Journal of Southeast Asian Earth Sciences, Vol. 14. Nos 3/4, pp. 221-229. 1996 Copyright fa 1996 Elsevier Science Ltd

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Granulites of Bhopalpatnam and Kondagaon belts, Bastar craton, M. P.: petrological and fluid inclusion studies

K. N. Prakash Narasimha,* A. S. Janardhan* and V. P. Mishrat *Department of Geology, University of Mysore, Manasagangotri, Mysore 570 006, India

tGeologica1 Survey of India, Raipur 492 002, M. P., India

(Received 10 January 1996; accepted for publication 24 April 1996)

Abstract-The Bhopalpatnam and Kondagaon granulite belts (BGB, KGB) occur surrounding the Bastar craton of central India. This paper deals with the geology, mineralogy and the fluid characteristics of these two belts. The geology of the two belts indicate that they abound in metasedimentary swathes. The metamorphic P-T conditions of the BGB range from 6 to 9 kbar at temperatures of 750°C whilst those of the KGB vary from 4 to 6 kbar at temperatures of 700°C. The BGB shows an IBC path, while the KGB exhibits a dominant ITD path. These trends, based on mineral chemistry, are corroborated by fluid-inclusion studies. The lithologies of the BGB exhibit high-density CO1 inclusions that represent the remnants of peak metamorphism. In contrast, the CO2 inclusions of the KGB are of low density, indicative of post-peak conditions. The studies suggest that the CO,-rich fluids may not have come from the supracrustal sediments. An external source, possibly underplated basalt, could have supplied the heat and the supercritical fluids. Based on lithological similarities, it can be stated that the BGB is an extension of the late Archaean Karimnagar granulite belt. The important problem which is still to be solved is the junction of the late Archaean BGB with the Eastern Ghats granulite belt. Copyright 0 1996 Elsevier Science Ltd

Introduction

Over the last decade, several works that dealt with the fluid inclusion of granulites of southern India have shown that fluids rich in CO* were indeed involved in the formation of these granulites (Santosh, 1985; Touret and Hansteen, 1988; Srikantappa er al., 1992). Fluid-in- clusion studies in granulites not only give an insight into the nature and composition of fluids involved in their formation but also provide useful clues on the post-peak evolutionary trends. In some of the above works, based on stable isotopic studies, the source of the fluids are also indicated.

The present paper deals with the Bhopalpatnam granulite belt (BGB) and the Kondagaon granulite belt (KGB), which surround the Central Indian or Bastar craton, since no attempts have been made so far to study the metamorphic conditions of these granulites either through mineral chemistry or fluid inclusions. The latter studies have more relevance as Ghosh, as early as in 1941, advocated that the granulite-facies chamockite rocks of this region were para in nature and formed from protoliths of banded iron formation (BIF) and carbonate sedimentary lithologies, aided by alkali influx, implying the involvement of fluids.

Bastar geology is little understood. Crookshank (1938, 1963) was one of the first geologists to work out the stratigraphy of the Bastar region. After detailed work, Mishra et al. (1988) have established the stratigraphy of the Bastar craton and the relation of the granulite belts to the various lithologies. In their work, the Sukma Gneisses are considered to be the oldest unit with ages around 3400-3000 Ma, and the Sukma Supracrustals equated with the (> 3000 Ma) Sargur supracrustals. The

BGB and the Dongargarh granites according to give ages of c. 2450 Ma.

Granulite belts of the Bastar area

them

The Bastar craton is surrounded by the BGB and the Karimnagar granulite belt to the south, the KGB to the northeast and the Eastern Ghats belt to the east. It is believed that the granulite belts of the Bastar region were cratonal and are not part of any mobile belts (Ramakrishnan, 1969). Recently, Rajesham et al. (1993) have described the geology of the Karimnagar granulite belt occurring to the south of the Godavari graben. Their work has relevance to the present paper, as the BGB occurs northeast of the graben. Figure 1 gives the positions of the Karimnagar belt and the BGB, which seem to be almost contiguous across the graben. Age data for Karimnagar charnockites around 2500 Ma (Rb-Sr method) obtained by Rajesham er al. (1993) are significant in comparing the BGB to that of the granulites of the Transition zone and the Biligiri Rangan hills of southern India, where the dominant granulite metamorphism occurred around 2500 Ma (Peucat et al., 1989; Janardhan et al., 1995). Furthermore, granites that are part of the Dongargarh granites of c. 2450 Ma occur in close association with the BGB. This again has similarities with the ages of granites of Karimnagar (Bhaskar Rao et al., 1995).

The finding of incipient chamockites east of Bijapur (Janardhan et al., 1995) in a manner much similar to that of the outcrops described from the Transition zone in southern Karnataka and the coeval ages of the granites and the charnockites of Karimnagar are critical and is similar to the scenario in southern Karnataka, where, in

221

222 K. N. Prakash Narasimha et al.

G u. XBC x bOKm

HYD 0

X

Fig. 1. Geologic outline and locations of field survey surrounding the Godavari valley. The map is based on Rajesham et al. (1993). Solid triangles with numerals are the locations of field observations: Al, Alluvium; BC, Bastar craton; BG, Bhopalpatnam granulite belt; C, Cuddapah super group and equivalent; DC, Dharwar craton; EG, Eastern Ghats granulite belt; GL, Lower Gondawana sediments; GU, Upper Gondawana sediments; KG, Karimnagar granulite belt; HYD, Hyderabad; KAM, Khammam; KRN, Karimnagar; KTG,

Kottagudem; RAJ, Rajahmundry.

the Transition zone, the Closepet granite and incipient charnockite give coeval ages around 2510 Ma (Friend and Nutman, 1992).

Bhopalpatnam granulite belt (BGB)

The BGB occupies the southwestern border of the Bastar craton and forms, as it were, the northern shoulders of the Godavari graben (Fig. 2). This granulite belt is exposed along a NW-SE-trending linear ridge rising 200 m above the gneissic plains and can be traced for a strike length of 250 km, with an average width of 20 km. Towards the northern part, the belt is at its broadest with a maximum width of 30 km. At its southern tip, the belt swerves from its NNW-SSE trend to a more E-W trend.

The BGB is essentially made up of tonalitic-trond- hjemitic charnockites with abundant enclaves of older supracrustals, the Sukmas, as can be seen in Ghosh’s (1941) type area. These supracrustals comprise essen- tially a K-rich pelite-carbonate-quartzite_BIF associ- ation, typical of continental marginal basin affinities and have striking similarities to that of the ancient Sargur supracrustals of 3100 Ma (Mishra, 1986). The pelite and carbonate lithologies possess mineral assem- blages, like Crd-Grt-Sil-Opx-Bt-Rt-Ilm-Kfs-Pl-Spl- Qtz, Wo-&p-Cal-Di-Adr-Grs and Grt-Pl-Qtz-Mag, which constrain well the P-T conditions of metamor- phism. BIF horizons have Opx-Grt-Pl and Opx-Grt with significant amounts of Cpx.* The presence of Cpx supports the original statement of Ghosh (1941) that the BIFs have admixed carbonates. Two-pyroxene granulite

* Mineral abbreviations used are after Kretz (1983).

bodies interbedded with the supracrustal lithologies have assemblages Grt-Qpx-Cpx-PI. These above assem- blages have been mostly used in quantifying the P-T conditions of metamorphism as the charnockites themselves are mostly non-garnetiferous.

Kondagaon granulite belt (KGB)

The KGB is an isolated belt occurring as low-lying mounds Xl-100 m above the gneissic plains and forms the northeastern border of the Bastar craton. This belt is not as well exposed as that of the BGB, with outcrops far and few in between. The KGB has many similarities with the BGB. It has a strike length of 50 km with an average width of about 10 km. Abundant supracrustal enclaves are also seen within the belt; however, pelitic lithologies seem to dominate followed by carbonate lithologies. Mishra et al. (1988) have correlated the KGB with the Deobagh belt (see Fig. 2). According to them, the Deobagh belt forms part of the 1000 Ma old Eastern Ghats belt. But the comparison is controversial, as this belt is invaded by the 2450 Ma Dongargarh granite suite.

Fluid-inclusion studies

Based on preliminary optical studies, samples of various lithologies were selected for a detailed study of fluid-inclusion species. Phase transitions of fluid inclusions were made on a temperature-calibrated LINKAM heating and freezing apparatus (with a range of - 180 to 600°C at the Department of Geology, University of Mysore). Microthermometric results are presented in Table 1. The density data have been calculated after the method of Brown and Lamb (1989).

Bhopalpatnam and Kondagaon belts, Bastar craton 223

+

lBHOG BELT

LEGEND

Indrovati group

Abuj.hmar group

Kotri super group

Precambrian BI F sequent

Dongargaih;: granite8 equ

Granulite complex

Gneissic complex Archoa

Fig. 2. Geological map of Bastar craton (Mishra et al., 1988). BGB, Bhopalpatnam granulite belt; KGB, Kondagaon granulite belt.

CO?-rich inclusions seem to be abundant in the gneiss, charnockite and pelitic granulites; in the talc-silicate assemblages, H20-rich inclusions form the dominant fluid phase. Fluid-inclusion data of the various lithologies of the BGB and KGB are presented below.

Gneiss

Gneissic mineralogy mainly includes Qtz-Kfs-Pl-Bt- Ep and Mag. Measurable fluid inclusions are found only in the larger and elongated quartz grains and are confined to the fractures in them. Monophase inclusions in these grains show melting temperatures of -59.5”C, indicating a near-pure Cot composition, with low densities of 0.890-0.874 g/cm3, based on homogenization temperatures of 6.88.3”C.

Incipient charnockite

The phenomenon of incipient charnockitization was noticed in partly developed quarries 3 km northwest of Bijapur town. In these local quarries, the older (c. 3000 Ma) Sukma gneisses are veined by pink granitic veins (probably part of the nearby porphyritic granites, equivalent in age to the Dongargarh granites). These veins occupy local shears. Where these veins taper off, one can notice greasy patches which on closer inspection contain orthopyroxene. Incipient charnock- ites show clear unaltered orthopyroxene surrounded by reddish brown biotite, which occurs along with platy plagioclase (An 23%), perthitic K-feldspar and quartz. Quartz grains show sutured borders with a

typical granoblastic texture and the same grades onto granitic texture.

COZ inclusions present in quartz grains are either randomly distributed or arrayed, varying in size from c 3 to 12 pm. The inclusions are monophase at room temperature and the melting temperature ranges from - 69.0 to - 57.2”C indicating them to be CO*-rich with miscible additional fluids like CH.,, Nz and HS, SO2 (Lamb, 1990; Touret and Hartel, 1990). The temperature of homogenization to liquid phase ranges from - 24.5 to 11°C yielding density values of 1.053-0.854 g/cm3.

Charnockites

CO*-rich inclusions (< 1-12 pm) are present in quartz grains that are bigger in size, elongated and with well-developed fractures. The inclusions are either randomly distributed or occur along secondary frac- tures. These inclusions are usually rounded to oval in shape and show rare negative crystal outlines.

Freezing experiments were carried out on CO?-rich inclusions present in the quartz grains. These monophase CO1-rich inclusions melt around the temperature range of -61.8 to - 57.6”C, which is the temperature of first melting (T,,,‘(Z) of crystalline CO* and are close to the triple point of pure CO2 (-56.6”(Z). Depression of melting temperature below the triple point may be due to the presence of other fluid phases that are miscible with CO1, viz. CH+ Nz, H2S and SO2 (Lamb, 1990; Touret and Hartel, 1990). The temperature of homogenization (ThoC) into liquid phase recorded for the COz-rich inclusion range from -9.3 to 30.6”C

Tabl

e 1.

Mic

roth

erm

omet

ric

resu

lts

of d

iffer

ent

litho

-uni

ts

of t

he

BG

B

and

KG

B

CO

Z in

clus

ions

(in

qua

rtz)

HZ0

inc

lusio

ns

(in q

uartz

)

d Sa

linity

d

Roc

k ty

pe

(2)

(gem

’)

(wt%

N

aCl

equi

v.)

&

(gem

’)

BGB 1.

Cha

rnoc

kite

V

P1

-61.

8 to

-5

8.6

+11.

2 to

+2

9.8

0.81

-0.7

4 F

2. C

ham

ocki

te

VP9

-5

6.9

to

-57.

6 -0

9.3

to

+30

0.97

-0.7

3 .r:

3.

Cha

moc

kite

vP

Io*

-69.

0 to

-5

7.2

-24.

5 to

+1

1 1 X

I4-0

.87

cd

4. C

ham

ocki

te

VP1

1

- 59

.8

+13.

3 to

+1

7 0.

85-0

.82

3 5.

Gt

Cha

moc

kite

V

P12

- 57

.6

+25.

5 to

30.

6 0.

77-0

.66

6 6.

Pel

ite

VP2

0 -6

6.2

to

-57.

3 -3

2 to

+2

7.4

1.08

-0.7

6 ti

7. G

neis

s V

P8

-59.

5 +

6.8

to

+8.3

0.

89-0

.88

8. C

alc-

silic

ate

VP1

4 -7

.3

to

-22

10.9

-23

+53

to

+157

0.

99-0

.91

2:

co

9. C

alc-

silic

ate

VP1

5 -2

.2

3.6

+124

to

+2

92

0.94

-0.7

3 a

10.

Cal

c-si

licat

e V

P17

-3.5

5.

6 +1

13

to

+208

0.

950.

85

r. B

P K

GB 1.

Cha

moc

kite

K

N8

-58.

8 +1

4 to

+2

3 0.

85-0

.79

2

2. C

ham

ocki

te

KN

12

- 59

.0

+ 16

.7 t

o +2

0 0.

83-0

.80

%

3. C

ham

ocki

te

KN

14

-60.

7 to

-5

8.5

+ 16

.8 t

o +3

0.5

0.83

-0.6

6 4.

Cal

c-si

licat

e K

N13

-0

.3

to

-2.8

0.

53.8

+9

6.8

to

+189

0.

98-0

.89

*Inc

ipie

nt

cham

ocki

te.

BG

B,

Bho

palp

atna

m

gran

ulite

be

lt;

KG

B,

Kon

daga

on

gran

ulite

be

lt.

Bhopalpatnam and Kondagaon belts, Bastar craton 225

which correspond to the density values of 0.980- 0.562 gcm3.

Garnetiferous charnockite exposures are generally scarce. However, one sample of garnetiferous charnock- ite from the Dantewara Ghat section was studied for fluid-inclusion species in garnet grains, but unfortu- nately the size of the inclusions were too small (3-6 pm) and hence they are not ideally suited for recording the phase transitions. However, the fact that these inclusions are found within the included quartz in garnet imply their primary nature. On close observation, these seem to be rich in COZ.

Low-density C02-rich inclusions dominate the charnockites of the KGB, in contrast to the highly dense CO*-rich inclusions of the BGB. COz-rich inclusions present in the charnockites occur along the healed fractures of the quartz grain, with their trails traversing the different grains of quartz, indicating them to be secondary inclusions. Homogenization of the CO?

inclusions (melting temperature of - 60.7 to - 58.5’C) is around the temperature range of 14-30.5”C with a mean peak between 20 and 25°C (Fig. 3(A)), which indicates comparatively lower density values of 0.8054775 gcm3.

Pelite

Measurable fluid inclusions are noticed in only one sample of the pelitic gneiss (VP20) of the BGB. These inclusions are hosted mainly in late quartz grains which are strained, stretched and have sutured boundaries. Inclusions are rounded to sub-rounded in shape with their size varying from < 3 to 10 pm. Monophase inclusions are C02-rich, as they melt at the temperature range of -66.2 to -57.3”C. Homogenization tempera- tures that occurred into liquid phase always show a range of -32 to 27.4”C, indicating density values of 1.084670 gcm3.

Fig. 3A

loo -

so 1

40

Th to c)

1 YI loo fs4 zoo 2w m

Fig.3c Th (“Cl

200

150

120

F

80

0

3s a0 -5 10 25 4s

‘Fig.3 B Th (“cl

so Y

40 -

30-

F

20 -

10 -

o-

,

“.7S

12

W ua 210

Fig. 3D Th ii:,

Fig. 3. (A) Histogram plot for CO2 inclusions of charnockites of KGB. (B) Histogram plot for CO! inclusions of granulites of BGB. (C) Histogram plot for Hz0 inclusions in talc-silicate rocks of BGB. (D) Histogram

plot for Hz0 inclusions in talc-silicate rocks of BGB.

226

9.00

K. N. Prakash Narasimha et al.

BGB KGB

+ Metapelites X Metapelites

8.00

7.00

6.00

e c

h’ 5.00

BGB : + Crd-Opx-Grt-PI-~-QtzfCed+Cm

0 GI+O~I-C~I-PI-Q~Z

A Grt-Opx-Cpx-PI-Amphi-Qtz-Opaq

Sil KGB : X Grt-Crd-Bt-PltQb~SiltSpl

I I I

500.00 600.00 700.00 800.00 900.00 Tin”C

Fig. 4. P-T path for Bhopalpatnam (BGB) and Kondagaon (KGB) granulite belts.

ThoC data were treated statistically for the COrrich inclusions of the various lithologies, and the histogram plots show two maximum peaks, - 20 and - 5°C and 10 and 25°C (Fig. 3(B)) and yield density values of 1.020-0.951 and 0.875-0.805 gcm3, respectively.

Calc-silicate rocks

trail bound traversing different grains of quartz, indicating their secondary nature. These H20-rich inclusions record temperatures of melting in the range of -0.3 to -2.8”C, yielding salinity values of 0.5-3.8 wt% NaCl equiv., and the homogenization temperature varies between the range of 96.8-189”C, with a mean peak between 140 and 180°C (Fig. 3(D)), corresponding to the density values of 0.940-0.912 gem’.

Calc-silicate lithologies of the BGB and the KGB, in The presence of high-density (1.053-0.854 gem’) general, have been migmatized and thus should be carbonic inclusions in incipient charnockite suggests that termed as talc-gneisses and exhibit talc-silicate-rich the inclusions are the remnants of peak metamorphism. portions alternating with feldspar-quartz-rich bands. Further, the presence of planar arrays of low-density Quartz grains present close to the talc-silicate bands and fluid inclusion conveys that the fluids are post-metamor- those within the talc-silicate bands were selected for phic. There is not much difference in the density values fluid-inclusion studies. The quartz grains are stretched of CO2 inclusions of Sukma gneisses and the incipient with sutured boundaries and are often traversed by charnockites (Table 1). This is because the samples come innumerable fractures. In intensely sheared carbonates, from the same block. One can notice the patchy mylonitic fabric has developed that contains porphyro- development of orthopyroxene throughout the block, blasts of plagioclase, garnet and clinopyroxene. Biphase hence the gneiss-chamockite samples from the same HZ0 inclusions present in these grains are larger in size block are apart by a few centimetres. Though there is than the COZ inclusions, and their size varies from 4 to variation in the rock type, the density values have 15 pm. HZ0 inclusions are rounded to sub-rounded and remained more or less similar and this has been have negative crystal shapes (sometimes as partial explained in the papers of Harris and Bickle (1989) and diamond-shaped inclusions). HZ0 inclusions that are Santosh et al. (1990). Based on stable isotope evidences, biphase at room temperature occur as isolated grains or they state that the fluid front moves ahead of the mineral as trails along the fractures of quartz. formation.

Aqueous rich inclusions show initial melting tempera- The petrographic observation of talc-silicate rock ture of 24.4 to -2.2”C, indicating salinity values of reveals the presence of wollastonite and scapolite. This 24.3-2.8 wt% NaCl equiv. (Brown and Lamb, 1989). assemblage has been noticed in the present study, in the Density values of these biphase H20-rich inclusions Dantewara Ghat section, in the heart of the granulite range between 0.957 and 0.930 gcm3 (Fig. 3(C)). belt, near the type locality of Ghosh (1941).

Calc-silicate rocks of the KGB contain biphase Calc-silicate assemblages commonly contain Grs- HzO-rich inclusions in quartz grains (2-3 to 15 pm), Cpx-Pl-Scp, apart from late Cal-Qtz-Kfs association. apart from isolated inclusions, and are found mostly as Thus, the mineral assemblages show definite signs of

Bhopalpatnam and Kondagaon belts, Bastar craton 221

previous metamorphism and migmatization. Thus, granulite terrains which exhibit a similar trend with carbonates having suffered a previous cycle of metamor- dominant IBC path, the heat source could have come phism and possible migmatization could not have from underplated basalts (Bohlen, 1987). Underplated contributed to much of the fluid phase required for the basalts, especially if they are slightly alkaline, could be 2500 Ma granulite formation. Further, late andradite- the source for supercritical fluids rich in CO*, Hz0 and magnetite after pyroxenes are rather common to these SOZ. At this stage, one can only speculate that talc-silicate assemblages, representing late oxidation- underpiated basaits may have provided the heat source carbonation reactions, which consume CO*. and fluids rich in CO2 for granulite metamorphism.

In the pelitic assemblages, close observation reveals the presence of minute dense and isolated fluid inclusions rich in COZ, with density values of 1.08 gcm3. These could be syn-metamorphic inclusions.

Discussion and conclusions

It is generally agreed that pelitic assemblages are the first to re-equilibrate during uplift, with the formation of gedrite, fibrolite + biotite assemblages. Thus, the pelitic assemblages of the BGB also exhibit retrogressive conditions indicative of uplift. The secondary planar arrays with density values around 0.67 gcm3 represent the post-peak metamorphic conditions.

Interpretation of fluid-inclusion data

Metamorphic P-T conditions were derived from the chemistry of co-existing various critical mineral assem- blages of the BGB and the KGB. The P-T estimates of BGB range from 6-9 kbar and 750°C whilst those of KGB vary from 4-6 kbar and 700°C. The P-T path (Fig. 4) based on the above data shows an overall anti-clockwise trend. It is generally agreed that, in

The isochores obtained for CO*-rich inclusions present in quartz grains of the BGB and KGB are plotted in Fig. 5. The density data were obtained from the statistically treated Th frequency histograms (Fig. 3(A), (D)). The P-T box for both the BGB and KGB based on independently derived P-T estimations using the chemistry of co-existing mineral assemblages have been $otted in Fig. 5. The CO* isochore (1.040 gem’) obtained for COZ inclusions in quartz passes through the lower part of the mineral P-T box, suggesting near-peak metamorphic fluid activity. How- ever, the majority of isochores of lower density CO, inclusions that form planar arrays in quartz grains of Bhopalpatnam and Kondagaon granulites shift signifi- cantly away from the mineral P-T box, indicating them to be post-peak fluid inclusions. The uplift path deduced

e

- CO irochonr -- H’ % i8ochor.s

wn K!x!C~t*, BPL Bhoplapatnrm

T(“C) Fig. 5. Graph showing fluid inclusion isochores and P-T box based on estimations from the chemistry of

co-existing mineral assemblages.

228 K. N. Prakash Narasimha et al.

from the combined mineralogic F-T data and fluid- inclusion isochores show characteristic convexity

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belt. The two belts are presently separated by the M.P. DST-DCS News Letter 5(l), 22-26.

Godavari graben (Fig. 1). The critical point raised here Kretz R. (1983) Symbols for rock forming minerals. Am. Mineral 68,

277-279. is where exactly the Bhopalpatnam belt of late Archaean Lamb W. (1990) Fluid inclusions in granulites: Peak vs retrograde age ends and/or meets the Eastern Ghats belt that formation. In Granulites and Crusral Evolution (edited by Vielzeuf underwent a peak granulite metamorphic event at D. and Vidal Ph.), Kluwer, Dordrecht, The Netherlands,

1000 Ma, which incidentally is the dominant metamor- pp. 419-433.

phic event of the Rayner complex of Eastern Antarctica. Mishra V. P. (1986) Ancient supracrustals of Bastar Craton, M.P.

More details on the tectonic evolution of the Bastar Abstract, workshop on Ancient supracrustals of Sargur type,

craton are needed to resolve the junction of the late University of Mysore, Mysore, pp. 53-56.

Archaean Bhopalpatnam granulite belt with that of the Mishra V. P., Pushkar Singh and Dutta N. K. (1988) Stratigraphy,

Eastern Ghats belt. structure and metamorphic history of Bastar Craton. Rec. Geol.

The Napier complex of Eastern Antarctica, with old Surv. India 117.

protolith ages and which has witnessed a dominant Peucat J. J., Vidal Ph., Bernard-Griffiths J. and Condie K. C. (1989)

Sr, Nd and Pb isotope systematics in the Archean low to high grade 2500 Ma old granulite event, has been compared to the transition zone of southern India: syn-accretion vs post-accretion Karimnagar and Bhopalpatnam belts (Yoshida, 1995). granulites. J. Geol. 97, 537-550.

This suggests that there is an age ‘polarity’ with the Rajesham T., Bhaskar Rao Y. J. and Murthi K. S. (1993) The

younger belts successively occurring towards the east. Karimnagar granulite terrane-a new sapphirine bearing granulite

Age polarity in South India shows a decrease from province, South India. J. Geol. Sot. India 41, 51-59.

2500-500 Ma towards the south. In general, in southern Ramakrishnan M. (1969) Geology along the D.B.K. Railway line

India, one can always find the older granulite belts close in Bastar district, M.P. Unpublished Prog. Rep., Geol. Sura. India,

to the cratonic nucleii. Calcutta.

Santosh M. (1985) Fluid evolution characteristics and piezothermic array of south Indian chamockites. Geology 13, 361-363.

Acknowledgements-The authors acknowledge the Depart- Santosh M., Harris N. B. W., Jackson D. H. and Mattey D. P. (1990) ment of Science & Technology for their financial support under Dehydration and incipient charnockite formation: a phase the DCS programme, and express their thanks to the equilibria and fluid inclusion study from south India. J. Geol. 98, Chairman, Prof. Satyanarayana, for extending the facilities of 9 15-926. the Department. Dr Srikantappa is thanked for permitting use Srikantappa C., Raith M. and Touret J. L. R. (1992) Synmeta- of the LINKAM fluid-inclusion stage. morphic high density carbonic fluids in the lower crust:

Bhopalpatnam and Kondagaon belts, Bastar craton 229

evidence from the Nilgiri granulites, southern India. J. Petrol. 33, by Vielzeuf D. and Vidal Ph.), pp. 397-417, Kluwer, Dordrecht, The 733-760. Netherlands.

Touret J. L. R. and Hansteen T. H. (1988) Geothermobarometry and Yoshida M. (1995) Assembly of East Gondwanaland during the fluid inclusions in a rock from the Doddabetta chamockite complex, Mesoproterozoic and its rejuvenation during the Pan-African Southern India. Rendiconti Sot. Ital. Mineral Petrol. 43, 65-82. period. In India and Antarctica during the Precambrian, Mem. 34

Touret J. L. R. and Hartel T. H. D. (1990) Synmetamorphic fluid (edited by Yoshida M. and Santosh M.), pp. 25-45. Geological inclusions in granulites. In Granulires and Crustal Evolution (edited Society of India, Bangalore.

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