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

从恒河平原到青藏高原的自然地理转变在空间上对应于我们星球上最深刻的气候转变之一。喜马拉雅晚新生代演化的几个流行的地球动力学模型的特点是降水，侵蚀岩石折返和变形之间的强烈反馈关系。如果有效的话，这些模型预测，喜马拉雅山的极端降水梯度应伴随着剥蚀率和变形模式的变化。以前在喜马拉雅山南翼沿着进行的验证这些预测的研究结果好坏参半，部分原因是这些研究是在穿越喜马拉雅山的主要河流的山谷沿着进行的。这些“Transhimalayan”河谷作为季风风暴北方渗透的通道，因此山脉波峰两侧的侵蚀率可能无法真正反映雨影的潜在影响。此外，极端切割的Transshimalayan河流在喜马拉雅山脉的隆升可能集中折返和模糊更广泛的模式与气候和区域构造。 我们奋进了解更多的挖掘模式，通过应用（铀-钍）/氦thermochronometer收集的岩石沿着一个样带，不遵循一个transshimalayan河的雨影。几个研究小组在尼泊尔中部和西藏南部的珠峰地区进行了近30年的研究，对该地区的基本构造地质有了非常好的了解，从而可以在适当的构造背景下解释所获得的数据。我们的目标是一个全面的数据集，适合于热动力学建模，旨在提供一个更好的理解喜马拉雅造山楔的降水和动力学的耦合影响。我们还利用所获得的一部分数据来探索珠峰以北绒布河谷的洛子峰和珠穆朗玛峰的时间和滑动历史。这是藏南拆离系统所有分支中研究得最好的两个，这是喜马拉雅山的一个主要构造特征。虽然藏南拆离系统在早中新世至中中新世的整个喜马拉雅地区都很活跃，但在包括绒布河谷在内的大多数地区，最年轻的运动的实际年龄受到很大限制。我们通过对副矿物的（铀-钍）/氦和裂变径迹工作，对两个determines的下盘的低温热结构提供了新的约束。绒布河谷的拆离岩出露是不寻常的：浅断层倾角和高起伏度共同提供了采样机会，在藏南拆离岩系的直接下盘中，在运输方向上的距离大于35公里。虽然许多研究侧重于气候变化在空间和时间上的全球影响，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，反过来说，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向北的移动，形成了两种截然不同的景观：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，以及青藏高原南部的高沙漠。 我们的工作旨在了解这种气候模式在时间上可能已经延伸了多远，以及它如何导致喜马拉雅山峰顶以北和以南的侵蚀率变化。这里学到的经验教训将告知在侵蚀过程中的区域气候变化的作用在美国和国外的看法。该项目正在资助一位才华横溢的女博士。这一计划旨在为博士生提供更多的机会，从而为正在进行的减少男女博士科学家之间的性别差距的努力做出贡献，这一问题在物理科学领域尤为严重。 此外，正在为公共博物馆的展览制作特别的多媒体展示，探索山区景观气候变化的科学。

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.