Electron probe micro analyser chemical zircon ages of the Khetri granitoids, Rajasthan, India: Records of widespread late Palaeoproterozoic extension-related magmatism

摘要

A number of granitoid plutons were emplaced in the northernmost entity of the Aravalli craton, the Khetri Copper Belt (KCB). We report here Th–U–Pb electron probe micro analyser chemical ages for zircon and monazite from two granitoid plutons of thenorth KCB, the Biharipur and Dabla. Zircons occurring in the granitoids depict well-developed magmatic zoning and are chronologically unzoned. Both the plutons and their diverse granitoid facies are coeval and provide ages around 1765–1710 Ma. Geochemical attributes of the studied plutons are typical of A-type within-plate granites and consistent with an extensional tectonic environment. Our new age data are comparable to the petrologically similar A-type granitoids of the Alwar re-gion, which have provided zircon chemical ages around 1780–1710 Ma. These analogous ages imply a widespread late palaeoproterozoic extension-related plu-tonism in the northern part of the Aravalli craton. The monazites, which were recovered only from the mafic magmatic rocks of the Biharipur pluton, yielded an isochron age of 910 ± 10 Ma, signifying an over-print of a younger Neoproterozoic thermal event in the region.