Evolution of normal faults within the Higher Himalaya - local phenomenon or regional trend?

了解古活动山带演化的最具挑战性的问题之一是背景中的正断层，否则就是与缩短有关的构造。在安第斯山脉、阿尔卑斯山以及喜马拉雅山脉的观察表明，地壳上部的伸展和正断层活动可与下层地壳或低地形地区的缩短和逆冲同时发生。在喜马拉雅造山带内部，记录了活动的北S向高海拔伸展断裂系统。这些紧密相间的断层是最年轻的构造特征，切割了所有先前存在的挤压构造。然而，它们的时空传播以及它们形成的原因在很大程度上仍不清楚。例如，在喜马拉雅西北地区，尚不清楚这些断层系统是局部现象，是否与Leo Pargil变质穹隆正在进行的挖掘有关，或者它们是否是具有区域重要性的构造框架的组成部分。近期地震、构造和地貌观测的伸展断层面解表明，苏特勒河谷(印度西北部喜马恰尔邦)存在活动的正断层，其中个别断层向南延伸至喜马拉雅前缘，向北延伸至青藏高原南部。在这一区域的南面，造山带中有一个椭圆形区域，那里的高折返速率与集中的高季风降水和明显的局部起伏相关。这一地区的热年代学数据表明，无论以前形成的构造边界如何，都能快速折返，因此强调了侵蚀控制折返的重要性。与更靠北的高喜马拉雅地区相比，该造山带具有地震活动的特征，表明N-S缩短。这三种现象的空间相关性表明，到目前为止，遗骸是受气候控制的。对来自本地台网的现有地震活动数据和将从我们自己的台网获得的数据进行严格的分析，将有助于更好地理解造山演化中这些差异的原因。对第四纪沉积物的额外古地震分析将进一步揭示喜马拉雅高海拔地区正断层的时间发展。

One of the most challenging problems in understanding the evolution of ancient and active mountain belts are normal faults in the setting which is otherwise characterized by structures related to shortening. Observations in the Andes, the Alps, as well as in the Himalaya shows that extension and normal faulting at upper crustal levels can occur contemporaneously with shortening and thrusting at lower crustal levels or in areas of low topography. In the internal sectors of the Himalayan orogen, active N-S striking extensional fault systems at high elevations are well documented. These closely spaced faults are the youngest structural features and cut all pre-existing compressional structures. However, their spatiotemporal propagation, as well as the reason for their formation remains largely unclear. For example, in the NW Himalaya, it is not known whether these fault systems are local phenomena and are related to ongoing exhumation of the Leo Pargil metamorphic dome or if they are an integral part of a structural framework of regional importance. Extensional fault plane solutions of recent earthquakes, structural, and geomorphic observations indicate active normal faulting in the Sutlej Valley (Himachal Pradesh, NW India), where individual faults extend southward toward the Himalayan front and northward into the southern Tibetan plateau. To the south of this region exists an ellipsoidal sector in the orogen, where high exhumation rates correlate with focused, high monsoonal precipitation, and pronounced local relief. Thermochronological data from this area indicate rapid exhumation irrespective of formerly generated structural boundaries, thus emphasizing the importance of erosion-controlled exhumation. In contrast to the region farther north in the Higher Himalaya, this sector of the orogen is characterized by seismicity indicating N-S shortening. The spatial correlation of these three phenomena suggests climatically controlled exhumation until present. A rigorous analysis of existing seismicity data from local networks and data to be obtained from our own network will help better understand the cause of these disparities in orogenic evolution. Additional paleoseismic analysis of Quaternary deposits will further help reveal the temporal development of normal faulting in the Higher Himalaya.