Journal of Southeast Asian Earth Sciences, Vol. 14. Nos 3/4, pp. 221-229. 1996 Copyright fa 1996 Elsevier Science Ltd Printed in Great Britain, All riehts resewed PII: S8743-9547(%)88%8-8 0743-9547196 ktl t 0.00 Pergamon 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