河西走廊新生代沉积物源变化记录的祁连山隆升过程

Qilian Shan, orogenic belt formed in the Caledonian, was reactivated and uplifted by the continuous collision between India and Eurasia plate during the Cenozoic. On the other hand, Qilian Shan is generally regarded as the northeastern margin of the Tibetan plateau and a deformative absorption area of strike-slip Altyn Tagh fault propagating northeastwards. Considering the particularly geological location of Qilian Shan, its deformation process and uplift history will provide great information on understanding the roles of Altyn Tagh fault and the dynamic mechanism of the Tibetan Plateau formation. However, the uplift history and process of Qilian Shan remains enigmatic. .Geologically, the central Qilian Shan is characterized as a metamorphic belt of Proterozoic, whereas northern Qilian Shan mainly composed of ophiolite and melange of early Paleozoic plate suture zone, the cover rocks and accumulation of intermontane basin of late Proterozoic and Mesozoic. If Qilian Shan was raised progressively by the expansion of Altyn Tagh fault propagating northeastwards, the Cenozoic sediments in the Hexi Corridor Basin might preserve the information about the uplift process, which also shows obvious difference between provenance age and lithological characteristics of these Cenozoic sediments. On the basis of our previous high-resolution Cenozoic magnetostratigraphy research, we are planning to assess the Cenozoic provenance change history through comparisons between detrtial zircon U-Pb ages along the continuous Cenozoic sediments and zircon U-Pb ages of rocks from the northern and central Qilian Shan terranes in detail, and combination of gravel and heavy mineral components, paleocurrent, tectonosedimentology of the Hexi Corridor Basin of the different stages with the previous achievements.This integrated strategy would prove valuable in answering these elusive questions, such as when did the central Qilian Shan and northern Qilian Shan begin to uplift and how did pattern and process of uplift of Qilian Shan in Cenozoic. The purposes of our project expect to reveal the timing of initiation, pattern and process of uplift of Qilian Shan in Cenozoic and the results should provide significant evidence on understanding the roles of Altyn Tagh fault and the dynamic mechanism of the Tibetan Plateau formation.

祁连山是加里东期造山带、在印-欧板块挤压下于新生代活化隆起成山，被认为是高原北部阿尔金走滑断裂东北端的形变吸收区，其变形隆升过程对揭示阿尔金断裂活动和理解高原北部变形隆升机制具非常重要的意义。然而，至今其隆升的时代和形式仍不清楚。中祁连主要由元古代结晶地块构成，而北祁连主要为早古生代板块缝合带蛇绿岩套、混杂岩等及晚古生代和中生代盖层组成。若祁连山为阿尔金断裂向东北扩展时逐步隆升的产物，则河西走廊沉积物就记录了该过程，它们在物源年代和岩性上就有显著差别。本申请将利用我们前期该区高分辨率新生代磁性地层年代控制的优势，系统测定河西走廊新生代地层碎屑锆石U/Pb年龄沿剖面的变化，结合碎屑成分和古水流变化等分析，并与中、北祁连不同时代岩性和代表性岩石锆石U/Pb年龄谱对比分析，确定中祁连是否早于北祁连隆升，北祁连何时隆升并何时阻断中祁连供给河西走廊的物源，为揭示新生代祁连山隆升时间和形式提供重要证据

祁连山是加里东期造山带、在印-欧板块挤压下于新生代活化隆起成山，被认为是高原北部阿尔金走滑断裂东北端的形变吸收区，其变形隆升过程对揭示阿尔金断裂活动和理解高原北部变形隆升机制具非常重要的意义。然而，至今其隆升的时代和形式仍不清楚。本项目利用我们前期该区高分辨率新生代磁性地层年代控制的优势，在对祁连山北缘酒泉盆地新生代沉积演化序列和盆地新生代不同时期沉积通量（主要代表祁连山新生代不同时期剥蚀变化趋势）研究基础上（图1、2、3、4），通过系统测定河西走廊西部酒泉盆地和东部新生代碎屑锆石 U/Pb 年龄沿剖面的变化（图5,6）、祁连山北缘酒泉盆地和祁连山南缘柴达木盆地新生代碎屑磷灰石以及祁连山不同构造带（北、中和南祁连）基岩磷灰石裂变径迹热年代（图7,8,9,10），结合碎屑成分和古水流变化等分析，推断祁连山不同构造带（北、中和南祁连）具同步、阶段性构造隆升，即祁连山新生代经历了60-50、45-37、35-30、25-20、16-12、10-8、3.6、2.6、和0.8Ma左右重大构造隆升事件。同时通过天水地盆新生代碎屑磷灰石裂变径迹年龄（图11）、碎屑锆石U-Pb测年、砾石成分统计和古流向分析等分析（图12,13），揭示了祁连山东部地区沉积演化和造山隆升过程（图14）。此外，通过对祁连山南缘柴达木盆地新生代环境代用指标的研究，揭示了柴达木地区11Ma以来气候干旱化逐步加剧特征（图15），认为我国中新世初期（约23-17 Ma）湿润地区主要为东部地区,中中新世 (约17 -11Ma)湿润区向西扩大到达柴达木盆地东部地区，之后在约11-5.3 Ma湿润区明显缩回，特别自5.3 Ma湿润区迅速向南撤, 上新世 (约5.3-2.6 Ma) 湿润区东北部撤到约35 °N、120 °E以南（图16），并认为亚洲夏季风演化和自然火灾趋势性变化主要受控于全球变冷（图17，18）。上述研究成果不仅为研究新生代祁连山隆升时间和形式提供重要证据，而且对理解亚洲内陆旱化及高原北部变形隆升机制具重要参考价值。