Initiation and Development of the Late Cenozoic Uplift of Daluo Mountains,Northeastern Margin of the Tibetan Plateau

Daluo Mountains lie at front of the arcuate tectonic belt at the northeastern margin of the Tibetan Plateau,and are the landform boundary zone between the active Tibetan Plateau and the stable North China Craton.Studying of the late Cenozoic uplift evolution of Daluo Mountains is important for understanding the expansion mechanism of the northeastern margin of the Tibetan Plateau and its influence on the western North China Craton.In this study,the late Cenozoic uplift of Daluo Mountains is constructed from the development of the late Cenozoic alluvial fan around Daluo Mountains.The entire sedimentary sequence and framework of the fan was revealed by the newly obtained drilling core data.The cosmogenic nuclide,optically stimulated luminescence,and detrital zircon U-Pb dating results provide new evidences for discussion about the initial timing of the late Cenozoic uplift of Daluo Mountains and the key stages of uplift during the Pleistocene.The late Cenozoic alluvial fan at front of Daluo Mountains overlies a set of fluvial-facies strata;therefore,development of the alluvial-fan marks the start of late Cenozoic uplift of Daluo Mountains.The timing of this event can be constrained to~4.64 Ma.Two extensive gravel layers(dated to ca.0.76–0.6 Ma and~0.05 Ma)developed during the Pleistocene,indicating two episodes of considerable uplift.This study provides a new time scale for the uplift and expansion of the arcuate tectonic belt at the northeastern margin of the Tibetan Plateau.

六盘山晚更新世以来抬升过程沉积响应及环境效应

六盘山构造带夹持于青藏高原与鄂尔多斯地块之间,记录了青藏高原抬升向东北方向推挤的远程效应。关于六盘山抬升过程的研究主要集中在白垩纪及新生代早期,而与人类活动密切相关的晚更新世的研究很少涉及。以盆山响应关系理论为指导,立足于与六盘山相邻的清水河盆地,开展系统的沉积学研究,查明清水河盆地晚更新世的地层序列、沉积充填过程,演绎了六盘山盆地晚更新世以来抬升的过程及其产生的环境效应。研究认为,清水河盆地晚更新世早中期发育2期古湖,以温暖湿润的气候环境为主,晚期由于相邻六盘山的快速抬升,湖水彻底退出了清水河流域,环境逐步开始恶化。晚更新世—全新世清水河流域发育了巨大的六盘山山前冲积扇,该扇体不断沿清水河河谷向东推移,有进一步阻隔清水河形成巨大堰塞湖的趋势。研究成果将为六盘山晚更新世抬升过程研究提供重要依据,为清水河流域的综合治理提供基础地质参考。