GEOCHRONOLOGICAL CONSTRAINTS OF GRANULITE TERRANES OF SOUTH-INDIA ANDTHEIR IMPLICATIONS FOR THE PRECAMBRIAN ASSEMBLY OF GONDWANA

Recent geochronologic data allow us to propose a new characterization of Precambrian granulite terranes in Peninsular India. The Archean gra nulite terranes, including the Godavari Granulite Belt (GGB) along the Godavari Valley and the Nilgiri-Madras Granulite Belt (NMGB) along th e southern fringe of the Dharwar Craton and north of the Palghat-Cauve ry Shear Zone, are characterized by metamorphic events at ca. 2.8-3.0 Ga and intense granitic activity at ca. 2.5 Ga associated with middle- to high-grade metamorphism. The Proterozoic granulite terranes includ e the Eastern Ghats Granulite Belt (EGGB) along the Bengal Bay Coast o f India, the Periyar-Madurai Granulite Belt (PMGB) south of the Palgha t-Cauvery Shear Zone and north of the Achankovil Lineament, and the Tr ivandrum Granulite Belt (TGB) south of the Achankovil Lineament. The P roterozoic granulite belts are characterized by model Nd ages (T-DM) o f mostly ca. 2.0-3.0 Ga with local 1.3-1.8 Ga. Intense deformation and regional high-grade metamorphism predates emplacement of A-type grani tic plutons at ca. 550-740 Ma and the last granulite metamorphism took place at ca. 550 Ma. Both GGB and NMGB have similar geochronologic ch aracteristics to the Napier Complex of East Antarctica in that they su ffered ca. 2.8-3.0 Ga and ca. 2.5 Ga tectonothermal events. EGGB, PMGB and TGB have similar ranges in Nd TDM ages as the Rayner and the Lutz ow-Holm complexes in East Antarctica. They are also similar to the Sri Lankan Precambrian, when the three Precambrian units in Sri Lanka are not differentiated and mixed altogether. In this assembled East Gondw ana, late Archean granulite terranes form a continuous belt from NMGB to GGB through the Napier Complex, forming a horseshoe-shaped belt sur rounding the Dharwar Craton. The Paleoproterozoic-Mesoproterozoic terr anes form a broad belt continuing from EGGB to PMGB through the Rayner and the Lutzow-Holm complexes. This belt forms a major part of the Me soproterozoic Circum East Antarctic Mobile Belt surrounding East Antar ctica, which is important for the assembly of East Gondwana. Within th e Proterozoic terrains, signatures in the distribution of TDM ages fac ilitate the differentiation of the Paleoproterozoic and Mesoproterozoi c terranes which have distinct distributional characteristics. Copyrig ht (C) 1996 Elsevier Science Ltd