西昆仑康西瓦断裂西段斜长片麻岩LA-ICP-MS锆石U-Pb定年及其构造意义

LA-ICP-MS zircon U-Pb dating of garnet-bearing muscovite-biotite plagioclase gneiss in western Kangxiwar fault of Western Kunlun and its tectonic significance

摘要: 在康西瓦断裂西段发育着一套含石榴子石二云斜长片麻岩。根据锆石的阴极发光图像和Th、U、REE等特征，锆石可分为岩浆成因和变质热液成因2类。利用LA-ICP-MS法进行锆石U-Pb定年，测得含石榴子石斜长片麻岩的源岩形成年龄为254.5Ma±4.2Ma(MSWD=0.16)，变质年龄为242.7Ma±2.3Ma(MSWD=0.11)。结合区域地质资料，含石榴子石二云斜长片麻岩的变质作用与古特提斯碰撞造山有关，表明西昆仑造山带在中三叠世早期(243Ma)仍处于古特提斯碰撞造山期。

Abstract: There exists garnet-bearing muscovite-biotite plagioclase gneiss in western kangxiwar fault. According to cathodoluminescence (CL) images and Th, U, REE characteristics, the zircons can be classified into magmatic zircons and metamorphic-hydrothermal ones. Zircon LA-ICP-MS U-Pb dating shows that the age of the protolith of the garnet-bearing plagioclase gneiss is 254.5Ma±4.2Ma (MSWD=0.16), and the age of its metamorphism is 242.7Ma±2.3Ma(MSWD=0.11). In combination with regional geological information, the authors hold that the metamorphism of garnet-bearing plagioclase gneiss was related to the collision and orogeny of Paleo-Tethys, suggesting that the Western Kunlun orogenic belt was still in the period of Paleo-Tethys collision in early Middle Triassic.