The discovery of Banguori-Boku ophiolite belt in northeastern Zanda County of west Tibet and its geological significance

Abstract: Located at the westernmost end of Yarlung Zangbo suture zone, the Bangguori-Boku ophiolite belt is composed of NW-striking Bangguori ophiolite and Boku melange 128 km in length and 5-10 km in width. Bangguori ophiolite consists of harzburgite and lherzolite comprising olivine (Fo=85.2~88.0, 86.6 on average), enstatite (Mg# =89.3~94.3, 91.2 on average), and diopside (Mg#=89.3~94.3, 93.1 on average), characterized by high Al2O3 (0.96%~2.10%) and Ti (173~261μg/g), close to the trace element content of MOR mantle rock, and depletion of REE with ΣREE being 0.33~0.71 times that of chondrite. Moreover, major and trace element characteristics indicate that Bangguori ophiolites are restites resulting from 6%~12% partial melting of the primitive mantle. Boku melange consists of groundmass of slate and silty slate, and rock mass of peridotite, gabbro, siliceous rock, sandstone and limestone. Studies show that Baoguori-Boku ophiolite belt was formed during Late Cretaceous, as evidenced by isotope dating of Bangguori ophiolite and radiolarians fossils from the silicolite rock mass of Boku melange. The results obtained by the authors demonstrate that Bangguori-Boku ophiolite belt resulted from Neotethys ocean subduction, and Bangguori ophiolite represents the residuum of Neotethys ocean lithosphere and belongs to the typical MOR-type ophiolite.