Geobarometry and geothermometry of garnet-bearing chamockitic and metapelitic assemblages from the high-grade terrain from South India indicate three fields of equilibration. High pressure granulites () are restricted to the charnockites and mafic granulites of the north slopes of the Nilgiris. These place a minimum constraint of ~30 km on the maximum thickness of late Archean crust. Medium pressure granulites () characterize the charnockites of the central Nilgiris and the Madras granulites to the east. Low pressure granulites () characterize the charnockites and metapelites south of the Bhavani shear zone, although migmatites from the Kodaikanal massif may reflect somewhat higher temperatures. All three granulite fields lie on a metamorphic geotherm (piezothermic array) which is strongly convex to the temperature axis and characteristic of convective heat transfer. The P/T fields encountered in the high grade terrain are therefore consistent with metamorphism induced by a -rich vapor phase rising from the mantle.