Geochemical and Sr-isotopic signatures in the 2.6 B.Y. Lepakshi granite, Anantapur district, Andhra Pradesh: implications for its origin and evolution

The predominantly leucocratic 2.6 b.y. old Lepakshi granite (a suite of granite, granodiorite and quartz-monzonite), near Hindupur in the Anantapur district of Andhra Pradesh is intrusive into the Archaean schistose rocks and contains xenolithic patches of amphibolite. Compositionally, it is predominantly quartz-monzonitic with granodiorite and granite variants. The relatively low initial 87Sr/86Sr (Sri = 0.7026) of this Lepakshi granite implies its derivation from a juvenile crustal source with very limited crustal residence time, indicating the absence of involvement of any metasedimentary source. The source also appears to have fair amount of mafic component. A volcanic arc type tectonic setting, along with the collision processes and the associated tectonic activity operating in tandem, resulting in an increased P-T regime, granulite facies metamorphism and anatectic melting at mid- to lower crustal levels is suggested for the origin of this granite. The large ion lithophile (LIL) elements removed from the lower crust (due to granulite facies metamorphism and the associated fluid activity) were incorporated in the granites of the Lepakshi type. (author). 45 refs., 12 figs., 2 tabs