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

尽管最近对大陆岩石圈对碰撞造山作用的力学和热响应的理解取得了进展，但仍然存在重要的争议。其中一个集中在大型走滑断层在大陆内变形中的作用，以及这些构造是否1)控制准刚性块体的侧向“逃离”以响应大陆收敛（例如，Tapponnier et al., 1982），或者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和Molnar， 1990）。对于沿走滑断层的位移变化，断层位移与周围地壳块体变形的关系，以及断层末端的滑动调节性质，这些模型做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这些预测的严格地质测试数量有限。昆仑断裂是青藏高原中东部的一级构造特征，它为检验走滑断裂在藏东活动变形中的作用提供了一个关键的机会。尽管全新世沿断层中部的滑动速率似乎是均匀的~11mm/年（Van der Woerd et al., 2000），但几项观测表明，沿昆仑断层东部的显著左侧剪切并未到达青藏高原边缘：1)在~102 E以东无法识别断层的遥感活动痕迹（如Tapponnier和Molnar， 1977）；2)野外观测（Kirby）证实，该区东部不存在与昆仑断裂相关的陡崖；3)大地测量表明，目前很少有可解析的左旋剪切穿过高原东缘（Chen et al., 2000）。如果我们要了解昆仑断层在西藏东部变形中的运动学和动力学作用，以及更广泛地了解走滑断层在大陆内变形中的作用，那么确定昆仑断层最东端的左侧向剪切发生了什么是至关重要的。PI建议测试关于在大陆内走滑断层的明显终止处转移和/或调节位移的机制的几个假设：假设1：位移被转移到运动连接的走滑断层：a。传送跨越高原边缘的位移，球体。将位移传递给高原边缘的缩短构造。假设2：位移被高原内的分布缩短所吸收，导致地壳增厚。假设3：位移表示断层响应于扩散的顺时针区域剪切的被动旋转。验证这些假设将集中在以下任务上：确定昆仑断层最东段晚更新世-全新世的滑动速率，并特别关注走向的潜在变化。建立候选容纳结构（高原内及其边缘）的几何、运动学和位移率。评估阿尼玛秦山（高原内缩短的主要候选）的差异岩石隆升和河流切割的大小和分布。这项研究有望为大陆内大型走滑断层末端的应变调节性质提供详细的年代学视角。PI将记录在这种结构的末端附近存在或不存在位移梯度。该研究将定义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构造的一些机制。最后，它将确定断层位移与边界块体变形的联系程度。综合结果将对大陆变形期间的挤压与旋转问题产生重要的新见解。

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.