Precise Rb-Sr age and enriched mantle source of the Sevattur carbanatites, Tamil Nadu, South India

Abstract

Whole-rock-mineral Rb-Sr isochrons of carbonatites and pyroxenites of the Sevattur carbonatite complex, Tamil Nadu, South India, yield precise and concordant ages of 771±18 Myr (million years) and 773±18 Myr respectively, which are interpreted as the time of their emplacement on the basis of field petrological evidences. Since the oxygen isotope composition (δ¹⁸O_SMOW ≈+7%) of the carbonatite is typical for a mantle origin, the initial Sr ratios of 0.70521±4 and 0.70536±13 for the carbonatites and pyroxenites imply a substantial enrichment of their subcontintal mantle source very much or just prior to the production of the carbonitite magma 770 Ma (million years ago).