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

青藏高原内的新生代伸展作用表现为一系列明显的N-S向裂谷。最近的全球定位系统研究表明，这些地块系统及其伴生的共轭走滑系统容纳了青藏高原内部N-S缩短和东西向扩张的很大一部分。这些构造的发育代表了变形样式的重大转变，标志着西藏地壳内向收缩应变场的过渡。确定这些构造的形成时间是了解高原演化的关键一步。为了检验已有的解释这些N-S向裂谷的假说，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是什么？(2)西藏中部共轭走滑变形与东西向伸展在时间和运动上的相互作用是什么？对于板内应变场的演化和裂谷形成的驱动力来说，区域同步和历时开始的裂谷作用或渐进的迁移和离散的断层起始事件具有非常不同的含义。目前，西藏新生代演化的不同地球动力学模型由于缺乏对裂谷开始的足够的时间约束而难以评价。中国地质调查局建议采用构造填图、磷灰石(U-Th)/He和裂变径迹测年相结合的综合方法，阐明与青藏高原中部新生代应变模式有关的断裂作用的时间和强度。直接测定出土断块中岩石冷却的热年代学方法将补充基于现场的裂谷系统运动学分析，并应有助于解决有关西藏裂谷的时间和地球动力学意义的突出问题。这项拟议的研究将对我们理解大陆-大陆碰撞过程中岩石圈的行为具有深远的影响。新的数据将提供对西藏在增厚后如何以及何时延伸的根本问题的见解，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，这些结果将有助于揭示青藏高原东西向伸展与地表隆起之间是否存在时间联系这一激烈争论的问题。考虑到青藏高原隆升对地区和全球气候的影响，PI预计他的结果将引起广泛范围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。拟议中的与中国科学院科学家的国际合作将允许科学思想和知识的交流。这次交流将使KU的学生受益匪浅，让他们接触到经典的喜马拉雅-藏族造山系统。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.