PETROiOGY AND GEOCHEMfSTRy OF AHAR RIVER GRANITE* NORTH WEST

OF UOAfPUR. RAMSTHAN

DISSERTATION SUBMITTED FOR THE DEGREE OF

jfMagter of ^Iiilosioplip IN

GEOLOGY

BY

ABDUL RAHMAN

DEPARTMENT OF GEOLOGY ALIGARH MUSLIM UNIVERSITY

ALIGARH (INDIA)

1 9 8 7

2 SEP 1988

Sed in I. oir tD atai

- >

c?^ '^ ^^'

DS1171

DEPARTMENT OF GEOLOGY

ALIGARH MUSLIM UNIVERSITY

Dr. Syed M. Zainuddin M.Sc, Ph.D.(U.S.A.;, Dated: November 17, 1987 Sigma XKU.S.A.;, F .G .S . (India J

This is to certify that Mr. Abdul Rahman has completed

his research work, presented in this thesis, under my

supervision for the degree of Master of Philosophy of the

Aligarh Muslim University, Aligarh. This work is original

and has not been submitted for any degree at this or any

other University.

( SYED M. ZAINUDDIN )

In the name of Allah, the Beneficent, Most Merciful

The author wishes to express his deep sense of gratitude

to his supervisor and guide Dr. S .M. Zainuddin, Reader,

Department of Geology, Aligarh Muslim University, Aligarh

for his keen interest and valuable guidance which led to the

completion of this research work. His thanks are also due

to Professor S.M. Casshyap, Chairman, Department of Geology,

Aligarh Muslim University, Aligarh for providing laboratory

and library facilities.

The author is extremely grateful to Dr. V.K, Srivastava,

Professor, Department of Geology, Aligarh Muslim University,

Aligarh for his keen interest, help and encouragement during

the course of the work. The author is also indebted to

Dr. Shahid Farooq for his kind help in chemical analysis.

Thanks are also due to Mr. Shamim Ahmad Khan, authors one

time colleague, for his kind cooperation. Help and

encouragement from authors friends and hostel roommates

are also gratefully acknowledged.

The author wishes to thank Mr. Zakir Husain, Librarian,

for his help in the course of study, Mr. Firoz Javed for

chemical analysis and Mr. Wasim Ahmad for typing of the

manuscript.

ABDUL RAHMAN

CONTENTS

Page

LIST OF TABLE I

LIST OF FIGURES II

INTRODUCTION 1

Geography of the Area 2

Previous Work 3

GEOLOGICAL SET-UP 6

PETROLOGY OF THE GRANITE 13

Modal Composition 13

Petrography 16

GEOCHEMISTRY OF THE GRANITE 30

Geochemical Analysis 31

Major Elements 32

Classification of Granite 43

Trace Elements 47

SUMMARY AND CONCLUSION 60

LIST OF REFERENCES 6 3

Table No. Page

1 Stratigraphic succession of the 6

Precambrian formation of Rajasthan

(Heron, 19 53).

2 Precambrian lithostratigraphy and n

tectono-magmatic sequence of the

Aravalli Super Group rocks (Anon,1981K

3 Modal composition of the Ahar River 14

Granite.

4 Chemical Analysis of the Ahar River 33

granite.

I I

F i g . No. £^22

1 Geological map of Ahar River g ran i te 8

northwest of Udaipur c i ty , Rajasthan.

2 I r r egu la r f ractures in K-feldspar f i l l e d lo

by thin veins of s i l i c i c m a t e r i a l .

3 Ternary diagram of quar tz -Plagioc lase- 15

K-feldspar modal values for Ahar River

g r a n i t e .

4 Modal values for quar tz-Plagioclase- 17

K-feldspar superimposed on S t recke isen ' s

c l a s s i f i c a t i o n .

5 Fresh and unal te red polygonal quartz i s

g r a in s .

5 Inclusions of quartz in microcl ine . 20

7 Quartz veins in microcl ine . 20

8 Recrys ta l l ized quartz g r a in s . 21

9 Elongated quartz grains pa r a l l e l to 21

f o l i a t i o n .

10(a,bJ Plagioclase grains showing bending, 23

f rac tur ing and d is loca t ion of twin

lamel lae .

Ill

Fig. No. Page

11 Bands of sericite filled in feldspar 25

fractures.

12 Bands of sericite and muscovite enveloping 2 5

the feldspar crystals.

13 Aggregates of quartz grains surrounded 27

by sericite.

14 Plagioclase grain showing combination of 21

albite and pericline twins.

15 Inclusions of apatite in biotite. 28

16 Plots of total alkalis vs. SiO„. 37

17 Variation diagram of major element oxides 33

as a function of the Si02 content of the

Ahar River granite.

18 Plots of major element oxides against 40

Solidification index (S.I.J.

19 Plot of Na20 and K^O contents of Ahar 41

River granite.

20 K^O - Na20 - CaO plot for Ahar River granite.42

21 Plots of Ahar River granite on K^o; Na^O 46

diagram of Hine et al (1978).

22 Plots of Al^O^/^'Z&O-^l^a^O^Y.^O) (molecular 48

proportions) against SiO , after Sandra

et al (1986).

IV

23 T e r n a r y d iag ram showing t h e Ahar R i v e r 49

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

of Al-Na-K, Ca and Fe+Mg a f t e r Hine

e t a l ( 1 9 7 8 ; .

24 V a r i a t i o n d i ag ram of S r , Rb and Ba as 51

a f u n c t i o n of t h e SiO^ c o n t e n t .

25 V a r i a t i o n d i ag ram of S r and Rb vs K 0 . 53

26 V a r i a t i o n d iagram of Zn, Cr and Ni as 56

a f u n c t i o n of t h e SiO^ c o n t e n t .

27 D i f f e r e n t i a t i o n t r e n d s of t h e Ahar R i v e r 58

g r a n i t e , a f t e r E l - B o u s e i l l y and

E l - S o k k a r y (197 5 ; .

CHAPTER - I

INTRODUCTION

The Ahar River granite, exposed towards northwest of

Udaipur city (Rajasthan^, covers an area of about 24 sq, kiris.

The area lies between latitudes, 24°36'38" and 24* 47' 30" and

longitudes^ 73 36' and 73°42*. The shape of the outcrop is

triangular. The granite occurs within low grade Aravalli

phyllites, bordered by the bands of quartzite and limestone

on its western and eastern margins respectively.

Heron (1953J conducted the first comprehensive study of

the area,* he considered the Ahar River granite as intrusive

into the Aravalli rocks of early Proterozoic age. The

granite is a fine grained type (aplogranite^ and forms bosses

with very irregular margins and satellite intrusions showing

all the features of intrusive granite (Heron, 1953 J.

Crawford (1970^ determined the radiometric age of the

Ahar River granite and concluded that it as intrusive into

the Aravallis. However, Roy et al (1985^, on the basis of

its stratigraphic position in relation to metasediments and

2

metavolcanics, inferred that the granite constitutes the

basement of the Aravallis. The relationship of the Ahar

River granite with the Aravallis has been controversial.

The proposed study was made to resolve this problem and

also to ascertain the origin of the granite.

Geography of the_Area

The Ahar River granite is exposed towards the northwest

of Udaipur city in Rajasthan, The area is easily accessible

by road,* a metalled road from Udaipur city to Bari Lake passes

through the area. Bus services are very frequent from Udaipur

city upto Bari Lake. Few cart tracks and pack tracks also

join the metalled road from nearby villages.

It is almost a plain area which has a maximum elevation

of 4000 feet above sea level. The Ahar River runs through

the northeastern side of the granite body. The river is

generally dry during cold and dry months of the year. The

climate is semi-arid and the rainfall is low. Vegetation is

generally poor and is controlled by the proximity of ground

water level. Cactus, bushes and spear grasses are common.

3

Gardening and agriculture is done in low lying areas,' the

source of irrigation is mainly the ground water. A low

lying narrow band in the southwestern margin is densly

forested.

Previous work

The Precambrian region of Rajasthan was first studied

by Hacket (1877i who surveyed a large area of this terrain

and determined the stratigraphic order of the rocks of

Aravalli range. He proposed a two-fold classification of

the Precambrian rocks of the area, Delhi Series and the

Aravalli Series. However, his rock formation grouping has

not been much accepted. Heron (1935J recognised three major

granitic intrusions in the region, Bundelkhand granite

(Pre Aravalli^, aplogranite (post Aravalli but pre Delhi J

and Erinpura granite (Post DelhiK Heron reported that this

aplogranite body is the most instructive intrusion in the

Aravalli rocks . The north and northeastern border of the

granite is fringed by limestone and phyllites. He reported

the presence of lenticular sheets. Wisps and Knots of aplo-

granites in the limestone, and abundance of limestone wedge.

4

xenolith and roof pendants in the granite, also granitic

intrusion of all sizes in the limestone. He concluded

that the aplogranite had intiruded into limestone. Evidence

of contact metamoirphism at the limestone contact is not

observed. However, silicification of limestone at the

contact is common.

Gangopadhyay (1961^ has reported the granite as massive

and homogeneous in composition and texture. The rocks is

sheared,* twinning in plagioclase is often deformed and bending,

fracturing, faulting and intricate folding are present.

Quartz is crushed and shows highly undulatory extinction.

He has observed that the twin composition plains in feldspar

grains are parallel to the conjugate shear plane. It is

inferred that the twinning in plagioclase is the result of

intragranular gliding along shear planes due to flattening

normal to foliation which resulted in the grain elongation

along the plane of schistosity.

Crawford (1970^ used the term Ahar River granite for

aplogranite, and determined the age 227 5 m.y. by Rb-Sr

methods. Chaudhry et al (1984} analysed a series of Ahar

5

River granite samples but they did not yield acceptable

isochrones. Anon (1981) grouped Udaipur, Salamber, Udaisagar

and Darwal granites as Synorogenic granites and gneisses.

The Ahar River granite has been correlated with pre-Aravalli

basement rocks by Roy et al (1985Ji.

A detailed lithological and stiructural study of the

area has been carried out by many workers. However, detailed

petrological and geochemical study to understand the petro-

genesis of the granite has not been undertaken by earlier

workers in the area. The aim of the present study is to

decipher and delineate different types of granite in the

area and to determine the orogin and the mode of emplacement

of granite. Further, the relation of the granite with the

Aravalli metasediments was studied.

6

CHAPTER - I I

GEOLOGICAL_S£T;UP

The A r a v a l l i r e g i o n i n s o u t h e r n R a j a s t h a n and n o r t h ­

e a s t e r n Guj a r a t , c o v e r i n g an a r e a of a b o u t one h u n d r e d

t h o u s a n d s q . k m s . , forms t h e w e s t e r n p a r t of t h e Bundelkhand

c r a t o n . The A r a v a l l i s p r o v i d e s a c l a s s i c example of t h e

P r e c a m b r i a n s u p r a - c r u s t a l e v o l u t i o n . Heron (1953J s t u d i e d

s y s t e m a t i c a l l y t h e s t r a t i g r a p h i c framework of t h e a r e a and

p r o p o s e d a f o u r f o l d c l a s s i f i c a t i o n of t h e P r e c a m b r i a n r o c k s

of R a j a s t h a n . Some m o d i f i c a t i o n s h a v e been s u g g e s t e d l a t e r ,

however , h i s s y n t h e s i s r e m a i n s t h e b a s i c framework of a l l

s u b s e q u e n t w o r k . The c l a s s i f i c a t i o n , p r o p o s e d by Heron,

i s as f o l l o w s ',

T a b l e - 1 . S t r a t i g r a p h i c s u c c e s s i o n of t h e P r e c a m b r i a n f o r m a t i o n of R a j a s t h a n (Heron, 19 53 J

Vindhayn sys tem

M a l a n i v o l c a n i c s

E r i n p u r a g r a n i t e s

D e l h i sy s t em

R a i l i o s e r i e s

Aplo g r a n i t e

A r a v a l l i sy s t em

Banded G n e i s s i c complex

and Bundelkhand g n e i s s e s

7

Heron (1953 J deciphered three major granitic intrusions

in this terrain. They are Bundelkhand granite, aplogranite

(around Udaipurj and Erinpura granite, of pre-Aravalli,

post-Aravalli but pre-Delhi and post-Delhi ages respectively.

The aplogranite is exposed in the northwestern and south­

eastern side of Udaipur city. The granite, intruded into

Aravalli rocks, is a fine grained type forming bosses with

very irregular margins and satellites intrusions. The

granite exhibits all the features of the intrusive type.

Crawford (1970J used the term Ahar River granite for

aplogranite.

The area under present investigation lies towards the

northwest of Udaipur city (Fig. 1 ) . The triangular - shaped

granite body is flanked by Aravalli limestone in the north

and eastern side and quartzite towards the south and west.

Phyllite, exposed towards the eastern side, grades into

biotite schist near the contact of the granite. Heron (19 53/

considered the fine grained biotite schist to be relatively

deep seated and a more metamorphosed representative of the

Aravalli phyllites. Coarsening of phyllite to form biotite

schist as a consequence of recrystallization may be attributed

71 i.0

8

N

LOCATION MAP

x'^x

-7

If*' X X

X ^ XX '* » XX V X

X X XTT * X " X X * X X X

- \ . # " •

„ x Xx

$ f } X xx i' X ,5 ^ x-^^

XX X

--^^-~A%h.

X XX X , •x j< X j( X x^^

X X X

I I i

/-l—1-. .-Lj.j.

t±r,iz] ^ J— .—1—j~ J—J ^•l—^T—1~^—i

xx^^JxtlilEt!

: ^

3 — I . .

J — \W^x\ AHAR Rr, ER GRANITE

iz

Mis. 1000 500

KMS

Q'JAR i Z IT i '

PHVLLITC

i " H H LtMESTC IE

7 3 , 4 0

2-

3 ^ "

FIG; 1 GEOLOGICAL MAP OF THE AHAR RIVER GRANITE NORTH­WEST OF UDAiPUR CITY, RAJASTHAN .

9

to the contact effect of the granite. The relationship of

granite and limestone is very complex/ the contact is

intricate because of numerous veins and apophyses of the

Ahar River granite enclosing and cutting across blocks of

limestone. In the central part of the outcrop towards the

western margin at the contact with metasediments, the

granite is coarser and aquires a porphyritic texture having

pink phenocrysts of feldspar. There is however, a complete

gradation from fine grained granite to the coarser pink and

porphyritic variety (Heron, 1953).

Occurrence of limestone and banded quartzite as xenoiiths

and roof pendants within the granite is common (Heron, 1953 J.

The central portion of the pluton comprises of normal granite

which grades into the fine grained aplitic rock towards the

limestone contact. Veins and sheets of this aplitic material

traverse the Aravalli biotite schists and limestone towards

its periphery. The field relationship of granite and

limestone provides evidence of intrusion. The outcrop of

limestone has general appearance of being set into the granite

with their stratification dipping at high angles to the north

or northwest as if the granite had cut its way upwards along

iO

bedding planes without collapse or rotation of the blocks

of limestone which had remained in position (Heron, 1953J.

The geology of the area has been reviewed by later

workers. On the basis of tectonic setting, lithostratigraphy,

deformational history, magmatism, metamorphism and radio­

active dating, the Aravalli Craton has been assigned to three

geological cycles, Bhilwara (> 2500 M.Y.), Aravalli (2500-

2000 M.Y.), and Delhi (2000-7 40 ? M.Y.;. Anon (1981)

summurised the new data and stratigraphic classification of

the region. In recent G.S.I, classification, the Ahar River

granite, Salumber, Udaisagar and Darwal granites have been

grouped as synorogenic granite, their age was dete.irmined as

227 5 M.Y. Table {2) shows the general lithostratigraphy and

tectonic sequence of the rocks in the area.

Roy and Paliwal (1981^ suggested that the Ahar River

granite is older than Aravallis. Roy et al (1985J have

deciphered the structural and stratigraphic relation of Ahar

River granite with early Proterozoic rocks. On the basis of

correlation of metasediments (which envelopes the south­

western side of the Ahar River granite^ with other regional

u

- 2 . t r e c a n i b r i a n l i t h o s t r a t i g r a p h y a n d t e c t o n c - r r . a g m a t i c s e q u t i n c e of t h e A r r i v a l

i n s o u t h e r n H a j a s t h a n cind n o r t h e a s t e r n G u j a r a t ( a f t e i A n o n , 1981 , ' .

1 o-jp*^

•J

<

K . j a a d n Form<?. t ion (C, J D

j r . i vLa 5 p u t a F o r m a t i o n ( C . ,

J b a n F o r m a t i o n iC )

N,'t :ur.ot , l- 'ornwiLion iC-,)

K h a n i l a F o r m a t i o n [C.)

L - j n o i a F o r m a t i o n (.C, )

Kridana F o r m a t i o n (L^J

b h u f i i d F o r m a t i o n lLc.J

C n a n d a n w a r a F o r m a t i o n ( L , )

b h a w a n t u r a F o r m a t i o n ( i-oJ

W a g i d o r a F o r m a t i c n ( L ^ J

K a l i n j o r a F o r m a t i o n ( L , J

6YNwRo.jt.NIC GiiMilTt . AND Cht.I6S CUDAIPUK,' bALUKEAR/ UDAISAGAR," DA.RWALl 22^

RAKHAB DCV ULTRAKAFIC SUITE

JHAKOL GROUP

S a r r d a j e e F o r m a t i o n {J . , J

v joran F o n n a t i o n C J , J

DCVDiA GROUP

D e v t h a r i F o r m a t i o n (DV )

D a p t i F o i - m a t i o n (DV }

Rama F o r m a t i o n (N, )

Koilmal F o r m a t i o n (t-l, }

M j j :D

« ^ o

D

a, li,

•- : 3

Khfiirii.or F o i m a t i o n ( B , J

. ' a r i a F o r m a t i o n IB )

j a j j a n q a r h F o r m a t i o n ( B , j

Ban. w a r a m i x e d g n e i s s e s (U J

tv imach F o r m a t i o n {U^)

B a l i c h a F o r m a t i o n ( U , J

t k i i n g a r h F o r m a t i o n ( U ^ i

o a b i n a Foini i L i o n (U )

I m 1 rj

I Z a w a r F o n n . (U_ I •'

] B a r a i M a g r a I F o r m a t i o n ' " 6 ' ] M- ind l i I Form/>t l r )n UK)

I f . I

( K r ^ . '

X I V. I

I

Forir.

Mor-T Form,:

ina i (m (K*-^;

u e o e r i S e c t o r

^-•iTi-ir K o t r a F o n n a t i o n ^0^Q>

B e r w a s F o r m . ( U ^ ;

J a i s a i T i a n d f o r m a t i o n ( D , .1

U e l w a r a F o r m a t i o n ( D „ ;

G u r a l i Q u a r t z i t e

J a i s a r n a n d _ S e c t o r

flabarmal F o r m a t i o n

D a k a n K o t r a Form Ei t ion

J a i s a m a n d F o r m a t i o n

D e i w a r a F o r m a t i o n ( D .

Ghatgl_3ector

J a g p u r a F o n r i a t i o n (

Kuk a n d p u r a F o r m a t i o n (D^^J

J a i s a m a n d F o r m a t i o n [D^)

D e l w a r a F o r m a t i o n ( D , J

Fo

- i i J _ k i _ i

1.-: i a Fr

'.an' ' .^r a rrr -•' L on

t h - : i i ,, V rmnt i -jr.

I •^, -. r ! ^ ; i - ,

( D ^ ;

UNUlFf tRbl^TIATbD URAMITtlS AND BAolC ROCKS

12

l i t h o l o g i e s , they have concluded tha t the Ahar River

g ran i t e i s not i n t ru s ive in to the Aravallis,* ins tead

i t cons t i t u t e the pre-Araval l i basement rock.

13

CHAPTER - III

PETROLOGY OF THE GRANITE

The Ahar River granite is a light green, fine grained

rock comprising of white feldspar at the southeastern side

which gradually changes to coarser grained type with pink

coloured feldspar towards northwestern side. The general

texture of the rock is hypidiomorphic granular. However,

some rocks are porphyritic,* large feldspar crystals are

enveloped by fine grains of quartz and feldspars. The

rock shows variation in the grain size. The major mineral

composition, however, is nearly the same throughout the

rock body. The granite is sheared,* irregular fracture

filled by thin veins of silicic materials are common

(Fig. 2), Petrographic study was carried out to decipher

the possible mode of origin and also to differentiate the

various types of granite in the area.

Modal Composition

The point count method of Chayes (19 55 J was employed to

14

determine the modal composition of the rock. The thin

sections were stained by the method suggested by Ruperts

et al (196 4 to differentiate K-feldspar from untwinned

plagioclase. Uncovered thin sections were etched for 15

seconds in HF, vapour, then immersed into the saturated

solution of sodium cobaltinitrite for 15 seconds. The

K-feldspars were stained bright yellow whereas, plagioclase

remained colourless. After staining the slide, modal

composition was determined. It was found that 1000 points

and above give optimum accuracy. An average of 1150 points

were counted. The range and average mode of granite

composition is presented in Table (3) •

Table -3. Modal composition of the Ahar River granite

( 11 samples )

M i n e r a l Mean Range

Q u a r t z 3 3 . 0 3 46 .23 - 1 9 . 8 4

K - f e l d s p a r 2 9 . 1 8 44 .40 - 1 3 . 9 6

P l a g i o c l a s e 26 .76 44 .98 - 8 . 5 5

M u s c o v i t e 6 . 9 4 13 .27 - 0 . 6 1

B i o t i t e 4 .45 7 . 2 0 - 1.70

C h l o r i t e 0 . 3 0 0 . 6 0 - 0 . 0 0

Sphene 0 . 4 5 0 . 6 0 - 0 . 3 0

Z i r c o n 0 . 1 0 0 . 2 0 - 0 . 0 0

A p a t i t e 0 . 1 0 0 . 2 0 - 0 . 0 0

1 r

o

o

s.

UJ to < o o y lij

< cc

o

o 00^

Nl (-a: < a

CM o

in

o

o

o

o CM

o 09

o en

4 o

on

tn Q _ i UJ

u.

CL hi

>

< X <

o a. tn

< > < Q O

Q: < (/5 Q _ i UJ U.

I

X

(/)

o Q. I

UJ if) < o o <

Q: < O u. o

< cr o <

> cc < z. (r UJ

(D

IB

I t i s evident from the Table t ha t the quartz i s the

most abundant mineral in the gran i te , comprising 33.03%/

the next dominant mineral i s K-feldspar which cons t i tu te

29.18% of the rock and t h i s i s followed by p lagioclase with

an average modal value of 26.76%. The modal quartz-potash

fe ldspar -p lagioc lase feldspar ( recalcula ted to 100%) was

p lo t t ed on the o r thoc lase -a lb i t e -quar t z ternary diagram

(Fig. 3). The p lo t s are sca t t e red in the ternary diagram/

no systematic var ia t ion corresponding to the geographical

locat ion i s observed. This diagram, superimposed on the

Strekiesens (1976 J c l a s s i f i c a t i o n scheme (Fig. 4), shows

tha t the g ran i te ranges from normal a lka l i g ran i te f i e ld

to granodior i te f i e l d .

Petrography

Quartz i s the most important cons t i tuent of the rock/

they are generally s t r a i n - f r e e , fresh and unal tered, with a

euhedral shape (Fig. 5). Quartz grains vary in s i ze from

fine to coarse . Thin veins comprising of small c rys ta l of

quartz and feldspars f i l l in the i r r e g u l a r f ractures within

la rge feldspar c rys t a l s (Fig. 2). Small grains of quartz

il

tsl

cr < ID

a

'in\

18

FIG: 2 IRREGULAR FRACTURES IN K-FELDSPAR FILLED BY THIN

VEIN OF SILICIC MATERIAL.

FIG: 5 FRESH AND UNALTERED POLYGONAL QUARTZ.

19

occur as inclusions in rnicrocline and p lagioc lase c rys ta l s

(Fig . 6). Sometimes, they also occur as veins within

feldspar c r y s t a l s (Fig, 1), Coarse quartz c rys t a l s occur

in c lu s t e r s of plygonal shape with t r i p l e point junct ions

exhibi t ing mosaic t ex ture (Fig . Q). They are probably

r e c r y s t a l l i z e d quartz g r a i n s . Effect of deformation on

quartz grains i s marked by the elongation of quartz and

development of foliation,* such quartz grains have undulose

ext inct ion (Fig. 9).

K-feldspar i s the next major mineral cons t i tuent of

the rock,* i t s modal value i s 29.18%. I t dominates over the

p lagioclase feldspar which cons t i t u t e 26.76% of the rock.

Generally, K-feldspars are rnicrocline, very few small grains

of or thoclase are also p resen t . Microcline c rys t a l s are

la rge and f resh . The c ry s t a l s are deformed and fractured,*

the f rac tures are f i l l e d with s i l i c i c m a t e r i a l . The large

grains are sometimes granulated at the boundary imparting a

mortar s t r u c t u r e . The K-feldspars are general ly perthi t ic ,*

f ine lamellae of a l b i t e , formed by replacement of microcline,

are included within the minera l s . All the a l b i t e grains

within microcl ine have s imi la r op t i ca l o r i en ta t ion as t ha t

20

F I G : 6 INCLUSIONS OF QUARTZ IN K-PELDSPAR

L K ^ ^ | ^ e >

H F I ^ '

F •^L,

'4 ' % -

r^^»>. -i^

*^B 1 ^ F I G : 7 QUARTZ V|]INS IN MICROCLINE.

21

FIG: 8 RECRYSTALLISED QUARTZ GRAINS

FIG: 9 ELONGATED QUARTZ GRAINS PARALLEL TO FOLIATI ON

23

FIG: 10(a,bJ PLAGIOCLASE GRAINS SHOWING BENDING,

- FRACTURING, AND DISLOCATION OF TWIN

LAMELLAE.

24

muscovites are well oriented along the cleavage planes,

Some plagioclase crystals are completely covered by flakes

of sericite and muscovite. Parallel banding and veins of

sericite and muscovite are present along parallel fractures

and margins of feldspar grains (Figs. 11 and 12), These

vein like branches of sericite and muscovite along

fractures in feldspar grains are attributed to the action

of fluid in the process of mineral alteration (Roy et al,

1985J . These muscovite and sericite grains are secondary,

a product of mineral alteration. The calcium released

from feldspar in this process formed fresh calcite which

either occur along the margins of large feldspar grains or

in the veins of polygonal quartz aggregates (Roy et al,

1985). Due to extensive alteration, the rock appears as a

sericite and quartz aggregates (Fig, 13). Some crystals of

muscovite in the rock are, however, of primary origin,

Gangopadhyaya (1961) suggested that the twin ccxnposition

planes in feldspar grains are parallel to the conjugate shear

planes and that the twining in the conjugate grains are the

result of intergranular gliding along shear planes due to

flattening normal to foliation. This suggests that the

23

FIG: 11 BAND OF SERICITE ALONG FRACTURE IN FELDSPAR

FIG: 12 BANDS OF SERICITE AND MUSCOVITE ENVELOPING

THE FELDSPAR CRYSTAL.

26

twining in plagioclase is secondary and has developed as a

result of post-crystallization deformation. The twining

follows albite law, sometimes combination of albite and

pericline law (Fig. 14^.

Accessory minerals include muscovite, biotite, sphene,

chlorite, apatite, and zircons. Muscovite content in the

rock ranges from 0.6% to 13.2% (Average 6,1%J in sample

No, 13 it is lowest (0.6%) and highest in sample No, 15

(13.2%j. Excluding these two samples, they vary from 2.01%

to 8,8%. Inclusions of apatite in the biotite grains are

present (Fig, 15J. Sphenes are generally euhedral in shape.

The field observation corroborated by the petrographic

study indicates the presence of a uniform homogeneous type

of granite in the area,

Gorai (1951J classified the plagioclase twining into

two types A-type and C-type, A-type twining is found both

in igneous and metamorphic rocks, whereas C-type twin develop

in crystals during growth and is restricted in magmatic rocks,

Absence of zoning and C-type twining in plagioclases

suggest a metasomatic origin of granite. However, presence

27

FIG: 13 AGGREGATES OF QUARTZ GRAINS SURROUNDED BY

SERICITE.

FIG: 14 PLAGIOCLASE GRAIN SHOWING COMBINATION OF

ALBITE AND PERICLINE TWINING.

28

FIG: 15 INCLUSION OF APATITE IN BIOTITE GRAINS

29

of limestone xenoliths in granite, and the intrusion of

granite liquid along fractures in limestone blocks is

evidence of magmatic origin of granite. Granite is highly

deformed marked by the bending of twin lamallae, strained

crystals of plagioclase and untwinned plagioclase crystals.

It may be possible that the zoning and C-twins were destroyed

during later deformation and alteration of plagioclase. As

such, it is inferred that the granite was emplaced in a

liquid state and hence of a magmatic origin.

30

CHAPTER - IV

GEOCHEMISTRY__OF_THE_GRANITE

The p e t r o l o g i c a l s t u d i e s a l o n e may n o t b e a d e q u a t e t o

d e c i p h e r t h e p e t r o g e n e t i c h i s t o r y of t h e r o c k . Geochemical

f i n g e r p r i n t p r o v i d e i m p o r t a n t i n f o r m a t i o n r e g a r d i n g t h e

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

a l s o h e l p f u l i n d e c i p h e r i n g t h e s e q u e n c e of e v e n t s i n v o l v e d

i n t h e rock f o r m a t i o n . The s t u d y of t h e f r a c t i o n a t i o n of

c e r t a i n m a j o r and t r a c e e l e m e n t s can be u s e d t o c o n s t r u c t

t h e p e t r o g e n e t i c model and t o d e t e r m i n e t h e c o m p o s i t i o n of

s o u r c e r e g i o n from which t h e y have been d e r i v e d .

Ra re E a r t h e l e m e n t s . I s o t o p e s , t r a c e e l e m e n t s and t h e i r

r a t i o s a r e v e r y h e l p f u l i n t h e s t u d y of t h e p e t r o g e n e s i s of

t h e r o c k and c o m p o s i t i o n of s o u r c e r e g i o n . Hanson (1978 ) ,

McCarthy (1976 , 7 8 ; , E l - B o u s e i l y and E l - S h o k a r y (1975) and

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

Rb, Ba, S r , and Ti and t h e i r r a t i o s t o d e c i p h e r t h e o r i g i n

of t h e g r a n i t i c r o c k and t h e i r c r y s t a l l i z a t i o n h i s t o r y .

P e a r c e e t a l (1984 ; u s e d Rb, Y, Yb, Nb, and Ta f o r t h e

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

31

the rocks i n to various types according to t h e i r t ec tonic

s e t t i n g . The grani tes have been c l a s s i f i ed in to I- type and

S-type, depending upon t h e i r source of or igin on the basis

of K 0/lSla^O r a t i o and S i l i c a content by Chappell and White

(1974K

Major oxide and t r ace elanent geochemistry of the Ahar

River g ran i te was car r ied out to determine the ccanposition

of the rock and i t s or ig in , whether S-type or I - t y p e . Such

type of study has not been ca r r i ed out on Ahar River grani tes

by the e a r l i e r workers.

Geochemical Analysis

Ten representa t ive samples of Ahar River g ran i te were

se lec ted for chemical analysis to determine the major and

t r ace element composition of rock. Major and t r ace elements

were analysed by the rapid analysis method of Shapiro and

Brannock (196 2; , the U.S.G.S. standards CM, GR and GSP

were used as re ference .

One gm of sample was digested with hydrofluoric acid

and perch lor ic acid, and then i t was t rans fe r red to 100 ml

volumetric f lask to prepare the standard solut ion which was

o ^

used to determine the concentration of major elements,

Na^O, K„0, CaO, MgO, Total Iron, and MnO on Double Beam

Atomic Absorption Spectrophotometer. Trace elements, Rb,

Ba, Sr, Cu, Co, Cd, Ni, Zn, Pb, and Li were also determined

on Atomic Absorption Spectrophotometer d i r e c t l y from standard

so lu t ion . Solution A was used to determine the concentration

of Si02 and A120T in the rock," i t was prepared by fusion of

0.1 gm of rock powder with NaOH p e l l e t s in nickel c ruc ib le .

The solut ion was mixed with 111 HCl and then t ransfer red to

one l i t r e voliometric f l a sk . The concentration of SiO„ and

AI2O0 was determined by Spectrophotometer using colour ions

of respect ive elements and measuring the absorbance on

se lec ted wavelength 6 40 mM for SiO^ and 47 5 mM for Al„0 .

The r e s u l t of major oxide elements and t race elements are

presented in Table (4J.

Major Elements

I t i s evident from Table 4 t ha t the concentration of

SiOp i s general ly high and does not show much variation,* i t

ranges from 72.16% to 77.6%. The amount of A1„0 i s also

f a i r l y uniform, i t var ies from 14.37% to 18.29%. CaO, Fe^O

M 0) a

Z

0) r-i

a,

CO

r-O)

<* CN

ro CM

CD r-\

\o rH

LD r-(

<

y3

in

H H (M

O

o ro

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LD

in

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•=* r-

i£>

en (N

o in in

r-

^ 00

t-i -*

ro r-

rH VO

00 CO

i£)

(N

o in

O in

r-ID

in

in <•

in rH

M) r-U3

r-ro <:)< fH

<X) r

rH

a> CN

CO rH

in • *

in rH

00 CN

*£)

• ^

r-i

-*

0> -*

^

vO ro ro

CO CN

<*

in CN

^

in CN

ro

CN •*

m

r-{ <*

in

vD in

^

rH

o rH

(X) ro

CN

CTi • *

CM

o I

ro

a\ rH

ro

ro in

CN

a\ in

CO

lO <!<

ro

CN fl

CN

in r-r-i

«*

o o

ro O

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-H

o o

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CN O

o

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a\ O

o

ro r-\

r-f

in «*

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00 iH

o

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o

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o

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o

VD VD

o

-* VD

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<-i in

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c ^

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<!* CO

o

CTi in

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<<

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00 iH

o

r-o o

CO rH

o

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CN CN

o

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o

in rH

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4* fO

O

1

1

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o o

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rx5 5 ^

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2

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o • H CO

ro D

CN O

CN (0 CN o (0

o

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s: o G S

o

CTi

VD

CTv ON

CO CTi

VD

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CO

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ON

in CN

CTi

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a\

CO CT>

in

in

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33

X5 4-1 G O U

+J O

C o u

I

0)

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0)

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r-<M

VD 00

VD in CN

CN • ^

y£> ro

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in

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cr> VD OJ

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r-

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• *

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cr. ro

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(Ti

ro O rH

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in 00 r-

X) o u •H

>-3 OK

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M U

34

r-ro

a\ VD CN

O in rH

o

00 CN

CTi ro ro

in • *

rH t

13 -P C 0

u in

rH O CN

o ON -H

CO 00 CN

00 (N rH

<y\ 00 CN

CTi CO

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ro in CN

r~ CN CN

00 .H o 00 o CT>

rH

r-

CN

ro ro

VD CO

in

ro

CN in rH

.

0)1

(U! r - l l M

CM

CM

n CM

00

VD

in

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o m •

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o n «

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r-O t

CM

00 -H •

og

vo O »

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' CN •

(N

H O •

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iN

VD iH • o

VD in •

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in in •

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<yi

o • iH

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a\ in • o

o r-\

• i-t

M

o • iH

rH

o CN

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o n

r-H VD ro

in VD n

CO O CM

CM O n

r-O '

in in m

00 i* t

o

a\ VD • o

r-{

00 • o

r tn •

O

O tn •

CM

o ** • O

on VD •

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c <* • o

r-{

• VD

in •

rH r-l

VD •

00

cr» •

O •

CN

CO •

ro

CO •

CM •

VD

rH CO •

(N

n

r-CM •

VD

n r~-•

rH

CO «* •

CM

t -H •

ro O rH

t-~ 00 •

r-i CN

rH 'l' •

CN

a\ 00 •

rH

ro m •

O

CN r-t • o

^ rH • o

rH rH • O

VD

cr» rH • o

r-H • o in O r-t • o

in CM rH t

o CM

< in

VD O •

CN

CN • ^

t

O

fO CTv CN

in CM •

O

in •

CO

vD r-•

in

rH CN • o

H H CM

CO og •

CM

CO n • o

a\ CO CM

c ^ • o

-* •

'

r~ CJ\ • en

^ i-i

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M g

u M

<;

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36

and MgO contents in the rock are low, cons t i tu t ing less than

1%. Concentration of Na20 i s higher than t h a t of K 0. The

a l k a l i content, however, var ies in r e l a t ion to the contact

of the gran i te with limestone,* a t the contact , the concentra­

t ion of Na O i s maxim\am and K O i s lowest e . g . sample No. 27

which has Na20 content of 6,28% (highest value) and 1.01%

K O (lowest value) in the rock. The t o t a l a l ka l i s (Na^O and

KjO) in the rocks do not vary much (Fig. 16) . The inverse

re la t ionsh ip in the Na and K concentration in the grani te

would suggest t ha t K has been replaced by Na at the con tac t s .

Presence of replacement p e r t h i t e s a t the contact corroborates

t h i s in fe rence . Concentration of MnO i s very low (generally

below detect ion limit)," i t was detected only in three samples.

Major oxides, p lo t t ed on Markers diagram (Fig. 17), do

not show any systematic va r ia t ion or s ign i f i can t re la t ionsh ip ,

Na O and K O p lo t s (Fig. 17) show an inverse relationship,*

samples with higher Na20 have a lower K O concentra t ion. The

K-feldspar (microcline) c ry s t a l s are per thi t ic ,* s imilar

opt ica l o r ien ta t ion of the included plagioclase c ry s t a l s

within the host microcline suggests an ionic exchange of Na

with K to form the p e r t h i t e . The var ia t ion trends of CaO,

37

7A 76

Si 02 (Wt.7o)

80

FiG. 16 PLOTS OF TOTAL ALKALIS vs.Si02 OF THE AHAR RIVER GRANITE.

20-5 +

6^10

; ix. i ! 20-

I O10 o0-5

U

3

2 T o

CM

' ^ o

70 71

38

«

72 73 76 78

FIG. 17

7A 75

Si02(wt.%) *

VARIATION DIAGRAM OF MAJOR ELEMENT OXIDES AS A FUNCTION

THE Si O j CONTENT OF THE AHAR RIVER GRANITE

39

Fe^O^, and MgO do not show any significant relationship.

The major oxides, plotted against Solidification Index

(S.I.J on Figure 18, do not reveal any trend or relationship.

When the major and trace element data, plotted on Marker's

variation diagram, do not show any clear relationship, this

indicates that the rocks are not probably related with the

simple fractional crystallization of a common parental magma

or partial melting of a common homogeneous source (Schuster

et al, 1985J .

The Ahar River granite has a molar concentration of

AljO in excess of CaO + .Na O + K O and hence may be termed

as peraluminous (Shand, 19 50J , The K^O increases in the

granite reciprocally to Na^O resulting in the variation of

K20/lSfa20 ratio from 0.16 to 1.1. The plots on Na^O vs K„0

diagram (Fig. 19 J reveals that the granite varies from

tonalite to adamellite in composition, ^^2^ ~ 2^ " ^^^

ternary diagram (Fig, 20j also shows variation in the

composition of granite from tonalite to quartz monzonite.

However, the plots on Figure (2J) are more concentrated towards

granodiorite than tonalite fields. As mentioned earlier,

there is evidence of exchange of K and Na ions in the rock.

o

o o o

o rsi

i t :

0

0

0

0

o csj a

0

15

O

<

*10

CO

70

2 1

1

2 1

A

2

8

6

A

2

^

-

-

-

•

•

a .

•

•

•

•

1

• •

• •

• •

•

•

•

•

• •

e

1

« •

• •

• — • •

•

•

•

•

•

•

• •

1

• • •

\ *

• • • .

• •

•

• • •

• • •

• •

1

•

•

•

•

•

•

•

1 1

•

•

•

•

•

•

0

1 1 1

40

0 0.5 10 15 20 2-5 30 3-5 AO A-5 50

S. I . ^

FIG. 1 8 PLOTS OF MAJOR ELEMENT OXIDES AGAINST SOLIDIFICATION

INDEX (S- I.) OF THE AHAR RIVER GRANITE .

41

O CNl

O

z

UJ

2: < o rr UJ

>

Q: < X <

UJ

U-

o CO 1— z UJ \-' z o o o

c z <r

O Z

o

o - J

CT) «—

o

cr> un CNI

42

K,0

\-60

\ 3 0 / " ^ - ^ GRANODIORITE

TONALITE

Na20

^-70

-80

70 60 50 £.0 FIG. 20 K 2 0 - N a 2 0 - C a O PLOT FOR AHAR RIVER GRANITE

30 20

-90

^ 10 CQO

43

I n v iew of t h i s , t h e i n f e r e n c e b a s e d on K„0 - Na^O c o n c e n ­

t r a t i o n i n t h e rock may n o t b e r e l i a b l e .

C h a p p e l l and Whi te (1974J s t u d i e d t h e g r a n i t e b a t h o l i t h

of Tasman o r o g e n e zone of e a s t e r n A u s t r a l i a . They c l a s s i f i e d

t h e g r a n i t e s i n t o I - t y p e and S - t y p e d e p e n d i n g upon t h e i r

s o u r c e of o r i g i n . A number of c r i t e r i a t o d i f f e r e n t i a t e t h e

g r a n i t e i n t o I - t y p e and S - t y p e h a v e been s u g g e s t e d by t h o n .

I - t y p e g r a n i t e s a r e d e r i v e d from i g n e o u s m a t e r i a l and

t h i s i s c h a r a c t e r i s e d by h i g h sodium c o n t e n t . High Na/K and

h i g h t o t a l Na, K and Ca i n r e l a t i o n t o Al a r e c h a r a c t e r i s t i c s

of i g n e o u s r o c k s . These c h a r a c t e r i s t i c s a r e r e t a i n e d d u r i n g

t h e g e n e r a t i o n of g r a n i t o i d magma. I - t y p e g r a n i t e s have low

87 86

i n i t i a l S r / S r r a t i o s ( 0 . 7 0 8 ) , h i g h oxygen f u g a c i t y and

t h u s h i g h f e r r i c / f e r r o u s r a t i o s . F r a c t i o n a t i o n of a m a n t l e

d e r i v e d b a s a l t i c p a r e n t magma p r o d u c e s an I - t y p e g r a n i t e , * as

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

from b a s i c t o a c i d i c . C h a r a c t e r i s t i c m i n e r a l s p r e s e n t i n

I - t y p e a r e b i o t i t e , h o r n b l e n d + s p h e n e + m a g n e t i t e . Such

g r a n i t e s a r e much more r e g u l a r i n c h e m i c a l and i s o t o p i c

4i

c o m p o s i t i o n b e c a u s e t h e y a r e d e r i v e d from a more homogeneous

s o u r c e .

Whereas , S - t y p e g r a n i t e s a r e d e r i v e d from a s o u r c e

r e g i o n w i t h i n t h e c o n t i n e n t a l c r u s t . S - t y p e c o n t a i n s low

Na and low Na + K + Ca/Al r a t i o , b e c a u s e Na and Ca a r e

r e l e a s e d d u r i n g w e a t h e r i n g p r o c e s s e s and a r e removed i n

s o l u t i o n . C l a y s , formed by w e a t h e r i n g , a b s o r b K d u r i n g

d i a g e n e s i s and s e d i m e n t a t i o n r e s u l t i n g i n t h e f o r m a t i o n of

a p e l i t i c s e d i m e n t a r y rock which i s s t r o n g l y p e r a l u m i n o u s ,

i . e . , Al/(Na+K+CaJ > 1.1 and h a s low Na/K. T h i s c h a r a c t e r i s t i c

i s r e t a i n e d d u r i n g t h e p r o d u c t i o n of S - t y p e g r a n i t e magma from

t h i s s o u r c e .

87 86 Magmas of S - t y p e g ran i to ids c o n t a i n h i g h Sr / S r r a t i o s

18 and a r e e n r i c h e d i n 0 (oxygen i s o t o p e ) c o m p o s i t i o n b e c a u s e

c i r u s t a l r o c k s h a v e h i g h c o n c e n t r a t i o n of Rb /S r r a t i o and

18 h i g h 6" 0 i n c o n p a r i s o n t o m a n t l e ( N e i l and C h a p p e l l , 1977J .

The f r a c t i o n a t i o n t a k e s p l a c e o v e r a more l i m i t e d r a n g e of

s i l i c a c o n t e n t t o p r o d u c e v a r i o u s S - t y p e g r a n i t e s from c r x i s t a l

m e l t . The c h a r a c t e r i s t i c m i n e r a l s a r e b i o t i t e + m u s c o v i t e +

c o r d i e r i t e + g a r n e t + i l m e n i t e , S - t y p e g r a n i t e e x h i b i t s more

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

45

source are more heterogeneous (white and Chappell, 1977).

This c l a s s i f i c a t i o n corresponds with the magnetite se r i es

g ran i te and i lmeni te se r i e s g ran i te as proposed by Ishihara

(1977J.

Hine e t al (1978) s tudied the kosciusko ba tho l i th of

Aus t ra l ia and used Na20 vs K O p lo t which charac ter i ses the

most fundamental chemical difference between the I and

S-type g r a n i t o i d s . The more potassium r ich S-type have lower

concentration of sodium. The d i s t inc t ion between two groups

i s very c l e a r . This i s a useful c r i t e r i a in recognizing I -

and S-type grani to ids (White and Chappell, 1974).

P e l i t i c rocks have high K concentration in re la t ion to

Na and Ca (Turekian and Wedephol, 1961,* Kolbe and Taylor,

1966) and t h i s i s re f lec ted in the high K/Na r a t i o of S-type.

This i s also exhibi ted in the AI2O2 / (Na20 + K 0 + CaO) > 1.1

values of S-type for kosciusko o a t h p l i t h . Hine et al (1978)

infer red tha t Al/(Na+K+Ca) < 1.1 designates I - t y p e . Sandar

and Alan (1986) used t h i s c r i t e r i a for Cheticamp pluton which

has an a f f in i ty with the S-type.

Hine et al (1978) d i f f e ren t i a t ed the I - type and S-type

4fi

6 -

o CM -J

O 3

•

-

I-Type

—

1

•

, 1

•

•

• •

1 . i

5 -Type

• • •

1 1 1 1 1 0

-U

3 A 5

^ 2 0 ( Wt.7<.) -

FIG. 21 PLOTS OF AHAR RIVER GRANITE ON K2O : Na2 0

DIAGRAM OF R. MINE et al (1978).

47

grani tes by mineral composition,* the I - type comprises of

p lag ioc lase + hornbland + b i o t i t e whereas, b i o t i t e +

p lag ioc lase or b i o t i t e + p lagioc lase + c o r d i e r i t e i s

c h a r a c t e r i s t i c of S-type.

The p lo t s of the Ahar River grani te on Na O vs K O

diagram (Fig. 21) f a l l in the I - type f i e l d . However, the

Al^O^ / (Na^O + K O + CaO; r a t i o which i s > 1.0 indicates

peraluminous c h a r a c t e r i s t i c of the rock. All the points on

A/KCN vs SiO^ diagram (Fig, 22) are concentrated in the f ie ld

of S-type. Sandar and Alan (1986 J applied t h i s diagram to

d i f f e r e n t i a t e the peraluminous from metaluminous f i e l d .

The S-type nature of g ran i te i s also infer red from the

p lo t s of data on Al-Na-K, Ca and Fe + Mg diagram (Fig. 21).

Na O vs K2O p lo t s for the c l a s s i f i c a t i o n of I and S-type

gran i te may not be acceptable in the case of Ahar River

g ran i te because there i s evidence of K ion replacement by

Na ion, whereby the concentration of sodium was increased.

Trace elonent d i s t r i bu t i on in a given rock i s re la ted to

t h e i r concentration in the parent magma and the c rys t a l l i za t ion

48

UJ a. > •

if)

CNI <SJ o

CVI

I • I I I • I CO CX) <r CM

MNO / V

o 00

ID

o

o o o

CM O

c o

O 0 0 u. CD Q. 3

I ° u • -

o <

©i +

iij o

CM O

<

9 ^

CO

O CNJ

<

U_ O

<

CN O CO

o <

CN eg

LL.

49

C71

(-o m o

o

lu Q: UJ Q a: o u o

o

o

2^

I

<

z l i j _j m 2 or o X

en

UJ

X

Q :

ai LL

1° ^

Q 2 < O

o is:" I o

s

u. o to 2: cr u I—

< — J o g <

o tr>

o

o

Q UJ

S 0-2 O

CO O

a

° i t o

u UJ h-2 < or

** Q:

UJ > Q:

Q: <

en

CM

o u.

o o

50

history of the rock. Depending upon the prevailing conditions,

a magma may follow different trends of crystallization.

McCarthy (1976 J described two extrane types of crystalli­

zation in a plutonic environment. One of these types is a

perfect equilibrium crystallization in which the entire solid

phase remains in equilibrium with the melt throughout the

crystallization. This type of crystallization results in a

solid of homogeneous composition, both mineralogically and

with respect to major and trace element abundances. The

other type is a perfect fractional crystallization where only

the surface of the crystal is in equilibrium with the melt.

During the crystallization, early formed solids are enriched

in compatible elements,' however, the abundance of such elements

decreases in successively formed solids. On the other hand,

incompatible elements are present in low concentration in

early formed solids but their concentration increases in

successively formed crystals (McCarthy and Hasty, 1976).

During crystallization of a granitoid melt, Ba, Sr and Ti

are highly compatible with the solid (McCarthy and Hasty,

1976/ Hahn Weiheimes and Ackermam, 1967).

51

Between these extremes, l i e s a continuxim of c r y s t a l l i ­

zation involving p a r t i a l equilibrium between so l id and mel t .

Crys t a l l i za t ion within t h i s continuum has important

consequences on the d i s t r i bu t i on of t r ace el orients in the

r e su l t an t so l ids (McCarthy and Hasty, 1976).

Trace el^nent data of Ahar River g ran i te was p lo t ted

on various diagrams to determine the var ia t ion trends of

elements, t h e i r mode of c r y s t a l l i z a t i o n and nature of source

from which they have been derived.

Trace elements were p lo t t ed on Harkers var ia t ion diagram

(Fig. 24-) to determine the var ia t ion trends of t r ace elements

in the rock. Plots of Rb, Ba and Sr do not show any s ign i ­

f icant r e l a t ionsh ip , the p lo t s are s c a t t e r e d . Rb concentration

in the gran i te var ies from 42-84 ppm,* the enrichment of Rb

from periphery towards cent re of the g ran i te body i s

s i g n i f i c a n t . A good pos i t i ve cor re la t ion i s evident between

K and Rb content in the rock. This var ia t ion i s c lear in

KjO vs Rb p lo t in Figure (25). K/Rb values ranges from

201-406, the average being 317.

Sample No. 15 from the contact of g ran i te and meta-

52

1A00-

^1000-

a a

S 600-

200

k 125-

J

? a S 75-jQ V-L-

25-

1 ' 200-

£ Q.

- 100-

•

•

•

1 I

• •

•

•

•

•

•

•

•

L _ i „

•

•

•

• •

•

•

•

•

• •

• •

•

• «

• • •

... 1 1 , L... 1 1

70 72 7A 76

Si02(wt.°/o)

78 80

FIG. 2^ VARIATION DIAGRAM OF 5r ,Rb,AND Ba, AS A FUNCTION OF THE S1O2 CONTENT OF THE AHAR RIVER GRANITE.

125

53

£ 9-75 a.

%•

25

£300 a a to

100

0

•

1 1

• • •

1 1 2 3

KoO (Wt.7o;

FIG 25 VARIATION DIAGRAM OF Sr AND Rb VS.K2O OF THE AHAR RIVER GRANITE .

54

sediments has unusually high concentration of Rb (127 ppm)

whereas, very low content of Sr and Ba, 50 ppm and 255 ppn

respectively. The anomaly in the concentration of Rb, Ba,

and Sr may be attributed to the effect of contact meta­

somatism. Interaction of granitoid with ground water on a

massive scale could cause redistribution of trace elements

(Taylor, 1971 J. It has been shown, for example, that the

whole rock Rb content increases with the degree of propyl!tic

alteration in porphyry copper deposits, while the Sr content

decreases (Olade and Fletcher, 1975K Similarly, Rb may

have been enriched and Sr depleted in sample No. 16 at the

contact,* as such, the sample has been disregarded.

Sr and Ba substitute potassium, especially at the later

stages of magmatic crystallization. The concentration of Ba

is high in the rock,* it ranges from 256-1311 ppm (Table 4j .

Towards the central portion of the rock body, Ba concentration

increases, whereas near the contact of granite with meta-

sediments, Ba is depleated in the rock. Sr concentration in

the granite is higher towards limestone contact but the value

decreases at the contact of metasediments. The concentration

of Sr in the rock varies from 71-260 ppm.

55

The d i s t r i bu t i on pa t te rn of Rb, Ba, and Sr shows that

the c r y s t a l l i z a t i o n of Ahar River grani te did not occur by

the equilibrivim mode. Same type of f rac t iona l c r y s t a l l i ­

zation i s more l i k e l y to have taken p l ace . As suggested by

McCarthy and Hasty (1976), during the f rac t iona l c r y s t a l l i ­

zation of a grani to id melt, concentration of Ba, Sr, and Ti

are high in ear ly formed so l ids because they are compatible

elements. Their abundance f a l l s in the successively formed

s o l i d s . Central port ion of the Ahar r i ve r g ran i te has higher

abundance of Ba and Sr than the per iphery. I t may be inferred

tha t the cent ra l pa r t of the pluton c r y s t a l l i z e d f i r s t and

the per ipheral body formed by l a t e r f rac t ionated magma. The

low content of Ba, Rb, and Sr towards the contact with the

country rock may also be due to l a t e r metasomatism.

Calvin (1985) suggested a p e l i t i c source of magma if

the Rb/Sr r a t i o > 0.5 (which i s higher than average crus ta l

r a t i o ) . Average Rb/Sr r a t i o of Ahar River g ran i te i s 0 .53 .

K/Ba var ies from 15.76 to 41,73 and Ba/Rb r a t i o var ies from

6.13 to 18.57 .

Cr, Ni, Zn, and Pb concentrat ions in the rock are high.

Ni and Cr show pos i t i ve t rend with s i l i c a , whereas Zn has a

56

, eof 70

^ 60

S 50

2 ^0

30

425

^-,00

375

\ 350

1 325

300

| 2 7 5 a 't:250 o

225

2\)

175

300

275

250

225 1

1 200 1 1

„ 1 7 5 E Q. a l 5 0

N125

100

75

50

-

-

-

-

-

-

-

_

-

~

-

! 70 71 72 73 74 75 76 77 78 79 60

SiOCWt.V.) »

FIG: 26 VARIATION DIAGRAM OF Zn,Cr,AND Ni,

AS A FUNCTION OF THE S1O2 CONTENT

OF THE AHAR RIVER GRANITF .

57

negative cor re la t ion (Fig. 26^. Li, Cu, Co, and Cd have

uniform d i s t r i b u t i o n . Plots of Pb vs SiO^ shows large

s c a t t e r of p o i n t s ,

El-Bousei l ly and El-Shokkary (1975J p lo t t ed the Rb, Ba,

and Sr values (ppm values reca lcula ted to 100%J on a ternary

diagram to determine the d i f f e ren t i a t ion t rend of the g ran i t i c

rocks . The ternary p lo t s of Rb, Ba, and Sr for Ahar River

g ran i te (Fig. 21) are concentrated in normal grani te f i e ld

and are confined to the Ba apex of the ternary diagram.

Turekian and Wadephol (1961-) termed such rocks as low Ca.

g r a n i t e s . Taylor e t al (I960) opined tha t they are typ ica l ly

associated with high temperature ( l eas t d i f fe rent ia tedJ

K-feldspar in normal g r a n i t e . Heier and Taylor (19^9) studied

the d i s t r i bu t i on pa t te rn of Rb, Ba and Sr in a lka l i feldspar

and observed tha t in a d i f f e ren t i a t ion s e r i e s , Ba decreases

more rapidly than Sr . As such, Ba/Sr r a t i o decreases with

increasing f r ac t iona t ion . From the ternary diagram, i t i s

evident tha t the rock i s not much d i f f e r en t i a t ed .

C r i t e r i a for c l a s s i f i c a t i o n in to I and S-type i s given

by White and Chappell (1974J. Geochemical and mineralogical

58

100 MOr,.

FIG. 27 DIFFERENTIATION TRENDS OF THE AHAR RIVER GRANITE AFTER EL-BOUSEILLY AND

EL-SOKKARY (1975).

59

characteristics of Ahar River granite correspond to S-type

granite. The granite has high silica content, 72-77%.

AI2O3 / (Na^O + K2O + CaO) is more than 1.1 which reveals

its peraluminous composition. These characteristics are

identical with the Kosciusko Batholith of Australia (Hine

et al, 1978) and Cheticamp pluton of Nova Scotia (Sandra and

Macdonald, 1986J which have been identified as S-type.

Presence of biotite and muscovite and absence of hornblende

with apatite and zircon as accessopy minerals signifies its

affinity with S-type. K^O / Na20 ratio are modified by the

exchange of K with Na ions . Peraluminous composition and

characteristic mineralogy of Ahar River granite indicates

its affinity with S-type granite.

The limestone and granite relationship indicates intrusive

nature and magmatic origin of the Ahar River granite. Lime­

stone xenoliths in the granitic rocks, and presence of

granitic veins indicates a magmatic origin of the granite.

These granitic veins have physical continuity with the granitic

pluton. The peraluminous nature of the granite as revealed by

the geochemical study suggests anatexis of aluminous sedimentary

rock which formed the granitic liquid.

60

CHAPTER - V

SUMMARY AND CONCLUSION

The granitic rocks exposed towards northwest of Udaipur

city was designated as Aplogranite by Heron (1953;. He

concluded that the granitic rocks correspond to post-Aravalli

but pre-Delhi igneous intrusions . The granite was designated

as the most instructive intrusion in the Aravalli rocks.

Aplogranite was later termed as Ahar River granite by

Crawford (1970) who calculated their age as 227 5 M.Y. by

Rb-Sr method. The Ahar River granite has been considered

to be synorogenic in nature (Anon, 1981;. Roy and Paliwal

(1981; and Roy et al (1985^, on the basis of regional

lithological correlation, consider the granite as pre-

Aravalli basement rocks.

Field relationship of granitic rocks with Aravalli

limestone suggests a magmatic origin of the granite.

Presence of limestone xenoliths in the granitic rocks and

the granitic material in limestone along fractures indicate

intrusion of granite into limestone. The granite is highly

sheared and fractured. Dislocation, fracturing and bending

61

of p lagioc lase twin lamellae ind ica tes p o s t - c r y s t a l l i z a t i o n

deformation. The rock var ies in composition from normal

a lka l i g ran i te to g ranod io r i t e . The petrographic study,

however, reveals a homogeneous composition of the rock.

Quartz i s the most abundant mineral in the rock comprising

33.03%, followed by K-feldspar and plagioclase t h e i r percentage

are 29.18 and 26.7 6 r e spec t ive ly . K-feldspar show p e r t h i t i c

intergrowth which i s formed by the replacement of K ion with

Na. All a l b i t e lamellae are ex t inc t at the same time on

ro ta t ion of microscope s t age . Among accessory minerals

muscovite, b i o t i t e , c h l o r i t e , sphene, a p a t i t e , and zircon

are p resen t . Presence of primary muscovite and absence of

magnetite and hornbland shows mineral c h a r a c t e r i s t i c s which

has a f f in i ty with S-type (Chappell and White, 1974J.

Geochemical data p lo t t ed on Si02 var ia t ion diagram,

reveals tha t they are not formed by the simple f rac t ional

c r y s t a l l i z a t i o n . The p lo t s of Rb-Ba-Sr ternary diagram

shows tha t the gran i te i s not very much d i f f e ren t i a t ed and

l i e s in normal grani te f i e l d s . The grani te i s inferred to

be S-type as indica ted by s i l i c a content (range 7 2.16% -

62

11.6%); high Al / (Na + K + Ca; > 1.1, plots of data on

Al - Na - K, Ca and Fe + Mg diagram, and presence of primary

muscovite.

High molar proportions Al / (Na + K + Ca) > 1.1

indicates peraluminous nature of the magma. The magma was

derived by the anatexis of aluminous metasedimentary rocks,

which produces granitoid rocks of S-type.

63

Anon, (1981)1 Explanatory brochure to the geo log ica l map

of t h e A r a v a l l i r eg ion , southern Rajasthan and

n o r t h e a s t e r n G u j a r a t . G . S . I . Pub. p p . 1-38.

Calvin , F.M., (1983)1 Are s t r o n g l y peraluminous magmas

de r ived from p e l i t i c sedimentary s o u r c e s . J o u r , of

Geology, v . 93, p p . 67 3-689.

Chappel l , B.W., and White, A . J . R . , (1974)1 Two c o n t r a s t i n g

g r a n i t e t y p e s . P a c i f i c Geology, v . 8, p p . 173-17 4.

Chaudhary, A.K., Gopalan, K. and S a s t r y , C.A., (1984)1

P r e s e n t s t a t u s of t h e geochronology of the Precambrian

rocks of Ra ja s than . Tec tonophys ics , v . 105, pp .131-140.

Chayes, F . , (1956)1 P e t r o g r a p h i c Modal A n a l y s i s . Wiley and

Sons, New York, p p . 1 1 3 .

Crawford, A.R., (1970)1 The Precambrian geochronology of

Rajas than and Bundelkhand, Northern I n d i a . Cand.

J o u r . Ear th S c i . , v . 7, p p . 91-110.

64

£ l - B o u s e i l l y , A.M. and El-Sokkary, A.A., (197 5 ) : The r e l a t i o n

of Rb, Ba and Sr in g r a n i t i c r o c k s . Chem. Geol . , v . 16,

p p . 207-219.

Gangopadhyaya, J . , (1961K Study on t h e deformation of the

Precambrian g r a n i t e s , n o r t h of Udaipur c i t y , Rajasthan

and t h e development of p l a g i o c l a s e twin in them. Quar t ,

J o u r , Geol . Min. M e t a l . Soc. I n d i a , v . 33, p p . 189-190.

Gorai , M., C1951K P e t r o l o g i c a l s t u d i e s on p l a g i o c l a s e t w i n s .

Amer. M i n e r a l o g i s t , v o l . 36, p p . 88 4 -901 .

Hacket, C.A., (1877)1 A r a v a l l i s e r i e s in n o r t h e a s t e r n

Rajpu tana . Rec. Geol . Surv . I n d i a , 10(2) , p p . 8 4-9 2 .

Hacket, C.A., (1881)1 Geology of t h e A r a v a l l i r eg ion , c e n t r a l

and e a s t e r n Rajpu tana . Rec. Geol . Su rv . I nd i a , 14(4) ,

p p . 229-30.

Hahn-Weinheimer, P . , and Ackerraan, H., (1967)1 Geochemical

i n v e s t i g a t i o n s of d i f f e r e n t i a t e d magmatic g r a n i t e

p lu tons of t h e southern Black F o r e s t , 1 1 . The joninq

of t h e Malsburg g r a n i t e p lu ton as i n d i c a t e d by the

elannents t i t a n i u m , zirconium, phosphorous, strontiurr, .

65

barium, jrubidium, potass ium and sodium. Geochim.

Acta, V. 31, p p . 2197-2218.

Hanson, G.N., (1978)1 The a p p l i c a t i o n of t r a c e elements to

t h e p e t r o g e n e s i s of igneous rocks of g r a n i t i c

compos i t ion . Ea r . P l a t . Sci . l e t t e r . , v . 38, pp.26-43

Marker, A., (1909)* The n a t u r a l H i s t o r y of Igneous Rocks.

New York.

Heier , K . S . , and Taylor , S.R., (19 59, a) I D i s t r i b u t i o n of

L i , Na, K, Cs, Pb and Ti in southern Norwegian

Precambrian a l k a l i f e l d s p a r s . Geochim. Cosmochim,

Acta, V. 15, p p . 282-304.

Heron, A.M., (1935)1 Synopsis of t h e pre-Vindhyan Geology

of Ra jpu tana . T r a n s . Na t . S c i . I n d i a , v . 1 ( 2 ) ,

p p . 1 7 - 3 3 .

Heron, A.M., (1953)1 Geology of c e n t r a l Ra jpu tana . Mem.

Geo l . Su rv . I n d i a , v . 7 9 .

Hine, R., Wil l iams, I . S . , Chappel l , B.W., and White, J . R . ,

(1978)1 Con t ra s t between I - and S- type g r a n i t o i d s

of t h e Kosciusko b a t h o l i t h . Geol . Soc . A u s t r a l i a ,

V. 25, n o . 4, p p . 219-234.

66

Ishihara, S., (1977 K The magnetite-series and ilmenite-

series granitic rocks. Ming. Geol., v. 27, pp.293-305.

Kolbe, P. and Taylor, S.R., (1966K Geochemical investigation

of the granitic rocks of the Snowy mountain area.

N.S.W. Jour. Geol. Soc. Aust., v. 13, pp. 1-25.

McCarthy, T.b., and Hasty, R.A., (1976K Trace element

distribution patterns and their relationship to the

crystallization of granitic melts. Geochim. Cosmochim.

Acta, V. 40, no. 11, pp. 13 51-13 58.

McCarthy, T.S. and Fripp, R.E.P., (1978)*. The crystalli­

zation history of a granitic magma, as revealed by

trace elenent abundances. Jour, of Geol., v. 88,

pp. 211-224.

Olade, M.A., and Fletcher, W.K., (1975)1 Primary dispersion

of Rb and Sr around porphyry copper deposits. Highland

valley, British Columbia. Econ. Geol., v. 70, pp.15-21

O'Neil, J.R. and Chappell, B.W., (1977K Oxygen and hydrogen

isotopex relation in the Berridale batholith. Jour.

Geol. Soc. London, v. 133, pp. 559-571.

67

Pearce, J.A., Nigel, B.W.H. and Andrew, G.T., (1984): Trace

element discrimination diagrams for the tectonic

interpretation of granitic rocks. Jour. Petro.,

V. 25/4, pp. 956-983.

Roy, A.B. and Paliwal, B.S., (1981JI Evolution of lower

Proterozoic epicontinental sediments I Stromatolite

bearing Aravalli rocks of Udaipur, Rajasthan, India.

Precambrian Res., v. 14, pp. 49-7 4.

Roy, A.B., Golani, P.R. and Bejarniya, B.R., (1985;: The

Ahar River granite, its stratigraphic and structural

relations with the early Proterozoic rocks of south­

eastern Rajasthan. Jour. Geol. Soc. India, v. 26,

no. 5, pp. 315-325.

Ruperto, V.L., Stevens, R.E. and Norman, M.B., (1964JI

Staining of plagioclase feldspar and other minerals

with F., D., and C. Red No. 2, U.S. Geol. Surv.,

Profess, paper 50/B, B-152-B-153.

Sandra M. Barar, Alan., S. Macdonald and John Blenkinsop,

(1986JI The Cheticamp plutonI a Cambrian granodiorite

intrusion in the western cape Breton Highlands. Nova

6

Scotia. Cand. J. Earth. Sci ., v. 23, pp. 1686-1699.

Shuster, R.D. and Bickford, M.E., (1985K Chemical and

isotopic evidence for the petrogenesis of the north­

eastern Idaho batholiths. Jour. Petro., v. 93, no. 6,

Shand, S.J., (1950;! Eruptine Rocks. Wiley, New York,

4th edition.

Shapiro, L. and Brannock, W.W., (1962K U.S. Geol. Surv.

Bulletin, 1144-A.

Streckeisen's, A.L., (1976K To each plutonic rock its

proper name. Earth Sciences Review, v. 12, pp. 1-33.

Taylor, S.R., and Heier, K.S., (1960J : The petrological

significance of Trace Elment Variations in alkali

feldspars. 21st Int. Geol. Congr. Copenhagen, Rept.

pt. 14, pp. 47-61.

Taylor, M.P,, (1971K Oxygen isotope evidence for large

scale interaction between meteoric ground water and

tertiary granodiorite intrusions. Western Cascada

Range, Oregon I Jour. Geophys. Res., v. 76, pp.

7855-7874.

69

Turekian, K,K. and Wedephol, W.H.^ (1961) : D i s t r i b u t i o n

of t h e elements in some major u n i t s of t h e e a r t h ' s

cxnast, Geo l . Soc . Amer. B u l l . , v . 7 2, p p . 17 5-192

White, A . J . R . and Chappel l , B.W., (1977K Ultrametamorphism

and G r a n i t o i d G e n e s i s . Tec tonophys ics , v . 43, p p .

7 -22 .

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