Geochemical Characteristics of Gabbro and Diabase in the Shemalagou Ophiolite in Tibet

Shemalagou ophiolite is located in the west segment of the Bangong Co-Nujiang ophiolite belt in western Tibet.It is an important member of the Gaize ophiolite.In order to acquire the tectonic property of the ophiolite and discuss its petrogenesis,the petrography and whole rock geochemistry are carefully studied.The ophiolite consists of mantle peridotite,gabbro and diabase.And gabbro's average content of SiO2 is 47.65%,the Mg# is 77.1,the gabbro's REE/chondrite pattern is similar to mantle peridotite's,Eu has positive anomaly;Diabase's average content of SiO2 is 50.52%,the Mg# is50~56.4,the samples have similar REE/chondrite pattern,∑REE is 45.58~66.55×10-6,the REE/chondrite pattern displays a flat mode.Ophiolite have geochemical characteristics of IAT-type and MOR-type.It may form in the back-arc basin tectonic setting,resulted from the back-arc oceanic crust formation which was a spreading center near the subduction zone.