Timing and Kinematics of Cenozoic of E-W Extension in Central Tibet Transition in the Strain Field of the Tibetan Plateau

青藏高原内的Stockli新生代伸展作用表现为一系列近南北向裂谷。最近的GPS研究表明，这些地堑系统和相关的共轭走滑系统容纳了很大一部分的内部N-S缩短和E-W扩展的青藏高原。这些构造的发展代表了变形方式的重大转变，标志着西藏地壳向收缩应变场的转变。确定这些结构形成的时间是理解高原演变的关键一步。为了检验解释这些南北向裂谷的现有假设，并理解西藏新生代东西向伸展的地球动力学意义，PI需要回答两个基本问题。(1)西藏东西向伸展的起始时间和空间分布如何？(2)西藏中部共轭走滑变形和东西向伸展之间的时间和运动学相互作用是什么？一个区域同步与穿时开始的裂谷或渐进迁移与离散事件的故障启动有非常不同的影响板内应变场的演变和裂谷形成的驱动力。目前，由于缺乏足够的裂谷开始时间限制，西藏新生代演化的不同地球动力学模型很难评估。PI建议使用一种综合方法，将结构测绘与磷灰石（U-Th）/He和裂变径迹测年相结合，以阐明与西藏中部新生代应变模式相关的断层的时间和幅度。 热年代学的方法直接定年的岩石冷却的折返断块将补充现场为基础的裂谷系统的运动学分析，并应有助于解决悬而未决的问题，西藏裂谷的时间和地球动力学意义。这项研究将对我们理解大陆-大陆碰撞过程中岩石圈的行为产生深远的影响。新的数据将有助于深入了解西藏如何以及何时在增厚后延伸的基本问题，这些信息对于评估整个地区的许多不同构造模型至关重要。此外，研究结果将有助于阐明青藏高原东西向伸展与地表隆升之间是否存在时间联系这一热点问题。鉴于青藏高原的隆起对区域和全球气候的影响，PI预计他的结果将引起广泛的地球科学家的兴趣。该项目还具有重大的教育和社会价值。拟议的与中国科学院科学家的国际合作将有助于交流科学思想和知识。这次交流将使KU学生受益匪浅，使他们了解经典的喜马拉雅-西藏造山系统。两名KU研究生将深入参与几次测绘探险，并将与加州大学洛杉矶分校和中国科学院的科学家密切合作。

0309976StockliCenozoic extension within the Tibetan Plateau is expressed as a series of prominentN-S trending rift valleys. Recent GPS studies show that these graben systems and associated conjugate strike-slip systems accommodate a significant portion of internal N-S shortening and E-W expansion of the Tibetan Plateau. The development of these structures represents a significant shift in deformational style and marks the transition to a constrictional strain field within the Tibetan crust. Determining the timing of the formation of these structures is a critical step in understanding the evolution of the plateau. In order to test existing hypotheses proposed to explain these N-S trending rifts and to understand the geodynamic significance of Cenozoic E-W extension in Tibet, the PI needs to answer two fundamental questions. (1) What is the timing of initiation and spatial distribution of E-W extension in Tibet? (2) What is the temporal and kinematic interplay between conjugate strike-slip deformation and E-W extension within central Tibet? A regionally synchronous versus diachronous onset of rifting or progressive migration versus discrete episodes of fault initiation have very different implications for the evolution of the intraplate strain field and the driving forces responsible for rift formation. Currently, the different geodynamic models for the Cenozoic evolution of Tibet are difficult to evaluate due to the lack of sufficient temporal constraints on the onset of rifting. The PI proposes to use an integrated approach, combining structural mapping with apatite (U-Th)/He and fission track dating, to elucidate the timing and magnitude of faulting associated with the Cenozoic strain pattern across central Tibet. Thermochronological methods directly dating the cooling of rocks in exhumed fault blocks will complement field-based kinematic analysis of the rift systems and should help resolve outstanding questions regarding the timing and geodynamic significance of the Tibetan rifts. This proposed study will have far-reaching implications for our understanding of how the lithosphere behaves during continent-continent collision. New data will yield insights into the fundamental problem of how and when Tibet extended after thickening, information that is critical for evaluating the many different tectonic models for this entire region. Furthermore, results will shed light on the hotly debated question of whether there is a temporal link between E-W extension and surface uplift of the Tibetan plateau. Given the implications of the uplift of the Tibetan plateau for regional and global climate, the PI expects his results to be of interest to a wide spectrum of geoscientists. This project also has substantial educational and societal merit. The proposed international collaboration with scientists from the Chinese Academy of Science will permit an exchange of scientific ideas and knowledge. This exchange will greatly benefit KU students, exposing them to the classic Himalayan-Tibetan orogenic system. Two KU graduate students will be deeply involved in several mapping expeditions and will work closely with scientists from UCLA and the Chinese Academy of Science.