Extensional Fault Systems in the Ama Drime Range, Southern Tibet

最近对喜马拉雅-西藏造山系统的研究主要集中在季风气候在其发展中的作用。在一个有争议的假设中，侵略性的季风降水目前吸引了一条从青藏高原下方向南流向喜马拉雅造山带前缘的中地壳通道。在这个项目中，亚利桑那州立大学的一个研究小组与中国科学院的科学家合作，正在验证这样的预测，即最近沿着青藏高原南缘在藏南阿玛德里梅山脉中新世藏南断裂系统的大致位置发生了一次活跃的滑脱。这一横向山脉具有变质核杂岩的总体形式，在东西方向上被直接接触到先前绘制的藏南断裂系统线条的正断层系统所包围。该团队正在绘制这些断层系统之间的关键交叉点，这些断层系统在喜马拉雅雨影内的这个高海拔地区暴露得非常壮观。利用构造地质、构造地貌、低温热年代学和宇宙成因核素测年等技术，建立了阿玛地块晚新生代的折返历史，并与藏南断裂带东西两侧的折返历史进行了对比。这些结果将被用来评估第四纪河道挤压的情况，或者证伪它，或者建立与挤压河道的上界结构有关的变形的结构和地貌后果。河道流的概念在构造学领域是一个新的和有争议的概念。这表明气候和构造之间存在着强烈的耦合。最初的渠道流挤压假说认为，早中新世向南的渠道挤压是通过两个北倾构造：中央主冲断和藏南断裂系统的滑移来调节的。这项研究探讨了季风引起的渠道流至今仍在继续的观点。这项工作的结果将是正在进行的关于喜马拉雅地区变形方式以及侵蚀和构造耦合程度的辩论的核心。

Recent research on the Himalayan-Tibetan orogenic system has focused on the role of monsoon climate in its development. In one controversial hypothesis, aggressive monsoon precipitation currently attracts the southward flow of a channel of middle crust from beneath the Tibetan Plateau to the Himalayan orogenic front. In this project, an Arizona State University research team, in collaboration with scientists from the Chinese Academy of Sciences, is testing the prediction that a recently active detachment occurs along the southern edge of the Tibetan Plateau at the approximate position of the Miocene South Tibetan fault system in the Ama Drime Range of southern Tibet. This transverse range has the overall form of a metamorphic core complex and is bound on the east and west by normal fault systems that strike directly into previously mapped strands of the South Tibetan fault system. The team is mapping critical intersections among these fault systems that are spectacularly exposed in this high-elevation region within the Himalayan rain shadow. They are also using the techniques of structural geology, tectonic geomorphology, low-temperature thermochronology, and cosmogenic nuclide dating to establish the late Cenozoic exhumation history of the Ama Drime massif and compare it with the exhumation history of the South Tibetan fault footwall east and west of the massif. These results will be used to evaluate the case for Quaternary channel extrusion and either falsify it or establish the structural and geomorphic consequences of deformation related to the upper bounding structure of the extruding channel.The concept of channel flow is a new and controversial idea in the field of tectonics. It suggests a strong coupling between climate and tectonics. The original version of the channel flow-extrusion hypothesis envisioned that Early-Middle Miocene southward extrusion of the channel was accommodated by slip on two north-dipping structures: the Main Central thrust and the South Tibetan fault systems. This study explores that idea that monsoon-induced channel flow continues today. The results of this work will be central to the ongoing debate over the style of deformation and the degree of erosion and tectonics coupling in the Himalaya.