J. metamorphic Geol., 1998, 16, 189–196 A corundum–quartz assemblage from the Eastern Ghats Granulite Belt, India: evidence for high P–T metamorphism? R. K. SHAW AND M. ARIMA Geological Institute, Yokohama National University, Tokiwadai 79–2, Hodogaya-ku, Yokohama 240, Japan (e-mail: arima@ed.ynu.ac.jp) ABSTRACT Corundum+quartz-bearing assemblages occur in small lenses in granulite facies metapelites in Rayagada, north-central part of the Eastern Ghats Granulite Belt, India. Corundum porphyroblasts and quartz coexist with porphyroblastic almandine-rich garnet, hercynite spinel, ilmenite and magnetite. Corundum and quartz are separated by sillimanite or a composite corona consisting of sillimanite and garnet, whereas corundum shows sharp grain boundaries with spinel, ilmenite and magnetite. Porphyroblastic corundum contains prismatic sillimanite inclusions in which irregularly shaped quartz is enclosed. Two distinct reactions are inferred from the textural features: corundum+quartz=sillimanite and spinel+quartz= garnet+sillimanite. From the petrographical features, we infer that corundum–quartz–garnet–spinel was the peak metamorphic assemblage. Although large uncertainties exist regarding the positions of the respective reactions in P–T space, from several published experimental results and theoretical calculations a peak metamorphic condition of 12 kbar and 1100 °C is estimated as the lower stability limit of the corundum–quartz assemblage. Decompression from the peak P–T condition to c. 9 kbar, 950 °C is inferred. Key words: Corundum–quartz; Eastern Ghats, India; high P–T granulites; high-T decompression. Peninsular India. In general, the EGGB exhibits INTRODUCTION evidence of three major deformation events (Halden et al., 1982; Bhattacharya et al., 1994; Shaw, 1996). The coexistence of corundum and quartz has been reported from granulites (Harris, 1981; Powers & Recent age data show three major clusters at c. 1400 Ma, c. 1000 Ma and c. 550 Ma (Grew & Bohlen, 1985; Santosh, 1987; Lal et al., 1987; Motoyoshi et al., 1990; Dasgupta & Ehl, 1993; Guiraud et al., Manton, 1986; Aftalion et al., 1988; Paul et al., 1990; Sarkar et al., 1994; Shaw et al., 1997). Two types of 1996), iron formations (Krogh, 1977), and hydrother- mal associations (Steefel & Atkinson, 1984). Textural P–T paths have been reported so far from the EGGB: first, isobaric cooling followed by isothermal decom- relations and their interpretation in most of the above occurrences favour a metastable coexistence of cor- pression (Kamineni & Rao, 1988; Sengupta et al., 1990; Dasgupta et al., 1995); and second, an initial undum and quartz, the exception being the study of Krogh (1977). Aramaki & Roy (1963) suggested that decompression followed by later cooling (Lal et al., 1987; Dasgupta et al., 1994; Sen et al., 1995). Major their experimental results did not preclude a stable corundum and quartz assemblage. However, on the rock types of the present study area include metapelites, orthopyroxene granulites and granitic gneiss (Shaw, basis of more recent experimental work, Carr (1969), Bohlen (1986), Shulters & Bohlen (1989) and Harlov 1996). The metapelites of Rayagada comprise two distinct & Newton (1993) concluded that coexistence of corundum and quartz is metastable. Recently, Guiraud assemblages (Shaw & Arima, 1997): the first is an Fe-rich assemblage, characterized by Fe-rich spinel et al. (1996) discussed the possibility of the stable coexistence of corundum and quartz in a high P-T and garnet; and the second is an iron-poor assemblage, characterized by Fe-poor spinel and garnet, together paragenesis from In Ouzzal. In this paper, we document discrete porphyroblastic corundum and quartz in the with the presence of cordierite and hematite. The corundum–quartz paragenesis occurs as small elon- granulite facies metapelites from Rayagada (19°10∞N, 83°25∞E), in the north central part of the Eastern gated lenses (up to 1 m in the long axis) in sharp contact with the surrounding Fe-rich metapelites. The Ghats Granulite Belt (EGGB), India. lenses are heterogeneous in both structural elements and mineralogical composition. A well-developed foli- GEOLOGICAL SETTING ation has been noted within these lenses, defined by elongated garnet–sillimanite and quartzofeldspathic The EGGB forms a linear belt of high grade metamor- phic rocks (mainly granulites), anorthosites, alkaline domains. This foliation is parallel to the dominant planar fabric of the area, corresponding to the D 1 and rocks and granites, exposed along the east coast of the 189 © Blackwell Science Inc., 0263-4929/98/$14.00 Journal of Metamorphic Geology, Volume 16, Number 2, 1998, 189–196