Investigating the Kinematic History of the Kongur Shan Normal Fault System, Western Tibet

西藏西部公古尔山正断层系运动史研究

• 批准号: 0126122
• 负责人: An Yin
• 金额: $ 21.32万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-02-15 至 2005-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0126122&HistoricalAwards=false
• 关键词: Investigating; Kinematic; History; Kongur; Shan

A first-order feature of the Tibetan Plateau is its triangular geometry on map view with itsnorth-south width increasing from ~500 km in the west to 1500 km in the east. This asymmetryhas been explained by either eastward extrusion of Tibet or partitioning of north-south shorteningin the Tian Shan and northern Tibet across the strong Tarim block. To quantify the role of lateralextrusion in accommodating intracontinental deformation during the Indo-Asian collision, wemust know the timing and magnitude of slip along major Cenozoic strike-slip faults in Asia. Thisgoal may be achieved by examining the termination structures of the strike-slip faults where theirmotion is transferred to dip-slip structures. In this proposal, we plan to investigate the temporaland spatial evolution of one of such structures: the 220-km long, north-trending Kongur Shanextensional system in the eastern Pamirs. In the lateral-extrusion model, the Kongur Shanextensional system is the northern termination of the ~1000-km long right-slip Karakorum fault,which is thought to have assisted Tibet to extrude hundreds of kilometers eastward. Because thesouthern end of the Kongur Shan system is assumed to link with the right-slip Karakorum fault,the extrusion model requires that the extensional system has progressively lengthened northwardand its total magnitude of extension decreases from south to north. Alternatively, the oroclinal-bendingmodel suggests that the development of the north-trending Kongur Shan system mayhave been related to pure bending of the Pamir-Nanga Parbat syntaxis system during Cenozoicnorthward indentation of the Pamir promontory. This hypothesis not only explains coeval east-westextension in the Pamirs and east-west contraction in the Nanga Parbat region in the westernHimalayan orogen, but also predicts specifically that the Kongur Shan extensional system shouldhave lengthened progressively southward and its total magnitude of extension decreases alongstrike to the south. The distinctive predictions regarding the extensional-magnitude distributionand propagation direction of the Kongur Shan extensional system by the two competing modelsform the basis of this proposal. We plan to conduct field mapping across the extensional systemin four different transects, each is about 20-40 km wide, which will allow us to construct a seriesof cross sections for estimating the magnitude of extension along individual segment of thesystem. Field mapping will focus on the question of whether the Kongur Shan extensionalsystem is actually linked with the Karakorum fault. We will integrate field mapping withthermobarometric, 40 Ar/39 Ar thermochronologic, and U-Th-Pb ion-microprobe geochronologicanalyses to constrain the P-T-t paths for both the hangingwall and footwall of the extensionalsystem. The results of this study will provide two important constraints on the tectonics of thewestern Himalayan orogen: (1) the timing and magnitude of eastward extrusion of Tibet, and (2)the dynamic cause for the initiation and development of coeval east-west extension andcontraction in the western syntaxis system.

为了量化印亚碰撞期间横向挤压在容纳大陆内变形中的作用，我们必须知道亚洲主要新生代走滑断层的滑动时间和大小。这一目标可以通过检查走滑断层的终止构造来实现，在那里它们的运动转移到倾滑构造。在本文中，我们计划研究其中一个构造的时空演化：位于帕米尔高原东部的长220公里、北向的孔古尔山伸展体系。由于假定孔gur山体系的南端与喀喇昆仑右滑断裂相连接，因此挤压模式要求伸展体系向北逐渐拉长，其总伸展幅度由南向北递减。另外，口斜-弯曲模式表明，北向孔古尔山体系的发育可能与新生代帕米尔-南加帕尔巴特合成体系在帕米尔角向北压陷期间的纯粹弯曲有关。这一假说不仅解释了西喜马拉雅造山带帕米尔高原的同时期东向西伸展和南嘎帕尔巴特地区的东向西收缩，而且具体地预测了孔古尔山伸展体系向南逐渐拉长，其总伸展幅度沿走向向南减小。两种相互竞争的模型对孔古尔山张拉系统的伸展震级分布和传播方向的不同预测构成了这一建议的基础。我们计划在四个不同的样带上进行扩展系统的野外测绘，每个样带的宽度约为20-40公里，这将使我们能够构建一系列横截面，以估计系统各个部分的扩展幅度。野外制图将重点关注孔古尔山伸展系统是否与喀喇昆仑断裂有实际联系。我们将把现场测绘与热气压、40 Ar/39 Ar热年代学和U-Th-Pb微探针地质年代学分析相结合，以限制伸展系统上盘和下盘的P-T-t路径。