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

Discontinuous 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 melange in the southern ophiolitic belt of the western ITSZ. Zircon from a gabbro yields an age of 243 +/- 1 Ma with epsilon(Hf)(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.

Automated summary

The study reveals that some mafic intrusions in the southern ophiolitic belt of Tibet represent remnants of middle Triassic oceanic lithosphere in the Indus-Tsangpo suture zone. This finding contrasts with the previous belief that the Neo-Tethys Ocean opened along the northern edge of Gondwana during the late Triassic-early Jurassic.