新疆东昆仑三岔顶地区长城系小庙岩组锆石U-Pb年代学特征及地质意义

Zircon U-Pb Chronological Characteristics and Geological Significance of Xiaomiao Formation of Changcheng System in Sanchading Area in Eastern Kunlun in Xinjiang Uygur Autonomous Region

三岔顶地区位于新疆东昆仑西段,属于昆南增生杂岩带,区内发育长城系小庙岩组变质岩,该套地层主要为一套长英质中级变质岩,主要岩石类型为石英岩类、片岩类、片麻岩类和斜长角闪岩类,变质程度达到高绿片岩相—低角闪岩相。锆石U-Pb年龄分别为(994±11)Ma、(775±12)Ma和(613.6±3.6)Ma,分析认为,这3组年龄为小庙岩组发生中深变质的年龄,并不代表岩石的形成年龄。综合野外地质特征及岩石地球化学特征,研究区小庙岩组变质岩为副变质岩,原岩为火山碎屑沉积岩,物源区以长英质为主,形成环境为活动大陆边缘环境。

Sanchading area is located in west part of eastern Kunlun in Xinjiang Uygur Autonomous Region.It belongs to Kunnan accretive complex belt.Metamorphic rocks in Xiaomiao formation in Changcheng system are developed in the area.According to detailed field geology and indoor observation,the formation is mainly a set of felsic medium metamorphic rocks,and main rock types can be classified into four categories:quartzite,schist,gneiss,and amphibolite.The metamorphic degree reaches high greenschist facies to low amphibolite facies.Zircon U-Pb ages are(994±11)Ma,(775±12)Ma and(613.6±3.6)Ma respectively.It is believed that these three ages are the ages of middle deep metamorphism of Xiaomiao formation,and do not represent the ages of rock formation.Based on field geological characteristics and rock geochemical characteristics,metamorphic rocks of Xiaomiao formation in the study area are parametamorphic rocks,the original rocks are pyroclastic sedimentary rocks,the provenance area is mainly felsic,and the formation environment is mainly active continental margin environment.