Collaborative Research: Extrusion and Rotation during Intracontinental Deformation: The Role of the Kunlun Fault in the Indo-Asia Collision

尽管最近在大陆岩石圈对碰撞造山作用的力学和热响应方面取得了进展，但仍存在重要的争议。其中之一集中在陆内变形过程中大型走滑断层的作用，以及这些构造是否1）控制准刚性块体响应大陆会聚的横向“逃逸”（例如，Tapponnier等人，1982），或2）反映了普遍变形和剪切地壳中应变的被动局部化（例如，England and and Molnar，1990）.这些模型对沿走滑断层沿着的位移变化、断层位移与周围地壳块体变形的关系以及断层末端滑动调节的性质作出了非常不同的预测。在西藏东部，关于活动变形性质的持续争论在很大程度上反映了对这些预测的严格地质检验的数量有限。昆仑断层是青藏高原中部和东部的一级构造特征，它为检验走滑断层在西藏东部活动变形中的作用提供了一个关键的机会。虽然全新世滑动速率似乎是均匀的，沿断层中心部分沿着约为11毫米/年（货车der Woerd等人，2000），几个观测结果表明，沿东昆仑断裂沿着的显著左旋剪切没有到达青藏高原的边缘：1）遥感上的断裂活动痕迹（例如，Tapponnier和Molnar，1977年）在~102 E以东无法区分; 2）野外观测（Kirby）证实，该地区以东不存在与昆仑断层相关的陡坎; 3）大地测量表明，目前，几乎没有可分辨的左旋剪切穿过高原东缘（Chen等人，2000年）。如果我们要了解昆仑断层最东端的左行剪切沿着发生了什么，这对我们理解它在西藏东部变形中的运动学和动力学作用，以及更一般地理解走滑断层在陆内变形中的作用是至关重要的。PI建议检验几个关于陆内走滑断层明显终止时位移转移和/或调节机制的假设：假设1：位移被转移到运动学链接，走滑断层：a。将位移传送到高原边缘以外的地方，球体。将位移传递给高原边缘的缩短构造。ce假设2：位移被高原内的分布缩短吸收，导致地壳增厚。ce假设3：位移代表断层对扩散的顺时针区域剪切的被动旋转。检验这些假设将集中于以下任务：确定了昆仑断裂带最东端沿着晚更新世-全新世的滑动速率，特别注意沿着走向的潜在变化。候选住宿建筑物的流离失所率阿尼玛卿山差异性岩石隆升和河流下切作用的大小和分布（高原内缩短的主要候选者）这项研究有望带来一个详细的年代学的角度来承担的性质ofaccommodation应变在终端的大型，陆内走滑断层。PI将记录此类结构端部附近是否存在位移梯度。这项研究将确定断层位移与区域变形模式的关系，并将确定位移转移到其他结构的一些机制。最后，它将确定断层位移与边界块体变形的联系程度。综合结果将产生关键的新的见解挤压与旋转在大陆变形的问题。

Despite recent advances in understanding of the mechanical and thermal response ofcontinental lithosphere to collisional orogenesis, important controversies remain. One of these centers on the role of large strike-slip faults during intracontinental deformation, and whether these structures 1) control the lateral 'escape' of quasi-rigid blocks in response to continental convergence (e.g., Tapponnier et al., 1982), or 2) reflect the passive localization of strain in a pervasively deforming and shearing crust (e.g., England and Molnar, 1990). The models make very different predictions regarding the variation of displacement along strike-slip faults, the relationship of fault displacement to deformation of the surrounding crustal blocks, and the nature of accommodation of slip at the terminations of the faults. In eastern Tibet, continuing debate over the nature of active deformation reflects, to a large degree, the limited number of rigorous geologic tests of these predictions.The Kunlun fault is a first-order structural feature in the central and eastern Tibetan Plateau, where it presents a key opportunity to test among competing hypotheses for the role of strike-slip faults in the active deformation of eastern Tibet. Although Holocene slip rates appear to be uniform at ~11mm/yr along the central portion of the fault (Van der Woerd et al., 2000), several observations suggest that significant left-lateral shear along the eastern Kunlun fault does not reach the margin of the Tibetan Plateau: 1) the active trace of the fault on remote sensing (e.g., Tapponnier and Molnar, 1977) cannot be distinguished east of ~102 E; 2) field observations (Kirby) confirm that scarps associated with the Kunlun fault are not present east of this region; and 3) geodetic surveys indicate that, at present, little resolvable left-lateral shear passes through the eastern margin of the plateau (Chen et al., 2000). Determining what happens to left-lateral shear along the easternmost portion of the Kunlun fault is critical if we are to understand its kinematic and dynamic role in deformation of eastern Tibet and more generally the role of strike-slip faults during intracontinental deformation.The PI's propose to test several hypotheses regarding the mechanisms of transfer and/oraccommodation of displacement at the apparent termination of an intracontinental strike-slip fault: ce Hypothesis 1: Displacement is transferred to kinematically linked, strike-slip faults that:a. transmit displacement across and beyond the plateau margin, orb. transmit displacement to shortening structures at the plateau margin.ce Hypothesis 2: Displacement is absorbed by distributed shortening within the plateau resulting in crustal thickening.ce Hypothesis 3: Displacement represents passive rotation of faults in response to a diffuse, clockwise regional shear.Testing these hypotheses will focus on the following tasks:ce Determining Late Pleistocene-Holocene slip rates along the easternmost segment of the Kunlun fault, with special attention to potential variations along strike.ce Establishing the geometry, kinematics, and rates of displacement on candidate accommodation structures (both within the plateau and at its margin).ce Assessing the magnitude and distribution of differential rock uplift and river incision in the Anyemaqen Shan (the prime candidate for shortening within the plateau)This study promises to bring a detailed chronologic perspective to bear on the nature ofaccommodation of strain at the terminations of large, intracontinental strike-slip faults. The PI's will document the presence or absence of displacement gradients present near the ends of such structures. The study will define the relationship of fault displacement to regional deformation patterns and will determine some of the mechanisms by which displacement is transferred to other structures. Finally, it will determine to what degree fault displacements are linked to deformation of the bounding blocks. The combined results will yield critical new insights into the problem of extrusion versus rotation during continental deformation.