柴达木盆地北缘早古生代碰撞造山系统

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

柴达木盆地北缘在早古生代形成了一条碰撞造山带,该造山带结构保存较完整,可分辨出深俯冲板片、火山岛弧带、蛇绿杂岩带、岛弧深成岩带等组成单元。其中,俯冲板块主要由中元古代鱼卡河岩群和中新元古代花岗片麻岩构成,在寒武纪末—奥陶纪可能全部或部分俯冲到岩石圈深部,发生了高压—超高压变质作用。火山岛弧主要由中基性火山岩、细碎屑岩等组成,成岩时代为晚寒武世—奥陶纪。蛇绿杂岩带由超镁铁质岩、辉长岩、玄武岩和少量硅质岩组成,形成于弧后扩张脊构造背景,成岩时代为寒武纪—奥陶纪。岛弧深成岩成分变化较大,由闪长岩变化到花岗岩,成岩时代为奥陶纪。而造山带北侧的欧龙布鲁克微陆块则具有双层结构,由德令哈杂岩和达肯大坂岩群构成基底,盖层为全吉群。

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.