柴达木盆地北缘埃姆尼克山在早新生代是否存在隆升作用？

The Qaidam Basin has become an ideal place for studying issues of basin-mountain coupling during the formation of the Tibetan Plateau due to its unique tectonic position and complete Cenozoic sequences. The northern Qaidam Basin was suggested to uplift since the middle Miocene according to recent research, However, the uncomformity of the Miocene Shangyoushashan Formation and the pre-Cenozoic strata around the Aimunike Shan found by the author is against the fact that early-Cenozoic strata have deposited over the study area, which indicates it may have early-Cenozoic tectonic event. This study plans to take a synthetical research on this issue including three approaches: (1) sedimentology analysis including clastic analysis, paleocurrent analysis, section sedimentary facies analysis and provenance analysis by detrital zircon dating; (2) structural analysis including field mapping and seismic section restoration, which help to reveal the early-Cenozoic deformation character and (3) Apatite fission track thermochronology integrated with Apatite (U-Th)/He thermochronology, which help to constrain the time-depth evolution of mountain rocks and reveal its uplift in the Cenozoic. This study will provide new constraint on the northward propagation of the effect of India-Asia Collision through the Cenozoic.

柴达木盆地由于其特殊的大地构造位置以及完整的新生代沉积记录，目前正成为研究青藏高原形成过程中盆山耦合问题的理想地区。目前的研究认为柴达木盆地北缘地区在中新世中期之后才开始造山隆升。然而笔者在之前的野外考察及室内研究过程中发现柴北缘埃姆尼克山地区发育了中新统上油砂山组和前新生界地层的角度不整合，鉴于研究区自始新统下干柴沟组上段以来就已接受沉积，因此这一不整合可能是由于早新生代时期的一次构造隆升所造成。本研究拟通过三个方面对其进行研究、证实，（1）沉积学分析，包括砾石成分分析、古水流统计、剖面沉积相特征以及碎屑锆石测年物源分析；（2）构造分析，包括野外构造填图以及地震剖面构造剥离分析，以描述早期变形的特征；（3）低温热年代学分析，利用磷灰石裂变径迹结合(U-Th)/He热年代学方法对新生代的隆升过程进行约束。本研究的成果将对印藏碰撞远程效应向北传播的过程提供新的地质约束。

柴达木盆地位于青藏高原的北部，其北缘地区和南祁连山毗邻，由于具有较完整的新生代地层记录，因此是研究新生代盆山演化的理想场所。本项目利用地震剖面解译、遥感影像解译、野外考察以及沉积特征分析和物源特征分析等手段，对埃穆尼克山地区的变形特征、地层分布特征和物源特征进行研究，并综合分析研究区新生代的变形时间、过程以及机制。本项目研究结果认为埃穆尼克山-欧龙布鲁克山在中新世中期发生断裂逆冲和隆升作用，导致该地区遭受剥蚀缺失下干柴沟组上段至下油沙山组地层，但是碎屑锆石年龄特征以及地震剖面结构特征指示在隆起形成后小于2Ma内该地区又发生了沉降作用，形成了上油砂山组地层和前新生界地层之间的不整合接触。结合前人的研究认识，本项目提出柴达木盆地在中新世中期受到挤压应力作用，导致了埃穆尼克山-欧龙布鲁克山的隆升，并且挤压应力在短时间内持续增强，进而导致柴达木盆地整体形成东西走向的挠曲，又使埃穆尼克山-欧龙布鲁克山地区发生沉降。本研究的成果为青藏高原北缘在中新世中期的隆升过程提供了重要的补充。