P-T CONDITIONS OF PELITIC GRANULITES AND ASSOCIATED CHARNOCKITES OF CHINWALI AREA, WEST OF DELHI FOLD BELT, RAJASTHAN

A brief account of the petrology and structure of medium grade pelitic granulites and associated charnockites occurring as slivers in the An asagar migmatitic gneiss is given. These granulite slivers have been t raced along strike up to 40 km and may cover a much wider area. Cordie rite bearing pelitic granulites associated with charnockites around Ch inwali were chosen for estimating metamorphic P-T conditions. The peli tic granulites are represented by the assemblage opx-cord-gt-bio-silli -plag-k felds- qtz. Biotite-fibrolite intergrowths grow on cordierite which has opx inclusions. Garnet is often smeared with graphite. Metam orphic conditions of pelite show peak pressures of 7.5 kb at 640-degre es-C. Charnockites generally record retrogressive pressure conditions of 5.7-4.0 kb. The mineralogy of the Chinwali granulites and P-T condi tion compare well with that of Sandmata granulites. The presence of th ese granulites, north of Ajmer, in basement migmatitic gneisses sugges t the presence of an older deep crustal fragment (ca. 1.7 Ga) along th e northwestern margin of the Aravalli Delhi Mobile Belt (ADMB) and bel ies the prevailing concepts of eastward crustal thickening and westwar d age polarity in the western Indian shield.