Petrogenesis of Late Stenian Syn-Orogenic A-Type Granites in the Chhotanagpur Gneissic Complex and Eastern Indian Shield

Abstract

We report the petrogenesis of arfvedsonite granites from the Dimra Pahar pluton in the Chhotanagpur Gneissic Complex based on petrology, whole-rock chemistry, mineral chemistry, and La-ICP-MS zircon U-Pb ages and Hf-Lu isotopic analyses. These granites are dominantly peralkaline, occasionally peraluminous, and demonstrate features of A1-type granites. The magma was emplaced at a shallow depth and had a high liquidus temperature, fO2 (>NNO), and water saturation. The zircons exhibit three distinct U-Pb isotopic ages. The oldest (1324 ± 6 Ma), large-sized inherited zircons (εHf(t) = +1.65 to +7.64), show complex zoning and signs of partial resorption. The euhedral, prismatic-bipyramidal zircons displaying oscillatory zoning (εHf(t) = −3.43 to +1.43) reveal a crystallization age of 1046 ± 7 Ma. Their thin periphery (εHf(t) = −3.23 to +0.27) grew during retrograde metamorphism (995 ± 6 Ma). The whole-rock geochemistry and the Hf-isotope values imply that the parental magma of these granites resulted from the anatexis of metasomatized lithospheric mantle sources. These granites intruded in a syn-orogenic (syn-collisional exhumation) stage of the orogeny. Show more