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 Kamataka and carbonates from the Madukkarai area in Tamil Nadu are reported. Carbonate rocks from both areas show preservation of sedimentary isotopic compositions. Bettadabidu carbonates have lower isotopic ratios (δ¹⁸0 = 15.8 SMOW ; δ¹³C = ·0.7 PDB) when compared to Madukkarai carbonates (δ ¹⁸0 = 20 SMOW; δ ¹³C = 2.0 POB). Oxygen and carbon isotopic values exhibit positive correlation indicating a progressive devolatilization process during regional metamorphism. The range in δ¹⁸0 values demonstrates that large quantities of a homogeneous metamorphic fluid have not pervasively infiltrated either terrane.