Proterozoic events in the Eastern Ghats Granulite Belt, India: Evidence from Rb-Sr, Sm-Nd systematics, and SHRIMP dating

Metamorphic and protolith ages of five rock types (mafic granulite, orthopyroxene granulite, leptynite, sillimanite granite, and metapelite) from Rayagada, in the north-central part of the Eastern Ghats Granulite Belt (EGGB), India, were determined from Rb-Sr and Sm-Nd whole rock and mineral isochrons in combination with SHRIMP U-Pb zircon data. Most of the whole rock isochron ages in both Sm-Nd and Rb-Sr systems point to either ∼ 1450 or ∼ 1000, Ma, and the mineral isochron ages are ∼ 1000, ∼ 800, and ∼ 550 Ma. SHRIMP U-Pb zircon ages of ∼ 940 Ma were obtained from metapelite, which are in close agreement with the Sm-Nd and Rb-Sr isochron ages. From all these data, four age clusters (∼1450, ∼1000, ∼800, and ∼550 Ma) have been noted. The 1450 Ma ages are interpreted to represent igneous protolith formation of mafic granulite and leptynite. The 1000 Ma age cluster is regarded as the intrusion ages of sillimanite granite, and charnockite, and associated granulite facies metamorphism. Two other age clusters (800 and 550 Ma) are regarded as metamorphic heating events. Earlier reports from the EGGB show two major agegroupings, one around 1450 Ma, characterized by alkaline magmatism and anorthositic intrusions, and the other at 1000 Ma, considered to be the major metamorphic and tectonothermal event. The present data are broadly similar with those reported from parts of East Antarctica with respect to the 1000 Ma and 550 Ma events and reconfirm that EGGB has been an integral part of eastern Gondwana.