MINERAL CHEMISTRY, REACTION TEXTURES, THERMOBAROMETRY AND P-T PATH FROM ORTHO-PYROXENE GRANULITES OF RAYAGADA, EASTERN GHATS, INDIA

Orthopyroxene granulites (charnockites, enderbites and associated rock s) form one of the major lithological units in Rayagada, in the north- central sector of the Eastern Ghats Granulite Belt of Peninsular India . Petrographic features show common occurrences of clinopyroxene lamel la within orthopyroxene host, although reverse relations have also bee n observed in some cases. Two types of coronal garnet with different c hemical compositions have been noted: one at the interface of orthopyr oxene and plagioclase, and the other rimming magnetite, also at the co ntact of plagioclase. Garnet-orthopyroxene thermometry from these rock s show temperature variations from 840 to 700 degrees C, whereas two-p yroxene and garnet-biotite thermometry yield temperatures around 750 a nd 700 degrees C, respectively. Garnet-orthopyroxene-plagioclase-quart z barometry ranges from 8.1 to 6.8 kbar. A near-isobaric cooling from a thermal maxima of similar to 840 degrees C, followed by decompressio n is characteristic of the deduced pressure-temperature (P-T) path. Th is shows significant similarities with the P-T path derived from assoc iated metapelites. Field and petrographic features collectively sugges t that these orthopyroxene granulites have suffered at least the secon d deformation event (D-2), which is the dominant ductile deformation o f the area. This event presumably took place around 1000 Ma and might be coeval to the mid-Proterozoic events of East Antarctica and other f ragments of Gondwanaland. Copyright (C) 1996 Elsevier Science Ltd