Remnants of middle Triassic oceanic lithosphere in the western Indus–Tsangpo suture zone, southwestern Tibet

Abstract

AbstractDiscontinuous ophiolites within the Indus–Tsangpo suture zone (ITSZ) in southern Tibet represent remnants of Neo‐Tethyan oceanic lithosphere, which are considered to have formed during the late Jurassic to early Cretaceous. We report field observations, petrological and geochronological data for some mafic intrusions in a tectonic mélange in the southern ophiolitic belt of the western ITSZ. Zircon from a gabbro yields an age of 243 ± 1 Ma with εHf(t) values of +7.9 to +13.2. Rare earth element (REE) pattern of this rock resembles that of normal mid‐ocean ridge basalt. We suggest that such gabbro and surrounding mafic–ultramafic rocks represent the remnants of middle Triassic oceanic lithosphere in the ITSZ. Our findings indicate that the Neo‐Tethys Ocean between India and the Lhasa terrane existed from at least the middle Triassic, contrasting with the commonly held view that the Neo‐Tethys Ocean opened along the northern edge of Gondwana during the late Triassic–early Jurassic.