阿中地块北缘库木达坂岩体群特征及锆石U-Pb测年

Characteristics and zircon U-Pb dating of the Kumdaban rock mass swarm on the northern margin of the Azhong block

分布于阿中地块北缘中浅变质岩隆起带之上的库木达坂岩体(群),为一规模较大的复式岩体,不同岩石类型之间接触关系清楚,由早到晚其侵位顺序为细粒黑云二长花岗岩→中粒含斑黑云二长花岗岩。岩石地球化学资料研究证明,该岩体群与大陆岛弧型花岗岩(CAG)相似,显示壳源花岗岩特点,岩体群中获得(449.7±5.8)Ma的单颗粒锆石U-Pb年龄值,确定该岩体群侵位时代为晚奥陶世,岩体形成可能与红柳构—拉配泉早古生代洋壳向南俯冲相关。

The Kumdaban rock mass swarm distributed in an uplift of medium- and low-grade metamorphic rocks on the northern margin of the Azhong block is a large-scale composite rock mass, in which the contact relationships between different rock types are very clear. From early to late, their emplacement order is finegrained biotitic monzogranite→medium-grained biotite monzogranite containing phenocrysts. The geochemical data of the rocks testify that the rock mass swarm is similar to the continental island-arc granite （CAG） and displays the features of crust-derived granite. The single-zircon U-Pb age of 449.7±5.8 Ma obtained from the rock mass swarm indicates a Late Ordovician age for the emplacement of the rock mass swarm. The formation of the rock mass may be related to the southward subduction of the Early Paleozoic oceanic crust in Hongliugou- Lapeiquan.