库木库里盆地及其周围山脉的盆山耦合过程:古地磁学和低温热年代学证据

The Qaidam and Hoh Xil basins both contain very thick Cenozoic sediments. The sediments of the Qaidam basin are continuous and span the entire Cenozoic in time. The sediments of the Hoh Xil basin span from Eocene to Miocene in time. However, it still remains unknown about the age of the Cenozoic strata of the Kumukuli basin which locates between the Qaidam and Hoh Xil basins. Therefore, investigating the tecto-sediemntary evolution of the Kumukuli basin and adjacent ranges, undoubtedly, will help to reveal paleogeographic reconstruction of the Northern Tibet and to understand when and how did the Tibet grow upward and outward. This project aims to study the tecto-sedimentary evolution of the Kumukuli basin and adjacent orogenic belts, where almost no detailed studies have been conducted so far, by using the two coupling perspectives between basin sediment and mountain bedrock. Firstly, we will use systematic low-temperature thermochronometer (apatite fission track and apatite U-Th/He) on two steep transects of the mountains (Qimantag and Aerka) north and south of the Kumukuli basin in order to obtain the timing and magnitude of bedrock rapid exhumation related to tectonic thrust faulting. Secondly, we will conduct detailed sedimentology, rock magnetism, magnetostratigraphy, and provenance analyses on the Baiquanhe and Guaiziliang sections in the central and western part of the Kumukuli basin respectively. These multidisciplinary studies attempt to derive the basal sedimentation age of the Kumukuli basin, the age of basin strata and its source variations. In combination with this and previous studies,we will deduce the whole process including when and how the bedrocks begin to exhume rapidly, and subsequently when and how the basin sediments respond to the tectonic movement.

柴达木盆地和可可西里盆地均含巨厚的新生代沉积，柴达木盆地含整个新生代沉积,可可西里盆地地层时代为始新世-中新世。但是，夹持于这两盆地之间的库木库里盆地的地层时代至今未知。研究库木库里盆地及其周缘山脉的构造-沉积演化，无疑对青藏高原北部的古地理重建，以及理解青藏高原何时和如何向上、向北生长具有重要的科研价值。 本项目拟采取盆山耦合的方法，对库木库里盆地及其南北两侧的祁漫塔格和阿尔喀山展开详细的构造-沉积演化调查。首先，对祁漫塔格和阿尔喀山进行系统的低温热年代学（磷灰石裂变径迹和磷灰石铀钍/氦）垂直断面研究，以获取山脉构造剥露的时间和幅度信息；然后对分别位于盆地中部和西部的百泉河和拐子梁剖面进行详细的沉积学、岩石磁学、磁性地层学、以及物源分析等，以获得盆地最早沉积时间、地层时代以及物源变化等信息。最终目的是揭示库木库里盆地及其南北侧山脉的盆山耦合过程。

库木库里盆地夹持于可可西里和柴达木两个大型新生代盆地之间，受阿尔金、东昆仑两条大型左旋走滑断裂带控制。本项目主要对盆地地层进行沉积学、构造学、古地磁学等研究；以及对盆地南北两侧山脉进行低温热年代学分析，共同探讨盆山耦合过程。最后在以下几个方面取得一些原创性成果。一、提出了新的两阶段高原隆升模型。通过沉积学、古地磁学和低温热年代学等研究手段，结合前人的研究成果，认为晚渐新世以来青藏高原北部存在两期明显的构造变形和隆升记录（25-18 Ma和15-0 Ma）。这一综合认识为进一步探讨高原构造变形和隆升的机制提供了重要的参考依据。二、获得了青藏高原隆升机制的新认识。通过古地磁构造旋转分析，创新性地提出了高原隆升与大型走滑断裂带的内在联系，这为认识青藏高原的隆升机制提供了新的视角。此外，通过对青藏高原及其周边区域进行地质综述，并结合前人的地球物理资料和地球动力学模拟，我们推测青藏高原（羌塘和松潘-甘孜地块）地幔岩石圈在约26 Ma发生了大幅地对流拆沉。这一基于晚渐新世至早中新世重大地质事件的综述，对于我们认识这一特定时期的高原变形、动力学过程与机制具有重要的意义。三、澄清了柴达木盆地北缘新生代沉积的物源。通过沉积学、古水流、碎屑锆石U-Pb测年等分析，结合前人的地球物理资料，结果一致地表明柴北缘路乐河组、甚至整个新生代地层均来源于北面的柴北缘逆冲褶皱带和南祁连山，而不是南面的东昆仑山和祁漫塔格。确定柴达木盆地新生代地层的物源是建立盆地系统动力学和讨论周缘山脉造山过程的关键。