2.9 b.y. Rb-Sr Age of the Granulite Facies Rocks of Satnur-Halagur and Sivasamudram Areas, Karnataka, South India

Abstract

Preliminary Rh-Sr isotopic studies of the granulites occurring SW of Kabbaldurga were undertaken to verify the possibility of an earlier granulite facies event. The Rb-Sr data obtained gives an imperfect isochron age of 2950 ± 234 m.y. with an initial ratio of 0.7032 ± 22 (MSWD = 52). The age obtained may correspond to subconcomitant protolith-metamorphism age or metamorphism alone. The high error may be due to non-cogenetic nature of the rocks analysed or a small disturbance of the Rb-Sr system during the 2500 m.y. high-grade event. The present study indicates probability of the occurrence of an early granulite facies event prior to 2500 m.y.