东昆仑造山带西段早古生代花岗岩锆石LA-ICP-MS年龄、岩石地球化学特征及地质意义

LA-ICP-MS zircon U-Pb ages, geochemical characteristics and their geological significances of theEarly Paleozoic granites in the western part of the East Kunlun Orogenic belt

笔者等对东昆仑造山带西段克其克孜苏花岗岩开展岩石学、岩石地球化学及LA-ICP-MS锆石U-Pb年代学研究,探讨岩体的形成时代、成因及地质意义。研究表明,克其克孜苏花岗岩中的锆石U-Pb加权平均年龄为442.3±4.4 Ma(MSWD=2.7),为晚奥陶世—早志留世,是区域上新解体出的早古生代花岗岩。花岗岩SiO_(2)含量为68.96%~70.40%,Na_(2)O含量为3.08%~3.14%、K_(2)O含量为3.93%~4.32%,铝饱和指数A/CNK介于1.06~1.13,属于高钾钙碱性过铝质岩石。岩石富集大离子亲石元素K、Rb和U、Th,而不同程度亏损Ba、Nb、Sr、Ti、Zr等高场强元素。结合区域资料及前人成果,本文认为克其克孜苏花岗岩与俯冲碰撞构造环境有关,可能代表了东昆仑造山带西段原特提斯洋在晚奥陶世—早志留世的俯冲消减作用,为东昆仑造山带原特提斯洋的构造演化和南昆仑结合带早古生代的岩浆活动提供了证据。

This paper provided petrographic and geochemical characteristics,LA-ICP-MS zircon U-Pb age of the Keqikezisu granite in the western part of the East Kunlun Orogenic Belt and discussed the formation age,genesis and geological significance of the rocks.The results show that the weighted age of zircon U-Pb in the Keqikezisu granite is 442.3±4.4 Ma(MSWD=2.7),demonstrated the rocks crystallizing time is Late Ordovician to Early Silurian,which is a newly disunited Early Paleozoic granite in the region.The content of SiO_(2) in the granite is 68.96%~70.40%,Na_(2)O is 3.08%~3.14%,K_(2)O is 3.93%~4.32%,and the Al saturation index(A/CNK)ranges from 1.06 to 1.13.The granite belongs to high potassium calc-alkaline peraluminous rocks.The Keqikezisu granite is enrichment in large ion lithophile elements(LILE)K,Rb,and U,Th,radioactive elements and different degree of loss Ba,Nb,Sr,Ti,Zr,high field strength elements(HFSE).Combined with the regional data and previous results,this paper believes that Keqikezisu granite is related to subduction and collision tectonic environment,and may represent subduction of the Proto-Tethys Ocean in the western section of the East Kunlun Orogenic Belt during the Late Ordovician to Early Silurian.The results provided evidence for the tectonic evolution of the Proto-Tethys Ocean in the East Kunlun Orogenic Belt and the Early Paleozoic magmatic activity in the South Kunlun junction belt.