东昆仑南缘阿尼玛卿构造带布青山地区两期蛇绿岩的LA-ICP-MS锆石U-Pb定年及其构造意义

LA-ICP-MS Zircon U-Pb Geochronology of the Two Suites of Ophiolites at the Buqingshan Area of the A'nyemaqen Orogenic Belt in the Southern Margin of East Kunlun and Its Tectonic Implication

东昆仑南缘布青山地区是阿尼玛卿蛇绿构造混杂岩带的西延组成部分,由各种不同构造岩片混杂堆积而成。通过对布青山地区得力斯坦沟和哈尔郭勒两处蛇绿岩的详细野外调查、岩石组合研究,对两处蛇绿岩中的辉长岩分别进行了LA-ICP-MS锆石U-Pb定年,得到206Pb/238U加权平均年龄为516.4±6.3Ma(MSWD=0.70)和332.8±3.1Ma(MSWD=0.75),分别代表了两处蛇绿岩中辉长岩的结晶年龄,表明布青山地区存在早寒武世和早石炭世两期蛇绿岩,这两期蛇绿岩的存在代表了布青山-阿尼玛卿构造带古洋盆两次扩张过程中岩浆活动的产物,表明了原特提斯洋与古特提斯洋的形成及其构造演化。

The Buqingshan area in the southern margin of the East Kunlun is the western extension of the A＇nyemaqen ophiolite mélange belt,which is made up of different tectonic rocks.After detailed field investigation and petrology studies on the ophiolites at Delisitan and Haerguole trenches in the Buqingshan area,the LA-ICP-MS zircon U-Pb dating of the gabbro samples from two suites of ophiolite yielded the ^206Pb/^238U weighted average ages of 516.4±6.3 Ma（MSWD=0.70）and 332.8±3.1 Ma（MSWD=0.75）respectively,both of which can represent their crystallization ages.The results reveal that two suites of ophiolite formed in early Cambrian and early Carboniferous might be the products of the magmatism resulting from two expansions of an ancient oceanic basin in the Buqingshan-A＇nyemaqen orogenic belt,indicating the formation of the Proto-Tethys and Paleo-Tethys and their tectonic development.