西昆仑库地北依莎克群玄武岩锆石U-Pb年龄、地球化学特征及构造意义

Geochemical Characteristics and Zircon U-Pb Ages of the Basalt of Yishake Group in Northern Kudi Area,Western Kunlun Mountains and Thire Tectonic Significance

西昆仑山分为北昆仑古生代复合沟弧带和南昆仑地块,依莎克群的形成时代和构造归属一直存在争议,库地蛇绿岩的形成时代亦无定论。本文运用电子探针微区成分分析和锆石U-Pb测年方法,对库地北西奴山依莎克群底部玄武岩中锆石进行了分析。获得依莎克群玄武岩中锆石LA-ICP-MS U-Pb年龄为519.5±1.2Ma,说明依莎克群玄武岩形成时代为中寒武世。与库地蛇绿岩构造环境和形成时代对比表明依莎克群玄武岩是库地蛇绿岩的组成部分,是原特提斯洋俯冲消减作用的产物。综合前人的年代学资料和本文成果表明库地蛇绿岩形成时代为中寒武世—晚寒武世。

Objectives： There is controversy in the formation time of the Yishake Group basalt on the north side of Kudi suture zone, Western Kunlun. Whether the basalt belongs to the ophiolite is controversial. Therefore, our research focuses on determining basaltic age and tectonic attribution. Methods：Based on the field work, through the mircroscope observation, the whole rock chemical analysis and the Zicon U-Pb isotopica analysis of the basalt. We determine basalt geochemical characteristics and isotopic age. Combined with ophiolite age and tectonic properties,we discuss basaltic formation and structural ownership. Results： Zircon LA-ICP-MS U-Pb age of 519.5 ± 1.2 Ma is obtained from Yishake Group basahs, which indicates that the formation time. It shows that the Yishake Group basalt is an integral part of the Kudi ophiolite , which Compares with the tectonic environment of the Kudi ophiolite and the age of formation. It is the product of the depletion of the Tethys ocean subduction. Yishake Group basalt shows that the age of the Kudi ophiolite is the Middle Cambrian--Late Cambrian,which Bases on the previous chronological data and the results of this paper. Conclusions： Yishake Group basalts are part of the formation of the ophiolite formations for the Middle Cambrian. The Kudi ophiolites and the Yishake Group Group basalts are the products of the subtraction of the subduction.