Stratigraphic and sedimentological constraints on the age and tectonic evolution of the Neotethyan ophiolites along the Yarlung Tsangpo suture zone, Tibet

Abstract

Ophiolitic rocks distributed along the Yarlung Tsangpo suture zone in southern Tibet are the few remaining fragmentary remnants of many thousands of kilometres of the ocean space that formerly existed between India and Eurasia. Portions of mid-Jurassic and mid-Cretaceous intra-oceanic island arcs can be recognized amongst those rocks that have been studied in detail. Complete suprasubduction zone ophiolite successions are preserved in the Dazhuqu terrane, which crops out both east and west of Xigaze. Radiolarians in inter-pillow cherts and immediately overlying sedimentary rocks indicate a Barremian ophiolite generation event. Palaeomagnetic data show that this ophiolite formed at equatorial latitudes south of the Lhasa terrane before its south-directed emplacement onto the northern margin of India. Highly refractory ultramafic rocks in the Luobusa ophiolite appear to be of Mid-Jurassic age and are potentially related to intra-oceanic island arc remnants in the nearby Zedong terrane. Ophiolitic massifs along the suture in western Tibet are thrust southwards onto northern India and record Late Jurassic ocean-floor development. Miocene north-directed back-thrusting associated with India-Asia collision has further complicated interpretation of regional geology. The ophiolitic rocks of the Yarlung Tsangpo suture zone provide evidence for the former existence of multiple oceanic island arc segments within Neotethys and suggest that consumption of the oceanic space between India and Asia was more complicated than has been predicted by existing models. © The Geological Society of London 2003.