Late proterozoic alkaline magmatism in the Eastern Ghats belt: Rb-Sr isotopic study on the Koraput complex, Orissa

Rb-Sr whole rock isochron age of 856±18 Ma on the Koraput alkaline complex provides evidence of late-Proterozoic alkaline plutonism in the Eastern Ghats Precambrian mobile belt. The low initial 87Sr/86Sr ratio (0.70286±5 ) suggests derivation of the complex from a mantle derived melt. Available age data suggest episodic nature of alkaline plutonism in the belt at Ca. 1250 Ma an d Ca. 850 Ma. Several important petrological processes, such as syntectonic metamorphism, charnockitisation due to CO2 fluid activity, crustal anatexis leading to generation of granitic melts and late- to post-tectonic alkaline plutonism and mafic dyke activity, that characterise the late-Proterozoic 900±100 Ma event in the Orissa segment of the Eastern Ghats belt, appear to be broadly interrelated. (author). 33 refs., 3 tabs., 3 figs