西藏南部康巴穹隆剥露历史分析:来自低温热年代学的证据

Exhumation history of the Kampa dome in the southern Tibet:Evidence from low-temperature thermochronology

造山带穹隆构造记录了陆-陆碰撞及其碰撞后地壳和地表演化过程的信息,是探讨造山带构造演化的重要窗口。康巴穹隆位于藏南特提斯喜马拉雅地区,是北喜马拉雅片麻岩穹隆带(NHGD)的组成部分,其剥露过程及其动力学机制仍然存在争议。通过对康巴穹隆核部花岗片麻岩开展锆石U-Pb、锆石裂变径迹(ZFT)年代学研究和三维数值模拟,获得了康巴穹隆的锆石U-Pb年龄为497.89±1.2Ma,锆石FT年龄(17~11 Ma)明显小于锆石U-Pb结晶年龄,说明这些径迹年龄是岩体冷却抬升形成的。Pecube三维数值模拟对穹窿核部样品的ZFT数据进行反演显示,康巴穹隆核部岩体自中新世以来经历15.9~11.4Ma和ca.4.2Ma两次快速剥露,结合区域构造演化,提出第一次快速剥露与藏南拆离系(STDS)的活动有关,第二次快速剥露是对气候变化过程的响应。

The orogenic dome structure records the crustal and terrestrial evolution process of the continental-continental collision and its post-collision is an important window for discussing the tectonic evolution of the orogenic belt.The Kampa dome located in the Tethys Himalayas,southern Tibet,is a component of the Northern Himalayan gneiss dome(NHGD),its exhumation process and its dynamic mechanism are still controversial.The zircon U-Pb,zircon fission-track(ZFT)age dating,and three-dimensional numerical simulation of the granite gneiss at the core of the Kampa dome are carried out,the zircon U-Pb age of the Kampa dome is obtained as:497.89±1.2Ma,The FT age of zircon(17-11 Ma)is significantly smaller than the crystallization age of zircon U-Pb,indicating that these ZFT ages are formed by the cooling and uplifting of the dome.The inversion of the ZFT data of the core samples by Pecube shows the Kampa dome has experienced two rapid exhumation events at 15.9-11.4 Ma and~4.2 Ma since the Miocene.Combined with the regional tectonic evolution,we propose that the first rapid exhumation is related to the activity of the South Tibet Detachment System(STDS),and the second rapid exhumation is a response to the climate changing process.