Erosion and Exhumation History of the Nepalese Frontal Himalaya Since Earliest Miocene Time: Constraints on Kinematic History

尼泊尔前缘喜马拉雅山自最早中新世以来的侵蚀和剥露历史：对运动学历史的限制

• 批准号: 1140068
• 负责人: Peter DeCelles
• 金额: $ 51.31万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-04-01 至 2016-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1140068&HistoricalAwards=false
• 关键词: Erosion; Exhumation; History; Nepalese; Frontal

The Himalayan Mountains in Nepal were formed over the last 55 million years by forces associated with the collision of the Indian and Asian continents. Since the onset of the collision, layered rocks draping the upper crust of India have been crumpled and shortened by at least 650 kilometers as the Asian landmass has overridden northern India. This process has produced the highest mountains on Earth. These mountains are important in many respects: they control the climate system of southern Asia, including the all-important Asian monsoon which provides rain in a region that would otherwise be much drier; they store water in the form of glaciers and snow, thus mitigating the effects of drought and providing hydroelectric power to much of southern Asia; they generate the sediments that form the agricultural breadbasket of the region, feeding approximately one quarter of the world?s population; and they embody a dramatic high mountain landscape upon which humans have been inspired to feats of adventure, exploration, and religious devotion. As the mountains have grown, continuous erosion has generated vast quantities of sediment that accumulates along the southern flank of the Himalaya in the Indo-Gangetic foreland basin and in deep sea fans that flank India on the floors of the Arabian Sea and the Bay of Bengal. This sediment provides a record of the history of growth of the Himalaya. Our project aims to reconstruct the history of deformation of the Himalaya in Nepal. The analysis is forensic, as we attempt to retrodeform the rocks that have been folded and thrust faulted in the Himalaya, according to constraints imposed by thermochronology, structural geology, geochronology, and the erosional sedimentary record. Thermochronology measures the time at which a mineral passes through its "blocking temperature" with respect to a particular radiogenic isotopic system en route to the topographic surface as the mountains are growing and erosion is exhuming the rocks. Thermochronological ages can be inverted to assess erosion rates and in some cases the timing of slip on major faults. We will also use Uranium-Lead geochronology to determine the ages of mineral grains in both the eroded sediments and the bedrock source areas of the mountain range. Together these data will allow use to (a) determine the timing of major thrust faulting events within the southern half of the Himalaya; (b) calculate the rate of exhumation of the mountains; and (c) determine precisely the specific sources of the sediments and when they were deposited. Our fieldwork will involve sample collection, and detailed documentation of sections of the sedimentary erosional products where they are uplifted and exposed in the frontal Himalaya. This work promises to elucidate the tectonic and erosional history of the Himalaya at an unprecedented level of detail, and has far-reaching implications for our understanding of changing seawater chemistry, the origin and timing of the South Asian monsoon, and the dynamic interplay between tectonics and climate in orographic systems. Within the context of ongoing research on Himalayan tectonics by numerous international groups, this work fills a gap in understanding of the critical last ~20 million years of deformation of the Himalaya, a timespan during which it is postulated that more than one half of the total Himalayan shortening took place, and during which many of the iconic features of the system developed, including the Main Central thrust, the South Tibetan detachment, the Greater Himalayan leucogranites, and the Lesser Himalayan duplex. Densely populated Nepal and northern India remain seismically active, with potential for a M8 earthquake in a major seismic gap in the western part of Nepal. Because estimates of earthquake probability are in part based on understanding of the long-term history of shortening in the frontal Himalaya, a small change in the long-term shortening rate would have significant implications for predictions of co-seismic fault slip.

在过去的5500万年中，尼泊尔的喜马拉雅山是与印度和亚洲大陆碰撞有关的力量。自碰撞发作以来，随着亚洲陆地已经覆盖了印度北部，印度上皮的分层岩石被皱眉并缩短了至少650公里。这个过程产生了地球上最高的山脉。这些山脉在许多方面都很重要：它们控制着南亚的气候系统，包括最重要的亚洲季风，该季风在否则会更干燥的地区提供降雨；他们以冰川和雪的形式存储水，从而减轻干旱的影响，并为南亚大部分地区提供水力发电。它们产生了构成该地区农业面包篮的沉积物，为世界大约四分之一的人口供养。他们体现了戏剧性的高山景观，在该景观上，人类受到了冒险，探索和宗教奉献的壮举的启发。随着山的发展，持续的侵蚀产生了大量的沉积物，这些沉积物沿着喜马拉雅山南部的印度 - 远程前陆盆地的南部侧面积累，在阿拉伯海和孟加拉湾地板上的印度侧面印度的深海风扇中。这种沉积物提供了喜马拉雅发展史的记录。我们的项目旨在重建尼泊尔喜马拉雅山变形的历史。该分析是法医的，因为我们试图根据热量，结构地质学，地球人工学和侵蚀沉积记录所施加的约束，试图将喜马拉雅岩在喜马拉雅折叠和推力断层的岩石翻新。热量照相学测量矿物通过特定的放射原源同位素系统在通往地形表面的特定放射线同位素系统方面通过其“阻塞温度”的时间，随着山脉的增长，侵蚀正在挖掘岩石。热量年龄可以倒置以评估侵蚀率，在某些情况下，主要断层的滑移时间。我们还将使用铀潜在的年代学来确定被侵蚀的沉积物和山脉的基岩源区域中的矿物颗粒年龄。这些数据将允许（a）确定喜马拉雅山南半部的重大推力断层事件的时机； （b）计算山区挖掘的速度； （c）精确确定沉积物的特定来源以及沉积时。我们的现场工作将涉及样本收集，以及在额叶喜马拉雅山升起和暴露的沉积侵蚀产品部分的详细文档。这项工作有望在前所未有的细节水平上阐明喜马拉雅山的构造和侵蚀历史，并对我们对不断变化的海水化学，南亚季风的起源以及构造和气候之间的动态竞争的理解具有深远的影响。 Within the context of ongoing research on Himalayan tectonics by numerous international groups, this work fills a gap in understanding of the critical last ~20 million years of deformation of the Himalaya, a timespan during which it is postulated that more than one half of the total Himalayan shortening took place, and during which many of the iconic features of the system developed, including the Main Central thrust, the South Tibetan detachment, the Greater Himalayan Leucogranites和较小的喜马拉雅复式公y。人口稠密的尼泊尔和北部印度仍然具有地震活跃，在尼泊尔西部的主要地震差距中可能发生M8地震。由于对地震概率的估计部分是基于对额叶喜马拉雅山缩短的长期缩短历史的理解，因此长期缩短率的微小变化将对共同性断层滑移的预测产生重大影响。