The South Purulia Shear Zone, eastern India: Its anatomy and implication for timing the Rodinia-age collision in the eastern part of the Central Indian Tectonic Zone

Abstract

The Proterozoic Central Indian Tectonic Zone (CITZ) is an ~1500-km-long collision zone between the North India and the South India blocks. The age of collision is debated, but constraining the age of collision is crucial for reconstructing the paleogeographic position of India in the Precambrian. In this study, mesoscale structures, metamorphic pressure-temperature path, U-Pb zircon dates, and monazite chemical dates are combined to constrain the collision age. In the eastern part of the CITZ, the North Singhbhum Mobile Belt (NSMB) comprising 1.5–1.3 Ga low-grade phyllites and schists and the 1.88 Ga Ranibandh granitoid are juxtaposed with the Chottanagpur Gneiss Complex (CGC; eastern CITZ) dominated by 1.76 Ga anatectic basement gneisses intruded by 1.67 Ga, 1.57 Ga, and pre-collisional 1.02 Ga felsic intrusives. The juxtaposition of the disparately evolved crustal domains along the South Purulia Shear Zone (SPSZ) involved top-to-the-south thrusting consistent with amphibolite facies loading. Continued oblique N-S shortening of the thickened crust led to nucleation of ESE-striking, steeply dipping left-lateral transpressional shear zones tens of kilometers wide that obliterated pre-collisional structures in the rheologically weak NSMB phyllites and schists but are weakly developed in the rheologically strong CGC rocks. The 1.02–0.91 Ga oblique collision between the North India and South India blocks along the SPSZ suggests the paleopole data pre-dating the collision are unlikely to ascertain the paleogeographic position of the Indian landmass because the landmass did not exist in its entirety before 1.02–0.91 Ga. But the paleopole data may help locate the North India and South India blocks independent of each other.