现代河砂低温热年代学记录的北祁连山新生代变形隆升历史

The northern Qilian Shan locates in the front edge of the northeastern growing Tibetan Plateau. The Cenozoic deformation and uplift history of the northern Qilian Shan provides significant constraint for clarify the growing process and mechanism of the Tibetan Plateau. On the base of previous research, we project a study on detrital apatite fission track and (U-Th)/He low-temperature thermochronology of modern river sands from different locations in the mountain front of the northern Qilian Shan (across the west and east), which may reveal the time of exhumation and deformation of the detrital provenance (the northern Qilian Shan) by the cooling age of minerals. Combining with the analyses of fault structures, deformation in rocks and strata, and the research achievement of predecessors in the northern Qilian Shan- Hexi Corridor region, the initiation time and development process of Cenozoic tectonic deformation in the northern Qilian Shan as well as the defromation difference in its different parts will be revealed. The results could provide important evidence for discussion in the tectonic evolution of the Qilian Shan and the uplift and expansion process and mechanism of the Tibetan Plateau.

北祁连山位于青藏高原东北向扩展的最前缘，其新生代变形隆升历史可为阐明高原生长过程及机制提供重要约束。本项目在前期研究基础上，拟重点以北祁连山前由西到东不同位置现代河流砂质沉积物为对象开展碎屑磷灰石裂变径迹和(U-Th)/He低温热年代学研究，以矿物的冷却年龄直接揭示碎屑物源区北祁连山的变形剥露时间，并结合北祁连山-河西走廊断裂构造和岩石地层变形分析以及前人研究成果，揭示北祁连山新生代构造变形开始时间、发展过程以及不同部位变形差异，为探讨祁连山构造演化及青藏高原隆升扩展过程和机制提供重要依据。

新生代印度-欧亚板块持续挤压汇聚造就了青藏高原的隆升，从而改变了亚洲构造、地形、气候格局，青藏高原隆升扩展过程和机制成为数十年来前沿热点科学问题。印度-欧亚板块碰撞发生在青藏高原南缘，祁连山位于青藏高原东北缘，因此祁连山新生代构造变形历史成为约束青藏高原隆升扩展过程与机制的关键。本项目选择祁连山及周缘新生代盆地为研究对象，综合祁连山原位基岩、周缘盆地沉积碎屑、现代河砂低温热年代学研究和盆地沉积物源分析，开展了祁连山新生代构造变形历史研究，揭示了祁连山新生代早期（60-50Ma）和中-晚中新世（15-8Ma）两期构造变形事件。. 主要研究内容包括：（1）河西走廊中段新生代沉积碎屑和现代河砂磷灰石裂变径迹热年代以及锆石U-Pb年龄物源分析揭示祁连山新生代早期（60-30Ma）和早-中中新世发生构造变形。（2）肃北盆地新生代沉积碎屑磷灰石裂变径迹热年代和锆石U-Pb年龄物源分析揭示祁连山60-50Ma、早中新世、中中新世发生构造变形。（3）柴达木盆地北缘新生代沉积碎屑磷灰石裂变径迹热年代和碎屑岩组分物源分析揭示祁连山60-50Ma、40-36Ma、~10Ma发生构造变形。（4）西宁盆地新近纪沉积碎屑磷灰石裂变径迹热年代分析揭示祁连山约8Ma构造变形。（5）南祁连柴达木山逆冲带和党河南山逆冲带原位基岩磷灰石裂变径迹和(U-Th)/He热年代分析揭示60-50Ma和15-8Ma构造变形。. 上述研究结果表明青藏高原东北缘祁连山新生代经历多阶段构造变形过程，且变形开始于新生代早期（60-50Ma），准同时响应印度-欧亚板块碰撞。该成果为进一步研究青藏高原隆升扩展过程和机制问题提供了科学证据。