晚新生代东帕米尔穹窿剥露的构造热年代学和三维数值模拟研究

The Tibetan Plateau is considered to be an internationally-known natural laboratory to probe the processes of the continental dynamics and the interactions among tectonics, surface processes and climatic change, two of the frontier topics in the geoscience community. The Eastern Pamir domes (i.e. Kongur Shan and Muztagata domes) are tectonically- and topographically-peculiar units in the Tibetan Plateau, bounded by the extensional system. As the processes of domal exhumation archive abundant information of the plateau deformation, surface processes and climatic change in the Late Cenozoic, they are ideal targets for studying the above issues. This study will start from knowing the cooling and exhumation history of the Eastern Pamir domes. To tightly constrain the onset timing and active stage of the Kongur Shan extensional system, we will carry out detailed work on the domes using tectono-thermochronology and three-dimensional (3D) thermo-kinematic modeling; to quantify glacial erosion, we will conduct elaborate studies on the glacial landforms by low-temperature thermochronology and 3D topography evolution modeling. We hope that combined tectonic with climatic results could (1) on one hand further constrain the thermo-kinematic processes inducing the cooling and exhumation of the Eastern Pamir domes, and provide new understanding of the Cenozoic uplift and deformation dynamics of the Pamir syntaxis and the Tibetan Plateau; (2) on the other hand evaluate the relative efficiency of tectonics and climate on the rock exhumation, to build rational model of the interactions among tectonics, surface processes and climatic change.

青藏高原是国际上公认的研究大陆动力学及"构造、地表过程和气候变化之间的相互作用"这两大地球科学前沿课题的极佳天然实验室。由伸展断裂带约束的东帕米尔穹窿（公格尔山和慕士塔格穹窿）是青藏高原十分特殊的构造和地貌单元，其剥露过程记录了晚新生代高原构造变形、地表过程和气候变化的丰富信息，是研究上述课题的理想对象。本研究强调从穹窿的冷却剥露历史作为切入点，通过对断裂带构造热年代学和三维热动力模拟的研究，精细约束断裂带的初始活动时间和活动期次；通过对冰川地貌的低温热年代学和地貌演化模拟的研究，量化冰川的侵蚀作用过程。综合构造和气候两部分研究成果，本项目希望一方面能精细刻画东帕米尔穹窿冷却剥露的热动力学过程，为帕米尔构造结乃至青藏高原新生代的隆升过程和变形动力学机制提供创新性的认识；另一方面可以评估构造和气候作用对岩石剥露过程的相对影响，为"构造、地表过程和气候变化之间的相互作用"建立合理的关系模型。

精细约束帕米尔－西昆仑造山带的构造变形时间、冷却剥露历史和地貌演化是揭示青藏高原造山过程以及中亚陆内动力学机制的关键。通过对东帕米尔典型构造部位的构造热年代学和三维热动力学模拟研究，厘定了该地区新生代构造变形的时空格架，提出帕米尔和天山在中新世中晚期开始对接的观点。围绕东帕米尔穹窿的形成过程和动力学机制，开展了详细的现代河流和冰川沉积物的碎屑锆石裂变径迹研究，精确圈定了穹窿的范围，约束了穹窿东侧的大型伸展断裂于~6-4 Ma同时活动，揭示东帕米尔穹窿~3-1 Ma的强烈剥露与冰川强烈侵蚀对断裂伸展的正反馈作用有关。选取帕米尔－西昆仑造山带山前塔西南盆地的其木干、柯克亚和桑株剖面的新生代沉积物作为研究对象，开展了综合的沉积学、全岩地球化学和碎屑锆石U-Pb/FT年代学研究，支持柯克亚剖面发现的火山灰及最新的地层时代划分，将塔里木西南部西域砾岩的底界年龄限定在~15 Ma，刻画了青藏高原西北部从二叠纪到中新世的构造和地貌的动力学演化过程，认为青藏高原西部广泛的岩石剥露和地表隆升以及喀喇昆仑的大型岩浆活动可以用印度板片断离引起的岩石圈向南北两侧双向楔冲的动力学模型来解释。沉积学、物源分析和裂变径迹数据支持青藏高原西北缘中新世中晚期广泛的挤压变形。综合分析认为帕米尔－西昆仑山脉从三叠纪—侏罗纪早期就已经出现，经历了中生代中晚期和新生代早期的活化造山和渐新世－中新世向外和向上生长过程。