Collaborative Research: Initiation and Long-Term Slip History of the Altyn Tagh Fault System, Northern Tibetan Plateau, NW China: A Tertiary Basin Piercing Point Study

阿尔金断裂系位于青藏高原北方边缘，是印度与欧亚大陆碰撞形成的最大、最引人注目、也是最神秘的特征之一。尽管人们对阿尔金断裂的构造地质和滑动历史普遍缺乏了解，但其构造意义一直是许多推测的主题，该断裂在喜马拉雅-青藏造山带模型中占有突出地位。最近试图获得更好的了解阿尔金断层主要是使用间接的方法来解释断层的起始年龄和位移的大小，或大地测量技术来解释滑动速率。使用地质穿刺点直接调查断层位移还没有被广泛尝试。因此，关于阿尔金断裂的断距历史，仍存在三个关键问题：（1）阿尔金断裂的形成时代是什么？(2)阿尔金断层的滑动速率在地质时期是如何变化的？(3)沿阿尔金断裂带的长度方向，滑动量沿着如何变化？为了回答这三个问题，有必要确定每个断层段上的预滑动和多个同滑动穿刺点。这些穿透点将允许确定断层每个段（西部、中部和东部）的断层偏移历史，从而证明滑动幅度、滑动速率以及这些参数沿断层长度的沿着变化。拟议的研究将直接解决阿尔金断层的第三纪滑动历史和断层上的滑动分布，通过确定多个始新世-上新世沉积物源匹配横跨断层的10个第三纪盆地，被截断的阿尔金断层。通过从单个盆地中识别出不同时代的多个刺穿点，可以重建整个第三纪断层段的滑动历史。此外，通过检查一系列盆地沿着长度的断层，沿走向的位移变化可以记录。这些结果将提供一个强大的和明确的数据集，从该数据集可以直接确定断层的时间和速率，这也将允许有关滑移幅度沿着断层的系统变化的想法进行测试。PI先前对阿尔金断层的研究（Ritts，1998年; Yue和Liou，1999年; Ritts和Biffi，2000年; Sobel等人，2001; Yue等人，在回顾中）已经证明他们有能力识别和记录阿尔金断层上各种年龄和各种类型的穿刺点。拟议的研究包括岩石地层学和年代地层学，物理沉积学和岩相，物源和古水流的十个第三纪沉积盆地被截断的阿尔金断层的文件。两个主要的野外季节将集中在沉积盆地的特征以及断层对面的潜在沉积物源岩上。在第三纪盆地的野外工作将包括测量剖面的描述、古水流和砾岩成分数据的收集以及地质绘图。在潜在沉积物源区的野外工作将侧重于岩性描述和中国制图的验证，以及收集潜在的源单元进行分析工作。分析技术将应用于砾岩碎屑和潜在的来源单位，以测试根据实地数据提出的沉积物-来源相关性。这些技术将包括岩相学检查、微量和主要元素地球化学、U-Pb和40 Ar/ 39 Ar年代学。泥岩的生物地层学分析将用于确认第三纪单元的年龄。这项研究将约束第三纪盆地的地质，以建立一系列的时间-位移曲线，以表征历史和沿走向的变化阿尔金断裂。由此产生的数据将更好地定义的作用，阿尔金断层在容纳新生代印度和亚洲之间的会聚，从而区分机制，如挤压构造在大陆变形的相对重要性。

The Altyn Tagh fault system, which delineates the northern edge of the Tibetan Plateau, is one of the largest and most striking, yet also most enigmatic features attributed to collision between India and Eurasia. In spite of a generally poor understanding of the structural geology and slip history of the Altyn Tagh fault, its tectonic significance has been the subject of much speculation, and the fault figures prominently in models of the Himalayan-Tibetan orogen. Recent attempts to gain better knowledge about the Altyn Tagh fault have primarily used indirect methods to interpret age of fault initiation and magnitude of displacement, or geodetic techniques to interpret slip rate. Direct investigation of fault displacement using geologic piercing points has not been widely attempted. As a result three critical questions remain concerning the offset history of the Altyn Tagh fault: (1) What is the age of initiation of the Altyn Tagh fault? (2) How has the slip-rate on the Altyn Tagh fault varied over geologic time? (3) How does the magnitude of slip vary along the length of the Altyn Tagh fault? In order to answer these three questions it is essential to identify pre-slip and multiple syn-slip piercing points on each segment of the fault. These piercing points will allow the history of offset on the fault to be determined for each segment of the fault (western, central, and eastern) and thus demonstrate slip magnitude, slip rate, and variation in these parameters along the length of the fault. The proposed study will directly address the Tertiary slip history of the Altyn Tagh fault and the distribution of slip on the fault, by identifying multiple Eocene-Upper Pliocene sediment-source matches across the fault for ten Tertiary basins that are truncated by the Altyn Tagh fault. By identifying multiple piercing points of various ages from a single basin, the slip history for that segment of the fault ca be reconstructed throughout the Tertiary. Furthermore, by examining a series of basins along the length of the fault, along-strike changes in displacement can be documented. These results will provide a robust and unambiguous data set from which the timing and rate of faulting can be directly determined, and that will also allow ideas about systematic changes in slip magnitude along the fault to be tested. The PI's prior work on the Altyn Tagh fault (Ritts, 1998; Yue and Liou, 1999; Ritts and Biffi, 2000; Sobel et al., 2001; Yue et al., in review) has demonstrated their ability to identify and document piercing points of a variety of ages and a variety of types on the Altyn Tagh fault. The proposed research includes documentation of lithostratigraphy and chronostratigraphy, physical sedimentology and lithofacies, provenance, and paleocurrents of ten Tertiary sedimentary basins that are truncated by the Altyn Tagh fault. Two major field seasons will focus on the characterization of sedimentary basins as well as potential sediment source terranes on the opposite side of the fault. Fieldwork in the Tertiary basins will include description of measured sections, collection of paleocurrent and conglomerate composition data, and geological mapping. Fieldwork in potential sediment source areas will focus on lithologic description and verification of Chinese mapping, as well as collection of potential source units for analytical work. Analytical techniques will be applied to conglomerate clasts and potential source units in order to test sediment-source correlations that are proposed based on field data. These techniques will include petrographic examination, trace and major element geochemistry, and U-Pb and 40 Ar/ 39 Ar geochronology. Biostratigraphic analysis of mudstones will be used to confirm the ages of the Tertiary units. This study will constrain the geology of Tertiary basins in order to construct a series of time- displacement curves to characterize the history and along-strike variability of the Altyn Tagh fault. The resulting data will better define the role that the Altyn Tagh fault plays in accommodating Cenozoic convergence between India and Asia, and thereby distinguish the relative importance of mechanisms such as extrusion tectonics in continental deformation.