积石峡至龙羊峡段黄河的形成与地貌演化研究

The process and mechanism within the response of a river system to external environmental change (e.g., tectonic movement and climatic change in different temporal and dimensional scales) attract wide attention from geomorphology. Over the past few years, the significant study progress on the evolution of drainage pattern has been made, as the advance in dating and provenance tracing technology. Despite these achievements, the further work to link the variation in drainage pattern to external environmental change is still weak. The key to understand the relationship is a detail construction for the development processes between the drainage patterns with different chronologies. The northeastern Tibetan Plateau experiencing significant tectonic movements and climate change, where the Yellow River between Jishi and Longyang gorges cuts through the Xunhua, Guide, and Gonghe basins, thus providing excellent insight into the drainage evolutionary processes from basin subsidence to excavation, and its driving mechanism. The geomorphic and sedimentary records within this area are therefore regarded as the study subject of this proposal. With the aid of provenance tracing, based on the zircon U-Pb age distributions of fluvial detritus, fabric construction, and lithology of gravel layer, the link between basin fills and fluvial sediments on geomorphic records will probably be established. Then, according to chronologic framework by paleomagnetic, cosmogenic nuclide, and OSL dating, the evolution processes between different drainage patterns may be described. The response policy of regional landscape and river system to external environmental change, under the condition of strong tectonic activity and high-cold climate, will be finally interpreted by this process analysis of fluvial evolution.

河流系统对不同时空尺度的构造活动、气候变化等外部环境变化的响应过程与机制一直是地貌学关注的重点问题之一。近年来，随着测年和物源示踪技术的发展，学术界已在流域水系格局变化研究方面取得了重要进展，但与外部环境变化的关系研究依然薄弱。其核心问题在于如何构建不同地质历史时期水系格局的演化过程。青藏高原东北部构造活动强烈、气候变化显著，其中积石峡至龙羊峡段黄河依次贯通循化、贵德和共和盆地，是探讨盆地沉降时的水系格局向现代深切河谷外流水系演化过程及驱动机制的理想区域。项目拟以区内地貌和沉积记录为研究对象，开展河流相碎屑锆石U-Pb定年示踪和砾石层组构与岩性统计，搭建盆地堆积物与地貌记录上的河流相沉积物之间的联系。再通过古地磁、宇生核素暴露/埋藏和OSL测年，获得不同时段水系格局的演化过程，尝试从中挖掘构造强烈活动区和高寒气候条件下区域地貌及河流系统对外部环境变化的响应规律。

河流系统对不同时空尺度构造活动、气候变化等外部因素的响应过程与机制一直是地貌学关注的重点科学问题之一。尽管近年来基于年代学和物源示踪技术的发展，学术界已在全流域水系格局演化研究方面取得了重要进展，但与外部环境变化的关系研究依然薄弱。其核心问题在于如何构建不同地质历史时期水系格局的演化过程。积石峡至龙羊峡段黄河切开青藏高原东北部的循化、尖扎、贵德和共和盆地，流域构造活跃、气候变化显著，是探索盆地堆积时的水系向现代深切河谷水系演化过程及驱动机制的理想区域。项目系统划分了这些盆地的地貌面序列和空间分布格局，同时调查并测试了其上河流相碎屑的组构、岩性和U-Pb年龄谱物源信息，恢复了各地貌面发育时期水系格局；进一步在宇生核素暴露、埋藏和光释光测年的限定下，初步建立了积石峡至龙羊峡段黄河流域从侵蚀夷平到盆地填充、再到河谷深切完整的河湖系统袭夺与串联方式水系演化过程。该研究不仅能与下游兰州段黄河研究成果联系，探讨巨型河流内部联动机制，而且还是突破地貌过程如何响应构造与气候耦合作用的理想窗口，对青藏高原东北部新构造定量研究和地质灾害评价有重要意义。