白垩纪以来羌塘盆地剥蚀过程及其对高原隆升的响应

The Qiangtang basin is located in the central zone of the Tibet plateau. The denudation process of the Qiangtang basin was a response to the uplift of the Tibet Plateau between Creteacous and Cenozoic, and has help to understand correctly the formation of the Tibet Plateau. In order to detect the denudation process of the Qiangtang basin, a systematic fission-track research, along the Nadigangri height section, north-south traversing line and the well cores, need to be put into practice. We hope that the trinity research (on the hill, level ground and underground) can find out the start time and evolutional stage of the Qiangtang denudation process with the help of the low temperature thermal chronology of multiple closed system, fission track thermal fitting and the detrital source research. After that, we establish a high quality denudation curve since the cretaceous of the Qiangtang basin. Through a comparative research on the different denudation between Qiangtang and other blocks in the Tibet Plateau and the difference in different tectonic units of the Qiangtang, we hope to find out the key geological issues, such as “early uplift”, and then discuss the uplift of the Tibet Plateu.

位于青藏高原腹地的羌塘盆地，其白垩纪以来的构造剥蚀过程是高原隆升的响应，也是正确理解高原隆升的一个关键环节。为了揭示羌塘盆地白垩纪以来的构造剥蚀过程，在盆地西部那底岗日剖面沿高程、在盆地内沿南北穿越线、在钻井岩心中沿深度分别进行系统地采集裂变径迹测年样品，希望通过山上、平地、地下三位一体的采样研究，再辅以典型岩体多封闭体系低温热年代学研究、未完全退火地层的碎屑物源研究以及裂变径迹热史拟合等，查明羌塘盆地白垩纪以来的剥蚀开启时间、阶段性等地质问题，建立白垩纪以来高质量的剥蚀曲线；再通过对比羌塘盆地内部各地质单元之间以及羌塘盆地与青藏高原其他地质体之间的隆升与剥蚀差异性，从而解决“早期隆升”等关键地质问题，最后探讨青藏高原隆升的模式与机制。

本项目在青藏高原腹地羌塘盆地地表采集系列磷灰石裂变径迹测年样品，在羌塘盆地首个地质科探井-羌科1井采集40件样品，获得了31个锆石U-Th/He年龄数据。磷灰石裂变径迹样品的表观年龄为（57±5）Ma～118±7）Ma，混合年龄分解出的峰年龄为（33±6）Ma～（132±7）Ma；表观年龄、分解的峰年龄及磷灰石裂变径迹热演化史反演结果证实，羌塘盆地的构造隆升主要发生于早白垩世、晚白垩世和新生代三个阶段，其中晚白垩世（约100～80 Ma）是构造隆升的主体阶段，隆升剥蚀的厚度约为3200 m。U-Th/He年龄介于（60.6±3）～（152±7.6）Ma之间，热史反演揭示其快速隆升与剥蚀始于82Ma，在55Ma左右就停止了剥蚀，暗示其可能获得了近于目前的海拔高度。