The ultrabasic and basic rocks and their tectonic settings in the Qoimaco region, Qiangtang on the Qinghai-Xizang Plateau

The ultrabasic and basic rocks widespread in the Qoimaco region, Qiangtang on the Qinghai-Xizang Plateau are dominated by the clinopyroxene peridotite-olivine gabbro-gabbro-diabase associations. Petrochemically, the olivine gabbro is characterized by lower SiO₂, K₂O, Na₂O, TiO₂ and P₂O₅, while the gabbro and diabase by higher Na₂O and TiO₂. On the whole, these associations of Himalayan in age display the features of higher MgO, Na₂O>K₂O, lower ΣREE, Sr and Ta. Moreover the accessory minerals are rich in magnetite. The (olivine) gabbro may be assigned to the oceanic tholeiite series, while the gabbro and diabase to the alkaline series. The tectonic settings of the ultrabasic and basic rocks in the Qoimaco region are the same as the mid-oceanic ridge basalts.