An Early Paleozoic collisional orogen on the northern margin of the Qaidam basin, northwestern China.

A collisional orogen formed in the Early Paleozoic is well preserved on the northern margin of the Qaidam basin. In this orogenic belt we may distinguish such units as the deep subducted slab, volcanic island-arc zone, ophiolite complex zone and island-arc plutonic zone. The subducted slab consists predominantly of the Mesoproterozoic Iqe Group complex and Meso- and Neoproterozoic granite-gneisses, and was probably all or partly subducted into the deep interior of the lithosphere during the terminal Cambrian-Ordovician and underwent HP-UHP metamorphism. The volcanic island-arc zone is chiefly composed of intermediate-basic volcanic rocks and fine clastic rocks, which formed during the Late Cambrian-Ordovician. The ophiolite complex consists of ultramafic rocks, gabbro, pillow lavas and minor cherts, which formed in a tectonic setting of the back-arc spreading ridge during the Cambrian-Ordovician.Island-arc pluton consists of diorite to granite, which formed in Ordovician. The Olongbruk microblock on the northern side of the orogen has a double-layer structure, i.e. a metamorphic basement composed of the Delingha complex and Daken Daban Group complex and a cover composed of the Quanji Group.