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

在了解古活山带的演化过程中，最具挑战性的问题之一是背景中的正断层，这些正断层的其他特征是与缩短有关的结构。在安第斯山脉、阿尔卑斯山脉和喜马拉雅山脉的观测表明，地壳上层的伸展和正断层作用可以与地壳下层或低地形地区的缩短和逆冲作用同时发生。在喜马拉雅造山带的内部扇区，高海拔地区活动的南北向伸展断裂系统得到了充分的记录。这些紧密间隔的断层是最年轻的构造特征，切断了所有原有的挤压构造。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然不清楚。例如，在西北喜马拉雅地区，尚不清楚这些断层系统是局部现象，是否与正在进行的利奥帕吉尔变质圆顶的发掘有关，还是它们是具有区域重要性的构造框架的组成部分。近期地震的伸展断层面解、构造和地貌观测表明，在印度西北部喜马偕尔邦的萨特莱吉山谷存在活跃的正断层，在那里，单个断层向南延伸至喜马拉雅前沿，向北延伸至青藏高原南部。在该地区的南部，造山带中存在一个椭球形扇区，在那里，高挖掘率与集中的高季风降水和明显的局部起伏有关。该地区的热年代学数据表明，无论以前生成的构造边界如何，挖掘都是快速的，因此强调了侵蚀控制挖掘的重要性。与更北的高喜马拉雅地区相比，这一造山带的地震活动特征表明南北向缩短。这三种现象的空间相关性表明气候控制的挖掘直到现在。对来自当地网络的现有地震活动数据和从我们自己的网络获得的数据进行严格分析，将有助于更好地理解这些造山带演化差异的原因。第四纪沉积的古地震分析将进一步揭示高喜马拉雅地区正断层的时间发育。

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.