北祁连洋早古生代双向俯冲的花岗岩证据

Double subduction of the Early Paleozoic North Qilian oceanic plate: Evidence from granites in the central segment of North Qilian, NW China

摘要: 提要：笔者主要对北祁连山中段的牛心山岩体、民乐窑沟岩体进行了锆石SHRIMP定年研究。结果表明：牛心山花岗岩的年龄为476 Ma，民乐窑沟花岗闪长岩的年龄为463 Ma。岩石地球化学显示，两岩体均具有大陆活动边缘的岩浆作用特征，结合岩体产出的区域构造位置及区域地质资料，笔者认为早古生代北祁连洋板块分别发生了向南、向北俯冲，其中向南俯冲形成牛心山花岗岩（476 Ma），向北俯冲，形成了民乐窑沟花岗岩侵入体（463 Ma）。

Abstract: Abstract：This paper deals with zircon SHRIMP dating of the Niuxinshan and Minleyaogou granites in the central segment of the North Qilian Mountains, NW China. The dating results indicate that the ages of the Niuxinshan granite and Minleyaogou granite are 476 and 463 Ma respectively. Petrogeochemistry shows that both granite intrusions have the features of active continental-margin magmatism. On the basis of these features, combined with the tectonic locations of granite occurrence and field observation data, the authors think that south- and north-directed subductions of the North Qilian oceanic plate took place in the Early Paleozoic, of which the southward subduction resulted in the formation of the Nixinshan granite (476 Ma) and the northward subduction gave rise to the Minleyaogou granite (463 Ma).