Sequences,geochemistry and genesis of the Bangong Lake ophiolites in Xizang

The Bangong Lake ophiolite zone is aligned to the western part of the Bangong-Nujiang suture zone,where the ophiolites are subjected to severe compression and tectonic deformation,giving rise to the formation of the ophiolitic mélange zone.The restored generalized section of the ophiolite sequences may be comparable with representative oceanic crust sections,including from the base upwards:① metamorphic peridotite composed of highly serpentinized orthopyroxene peridotite and dunite;② cumulates composed of bedded gabbro and peridotite;③ gabbro-diabase dike swarms;④ mafic lava including massive and pillow lava;⑤ abyssal-bathyal sediments composed of radiolarian siliceous rocks,turbidite and limestone.The geological, tectonic and geochemical data show that the ophiolites in the study area were formed in the Meso-Tethyan mid-oceanic ridge and oceanic-island environments.The Meso-Tethyan Ocean may be a mature oceanic basin rather than a small poorly developed intercontinental oceanic basin or marginal sea basin.