Bulk rock and zircon geochemistry of granitoids from the Chotanagpur Granite Gneissic Complex(CGGC): implications for the late Paleoproterozoic continental arc magmatism in the East Indian Shield

摘要

The north-eastern part of the Chotanagpur Granite Gneissic Complex (CGGC) exposes a vast expanse of felsic orthogneisses (1450Ma magmatic crystallization age) containing a variety of metamorphosed supracrustal rocks and augen gneiss. However, origin and timing of emplacement of the protolith of the augen gneiss are not well constrained. Owing to lack of detailed study and paucity of exposures, the antiquity of the basements of the CGGC also remains poorly understood. To address this issue, we present bulk rock geochemical data and the U-Pb and Lu-Hf isotope composition of zircon from augen gneisses from two adjoining areas within the CGGC. Our obtained data suggest that the augen gneiss have been derived from hybrid source involving older crustal rocks and metasomatised mantle. The bulk rock and zircon geochemistry also suggest that the protolith of the augen gneiss was emplaced in an early Paleoproterozoic basement in a continental arc setting. U-Pb ages of the magmatic zircon grains constrain the age of intrusion at ca. 1710Ma and ca. 1635Ma. The timing of this late Paleoproterozoic felsic magmatism overlaps with the timing of the regional high-to-ultrahigh-temperature granulite facies metamorphism in the CGGC.