MIDCRUSTAL CONTACT-METAMORPHISM AROUND THE CHIMAKURTHY MAFIC-ULTRAMAFIC COMPLEX, EASTERN GHATS BELT, INDIA

Pelitic rocks were thermally metamorphosed at the contact of the Chima kurthy mafic-ultramafic igneous complex, Eastern Ghats Belt, India. Th e rocks show progressive change in mineralogy from biotite-sillimanite -quartz-garnet-K-feldspar (association I, 150 m from the intrusive con tact) to garnet-spinel-cordierite-K-feldspar-sillimanite (association II, 20-30 m from the intrusive contact) to te-K-feldspar-(cordierite-o rthopyroxene-K-feldspar symplectite after osumilite)-spinel-FeTiAl oxi des with/without garnet (associations III and IV, 5 m from the intrusi ve contact), and finally to spinel-orthopyroxene-cordierite-K-feldspar (association V, xenoliths). Oxide mineral clots in associations III a nd IV resemble emery-type rocks. Initial mineral reactions involved bi otite-dehydration melting with partial segregation of the melt. Down-t emperature mineral reactions were largely diffusion controlled and pre servation of symplectitic and coronitic textures in microdomains is co mmon. Interpretation of reaction textures in relevant petrogenetic gri ds for the sytems KFMASH and FMAS and combined with geothermobarometry suggest that the pelitic rocks were thermally metamorphosed at c. 6 k bar pressure along a heating-cooling trajectory within the temperature interval between c. 750 degrees C and c. 1000 degrees C.