东帕米尔山前晚新生代沉积物源示踪及对公格尔伸展系统启动时间的约束

The Kongur extensional system lies along the eastern margin of the Pamir, accommodating the east-west extension in this region. The initiation of the Kongur extensional system represents a significant change in tectonic stress in the Pamir. Determining its starting time is critical for understanding the formation and kinematics of the Pamir. The development of the Kongur extensional system will trigger the rapid exhumation of the Eastern Pamir Domes and lead to the formation of watersheds, preventing the material from west of the watershed from being transported eastward and forcing it to travel along the north-south fault system to the ends of the domes, the final manifestation of which is the change of sediment provenance. This application is guided by the basin-mountain coupling theory and follows the main line of sedimentary response to extensional system activity. Sedimentology analysis and integrated provenance diagnosis, including gravel statistics, sandstone compositions, heavy mineral combinations, single mineral dating, and Sr-Nd isotopes, will be conducted on the late Cenozoic sediments of the Aertashi and Qimugan sections in the East Pamir front, to determine the time of material from west of the Eastern Pamir watershed disappearing at Qimugan and increasing at Aertashi, which allows to constrain the starting time of the Kongur extensional system from the perspective of sedimentary response.

公格尔伸展系统沿帕米尔东部边缘展布，调节了帕米尔的东西向伸展，其启动代表帕米尔地区构造应力的重大变化，确定其启动时间对理解帕米尔的形成和动力学机制有重要意义。公格尔伸展系统的发育会引发东帕米尔穹隆的快速剥露，并导致分水岭的形成，阻止分水岭以西的物质向东搬运，迫使这些物质沿着南北向断裂系统搬运到穹隆两端，最终表现为沉积物物源的变化。本申请以盆山耦合理论为指导，以公格尔伸展系统活动的沉积响应为主线，选择东帕米尔山前阿尔塔什和其木干两个典型剖面的晚新生代沉积为研究对象，开展系统的沉积学和综合物源示踪分析（砾石统计、砂岩碎屑统计、重矿物组合、单矿物定年和Sr-Nd同位素），以确定东帕米尔分水岭以西物源在其木干消失而在阿尔塔什增加的时间节点，从沉积响应的角度约束公格尔伸展系统的启动时间。

东帕米尔公格尔伸展系统的活动历史对理解该区新生代构造演化具有重要意义，目前对该系统的初始活动时间的约束主要基于断层下盘岩石的低温热年代学数据；但是，强烈的剥蚀可能导致已有的热年代学数据并未包含该系统初始活动的信息。本项目对东帕米尔山前阿尔塔什剖面和其木干剖面晚新生代沉积系统开展野外沉积体系分析和物源时空演变研究，发现在~15 Ma时东帕米尔分水岭以西物源在其木干消失而在阿尔塔什迅速增加，具体表现为：在阿尔塔什剖面中≤15 Ma样品中碎屑锆石的寒武纪和三叠纪组分显著增加，而奥陶纪-志留纪（400-500 Ma）组分则显著减少；在其木干剖面，碎屑锆石U-Pb年龄谱却显示二叠纪-三叠纪（200-300 Ma）的年龄组分明显增加，而寒武纪和新生代锆石减少甚至消失。上述现象可能反映公格尔伸展系统在~15 Ma开始启动，以致该系统两侧剥蚀增加并通过塔什库尔干河搬运到阿尔塔什地区，而其木干地区则只接受东帕米尔风水岭以东的物源。对阿尔塔什火山滑坡碎屑流堆积物开展了沉积学、岩相学、显微组构和年代学分析，发现该堆积物形成时包含大量处于玻璃转换温度的熔岩，属同喷发的产物，其沉积时间为约11 Ma，该年龄可以用于约束塔西南地区新生界年代框架。