Collaborative Research: Development of Extensional Systems in Regions of Hot, Thick Crust: Insight from Tibet

该项目将研究现代大陆伸展系统和相关盆地如何在热厚地壳地区发展。西藏是地球上最厚的地壳之下，可以说是在中地壳水平流动，并积极地向东-西延伸，超过印度和亚洲之间总南北收敛率的三分之一。近年来的研究表明，藏北向正断层及其邻近盆地的特征随伸展幅度的变化而系统地变化，并可能提供断陷盆地在渐进伸展过程中演化的序列快照。新生裂谷的特征是以高角度正断层为界的半地堑盆地。相比之下，更发达的裂谷是有界的低角度拆离断层的特点是盆地进行切割与盆地内的排水划分在推断的最大延伸的地区。本研究的目标是测试的假设，西藏裂谷开始作为高角度的正断层和相关的半地堑，演变成拆离断层活动在地壳的最高水平和以上的裂谷盆地填充隆起和侵蚀，响应于渐进的构造卸载和均衡反弹。 本项目将通过地质和构造制图、宇宙成因年代测定、盆地分析和低温热年代学，对该假设以及沿着几种备选方案进行测试，方法是在西藏中部沿着一口出露的井。该项目是堪萨斯大学、亚利桑那大学、得克萨斯大学、加拿大达尔豪西大学和中国青藏高原研究所的师生之间的一项多学科合作研究成果。该项目的成果将详细记录现代伸展系统如何在热厚地壳下的活跃造山作用地区发展，从而产生重大的科学影响。结果将允许测试对比模型的发展变质核杂岩和低角度的正断层，并可能揭示新的光的作用，中地壳流动在大陆伸展过程中，提高均衡反弹。

This project will investigate how modern continental extensional systems and associated basins are developing in regions of hot, thick crust. Tibet is underlain by the thickest crust on Earth that is arguably flowing at mid-crustal levels, and is actively extending East-West at greater that one-third the total North-South convergence rate between India and Asia. Recent studies show that North-trending Tibetan normal faults and adjacent basins vary systematically in their characteristics as a function of extension magnitude, and may provide sequential snapshots of rift basin evolution during progressive extension. Nascent rifts are characterized by half-graben basins bounded by high-angle normal faults. In contrast, more evolved rifts are bounded by low-angle detachment faults characterized by basins undergoing incision with intrabasin drainage divides in areas of inferred maximum extension. The goal of this research is to test the hypothesis that Tibetan rifts initiate as high-angle normal faults and associated half-grabens that evolve into detachment faults active at uppermost crustal levels and above which rift basin fill is uplifted and eroded, in response to progressive tectonic unloading and isostatic rebound. This hypothesis, along with several alternatives, will be tested in this project along a well exposed in central Tibet by using geological and structural mapping, cosmogenic dating, basin analysis, and low-temperature thermochronology. The project is a multi-disciplinary and collaborative research effort between faculty and students at the University of Kansas, University of Arizona, University of Texas, Dalhousie University in Canada, and the Institute of Tibetan Plateau Research in China.Project findings will have a major scientific impact by documenting in detail how modern extensional systems develop in regions of active orogenesis that are underlain by hot, thick crust. The results will allow testing of contrasting models for the development of metamorphic core-complexes and low-angle normal faults, and may shed new light on the role of mid-crustal flow in enhancing isostatic rebound during continental extension.