and have fractionated Fe-Ti oxides, it appears

that their Ti and Zr abundances are controlled by both o-f

these processes. These Ti and Zr distributions are however,

instructiye as they suggest decoupling between them. Such

decoupled behaviour is a characteristic feature of island arc

basalts (Pearce, 1982; Rogers et al ., 1984).

The low HFSE of island arc basalts are generally

attributed to the^stabilization of HFSE bearing phases such

as apatite, ilmenite, rutile, sphene and zircon under hydrous

partial melting (Saunders et al . , 1980; Pearce, 1982).

However, in absence of sufficient fluids or a larger degree

of partial melting would completely melt these phases and it

would be partitioned into the melt <Condie, 1985). In case

of Dhanjori and Jagannathpur volcanics various lines of

evidence such as silica and LILE variation, low theta

indices, modes of iron enrichment, Ti02/P205, Ti/V, Ti/Zr and

Ti/Y ratio suggest that aquous fluids were not sufficient and

as the result stabilization of HFSE probably could not take

place in the mantle sources.

Tholelites with greater REE contents C(La)^ ~30 to SO;

<Lu)p, ~5 to 20] and <La/Lu)p, ratios are assumed to melt from

peridotite with REE enriched over chondrite C<La)p| ~5 to 20;

<Lu)j ~2 to 7] and <La/Lu)^ ratios greater than one <e.g.

Green, 1973; Frey et al., 1978). Total REE contents in

Dhanjori and Jagannathpur are low to moderate as their <La)_

ranges from ~9 to 51 and ~24 to 71 and (Lu)^ ranges from ~13

to 15 and "9 to 15 respectively. As compared to HREE, the

153

LREE of Dhanjori and J a g a n n a t h p u r v o l c a n i c s a r e no t o n l y

e n r i c h e d [ ( C e / Y b ) ^ = 2 . 5 t o 3 . 1 7 a n d 1 . 7 3 t o 4 . 2 5

r e s p e c t i v e l y ] but show l a r g e r v a r i a t i o n s than HREE. Saunders

(1984) has po in ted ou t t h a t magmat ic p r o c e s s e s t h a t can

produce s i g n i f i c a n t v a r i a t i o n s in LREE/HREE r a t i o s a r e the

high p r e s s u r e - f rac t iona l c r y s t a l l i z a t i o n and e q u i l i b r i u m

p a r t i a l m e l t i n g . High p r e s s u r e f r a c t i o n a l c r y s t a l l i z a t i o n

involv ing garne t ( i . e . e c l o g i t e f r a c t i o n a t i o n ; O'Hara, 1975)

may a l t e r LREE/HREE r a t i o s i g n i f i c a n t l y because garne t has

higher p a r t i t i o n c o e f f i c i e n t s fo r HREE ( S a u n d e r s , 1 9 8 4 ) .

Both Dhanjori and Jagannathpur v o l c a n i c s con ta in r e s idua l

garnet in t h e i r r e s p e c t i v e s o u r c e and show h igh p r e s s u r e

f r a c t i o n a t i o n of cl i n o p y r o x e n e . Hence t h e o b s e r v e d REE

p a t t e r n s of these vo l can i c s may be a t t r i b u t e d to t he se two

f a c t o r s .

CHAPTER VII

TECTONIC IMPLICATIONS

The Singhbhum craton exhibits complex phases of various

tectonism in its prolonged geological history, commencing

•from the early Archaean times (Saha and Ray, 1984; Saha et

al., 1988). Although extensive studies have been undertaken

to contribute and unveil the various phases o-f tectonism,

they have at the same time raised certain controversies.

Most of the controversies are perhaps due to the dual concept

regarding the stratigraphic and tectonic classification of

the rocks of this craton <Sarkar and Saha, 1963, 1977, 1983;

Iyengar and Anandal war , 1965; Banerji, 1974; Iyengar and

Murthy, 1982; Sarkar and Chakraborti, 1982). The disputes

between the two schools of thought mainly concentrate on the

evolution of BIF sequences and their relationships with the

Singhbhum Granite (Naqvi and Rogers, 1987).

The basic volcanism occurring in the Singhbhum craton

needs particular attention to resolve the fundamental

disputes regarding its tectonic evolution. The geochemical

attributes of volcanic rocks wx 1 1 provide insight into the

tectonic settings and related crustal processes in this

craton. Till date due to lack of precise age data no

chronostratigraphic consideration has been given to the basic

volcanic suites of the Singhbhum craton. Various workers

have correlated these basic volcanics with the Dalma

volcanics of Singhbhum erogenic belt and have assigned them

16i

middle Proterozoic age (Sarkar and Saha, 1977, 1983; Gupta et

al . , 1980; Iyengar and Murthy, 1982). However, due to

inadequate age and geochemical data, it seems difficult to

accommodate all these volcanics in a single geotectonic

model. As one of objectives of the present investigation is

to utilize the geochemical data of Dhanjori and Jagannathpur

volcanics, to observe their tectonic significance it is

necessary to determine the degree to which tectonic

conclusions can be drawn.

Although Dhanjori and Jagannathpur volcanics have been

considered contemporaneous,their stratigraphic positions have

been a matter of controversy (Dunn, 1940; Dunn and Dey, 1942;

Iyengar and Anandalwar, 1985; Sarkar and Saha, 1977, 1983;

Iyengar and Murthy, 1982; Gupta et al . , 1985). However, a

number of workers agree that both of these volcanics are

younger than the flysch type metasedimentary rocks of

Singbhum orogenic belt since the rocks of north and south

Singhbhum thrust belong to one single stratigraphic unit

(e.g. Dunn, 1929, 1940, 1966; Dunn and Dey, l9'V2; Iyengar and

Anandalwar, 1965; Iyengar and Murthy, 1982; Sarkar, 1982;

Sarkar and Chakraborti, 1982) rather than two different

stratigraphic and orogenic belts as proposed by Sarkar and

Saha <1963, 1977^ 1983). It therefore seems reasonable that

Singhbhum orogenic belt has a bearing on the evolution of

these volcanics.

In recent years, several models have been proposed for

the evolution of Singhbhum orogenic belt (Sarkar and Saha,

162

1977, 1983; Gupta e t a 1 . , 1980; Bose and C h a k r a b o r t i , 1 9 8 1 ;

SarUar , 1 9 8 2 ) . A H these mode ls o v e r l o o k e d the l i t h o l o g i c a l

make up o f S i n g h b h u m c r a t o n a n d d i d n o t c o n s i d e r t h e

i m p l i c a t i o n s o-f v o l c a n i s m and d i - f - f e ren t phases o-f g r a n i t i c

a c t i v i t y . As a r e s u l t t hese mode ls show w i d e d i v e r g e n c e and

a r e u n a b l e t o accommodate D h a n j o r i and J a g a n n a t h p u r v o l c a n i c s

i n t h e concep tua l -framework o-f p l a t e - t e c t o n i c s .

A ma jo r p rob lem e x i s t i n g t o d a y i s t h e r o l e o-f p l a t e

t e c t o n i c s i n t he Precambr ian e r a ( K r o n e r , 1 9 8 1 ) . The re a r e

two ex t reme s c h o o l s o-f t hough t r e g a r d i n g t h e r o l e of p l a t e

t e c t o n i c s d u r i n g t h e P r e c a m b r i a n . T h e s t r i c t l y

u n i f o r m i t a r i a n s c h o o l s u g g e s t s t h a t p l a t e t e c t o n i c s h a v e

a l w a y s o p e r a t e d on t h e E a r t h and P recambr ian rock r e c o r d can

be i n t e r p r e t e d i n t e r m s o f p r e s e n t l y o p e r a t i n g g l o b a l

mechanism ( e . g . B u r k e e t a l . , 1 9 7 6 ; W i n d l e y , 1 9 8 1 ) . The

o t h e r n o n - u n i f o r m i t a r i a n schoo l sees ma jo r d i f f e r e n c e s i n t h e

geo logy of P recambr ian t e r r a i n s as compared t o Phanerozo ic

s e t t i n g s a n d s u g g e s t s a v a r i e t y o f m o d e l s f o r c r u s t a l

t e c t o n i c s , based e i t h e r on d o m i n a n t l y v e r t i c a l m o v e m e n t s

( e . g . R a m b e r g , 1 9 6 7 ; S t e p h a n s o n a n d J o h n s o n , 1 9 7 6 ;

Schwerd tner e t a l . , 1 9 7 9 ) o r on h o r i z o n t a l d i s p l a c e m e n t s

(Watson , 1976; S u t t o n , l 9 7 7 ; D i m r o t n , i 9 8 1 ) w i t h i n l a r g e

c o n t i n e n t a l segments .

A t h i r d v iew has now e m e r g e d r e c e n t l y a n d t r i e s t o

r e c o n c i l e t he d i f f e r e n t i n t e r p r e t a t i o n s on the assump t i on

t h a t g l o b a l t e c t o n i c s d i d no t s t r i c t l y f o l l o w u n i f o r m i t a r i a n

p r i n c i p l e s , m a i n l y because o f t h e p h y s i c o - c h e m i c a l c o n d i t i o n s

16?

in the 1ithosphere and underlying mantle which have changed

through geologic time <Hargraves, 1981; Condie, 1982c, 1985;

Campbell and Jarwis, 198-4; Taylor, 1987). This view accepts

the basic concept that global tectonics and crustal evolution

result from the interaction of lithospheric plates. In the

recent years, with the addition of new and more reliable data

(e.g. Hoffman, 1980; Naqvi, 1985; Kerr, 1986; Condie, 1987;

Jia Chengzao, 1987; Ulatters and Pearce, l987; Naqvi et al . ,

1988; Condie, 1989) extension of plate tectonics into the

Precambrian is gradually gaining ground.

Basically, magma distribution seems to be related to

tectonic stresses in the crust and upper mantle.

Environments of extensional stress such as ocean ridges,

marginal sea basins and continental rifts are characterized

by tholeiite series or in case of continental rifts by

bimodal volcanism involving tholeiite or alkali series. In

contrast, island arcs and continental margins associated with

dominantly compressive stresses are the sites where magmas of

calc-alkaline series are formed (Condie, i982c). Major and

trace element concentrations of Dhanjori and Jagannathpur

volcanics as discussed under the head of magma classification

(Chapter V) suggest their association with converging plate

i.e. arc environment. Moreover, these volcanics neither show

bi-modal distributions (Fig. 58) nor have lithological

associations similar to that found with Archaean as well as

early and middle Proterozoic suites studied by Condie (1981,

1982b). These volcanics are therefore not explicable as the

164

0 DHANJORI VOLCANICS JAGA.NNATHPUR VOLCANICS

20 40 60 80 100 DIFFERENTIATION INDEX

Fig.58. Histogram showing unimodal

distribution of Dhanjori and Jagannathpur

vocanics, indicating convergent zone

tectonic conditions during the eruption

of these volcanics.

165

continental rift volcanics as have been proposed by many

workers (e.g. Sarkar and Saha, 1977, 1983; Gupta et al.,

1980; Iyengar and Murthy, 1982).

Although the chemical characteristics of Dhanjori and

Jagannathpur uolcanics are very similar to those of island

arc basalts, their eruption on a continental crust is evident

from the field characters. The plots of Dhanjori and

Jagannathpur volcanics on the K2O - Ti02 - ^2^5 diagram (Fig.

59) of Pearce et al., (1975) also support the contention that

both of these volcanics are erupted on the continental crust.

Pearce <1983) has shown that when a basalt suit has been

identified as having volcanic arc character, plotting Zr/Y

ratio against Zr provides an effective mean of discriminating

between oceanic and continental arc settings. Basalts in the

latter environment plot towards high Zr/Y ratio. Dhanjori

and Jagannathpur lavas contain high Zr and Zr/Y ratio and

thus can be characterized as having continental arc

affinities (Fig. 60).

krôlcanic rock associations of island arcs and

continental margins range in character from tholeiitic basalt

associations in immature arcs to cal c-al kal i ne andesite

associations, characteristics of mature arcs, continental

margins and continental collision zones. The field

characters as well as geochemical data on Dhanjori and

Jagannathpur volcanics indicate that both ot these suites are

not associated with 'active Andean type' continental margin.

Dhanjori volcanics form the upper part of the molasse

ISG

Fig. 59. K2O - Ti02 - 2* 5 ternary diagram (after Pearce

et al. , 1975) for Dhanjori and Jagannathpur volcanics

illustrating continental set up for their eruption.

167

100

10 N

oDHANJORl VOLCANICS • JAGANNATHPUR VOLCANICS

o

o

10

inental Arc

anic Arc

100

Zr ( ppm)

1000

Fig.60. Zr versus Zr/Y oceanic - continental volcanic

arc discrimination diagram (after Pearce, 1983) for

Dhanjori and Jagannathpur volcanics, indicating

their continental arc setting.

168

vo l c a n o - p l u t o n i c ( D h a n j o r i ) b a s i n ( S a r k a r , 1 9 8 2 ) w h e r e a s

Jaganna thpur v o l c a n i c s occur as - f a u l t e d o u t l i e r s w i t h i n t h e

Noamund i -Ko i r a BIF sequence ( B a n e r j e e , 1 9 8 2 ) . The p r o x i m i t y

o f D h a n j o r i b a s i n w i t h t h e S i n g h b h u m G r a n i t e a s w e l l a s

• f l ysch t ype me tased imen t s a n d t h e a b s e n c e ^ N e w e r D o l e n t e

dykes i n D h a n j o r i s e d i m e n t a t i o n ( B a n e r j e e , 1982; i n d i c a t e

t h a t t he b a s i n was p r o b a b l y -formed due t o t he - f a u l t i n g o-f

' s t a b l e ' c o n t i n e n t a l ma rg in < B o i l l o t , 1 9 8 1 ) . On the o t h e r

hand , m iogeosync l i n a l s e d i m e n t a t i o n o-f B l F ( R a i e t a l . ,

1 9 8 0 ) , u n d e r l a i n by Bona i v o l c a n i c s , l y i n g on t h e c o n t i n e n t a l

c r u s t ( B a n e r j e e , 1982) and a s s o c i a t e d Newer D o l e r i t e dyke

swarm (Saha e t a l . , 1 9 7 3 b ) a r e t h e - f e a t u r e s s u g g e s t i v e o-f

' s t a b l e ' c o n t i n e n t a l ma rg in (Dewey, 1969, B o i l l o t , 1981) a t

t h e base of Jaganna thpu r v o l c a n i c s .

Brown (1982) s u g g e s t e d t h a t ARM d i a g r a m i s t h e m o s t

u s e f u l d iag ram i n t e c t o n i c s t u d i e s b e c a u s e i t p r o v i d e s a

c rude p i c t o r i a l d e f i n i t i o n o f a r c m a t u r i t y . A c c o r d i n g t o

B rown ( o p . c i t . ) t h e m o s t ' p r i m i t i v e ' a r c m a g m a s s h o w

t h o l e i i t i c F e - e n r i c h m e n t t r e n d a r e c a l c i c i n t e r m s of Peacock

(1931) index whereas o t h e r m a t u r e a r c v o l c a n i c r o c k s h a v e

c a l c - a l k a l i n e t r e n d s , lack i r o n e n r i c h m e n t on AFM d iag ram and

f o r t h i s reason t hey a r e c a l c - a l k a l i ne r e g a r d l e s s o f t h e

o r i g i n a l d e f i n i t i o n o f t he t e r m . S i n c e D h a n j o r i v o l c a n i c s

shcHA) t h o l e i i t i c F e - e n r i c h m e n t a n d a r e c a l c i c i n t e r m s o f

P e a c o c k i n d e x , t h e y Are r e g a r d e d a s ' p r i m i t i v e ' a r c

t h o l e i i t e s . I n c o n t r a s t , Jaganna thpur v o l c a n i c s l ack i r o n

e n r i c h m e n t t r e n d ( F i g . 11) t hough t h e y a r e c a l c i c i n t e rms o f

Peacock i n d e x . They a r e t h e r e f o r e c o n s i d e r e d as r e l a t i v e l y

169

mature arc tholeiites. This maturity may be attributed

either to crustal thickness or to the duration o-f plate

subduct ion.

Crustal thickness apppears to be a major control on the

major element composition o-f arc related magmas in that more

tholeiitic associations, characterized by lower mean Si02,

K-7O and more Fe-enrichment, are associated with thinner crust

and more calc-alkaline associations, characterized by higher

mean Sio2 and K2O and less Fe-enrichment, are associated with

thicker crust (Coulon and Thorpe, 1981; Baker, 1982>. Since

Dhanjori volcanics contain lower mean Si02, K2O and more Fe-

enrichment as compared to Jagannathpur volcanics ^Tabie Vl I

it seems that Dhanjori volcanics are erupted on a relatively

thinner crust than the Jagannathpur volcanics.

Summarizing the above observations, it seems reasonable

that the possible model involves the initiation o-f the plate

convergence at previously stable continental margin. In view

o-f the above considerations it may be suggested that Dhanjori

and Jagannathpur volcanics represent the volcanic acitivity

very similar to that occurs in the early stage o-f arc

development. Both of these volcanics contain samples which

possess geochemical -features similar to boninitic rocks.

However, due to their higher TiD2 contents, these volcanics

cannot be classified as boninite series rocks. Therefore,

the term transitional boninite (Beccaluva and Serri, 1988;

seems more appropriate for these samples. Boninites and/or

transitional boninites associated with tholeiites are

17u

generally considered as a product o-f subduction related

melting and represent early phases of arc volcanism (Hickey

and Frey, 1982; Hawkins et al . , 1984; Bloomer and Hawkins,

1987; BeccaluMa and Serri, 1988). Such rocks have also been

reported -from the continental margin setting (Wood, 1980).

CHAPTER VIII

SUhtViRY AND CONCLUSIONS

In the eastern India, Singhbhum craton is the most

intensely studied region and almost all aspects o-f its

geology are heatedly debated. The most outstanding o+ all

the controversies is perhaps the dual concept regarding the

stratigraphic and tectonic evolution o-f the rocks o-f BIF

sequence. According to one school, in spite o-f structural and

metamorphic contrasts, the rocks o-f BIF belong to one broad

stratigraphic unit whereas the other school classi-fied the

rocks o-f BIF into two stratigraphic units. Radiometrical 1 y

determined isochron ages are sparse -for the Singhbhum

Granite. Although there are wide occurrences of basic

volcanic rocks, they have not been given due consideration to

get the solution o-f the problem. Among these Dhanjon and

Jagannathpur Vôlcanics occupy critical positions in various

proposed stratigraphic successions. They are assigned to

middle Proterozoic age and have been correlated with the

Dal ma metavolcanic suite o-f Singhbhum orogenic belt.

Dhanjori volcanics occur as the upper most -formation

within the Dhanjori basin while Jagannathpur volcanics are

found to be faulted out-liers of the Noamundi-Koira sequence

of BIF. Dhanjori volcanics have undergone shearing and low

grade metamorphism. However, their magmatic textures are

still preserved. Jagannathpur volcanics are not affected by

post-igneous low grade greenschist metamorphism. Both of

172

t hese v o l c a n i c s u i t e s r e v e a l a c l o s e s i m i l a r i t y i n t h e i r

m i n e r a l assemblage and t e x t u r a l r e l a t i o n s .

D h a n j o r i v o l c a n i c s a r e m o s t l y b a s a l t s w h e r e a s

Jagannathpur v o l c a n i c s a r e m o s t l y b a s a l t i c a n d e s i t e s . The

ma jo r e lement c o m p o s i t i o n s o-f t hese v o l c a n i c s a r e p e c u l i a r .

None o-f t h e sample o-f t h e s e v o l c a n i c s u i t e s f o l l o w t h e

d £ - f i n i t i o n o t k o m a t i i t e . Both o f t hese s u i t e s c o n t a i n h i g h

S i 0 2 and l o w e r AI2O3 c o n t e n t s t h a n t h e Archaean t h o l e i i t e s .

Wide v a r i a t i o n s i n T i 0 2 c o n t e n t s , CaO/Ti02 and A l 2 0 3 / T i 0 2

r a t i o s i n bo th o f t hese s u i t e s i n d i c a t e t h a t t h e i r Ca and Al

a r e h e l d i n t h e r e s i d u a l m a n t l e phases such as c l i n o p y r o x e n e ,

p l a g i o c l a s e , s p i n e l and g a r n e t .

H ighe r T i 0 2 c o n t e n t s a n d l o w e r v a l u e s o f N i a n d M g -

numbers i n D h a n j o r i v o l c a n i c s as compared t o Jagannathpur

v o l c a n i c s a r e p r o b a b l y s u g g e s t i v e o f l a r g e r o l i v i n e

f r a c t i o n a t i o n i n D h a n j o r i v o l c a n i c s than t h e Jagannathpur

v o l c a n i c s . Ca0/A l203 r a t i o s o f D h a n j o r i and Jaganna thpur

v o l c a n i c s a r e a l s o w i d e l y v a r i a b l e . Most o f t h e samples of

D h a n j o r i v o l c a n i c s c o n t a i n C a 0 / A l 2 0 3 r a t i o g r e a t e r t h a n

c h o n d r i t e or p r i m i t i v e u p p e r m a n t l e v a l u e ( 0 . 9 ; w h i l e i n

Jaganna thpu r v o l c a n i c s m a j o r i t y of t h e samples have lower

C a 0 / A l 2 03 r a t i o t h a n c h o n d r i t e v a l u e . H o w e v e r , t h e i r

a n t i p a t h e t i c r e l a t i o n s h i p s between CaO/AI2O3 r a t i o and Mg-

number i n d i c a t e t h a t c l i n o p y r o x e n e i s a ma jo r f r a c t i o n a t i n g

phase i n b o t h of t h e s e s u i t e s .

173

D h a n j o r i v o l c a n i c s show a s y m p a t h e t i c r e l a t i o n s h i p

between K2O and T i 0 2 and t h e i r Mn0 /T i02 r a t i o i n c r e a s e s w i t h

d e c r e a s i n g T i 0 2 c o n t e n t . F u r t h e r m o r e , t h e i r i r o n e n r i c h m e n t

t r e n d a n d F e 2 0 3 / F e 0 r a t i o a r e i n d i c a t i v e o-f a m p h i b o l e

• f r a c t i o n a t i o n . On t h e o t h e r hand , i n Jaganna thpur y o l c a n i c s

KoO has no r e l a t i o n s h i p w i t h T i 0 2 and t h e i r K 2 0 / T i 0 2 r a t i o s

a r e h i g h . T h e i r M n 0 / T i 0 2 r a t i o i n c r e a s e s w i t h d e c r e a s i n g

T i 0 2 c o n t e n t . R e l a t i y e l y h i g h Si02> l a c k o-f i r o n en r i chmen t

and h i g h Fe203/Fe0 r a t i o i n t h e s e v o l c a n i c s are s u g g e s t i v e o-f

t i t a n o - m a g n e t i t e - f r a c t i o n a t i o n .

F r a c t i o n a t i o n of a m p h i b o l e a n d / o r t i t a n o - m a g n e t i t e have

been sugges ted as the mechanism -for t h e o r i g i n o-f b a s a l t i c

magmas i n ca 1 c - a l k a l i n e s e r i e s . I t t h e r e f o r e a p p e a r t h a t

D h a n j o r i and J a g a n n a t h p u r v o l c a n i c s a r e c o m p a r a b l e w i t h

i s l a n d a r c t h o l e l i t e s .

I n compar ison t o MORB, l a r g e i o n l i t h o p h i l e e l e m e n t s

( L I L E ) a r e e n r i c h e d w h e r e a s h i g h f i e l d s t r e n g t h e l e m e n t s

<HFSE) excep t Zr a r e d e p l e t e d i n D h a n j o r i v o l c a n i c s . I r o n

en r i chmen t t r e n d and low v a l u e s of Ni and Cr a r e t y p i c a l t o

t h a t f ound i n i s l a n d a r c t h o l e i i t e s . A l o n g w i t h t h e i r o n

d e p l e t i o n , J a g a n n a t h p u r v o l c a n i c s c o n t a i n h i g h N i a n d Cr

c o n t e n t s . L ILE a r e a l s o e n r i c h e d and b a r r i n g Z r , HFSE a r e

d e p l e t e d i n compar i son t o MORB. T h i s s u i t e t h e r e f o r e a p p e a r s

t o be comparab le w i t h modern b o n i n i t i c r o c k s .

The decoup led b e h a v i o u r o f v a r i o u s m a j o r a n d t r a c e

e l e m e n t s , LREE e n r i c h e d and f l a t HREE p a t t e r n s sugges t t h a t

bo th D h a n j o r i and J a g a n n a t h p u r v o l c a n i c s Are r e l a t e d t o

174

similar magmatic sources in the upper mantle, having

undergone variable degrees o-f partial melting and

differentiating under di-f-ferent physico-chemical conditions.

The unimodal distribution o-f these volcanic suites and

their chemical characters indicate their convergent zone

(i.e. arc) related tectonic settings. Their occurrence on

thick continental crust is also consistent with the changed

tectonic style of Proterozoic era. In order to achieve a

better understanding of the tectonic settings of these

volcanic suties, various existing evolutionary models for

Singhbhum craton and Singhbhum orogenic belt are also taken

into consideration. It appears that plate activation model

for the tectonic evolution of these volcanics will be more

suitable than the rifting or collision related models of

evol ut ion.

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Z

TABLE II Instrumental parameters

177

Element Equipment used

Wave length Slit Detection limit (nm> mm) tppm)

Si02

AI2O3

TiOj

P2O5

Fe203

(Total Iron as Fe203)

U W S *

do

do

do

do

640.0

475.0

400.0

420.0

560.0

1 .0

1 .0

1 .0

1 .0

0.5

10

10

20

20

10

MgO AAS** 202.5 1 .0 10

CaO

Na20

KoO

MnO

Ni

Co

Cr

Cu

Pb

2n

Li

Rb

Sr

do

do

do

do

do

do

do

do

do

do

do

do

do

422.7

569.6

769.9

279.5

232.0

240.0

525.0

328.0

217.0

213.0

670.0

780.0

460.0

0.5

0.2

0.5

0.2

0.1

0.1

0.2

0.2

1 .0

0.5

1 .0

0.2

0.2

10

* UV-Visible Spectrophotometer

** Atomic Absorption Spectrophotometer

178

TABLE I I I . Majo r element abundances ( i n wt .Vi ) and CIPU) n o r m a t i v e composit ions of Dhan jor i v o l c a n i c s .

Sample No.

Si02

Ti02

Al 2O3

Fe203

FeO

MgO

CaO

HA2O

K2O

nnO

Pr.Oc.

LOT

Total

Dll

45.42

1.14

12.05

5.24

12.60

7.36

10.00

2.13

1.28

0.21

0.23

1.64

99.30

D2

Maj

53.18

1 .23

10 .92

5.45

1U.52

5.44

8.15

3.66

0.70

0.22

0.17

1 .01

100.65

D5 D7 D9

or element oxides

54.15

1.17

10.87

6.47

10.12

5.52

7.62

3.39

0.71

0.16

0.15

0.89

101.22

55.12

1.19

12.80

4.02

8.44

4.84

6.80

4.44

0.24

0.13

0.16

2.00

100.18

56.78

1.07

12.60

4.12

7.20

5.01

7.47

4.18

0.71

0.14

0.15

1.40

100.83

DIO

50.80

1 .13

12.47

3.49

10.40

6.63

10.14

2.30

0.59

0.21

0.13

1 .45

99.74

D12

49.81

0.95

12.68

3.06

10.04

7.04

10.57

2.08

0.63

0.25

U.lO

1 .60

98.89

Q

O r

Ab

An

Di

Hy

01

Mt

n Ap

7.75

18.45

20.00

24.15

3.90

15.19

7.78

2.22

0.56

4.18

4.15

31 .08

11.34

23.25

1:15.33

7.93

2.34

0.40

C . I . P . U . Norms

7 .56 6 .37 7 .83

4 . 1 8 1.44 4 . 2 2

2 8 . 5 9 3 8 . 2 7 3 5 . 5 7

12 .30 1 4 . 5 ! 13 .60

2 0 . 0 7 1 5 . 4 3 18 .52

1^5.33 15 .38 15 .32 1 1 . 8 5

9 . 3 5 5 .94 6 . 0 0

2 . 2 1 2 . 3 0 2 . 0 4

0 . 3 5 0 . 3 8 0 . 3 6

3.20

3.54

19.80

22.34

23.06

20,42

1 .99

3.83

18.12

24.09

23.63

21 .66

5.15

2.18

U.31

4,57

1.86

0.24

17;

TABLE I I I (Con td . )

Samp 1e No.

SiOo

Ti02

AI2O3

FSoOg

FeO

MgO

CaO

Na20

K2O

MnO

R2O5

LUl

Total

Q

Or

Ab

An

Di

Hy

Oi

nt

n

Ap

DIJ

50.18

0.91

11 .55

4.11

10.04

7.43

11.45

1.72

0.96

0.23

0.18

1 .20

99.96

2.56

5.74

14.74

21.22

28.77

18.75

6.03

1 .75

0.43

D15

Maj

50.59

1 .56

11 .28

5.05

10.12

6.63

10.90

1 .82

0.79

0.21

0.25

1 .50

100.70

5.87

4.71

15.52

20.44

26.56

15.94

7.38

2.99

0.59

D23 D27 D29

or element oxides

51.87

1.17

11.17

4.69

10.34

6.54

11.34

1 .67

0.85

0.17

0.23

1 .54

101.60

C.I.P.W.

6.74

5.02

14.12

20.46

28.17

15.93

6.79

2.22

0.54

51 .63

1 .02

12.28

4.48

9.40

6.80

10.83

2.00

0.48

0.15

0.16

0.76

99.99

Norms

6.17

2.86

17.05

23.29

24.39

17.37

6.55

1 .95

0.38

49.54

0.87

12.88

3.87

9.76

•7 ••>•".•

11 .14

1 .83

0.39

0.19

0.10

1.57

99.36

3.14

2.36

15.83

26.36

24.17

20.47

5.74

1.69

0.24

D32

50.51

1 .05

12.22

4.47

10.00

6.53

10.46

2.10

0.55

0.11

0.20

1 .15

99.35

4.85

3.31

18.09

22.70

23.56

18.35

6.59

2.03

0.53

D35

50.93

0.69

12.37

3.41

8.80

7.96

11 .29

1.96

0.34

0.19

0.05

1 .34

99.33

3.52

2.05

16.92

24.44

26.40

20.16

5.05

1 .34

0.12

180

TABLE III <Contd.>

Sample No.

Si02

TiQ2

AI2O3

Fe203

FeO

MgO

CaO

Na20

KjO

MnO

P2O5

LOI

Total

Q

Or

Ab

An

Di

Hy

Oi

nt

n

Ap

D37

51 .00

1 .07

11.65

4.02

12.12

5.58

9.51

1 .46

0.59

0.09

0.12

1.93

99.04

9.20

3.59

12.71

24.17

19.64

22.32

5.99

2.09

0.29

D39

MaJ

51 .30

0.76

12.36

3.29

8.64

7.94

11.57

1 .84

0.34

0.20

0.10

2.47

100.81

4.41

2.04

15.83

24.87

26.74

19.54

4.85

1.47

0.24

D42 D3 D19

or element oxides

50.94

0.69

11 .73

3.44

8.20

8.47

12.47

1.65

0.76

0.18

0.17

1 .60

100.30

C.I.P.W.

2.69

4.55

14.15

22.65

31.57

17.61

5.05

1.33

0.41

55.39

0.74

6.36

2.43

10.00

11 .14

10.52

2.73

0.15

0.21

0.06

1.25

100.98

Norms

3.08

0.89

23.16

4.67

38.39

24.73

3.53

1 .41

0.14

58.50

0.59

9.49

2.86

7.40

9.51

10.97

0.80

0.65

0.11

0.16

1.30

101.04

16.32

3.80

6.70

20.17

26.35

21.08

4.10

1 .11

0.37

D41

53.00

0.84

8.55

3.68

9.72

8 . V4_

9.29

2.96

0.34

0.18

0.11

1.54

99.03

3.25

2.06

25.66

9.26

30.33

22.07

5.47

1 a 0 0

0 .26

181

TABLE IV. Major element abundances <in wt.%> and CIPW normative compositions o-f Jagannathpur volcanics.

Sample No. J12 J45 J103 J5 36

Major element oxides

J15 J73

Si02

TiO^

Al2°3

Fe203

FeO

MgO

CaO

Na20

MnO

P2O5

LOT

Total

50.50

1.01

14.04

4.27

7.12

8.21

7.66

2.74

1.69

0.17

0.36

2.76

100.53

47.29

0.43

9.71

4.45

7.20

21.33

7.69

1.58

0.24

0.20

0.40

1 .21

5.19 54.74

0.58 0.56

9.07 10.04

1.44 3.22

6.20 6.92

9.61 10.29 12.47

6.71 9.82 9.52

1 .84

1 .52

0.54

16.41

1.92

7.82

3.14

0.53

0.13 0.16

0.20 0.04

1.73 3.44

0.82

0.35

0.18

0.O6

1 .15

51 .79

0.68

10.65

6.71

5.08

13.56

8.98

1 .01

0.92

0.17

0.07

1 .16

100.78

54.94

0 .60

9.66

4.87

5.56

13.19

7.31

0.97

1 .40

0.14

0.06

1 .70

100.40 101.37 100.09 99.59 100.03

C.I.P.U. Norms

6.17 10.85 G

Or

Ab

An

Di

Hy

01

Mt

n

AD

10 .21

2 3 . 7 1

21 .50

12 .04

2 3 . 0 8

0 . 3 0

6 . 3 2

1 .96

0 . 8 7

1 .42

1 3 . 3 5

18 .66

15 .17

1 6 . 9 3

2 7 . 1 2

6 . 4 4

0 . 8 2

0 . 1 0

3.18 9.34 .09

27.01 16.19 7.02

2 8 . 8 5 12 .48 2 2 . 9 4

2 . 9 7 3 0 . 4 6 19 .54

2 9 . 4 8 2 1 . 9 4 3 1 . 6 4

4 . 1 6

2 . 8 3 2 . 1 7 4 . 7 2

1.04 1.15 1.08

0 . 4 8 0 . 1 0 0 . 1 4

6 . 6 2

5 . 4 6

8 . 5 8

2 1 . 8 9

17 .57

2 8 . 6 6

9 . 5 5

8 .21

8 . 1 4

1 7 . 7 3

11 . 4 4

3 5 . 4 3

9 . 7 7

1 .30

U.17

7 . 0 1

1 . 1 3

1 .41

182

TABLE IV < C o n t d . ;

Samp 1e N o .

B i 0 2

T i 0 2

A 1 2 0 3

F e 2 0 3

FeO

MgO

CaO

NaoO

K2O

nnO

P2O5

L O I

T o t a l

Q

O r

Ab

An

D i

Hy

01

Mt

11

Ap

J 9 4

51 . 5 4

0 . 6 3

1 0 . 2 5

3 . 8 3

6 . 5 2

1 4 . 0 5

8 . 1 8

0 . 8 6

1 . 3 5

0 . 1 8

0 . 0 5

2 . 2 5

9 9 . 6 9

3 . 8 0

8 . 1 9

7 . 4 7

2 0 . 6 5

1 6 . 4 4

3 6 . 4 2

5 . 7 0

1 . 2 3

0 . 1 2

J l

M a j

5 5 . 9 9

0 . 6 3

lai . 7 8

3 . 9 5

7 . 3 6

8 . 3 9

5 . 8 0

2 . 7 1

1 . 4 6

0 . 1 6

0 . 0 5

1 . 7 8

1 0 0 . 0 6

7 . 7 4

8 . 6 9

2 3 . 1 0

1 8 . 5 3

8 . 1 8

2 6 . 6 8

5 . 7 7

1 . 2 0

0 . 1 2

n o J 2 5 J 2 6

o r e l e m e n t o x i d e s

5 1 . 6 5

0 . 5 8

1 5 . 9 7

3 . 7 8

6 . 3 2

6 . 2 0

7 . 0 2

2 . 4 2

3 . 1 7

0 . 1 4

0 . 1 0

0 . 9 0

9 8 . 4 5

C . I . P . W .

0 . 0 7

1 9 . 2 0

2 0 . 9 9

2 3 . 9 4

9 . 0 0

1 9 . 8 2

5 . 6 2

1 . 1 3

0 . 2 4

5 2 . 2 1

0 . 6 8

1 2 . 5 0

3 . 2 7

7 . 5 6

8 . 4 6

8 . 2 3

3 . U 2

0 . 4 3

0 . 1 7

0 . 0 5

2 . 4 7

9 9 . 0 5

N o r m s

2 . 8 5

2 . 6 3

2 6 . 4 6

1 9 . 9 6

1 7 . 7 8

2 3 . 9 5

4 . 9 1

1 . 3 4

0 . 1 2

5 6 . 7 7

0 . 9 7

1 2 . 6 4

2 . 9 6

8 . 3 6

3 . 2 9

6 . 7 3

2 . 6 3

2 . 0 4

0 . 1 5

0 . 1 0

3 . 0 3

9 9 . 6 7

1 3 . 2 6

1 2 . 4 7

2 3 . 0 3

1 7 . 2 4

1 3 . 9 3

1 3 . 4 9

4 . 4 4

1 . 9 1

0 . 2 5

J 3 2

5 5 . 5 0

0 . 6 0

1 2 . 0 1

2 . 7 8

7 . 2 0

9 . 1 5

6 . 7 8

3 . 2 0

0 . 4 7

0 . 1 6

0 . 0 4

2 . 4 4

1 0 0 . 3 3

6 . 0 3

2 . 8 3

2 7 . 6 6

1 7 . 3 9

1 3 . 4 9

2 7 . 2 2

4 . 1 2

1 .16

0 . 1 0

J 3 3

5 4 . 9 2

0 . 6 3

1 2 . 2 5

2 . 8 8

7 . 8 8

8 . 2 9

6 . 2 2

• ^ . 8 2

0 . 9 0

0 . 1 7

0 , 0 3

J . 03

1 0 0 . 0 2

7 . 2 2

5 . 4 8

24 . 6U

1 8 . 6 7

1 0 . 5 1

2 7 . 9 0

4 . 3 0

1 . 2 3

0 . 0 7

TABLE IV (Contd . )

183

Sample No.

Si02

TiOo

HI 2O3

Fe203

FeO

MgO

CaO

Na20

K2O

MnO

LOI

Total

J34

57.90

0.75

1J.22

3.43

7.00

5.73

5.57

1 .70

2.10

0.14

0.08

1 .94

99.56

J36

Maj

55.82

1 .04

12.95

3.94

8.16

3.75

6.45

2.71

1 .94

0.16

0.10

2.23

99.25

J43 J46 J53

or element oxides

56.80

0.74

12.87

3.25

7.04

5.87

6.54

2.19

1.67

0.14

0.07

2.25

99.43

55.30

1.02

12.84

3.90

8.68

3.97

5.75

2.99

2.60

0.15

0.10

1.88

99.18

49.50

1.49

12.40

4.35

7.76

8.23

9.10

2.47

0.63

0.19

0.33

3.07

99.52

J54

55.86

0.61

12.97

2.08

8.06

6.37

7.85

2.90

0.87

0.16

0.04

2.27

100.04

J55

56.59

0.67

11 .28

2.49

7.40

8.45

6.15

2.85

1 .12

0.17

0.05

2.32

99.54

Q

Or

Mb

Hn

Di

Hy

01

Mt

II

Ap

C . I . P . U . Norms

17 .07 1 2 . 1 8 10 .11 8 .08 2 . 8 7

12 .71 11 .82 10 .08 15 .79 3 . 8 6

14 .74 2 3 . 6 4 :^5.15 2 6 . 0 0 2 1 . 6 7

2 2 . 7 8 17 .98 17 .49 14 .32 2 1 . 6 6

4 , 0 7 11 .90 1 2 . 3 8 1 1 . 9 l 1 8 . 4 6

2 1 . 9 0 14 .34 18 .37 1^.36 2 1 . 2 2

4 . 8 1 5 .81 6 . 5 4

1.43 1.99 2 . 9 3

U.17 0 . 2 4 0 .81

8.08

5.26

25.10

20.26

15.85

21 .10

8.80

6.81

24.81

15.10

12.92

Z6.43

5.09

1 .46

0.l9

5.89

2.04

0.24

3.09

1 .19

0.10

3.71

1 .31

0.12

TABLE I V < C o n t d . )

184

S a m p l e N o . J 5 6 J63 J66 J75 J76

Major element oxides

5 3 . 5 7 5 6 . 0 3 5 2 . 4 0 5 6 . 5 0

1 . 2 1 0 . 6 8 0 . 9 0

1 2 . 5 4 1 2 . 5 0 1 1 . 2 5

4 . 6 1 3 . 1 3 0 . 4 4

j s : J 8 3

S i 0 2

T i 0 2

A I 2 O 3

"=^^203

FeO

MgO

CaO

Na20

MnO

P2O5

L O I

T o t a l

5 3 . 0 5

0 . 9 1

1 3 . 3 1

3 . 9 2

8 . 1 2

4 . 9 0

9 . 0 4

3 . 3 8

0 . 3 0

0 . 1 6

0 . 1 0

3 . 9 0

101.OV

0 . 6 2

1 1 . 8 0

2 . 2 5

8 . 0 0

8 . 0 6

7 . 5 7

2 . 8 0

0 . 7 6

0 . 1 7

0 . 0 5

3 . 2 1

7 . 8 8 7 . 2 0 9 . 0 8

4 . 0 8 8 . 4 6 3 . 7 2

4 . 9 7 8 . 2 3 1 3 . 7 6

3 . 2 8 3 . 0 2 0 . 9 3

1 . 5 9 0 . 4 3 0 . 0 4

0 . 1 7 0 . 1 7 0 . 1 1

0 . 1 3 0 . 0 5 0 . 1 2

3 . 6 1 3 . 0 1 2 . 4 6

5 3 . 8 4

0 . 7 2

1 3 . 6 8

4 . 2 2

6 . 8 4

7 . 5 3

7 . 0 4

2 . 6 4

1 . 5 0

0 . 1 0

0 . 0 8

3 . 5 9

5 5 . 8 6

0 . 6 2

1 2 . 0 5

2 . 6 1

7 . 4 8

8 . 6 0

6 . 0 0

2 . 6 5

1 . 1 2

0 . 1 5

0 . O 3

3 . 2 9

Vb.86 100.14 99.28 99.31

C.I.P.U. Norms

12.82 3.31 18.87

9.73 2.64 0.24

28.75 26.55 8.13

15.33 20.03 27.26

7.69 17.81 35.67

16.00 23.49 7.12

101.78 100.46

Q

Or

Ab

An

Di

Hy

01

Mt

n

Ap

6 . 4 3

1 . 8 2

2 9 . 4 3

2 0 . 8 5

2 0 . 2 1

1 3 . 3 4

5 . 2 8

4 . 7 0

2 4 . 7 7

1 8 . 1 8

1 6 . 8 9

2 5 . 4 4

5.98

9.03

22.75

21 .44

10.97

8.44

6.81

23.08

18.19

9.91

22.03 28.39

5.85

1.78

3.41

1 .23

0.12

6.98 4.71 0.66

2.33 1.34 1.76

0.32 0.12 0.29

6 . 2 3

1 .39

0 . 1 9

3 . 8 9

1 . 2 1

0 . 0 7

185

TABLE IV (Contd . )

Sample No.

Si02

TiO^

A1203

Fe203

FeO

MgO

CaO

Na.20

K2O

nnO

P2O5

LOI

Total

Q

Or

Ab

An

Di

Hy

01

Mt

11

Wp

C

J84

50.09

0.61

12.64

5.02

6.60

13.10

8.74

0.96

0.27

0.18

0.06

1.B5

100.12

5.09

1.62

8.27

29.90

10.99

35.41

7.41

1 .la

0»15

J85

Maj

54.41

0.71

13.40

3.33

7.16

7.24

7.30

3.27

1 .27

0.16

0.08

2.10

100.43

3.84

7.63

28.14

18.44

14.48

21 .00

4.91

1 .37

0.19

J86 J936 J96

or element oxides

57.01

1 .22

12.05

7.19

5.48

5.36

4.33

2.70

2.13

0.18

0.12

2.62

100.39

C.I.P.W.

16.83

12.87

23.37

14.80

5.05

13.77

10.66

2.37

0.29

5:.i.37

0.66

12.43

4.40

6.64

8.42

7.52

2.94

0.66

0.20

0.05

3.81

100.10

Norms

4.76

4.05

25.84

19.49

15.20

22.62

6.62

1 .30

0.12

54.04

1 .32

13.43

6.10

7.00

6.11

3.80

1.80

2.74

0.15

0.12

3.75

100.36

13.95

16.76

15.77

18.70

21 .87

9.16

2.60

0.29

0.91

J113

54.04

0.60

13.29

2.31

7.32

6.20

9.28

2.71

0.60

0.16

0.04

2.63

99.18

7.35

3.67

23.75

jiLid . 1 xi

19.87

17.50

3.47

1 .18

0.10

J173

56.50

0.40

12.60

4.03

5.20

10.15

4.97

2.91

0.73

0.14

0.27

2.32

100.22

10.13

4.41

25.15

19.57

3.03

30.33

5.97

0 . 78

0.65

ISS

TABLE V. Trace element concentrations <in ppm) o-f Dhanjori volcanics.

Ni

Co

Cr

V

Cu

Pb

Zn

Li

Rb

Sr

Ba

2r

Y

La

Ce

Sm

Eu

Tb

Yb

Lu

Dll

66

52

74

16

94

10

73

132

D2

80

89

51

75

104

4

7

240

D5

75

45

53

81

65

7

7

147

D7

154

62

46

262

179

13

39

3

44

281

97

236

14

D9

88

41

12

102

57

10

7

247

DIO

81

101

167

321

39

17

86

9

28

142

141

2l2

16

D12

89

93

148

315

63

17

173

6

34

129

218

196

8

187

TABLE V <Contd.)

Ni

Co

Cr

V

Cu

Pb

Zn

Li

Rb

br

Ba

Zr

Y

La

Ce

Sm

Eu

Tb

Yb

Lu

D13

79

43

107

94

158

26

107

D15

48

48

59

118

80

17

13

161

023

75

57

75

121

39

14

7

1U7

027

80

97

131

307

113

17

27

9

39

156

47

203

029

99

92

195

315

61

15

44

7

30

141

58

200

16

032

65

67

117

308

89

21

19

13

42

122

55

194

41

035

107

83

260

304

103

15

79

6

23

180

30

189

3

16.10

31

4.20

I.IS

0.76

2.4U

0.53

Ni

Co

Cr

V

Lu

Pb

Zn

Li

KD

Sr

Ba

Zr

Y

La

Ce

Sm

Eu

Tb

Yb

Lu

94

94

98

325

146

19

10

58

152

54

211

11

91

91

224

322

67

13

48

3

37

133

95

199

69

69

163

113

65

331

89

1491

251

79

15

86

185

37

624

15

26

7

142

30

153

37

206

8

6

15

0.81

0.40

1.80

0.43

7

54

245

99

770

285

59

140

79

196

189

TABLE VI. Trace Element Concentrations <in ppm) o-f Jagannathpur volcanics

Ni

Co

Cr

V

Cu

Pb

Zn

Li

Rb

Sr

Ba

Zr

Y

La

Ce

Sm

Eu

Tb

Yb

Lu

J12

124

53

314

290

75

19

30

120

309

191

230

45

15.

30

4.

1 .

0.

1 .

0.

.10

.40

.18

.53

.80

,33

J45

900

69

5400

282

61

IS

95

49

63

55

49

164

C|

7.

12

2.

0.

0.

1 .

0.

.80

.30

,81

,45

,63

,43

J103

172

65

601

118

15

108

14

53

527

131

16

J5

236

26

692

280

83

19

71

13

49

97

258

216

41

J6

313

53

1065

282

56

17

85

17

24

399

55

209

25

J15

302

54

850

294

81

19

90

26

44

474

334

173

38

J73

269

54

730

82

15

15

30

24

246

389

153

41

190

TABLE y i (Contd . )

Nl

UO

Cr

V

Cu

Hb

Zn

Ll

Rb

Sr

Ba

Zr

Y

La

Ce

Sm

Eu

Tb

Yb

Lu

J94

259

46

874

274

86

13

95

27

12

47

306

133

38

Jl

172

56

531

283

79

17

99

24

91

385

416

219

22

J22

141

37

97

284

42

19

83

2o

111

613

365

227

41

J25

215

56

513

269

97

17

104

26

44

145

167

164

38

J26

55

51

45

283

116

17

85

12

96

294

410

195

25

J32

206

66

624

290

76

15

95

22

46

150

127

210

45

J33

189

65

453

277

91

15

34

23

35

193

253

161

15

191

TABLE V I (Contd . )

Ni

Co

Cr

V

Cu

Pb

Zn

Li

Rb

Sr

Ba

Zr

Y

La

Ce

Sm

Eu

Tb

Yb

Lu

J34

76

58

175

270

93

17

108

22

77

239

575

220

16

J36

67

58

38

279

109

15

104

24

49

331

483

200

25

J43

120

45

213

263

107

19

90

16

54

311

539

151

J46

102

56

70

293

119

19

99

13

76

164

476

211

J53

178

55

409

279

80

17

120

17

24

309

302

238

35

354

148

49

291

283

106

17

50

16

61

239

228

143

J 55

191

58

541

288

03

17

97

16

4fe

190

370

137

38

in TABLE vi ûontd.;

Ni

Co

Cr

V

Cu

Pb

Zn

Li

Rt»

Sr

Ba

Zr

Y

La

Ce

Sm

Eu

Tb

Yb

Lu

J56

134

54

67

299

125

15

104

. 13

98

60

192

6

J63

199

53

610

296

83

15

101

16

23

181

137

180

•

J66

160

52

55

274

145

15

97

16

49

365

500

216

20

J75

223

57

477

292

94

19

95

19

35

180

92

139

3

J76

124

63

60

268

101

15

53

13

35

292

67

184

15

22.

45

5.

1.

0.

2.

0.

,60

.80

,78

.80

,6U

,53

J82

186

41

315

284

82

19

90

22

47

371

289

216

11

J83

186

61

542

271

82

13

95

19

49

253

237

168

5

19,

TABLE y i <Contd.)

Ni

Co

Cr

V

Cu

Pb

Zn

Li

Rb

Sr

Ba

2r

Y

La

Ce

Sm

Eu

Tb

Yb

Lu

J84

140

47

225

284

90

17

90

16

55

270

289

209

15

J85

223

86

651

302

29

17

102

33

14

116

12

187

22

J86

199

56

210

270

160

13

122

19

68

538

866

199

35

J93

180

66

471

290

85

17

101

12

14

131

212

169

19

.J96

202

58

98

265

196

15

131

24

61

585

986

211

45

J113

140

54

264

277

81

17

71

14

54

188

105

212

30

J173

104

64

216

268

93

15

108

16

61

270

627

232

16

TABLB VII. Ranges of variation and average chemical conpositions o£ Dhanjori and Jagannathpur volcanics

1^4

Component

SiO 2

TlO 2

Al 0 2 3

r« 0 2 3

FeO

MgO

CaO

Na 0 2

K 0 2

HnO

P 0 2 S

LOI

Nl

Co

Cr

V

Cu

Pb

Zn

Ll

Rb

Sr

Ba

Zr

If

La

Ce

S(i

EU

Tb

Yb

Lu

Dhanji

Min.

45,

0.

6.

2,

7.

4.

7,

0.

0,

0.

0,

0,

48

37

12

251

15

13

19

2

7

54

30

189

3

6

IS

2

,42

,59

,36

,43

,20

,84

,47

,80

.15

,09

,05

,76

0.81

0.40

1.80

0.43

or 1 Volcan

Max.

58.50

1.56

12.88

6.47

12.60

11.14

12.47

4.44

1.28

0.25

0.25

2.47

331

126

1491

325

179

21

173

17

73

281

218

236

41

16.10

31

4.20

1.18

0.76

2.40

0.53

ics

Avg.

52.03

0.99

11.44

4.08

9.69

7.12

10.12

2.33

0.60

0.18

0.15

1.46

110

69

242

302

86

16

71

8

29

153

83

204

14

11.05

23

3.1

0.99

0.58

2.10

0.48

Jagannathpur Volcanics

Hin.

47.29

0.40

9.07

0.44

5.08

3.29

3.80

0.82

0.04

0.10

0.03

0.90

55

26

38

263

29

13

50

12

12

47

12

131

3

7.80

12

2.30

0.81

0.4S

1.63

0.33

Max.

57.90

1.49

16.14

7.19

9.0«

21.33

13.76

3.38

3.17

0.20

0.40

3.90

900

B6

5400

302

196

19

131

49

120

613

986

238

45

22.60

45

5.80

1.78

0.80

2.60

0.53

Avg.

54.06

0.76

12.09

3.61

7.18

8.30

7.33

2.38

1.18

0.16

0.10

2.49

195

55

537

281

94

16

95

20

52

273

317

189

26

15.16

29

4.17

1.25

0.59

2.01

0.43

135

TABLE VIII Element ratio in Dhanjori Volcanics

K20/Na20

CaO/Al 2O3

MgO/Al 2O3

FeO*/MgO

Fe203/Fe0

Al203/1102

Ca0/Ti02

K20/Ti02

Ti02/P205

D.I.

Q Index

Mg-Number

Ni/Co

Cr/Ni

Ti/V

K/Rb

Rb/Sr

K/Sr

Ca/Sr

Ba/Rb

Ba/Sr

K/Ba

Ti/Zr

Zr/Y

Ti/Y

Dll

0.60

0.82

0.61

2.34

0.41

10.57

8.77

1.12

4.95

26.20

26.33

48.06

1 .27

1 .12

145.47

0.55

80.45

541.36

D2

0.19

0.74

0.49

2.83

0.51

8.87

6.62

0.56

7.23

39.41

23.99

45.03

1 .77

0.63

828.57

0.02

24.20

24.25

D5

0.20

0.70

0.50

2.88

0.64

9.29

6.51

0.60

7.80

40.33

26.70

46.37

1.66

0.70

842.85

0.04

40.06

370.06

D7

0.05

0.53

0.37

2.48

0.47

10.75

5.71

0.20

7.43

46.08

2/.39

47.58

2.48

0.29

7.22

45.45

0.15

7.11

172.95

2.20

0.34

20.61

30.22

16.85

509.50

D9

0.17

0.59

0.39

2.17

0.57

11.77

6.98

0.66

7.13

47.62

28.25

52.46

1.42

0.13

842.85

0.02

842.85

215.78

DlO

0.25

0.81

0.53

1 .98

0.33

11 .03

8.97

0.52

8.69

26.54

34.35

50.25

0.80

2.06

21 .10

175.00

0.19

34.50

510.56

5.03

0.99

34.75

31 .95

13.25

423.27

D12

0.30

0.83

0.55

1 .81

0,30

13.34

11 .12

0.66

9.50

23.95

34.77

52.63

0.95

1 .66

17.85

152.94

0.26

40.31

585.27

6.41

1 .68

23.85

29.05

24.50

711.87

196

0 . 5 6

1.83

0 . 3 9

0 . 5 3

2 . 1 4

0 . 4 4

0 . 6 4

1 .48

0 . 3 8

TABLE VIII (Contd.)

D13 D15 D23 D27 D29 D32 D35

K20/Na20 0.55 0.43 0.51 0.24 0.2l 0.26 0.17

Ca0/Hl203 0.99 0.96 1.01 0.98 0.86 0.85 0.91

Mg0/Al203 0.64 0.58 0.58 0.55

FeO*/MgD 1.84 2.21 2.22 1.97

Fe2Q3/FeO 0.40 0.49 0.45 0.47

Al203/TiD2 12.69 7.23 9.54 12.03 14.80 11.63 17.92

Ca0/Ti02 12.58 6.98 9.69 10.61 12.80 9.96 16.36

K20/Ti02 1.05 0.50 0.72 0.47 0.44 U.52 0.49

Ti02/P205 5.05 6.24 6.88 6.37 8.70 5.25 13.80

D.I. 23.03 26.10 25.88 26.08 21.32 26.24 22.49

e- Index 34.4^ 34.54 36.53 37.06 37.32 35.00 37.30

Mg-number 53.98 50.98 47.49 53.40 53.99 50.75 58.91

Ni/Co 1.84 1.00 1.32 0.82 1.02 0.97 1.29

Cr/Ni 1.35 1.22 0.78 1.63 1.96 1.80 2.42

Ti/V 19.91 16.55 20.43 13.60

K/Rb 306.15 503.84 100.70 100.00 106.66 107.14 80.0

Rb/Sr 0.24 0.08 0.06 0.25 0.21 0.34 0.12

K/Sr 74.39 40.68 65.88 25.00 22.69 36.88 15.55

Ca/Sr 764.48 483.85 748.59 585.27 564.53 613.11 448.33

Ba/Rb 1.20 1.93 1.3o 1.30

Ba/Sr 0.30 0.41 0.45 0.16

K/Ba 82.97 55.17 81.81 93.33

Ti/Zr 29.05 26.08 32.44 21.88

Zr/Y 12.50 4.73 63.0

Ti/Y 326.00 153.50 1379.0

197

TABLE V I I I <Contd.)

K20/Na20

CaO/Al 2^3

MgO/Al 2O3

FBO*/ngO

Fe203/Fe0

Al203/Ti02

Ca0/Ti02

K20/Ti02

Ti02/P205

D.I.

©-Index

Mg-Number

Ni/Co

Cr/Ni

Ti/V

K/Rb

Rb/Sr

K/Sr

Ca/br

Ba/Rb

Ba/Sr

K/Ba

Ti/2r

Zr/Y

Ti/Y

D37

0.40

0.81

0.47

2.81

0.33

10.88

8.88

0.55

8.91

25.49

38.78

42.18

0.75

1 .04

19.73

84.48

0.38

32.23

447.36

0.93

0.35

90.74

30.40

19.18

583.18

D39

0.18

0.93

0.64

1 .46

0.38

9.39

15.22

0.44

7.60

22.28

38.61

59.27

1.34

2.46

14.14

75.66

0.27

21.05

621.80

2.56

0.71

29.74

22.89

D42

0.46

1 .06

0.72

1 .33

0.41

17.00

18.07

1.10

3.83

21.39

36.76

62.13

1 .72

2.36

900.00

0.04

44.36

627.46

D3

0.05

1 .65

1.75

1 .09

0.24

8.59

14.21

0.20

12.33

27.13

21.08

63.84

3.72

4.50

17.67

40. UU

0.18

7.84

491.50

1.23

0.24

32.43

21.53

25.75

554.50

D19

0.81

1.15

1 .00

1 .04

0.38

16.08

18.59

1 .10

3.68

26.32

48.49

67.08

4.86

3.47

770.00

0.12

99.81

1451.85

D41

0.11

1 .08

1 .04

1 .57

0.38

10.17

11.05

0.40

7.63

30.97

24.33

59.29

2.47

3.14

17.67

47.45

0.40

20.00

474.28

1 .33

0.56

35".44

25.69

39.20

1UU7.2

198

TABLE IX Element ratio in Jagannathpur- Uolcanics

Na20/K20

CaO/Al 2O3

MgO/AI 2O3

FeO*/MgO

Fe203/Fe0

Al203/Ti02

Ca0/Ti02

K20/Ti02

Ti02/P205

D.I.

5-Index

Mg-Number

Ni/Co

Cr/Ni

Ti/V

K/Rb

Rb/Sr

KVSr

Ca/Sr

Ba/Rb

Ba/Sr

K/Ba

Ti/Zr

Zr/Y

Ti/Y

J12

0.61

U.54

0.58

1.33

0.59

13.90

7.50

1.67

2.80

33.92

29.35

64.66

2.33

2.53

20.87

116.66

0.38

45.30

177.02

1.59

0.61

73.29

26.32

5.11

134.55

J45

0.15

0.79

2.19

0.52

0.61

22.58

17.88

0.55

1.07

14.76

33.48

82.46

13.04

6.00

9.14

30.15

1 .10

34.54

1000.00

0.77

0.89

38.77

15.71

32.8

J103

0.16

0.41

0.59

0.99

0.24

29.88

12.42

0.98

2.70

30.19

34.98

66.10

2.65

3.49

81.13

0.10

8.15

90.89

15.26

8.18

515.6 202.31

J5

0.82

1 .08

1 .13

0.72

0.23

15.60

16.93

2.62

14.50

31.70

31.22

72.46

9.07

2.93

12.41

262.25

0.49

129.89

723.71

5.37

2.65

48.83

16.09

5.26

84.80

J6

0.42

0.94

1.24

0.78

0.46

17.92

17.00

0.62

9.33

19.95

46.15

74.04

5.90

3.40

11.90

120.83

0.07

7.26

170.42

2.29

0.13

52.72

16.06

0 m 3'0

134.28

J15

0.91

0.84

1 .27

0.81

1.32

15.66

13.02

1 .35

9.71

20.65

40.09

81 .94

5.59

2.81

13.86

17: .72

0.09

16.03

135.44

7.59

0.70

22.75

23.56

4.55

107.28

J73

1 .44

0.75

1 .36

0.75

0.87

16.1

12.18

2.33

10.00

25.90

39.90

79.00

4.98

2.71

12.75

483.33

0.09

47.15

212.19

16.20

1.58

29.82

23.50

3.73

87.73

TABLE IX (Contd . )

19S

K20/Na20

CaO/Al 2O3

ngU/AI 2O3

Fea*/MgO

Fe203/Fea

Al203/1102

CaQ/Ti02

K2/Ti02

Ti02/P205

D.I.

&-Index

Mg-Number

Ni/Co

Cr/Ni

Ti/V

K/Rb

Rb/Sr

K/Sr

Ca/Sr

Ba/Rd

Ba/Sr

K/Ba

Ti/Zr

Zr/Y

1 l/Y

J94

1.56

0.79

1 .37

0.70

0.08

16.26

12.98

2.14

0.07

19.45

37.94

77.85

5.63

3.37

13.78

933.33

0.25

238.29

1244.68

25.50

6.51

36.60

28.39

3.50

99.39

Jl

0.53

0.45

0.65

1.30

0.53

20.28

9.20

2.31

0.07

39.5li

32.90

62.94

3.07

3.08

13.34

132.96

0.23

31 .42

107.79

4.57

1 .08

29.08

17.24

9.95

171.67

JZ2

1.30

0.43

0.38

1.60

0.58

27.53

12.10

5.46

0.17

40.26

30.03

60.13

3.81

0.68

12.24

236.93

0.18

42.90

81.89

3.28

0.59

72.05

15.31

5.53

84.90

J25

0.14

0.65

0.67

1 .24

0.43

18.38

12.10

0.63

0.07

31.94

31 .81

63.97

3.84

2.38

15.15

79.54

0.30

24.13

405.51

3.79

1 .15

20.95

24.85

4.31

107.28

J26

0.77

0.53

0.26

3.34

0.35

13.03

6.93

2.10

0.10

48.76

32.47

38.39

1.07

0.81

20.54

176.04

0.32

57.48

163.60

4.27

1.39

41 .21

29.82

7.80

232.60

J32

0.14

0.56

0.76

1 .06

0.38

20.01

11 .30

0.78

0.06

36.53

32.94

66.85

3.12

3.02

12.40

84.78

0.30

26.00

323.33

2.78

0.84

30.70

17.12

4.66

79.93

J33

0.31

0.50

0.67

1 .26

0.36

19.44

9.87

1 .42

0.04

37.31

33.77

62.t.2

2.90

2.39

13.63

211.42

0.18

38.34

230.56

7.22

1 .31

29.40

23.45

10.73

251.79

zoo TABLE IX <Contd.)

J34 J36 J43 J46 J53 J54 J55

K20/Na20 1.23 0.71 0.76 0.86 0.25 0.30 0.39

Ca0/Al203 0.42 0.49 0.50 0.44 0.73 0.60 0.54

ngU/ttl203 0.43 0.28 0.45 0.30 0.66 0.49 0.74

FeO*/ngO 1.75 3.12 1.69 3.07 1.41 1.55 1.14

FeoOo/FeO 0.49 0.48 0.46 0.46 0.56 0.25 0,33

A1203/1102 17.62 9.25 17.39 12.58 8.32 21.26 16.83

Ca0/Ti02 7.42 6.20 8.83 5.63 6.10 12.86 9.l7

K20/Ti02 2.8 1.86 2.25 2.54 0.42 1.42 1.67

Ti02/P205 '^•3"7 10.40 10.57 10.21 4.51 15.25 13.40

D.I. 44.51 47.62 45.34 49.87 28.40 38.44 40.40

S-Index 39.90 32.09 37.06 27.21 31.64 35.18 32.01

Mg-Number 56.49 42.14 56.95 42.04 62.75 55.63 64.46

Ni/Co 1.31 1.16 2.66 1.82 3.23 3.02 3.29

Cr/Ni 2.30 0.56 1.77 0.68 2.29 1.96 2.83

Ti/V 16.65 22.34 16.86 22.87 32.01 12.92 13.94

K/Rd 225.97 328.57 255.55 275.64 216.66 118.03 202.17

Rb/Sr 0.32 0.14 0.17 0.47 0.07 0.25 0.24

K/Sr 72.80 48.64 44.37 131.09 16.82 30.12 48.94

Ca/Sr 166.52 250.60 150.16 139.27 210.35 234.72 231.57

Ba/Rb 7.46 9.85 9.98 6.10 12.58 3.73 8.04

Ba/Sr 2.40 1.45 1.90 2.90 0.97 0.95 1.94

K/ba 30.26 33.33 25.60 45.16 17.21 31.57 25.13

Ti/2r 20.43 31.17 29.37 28.98 37.52 25.57 29.32

"Zr/Y 13.75 8.0 6.80 3.60

Ti/Y 281.0 249.40 255.20 105.71

IABLE IX ( C o n t d . )

20i

K20/Na20

CaO/Al 2O3

MgO/Al 2O3

FeO*/ngO

Fe203/FB0

Al203/1102

CaO/TiOj

K2a/Ti02

Ti02/P205

D.I.

©-Index

Mg-Number

Ni/Co

Cr/Ni

Ti/V

K/Rb

Rb/Sr

K/Sr

Ca/Sr

Ba/Rb

Ba/Sr

K/Ba

Ti/Zr

Zr/Y

Ti/Y

J56

0.08

0.67

0.36

2.37

0.48

14.62

9.93

0.32

0.10

37.68

32.28

48.89

2.48

0.34

26.47

24.48

97.26

10.20

0.61

26.40

33.58

32.00

362.70

J63

0.27

0.47

0.68

1 .24

U.28

19.03

12.20

1.22

0.08

34.74

31.95

61 .53

3.75

3.06

12.55

273.91

0.12

34.80

298.89

5.95

0.75

45.98

20.65

J66

0.48

0.39

0.32

2.95

0.59

10.36

4.10

1 .31

0.10

51 .30

29.38

45.10

3.07

0.34

26.47

48.97

0.13

36.16

336.64

1 .91

1.36

4.47

29.32

10.8

362.70

J75

0.14

0.65

U.67

1 .18

0.43

18.38

12.10

0.63

0.07

32.50

31 .81

65.05

3.91

2.13

15.33

100.00

0.19

19.44

326.66

2.62

0.51

38.04

32.20

46.33

1492.33

J76

0.04

1.22

0.33

2.54

0.04

12.50

15.28

0.04

0.13

27.23

49.97

39.38

1.96

0.48

20.13

8.57

0.11

1.02

57.43

12.73

0.22

20.32

36.75

12.26

359.73

J82

0.56

0.51

0.55

1.41

0.61

19.00

9.77

2.08

0.11

37.75

33 .63

63.53

4.53

1 .69

14.88

263.82

0.12

33.42

135.57

6.14

0.77

42.90

20.55

19.63

392.36

J83

0.42

0.49

0.71

1 .14

0.34

19.43

9.67

0.42

0.04

38.33

34.24

64.60

3.05

2.91

13.71

189.79

0.19

36.75

169.56

4.83

0.93

39.24

22.12

33.60

743.40

202

TABLE IX (Contd . )

K20/Na20

CaO/Al 2O3

MgQ/Al203

FeO*/MgO

Fe2Q3/FeO

Al203/Ti02 *

Ca0/Ti02

K20/Ti02

Ti02/P205

D.I.

©-Index

lig-Number

Ni/Co

Cr/Ni

Ti/V

K/Kd

Rd/ar

K/Sr

Ca/Sr

Ba/Rb

Ba/Sr

K/Ba

Ti/Zr

Zr/Y

Ti/Y

J84

0.28

0.69

1.03

0.84

0.76

20.72

14.32

0.44

10.16

14.97

43.13

75.89

2.59

2.91

12 .1U

157.14

0.12

18.96

538.79

0.85

0.10

183,33

19.55

8.50

166.22

J85

0.38

0.54

0.54

1 .40

0.46

18.87

10.28

1 .76

8.87

39.61

30.72

61 .57

2.98

O.bl

20.5 4

190.90

0.20

38.88

163.60

4.27

1.07

41 .21

29.82

13.86

232.60

J86

0.78

0.35

0.44

2.22

1 .32

9,87

3.54

1.74

10.16

53.07

30.69

60.83

3.55

1 .05

27.08

258.82

0.12

32.71

57.43

12.73

1.60

20.32

36.75

5.68

208.97

J93

0.22

0.60

0.67

1 .25

0.68

18.83

11.39

1 .00

13.20

34.64

31 .27

66.82

2.73

2.61

13.64

385". 71

0.10

41.22

409.92

15.14

1.61

25.47

23.41

8.89

208.26

J96

1.52

0.28

0.45

2.04

0.87

10.17

2.87

2.07

11 .00

46.47

33.31

58.08

3.48

0.48

29.86

372.13

0.12

38.80

46.49

16.16

1 .68

23.02

37.50

4.68

175.84

J113

0.22

0.69

0.46

1 .51

0.32

22.15

15.46

1 .00

15.00

34.77

35.99

57.37

2.59

1 .88

12.98

90.74

0.28

26.06

352.65

1.94

0.55

46.66

16.96

7.06

119.90

J173

0.25

0.39

0.80

0.86

0.77

31 .50

12.42

1 .82

1 .48

39.68

33.73

75.61

1.62

2.07

8.94

98.36

0.22

0 0 0 0

l3l.48

10.27

2.32

9.56

10.33

14.50

149.87

203

TAM.E X. Average chenical conpositions oi Dhanjori and Jagannathpur Volcanics conpared with other volcanic rocks.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Si02 52.03 54.06 50.5 48.8 47.3 50.2 49.5 56.7 58.9 55.1 49.8 50.3 51.1 59.5 60.8 58.0

Ti02 0.99 0.76 0.60 0.73 O.SO 0.94 1.49 0.92 0.65 0.95 1.5 2.2 0.83 0.70 0.77 0.27

AI2O3 11.44 12.09 11.0 13.0 9.08 15.5 17.2 14.0 15.5 15.9 16.0 14.3 16.1 17.2 16.8 13.9

FejOs 4.08 3.61 1.53 1.94 2.98 1.63 2.80 2.3 1.5 1.99 2.0 3.5 3.0 6.8* 5.7* 1.10

FeO 9.69 7.18 9.23 9.68 7.80 9.26 9.17 7.0 4.5 5.86 7.5 9.3 7.3 6.75

HgO 7.12 8.30 10.2 11.8 21.0 7.53 6.82 5.40 4.5 4.3 7.5 5.9 5.1 3.4 2.2 9.64

CaO 10.12 7.33 11.8 8.24 7.81 11.6 8.79 6.6 5.1 5.9 11.2 9.7 10.8 7.0 5.6 7.5

Na20 2.33 2.38 1.87 1.48 0.87 2.15 2.70 3.40 4.0 3.9 2.8 2.5 2.0 3.68 4.10 1.99

K2O 0.60 1.18 0.17 0.15 0.16 0.22 0.69 0.67 1.9 1.1 0.14 0.8 0.30 1.6 3.25 0.60

P2O5 0.15 0.10 0.06 0.09 0.9 0.10 0.17 0.20 0.16 0.15 0.05

NnD 0.18 0.16 0.20 0.21 0.19 0.22 0.18 0.17 0.2 0.17 0.19

H2O 1.46 2.49 2.4 3.0 2.5 1.62 2.04 3.0 3.0 2.8 1.3 0.65 0.50

Ni 110 195 360 390 640 140 125 70 60 55 100 100 25 18 3 220

Co 69 55 50 69 80 52 55 25 23 29 32 40 20 24 13

Cr 242 537 920 900 1750 490 250 125 88 105 300 100 50 56 3 600

V 302 281 250 270 235 260 365 300 300 270

Cu 86 94 110 100 60 36 64 70 90 80

Rb 29 52 22 75 30 30 90 8

204

TABLE X.(Contd.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Sr 153 273 100 9^ 60 100 190 278 580 210 135 350 225 385 <S20

Ba 83 317 20 80 90 230 547 361 11 200 40 270 400

Zr 204 189 33 37 30 S3 135 150 190 104 100 200 60 110 170

Y 14 26 17 22 .16 20 30 25 35 40 30 30 20 110 170

La 11.05 15.16 3.0 1.9 0.86 3.6 13 13 34 12 3.5 27 3.9 12 13

Ce 23 29 7.9 5.9 2.9 9.2 30 31 70 30 12 140 7 24 23

SR 3.1 4.17 1.6 1.5" 1 2 4.0 3.6 6.7 7.3 3.9 8.2 2.2 2.9 4.5

Eu 0.99 1.25 0.55 0.57 0.39 0.73 1.3 1.1 1.9 2.0 1.5 2.0 0.9 1.0 1.4

Tb 0.58 0.59 0.68 1.1

Yb 2.10 2.01 1.5 1.8 1.1 1.9 2.2 1.8 2.4 6.1 3.0 2.5 2.0 1.9 3.2

Lu 0.48 0.43 0.23 0.29 0.18 0.31 0.38 0.30 0.30 1.10 0.30 0.40 0.30

[1] Average Dhanjori Volcanics, [21 Average Jagannathpur volcanics, [31 Average Archaean basaltic

konatiite type I (Condie, 1981), [4] Average Archaean basaltic konatiite type II (Condie, 1981), [5]

Average Archaean basaltic konatiite type III (Condie, 1981), [61 Average Archaean depleted tholeiite

(Condie, 1981), [71 Average Archaean enriched tholeiite' (Condie, 1981), [8] Average Archaean andesite type

I (Condie, 1982b), [91 Average Archaean andesite type II (Condie, 1982b), [101 Average Archaean andesite

type III (Condie, 1982b), (111 Average nid-oceanic ridge basalt (Condie, 1982c), [121 Average continental

rift tholeiite (Condie, 1982c), 1131 Average arc tholeiite (Condie, 1982c), [14] Average low K-andesite

(Condie, 1982c), [151 Average high K-andesite (Condie, 1982c), (161 Average boninite (Kuroda et al.,

iy/»).

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