OXYGEN AND CARBON ISOTOPIC COMPOSITION OF PRECAMBRIAN CARBONATES FROM KARNATAKA AND TAMILNADU, INDIA

Oxygen and carbon isotopic compositions for carbonate rocks from the Sargur Group in Karnataka and carbonates from the Madukkarai area in Tamil Nadu am reported. Carbonate rocks from both areas show preservation of sedimentary isotopic compositions. Bettadabidu carbonates have lower isotopic ratios (delta O-18 = 15.8 SMOW ; delta C-13 = - 0.7 PDB) when compared to Madukkarai carbonates (delta O-18 = 20 SMOW; delta C-13 = 2.0 PDB). Oxygen and carbon isotopic values exhibit positive correlation indicating a progressive devolatilization process during regional metamorphism. The range in delta O-18 values demonstrates that large quantities of a homogeneous metamorphic fluid have not pervasively infiltrated either terrane.