西藏山南列麦始新世花岗岩独居石U-Th-Pb年龄及地质意义

Monazite U-Th-Pb age of Liemai Eocene granites in the southern Tibet and its geological implications

西藏山南隆子县列麦地区始新世花岗岩的成岩时代和背景对喜马拉雅地区同碰撞阶段的构造演化具有重要意义。本文对隆子县列麦乡界归党村的白云母花岗岩开展独居石LA-ICP-MS U-Th-Pb测年,独居石40个测点的208 Pb/232 Th加权平均年龄为41±0.1Ma(MSWD=1.4),形成于始新世中期。结合区域上的始新世岩浆岩活动和区域变质作用,本文认为在50~45Ma印度下地壳发生中-高压变质和部分熔融;45Ma新特提斯洋洋壳板片断离,软流圈地幔上涌;45~41Ma喜马拉雅发生短暂的拉张环境导致大量的埃达克质岩浆岩侵位和麻粒岩的折返。

The age and tectonic setting of Eocene granites from Liemai in Longzi County,Tibet are of great significance to the tectonic evolution of the Himalayan region in the syncollision stage.In this paper,monazite LA-ICP-MS U-Th-Pb dating has been carried out for muscovite granites in Jieguidang.The weighted average age of 208 Pb/232 Th is 41±0.1 Ma(MSWD=1.4,n=40),which was formed in the Middle Eocene.Combined with the Eocene magmatic rocks and metamorphism in the region,it is considered that the middle high pressure metamorphism and partial melting occurred in the India lower crust at 50-45 Ma.The Neo-Tethys oceanic crust plate separated and the asthenosphere mantle upwelling occurred at 45 Ma.The Himalaya experienced a short-term extension environment,which resulted in a large number of adakitic magmatic rock emplacement and eclogite exhumation at 45-41 Ma.