CARBON AND OXYGEN ISOTOPIC VARIATION IN TAMIL-NADU CARBONATITES, SOUTH-INDIA

Carbonatites of Tamil Nadu (Samalpatti, Sevattur, Hogenakkal and Pakka nadu-Mulakkadu area), tectonically emplaced along faults/fractures of Neo-proterozoic Koratti Fault Zone are predominantly calcio-carbonatit e to ferro-carbonatite. Their magmatic origin is indicated by intrusiv e nature, association with alkaline-peralkaline complexes, degree and extent of fenitization and presence of diagnostic accessory mineral ph ases. The stable isotopic ratios (delta(13)C and delta(18)O) reported in the present work provide conclusive evidence of their magmatic orig in. Enrichment of O-18 in some Of the ferrocarbonatites appears to be a post-magmatic phenomenon and can be attributed to low temperature hy drothermal alteration.