Mesoproterozoic P–T–t–d history in the Vinjamuru domain, Nellore schist belt (SE India), and implications for SE India–East Antarctica correlation

Abstract

The Vinjamuru Domain is an important crustal segment in the Nellore schist belt (NSB) and the tectono-metamorphic evolution of the belt provides insights into Proterozoic orogenesis in southeastern India, and is also relevant to an Indo-Antarctic correlation in the Late Paleoproterozoic and Middle Mesoproterozoic. Garnet-staurolite-kyanite bearing metapelites in this domain exhibit three metamorphic stages, e.g. M1S, M2S and M3S in the Saidapuram–Sangam area (sector-S) and M1N, M2N and M3N in the Vinjamuru–Malakonda area (sector-N). In both sectors, the metapelites exhibit shallow foliation (S2) axial planar to recumbent folds (F2) of an earlier schistosity (S1), and overprinted by gently-plunging upright F3 folds, with axial planar fabric (S3) trending north in sector-S, and NNE in sector-N. Syn-D3S garnet + staurolite + kyanite + muscovite + biotite + quartz + ilmenite ± plagioclase and garnet (late-D2N to early-D3N) + kyanite + muscovite + biotite + quartz + ilmenite + plagioclase ± staurolite assemblages characterize the peak metamorphic episodes in the sector-S (M3S, P = 8.8–9.2 kbar, T = 630–650 °C) and sector-N (M3N, P = 6.5–7.5 kbar, T = 620–640 °C) respectively. The peak P–T conditions in the metapelites (M3S/M3N) are broadly contemporaneous with the steep-dipping S3S in sector-S and shallow-dipping S2N in sector-N. Total-Pb monazite dating in the chemically distinct monazite domains yields age populations at 1.65–1.55 Ga, 1.50–1.40 Ga, 1.38–1.25 Ga and 0.84–0.76 Ga. The oldest age population (1.65–1.55 Ga) possibly corresponds to large-scale reworking of the pre-existing crust in the Vinjamuru domain. Subsequently, the domain experienced prograde metamorphism (M1S/M1N–M2S/M2N) between 1.50 and 1.40 Ga, which may be attributed to a mid-crustal shortening within the NSB. The 1.38–1.25 Ga ages correspond to upper amphibolite facies metamorphism (M3S/M3N) and coincides with widespread felsic plutonism in the NSB. The Neoproterozoic ages (0.84–0.76 Ga) arguably represent an alteration event that affected the NSB during Rodinia supercontinent breakup. The Mesoproterozoic metamorphism and the long-lived orogenic events (1.65–0.76 Ga) in the Vinjamuru domain are similar to those recorded in the basement rocks of East Antarctica, suggesting a possible tectonic linkage along accretionary margins.