Shrimp U-Pb Ages of Detrital Zircon in Sargur Supracrustal Rocks in Western Karnataka, Southern India

Abstract

Abstract New limits have been set on the age of the provenance and the depositional period of the oldest known Archaean supracrustal rocks (Sargur Group) in southern India. Detrital zircon grains from a pelitic schist and a quartzite within major tracts of supracrustal rocks older than their host regional grey orthogneisses (peninsular Gneiss, c. 3000-2900 Ma) have yielded U-Pb ages in the range 3580-2960 Ma. The data indicate that granitoid rocks in the age range 3580-3130 Ma were a significant component of the provenance of the sedimentary protoliths. Ages younger than 3130 Ma are attributed to effects of high-grade metamorphism during emplacement of the igneous precursors to the host orthogneisses. Exhumation of the granitoid provenance, deposition of the sedimentary protoliths, intrusion of major gabbroic and peridotitic complexes and possible basaltic volcanism represented by amphibolites in the tracts of supracrustal rocks took place in the period 3130-2960 Ma. This age range is at variance with previous suggestions that the Sargur Group represents early Archaean or primitive crust.