Climatic and Tectonic Insights from Low-Temperature Thermochronometry Across the Himalayan Rain Shadow, Everest Region, Nepal and Tibet

喜马拉雅雨影区、珠穆朗玛峰地区、尼泊尔和西藏的低温测时法对气候和构造的见解

• 批准号: 1346360
• 负责人: Kip Hodges
• 金额: $ 24.58万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-04-01 至 2019-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1346360&HistoricalAwards=false
• 关键词: Climatic; Tectonic; Insights; Low; Temperature

The physiographic transition from the Gangetic Plains to the Tibetan Plateau corresponds in space to one of our planet's most profound climate transitions. Several popular geodynamic models for the late Cenozoic evolution of the Himalaya feature a strong feedback relationship between precipitation, erosional rock exhumation, and deformation. If valid, these models predict that the extreme precipitation gradient across the Himalaya should be accompanied by variations in denudation rate and deformational patterns. Previous studies along the southern Himalayan flank conducted to verify these predictions have had mixed results, partly because they were done along the valleys of major rivers that cut across the Himalaya. These 'Transhimalayan' river valleys serve as pathways for northern penetration of monsoon storms, such that erosion rates on either side of the range crest may not truly reflect potential effects of the rain shadow. In addition, extreme incision of the Transhimalayan rivers during uplift of the Himalaya may focus exhumation and obscure broader patterns related to climate and regional tectonics. We endeavor to learn more about exhumation patterns across the rain shadow by applying the (Uranium-Thorium)/Helium thermochronometer to rocks collected along a transect that does not follow a Transhimalayan river. Nearly three decades of research in in the Everest region of central Nepal and southern Tibet by several researcher groups has resulted in an unusually good understanding of the basic structural geology of the region, permitting interpretation of the data obtained in appropriate structural context. Our goal is a comprehensive dataset suitable for thermal-kinematic modeling aimed at providing an improved understanding of the coupled influence of precipitation and dynamics of Himalayan orogenic wedge. We are also taking advantage of a portion of the data produced to explore the timing and slip history of the Lhotse and Qomolangma detachments in the Rongbuk Valley north of Mount Everest. These are two of the best studied of all strands of the South Tibetan detachment system, a major tectonic feature in the Himalaya. While the South Tibetan detachment system is known to have been active throughout the Himalaya in Early to Middle Miocene time, the actual age of youngest movement is poorly constrained in most areas, including the Rongbuk Valley. We are providing new constraints on the low-temperature thermal structure of the footwalls of the two detachments here through (Uranium-Thorium)/Helium and fission track work on accessory minerals. Exposures of the detachments in the Rongbuk Valley are unusual: shallow fault dip angles and high relief conspire to provide sampling opportunities over as distance of greater than 35 kilometers in the direction of transport in the immediate footwall of the South Tibetan detachment system. While much research focuses on the global impacts of climate variations in space and time, some of the greatest frontiers for research are at smaller, regional scales. On those scales, we are addressing questions about how climate variations relate to other natural earth system processes. Of particular interest for this study is how mountain ranges affect local climate and, conversely, how local climate can influence the erosional history of a mountain range. The high mountain ranges of the Himalaya retard the northward track of the South Asian monsoon system, creating two very different landscapes: the heavily forested slopes of the southern Himalayan flank, which receive some of the highest recorded annual rainfall totals on earth, and the high deserts of the southern Tibetan Plateau. Our work is aimed at understanding how far back in time this climatic pattern may have extended and how it might cause variations in erosion rate north and south of the Himalayan crest. The lessons learned here will inform perceptions of the role of regional climate variation in the erosional process both in the United States and abroad. The project is supporting a talented female Ph.D. candidate, thereby contributing to on-going efforts to reduce the gender disparity between male and female doctoral level scientists, a problem that is particularly acute in the physical sciences. In addition, special multimedia displays are being created for public museum exhibitions exploring the science of climate variations in mountainous landscapes.

从恒河平原到青藏高原的地貌转变在空间上与地球上最深刻的气候转变之一相对应。喜马拉雅山新生代晚期演化的几种流行的地球动力学模型都具有降水、侵蚀岩折返和变形之间强烈的反馈关系。如果有效，这些模型预测喜马拉雅山的极端降水梯度应该伴随着剥蚀率和变形模式的变化。此前为验证这些预测而在喜马拉雅山南翼进行的研究结果好坏参半，部分原因是这些研究是沿着横贯喜马拉雅山的主要河流的山谷进行的。这些“Transhimalayan”河谷是季风风暴向北渗透的通道，因此山脉顶部两侧的侵蚀率可能无法真正反映雨影的潜在影响。此外，喜马拉雅山隆起期间跨喜马拉雅河的极端切割可能会集中折返并掩盖与气候和区域构造相关的更广泛模式。 我们通过将（铀-钍）/氦测温仪应用于沿着不沿跨喜马拉雅河的横断面收集的岩石，努力了解更多关于雨影区的折返模式。多个研究小组在尼泊尔中部和西藏南部的珠穆朗玛峰地区进行了近三十年的研究，对该地区的基本构造地质学有了异常良好的了解，从而可以在适当的构造背景下解释所获得的数据。我们的目标是建立一个适合热运动学建模的综合数据集，旨在更好地理解降水和喜马拉雅造山楔动态的耦合影响。我们还利用所产生的部分数据来探索珠穆朗玛峰以北绒布谷的洛子峰和珠穆朗玛峰支队的时间和滑动历史。这是藏南滑脱系统所有分支中研究最深入的两个，而藏南滑脱系统是喜马拉雅山的一个主要构造特征。虽然众所周知，藏南支队系统在早中新世时期在整个喜马拉雅山地区都很活跃，但在包括绒布谷在内的大多数地区，最年轻的活动的实际年龄并没有得到很好的限制。我们通过（铀-钍）/氦和辅助矿物的裂变径迹工作，对两个支队下盘的低温热结构提供新的约束。绒布河谷分离层的暴露是不寻常的：浅断层倾角和高浮雕共同为藏南分离层系统直接下盘的运输方向超过 35 公里的距离提供了采样机会。虽然许多研究都集中在气候变化在空间和时间上对全球的影响，但一些最大的研究前沿是在较小的区域尺度上。在这些尺度上，我们正在解决有关气候变化如何与其他自然地球系统过程相关的问题。这项研究特别感兴趣的是山脉如何影响当地气候，以及反过来，当地气候如何影响山脉的侵蚀历史。喜马拉雅山脉的高山阻碍了南亚季风系统的向北移动，形成了两种截然不同的地貌：喜马拉雅山南翼森林茂密的山坡，这里的年降雨量是地球上有记录以来最高的，而喜马拉雅山的高山则阻挡了南亚季风系统的北移，形成了两种截然不同的景观：青藏高原南部的沙漠。 我们的工作旨在了解这种气候模式可能延续多久，以及它如何导致喜马拉雅山脊北部和南部侵蚀率的变化。这里吸取的经验教训将有助于人们了解区域气候变化在美国和国外侵蚀过程中的作用。该项目正在支持一位才华横溢的女性博士。候选人，从而为减少男女博士级科学家之间的性别差距做出贡献，这一问题在物理科学中尤为严重。 此外，正在为公共博物馆展览创建特殊的多媒体显示器，探索山区景观气候变化的科学。