Collaborative Research: Orogen-parallel Mid-crustal Flow and Exhumation of Domes Along the Southern Margin of the Tibetan Plateau

地球上一些最大、最有趣的地质和地理特征，包括阿尔卑斯山/喜马拉雅山脉，都是大陆碰撞的结果。由于大陆碰撞系统是贯穿地球S历史的一大部分深刻的地质变化的原因，了解它们的复杂动力学对地球科学具有重要意义。基于碰撞系统侵蚀核心中保存的岩石和结构的地质学研究，为了解造山的基本过程提供了重要的见解，包括变质作用、熔融、变形和折返。这项工作的结果将有助于完善我们的知识，不仅是关于个别过程，而且还包括它们相互作用以构建和摧毁大型山链的程度。来自该项目的数据将成为编制课程材料的基础，这些材料将分发给中学教师，并将成为一个网站，专门突出喜马拉雅地区活跃的地球科学项目。该项目还将支持对研究生和本科生的指导和教育，并将在美国国家科学基金会国际科学和工程办公室的帮助下，启动一项广泛的科学国际合作。喜马拉雅山脉为研究活动碰撞系统中地壳岩石的演化提供了一个难得的机会。沿着碰撞前缘，束缚这些中地壳岩石的主要构造，即下方的主要中央逆冲和上方的藏南拆离，被像Leo Pargil这样的年轻变质穹隆错开或重新激活，这是本研究的重点。这些穹隆为研究部分熔融的产生、部分熔融与折返之间的潜在反馈、剪切带成核的影响以及穹隆形成过程中地壳的流变性提供了重要的机会。Leo Pargil穹隆的高品位岩石是在伸展和穹隆形成过程中沿着造山带平行的逆冲断裂和低角度拆离断裂活动的会聚背景下折返出来的，直到中新世中期才开始活动。该项目将与美国和国际学术组织合作，采用基于现场和实验室的跨学科调查，通过1)地质填图和详细的微结构分析，2)同位素年代学(U/Pb，Ar/Ar，[U+Th]/He)，以及3)确定变质P-T-t轨迹来探索这些岩石的演化。将Leo Pargil的结果与喜马拉雅前缘其他穹隆的结果进行对比，建立中中新世以来青藏高原南缘造山带平行中地壳运动的时间和运动学的高分辨率模式。

Some of Earths largest and most intriguing geologic and geographic features, including the Alpine/Himalayan mountain chain, are the result of continental collision. Because continental collision systems are responsible for profound geologic change throughout a large portion of Earth?s history, understanding their complex dynamics is of fundamental importance to Earth Science. Geologic studies based on the rocks and structures preserved in eroded cores of collisional systems provide critical insights into the fundamental processes of mountain building including metamorphism, melting, deformation, and exhumation. Results of this work will help refine our knowledge, not only of individual processes, but also the extent to which they interact to both construct and destruct large mountain chains. Data from this project will form the basis for the development of curricular materials that will be distributed to middle school teachers and a website devoted to highlighting active geoscience projects in the Himalayas. This project will also support mentoring and education of graduate and undergraduate students, and with the help of the NSF Office of International Science and Engineering will initiate a wide-ranging international collaboration on the science. The Himalaya provide an exceptional opportunity to investigate the evolution of mid-crustal rocks in an active collisional system. Along the collisional front, the major structures that bound these mid-crustal rocks, the Main Central thrust below and South Tibetan detachment above, are offset or reactivated by young metamorphic domes like the Leo Pargil, the focus of this study. Such domes provide an important opportunity to study the generation of partial melt, the potential feedback between partial melt and exhumation, the affects of shear zone nucleation, and the rheology of the crust during dome formation. The high-grade rocks of the Leo Pargil dome have been exhumed during extension and dome formation within an active convergent setting along orogen-parallel thrust faults and low angle detachment faults that were active until the middle Miocene. In collaboration with US and international academic organizations this project will employ a field-and lab-based interdisciplinary investigation to explore the evolution of these rocks using 1) geologic mapping and detailed microstructural analysis, 2) isotope geochronology (U/Pb, Ar/Ar, [U+Th]/He), and 3) determination of metamorphic P-T-t paths. Results from Leo Pargil will be contrasted with that from other domes along the Himalayan front to generate a high-resolution model for the timing and kinematics of orogen-parallel mid-crustal flow and exhumation along the southern margin of the Tibetan plateau since the middle Miocene.