Collaborative Research: Utilizing Cooling Histories to Determine the Sequence and Rates of Thrusting

该提案旨在了解尼泊尔中部和西部喜马拉雅造山带的构造，构造和挖掘。主要研究人员正在研究在两个大陆碰撞的会聚边缘板块构造系统中，断层的大小、几何形状和速率如何与隆起和挖掘有关。这项研究将使主要研究人员能够限制断层的大小和年龄，并深入了解尼泊尔喜马拉雅地区印度和亚洲之间的基本板块边界上这些断层的几何形状，这将为板块边缘如何随着时间的推移而演变提供基本的见解。该地区是大型破坏性地震的发生地，这些地震是断层几何形状和断层移动速度的函数；因此，这项研究有可能进一步了解地震活动活跃的地区。这个建议结合了热计时法（矿物冷却的年龄）和数值模拟来确定断层的大小、几何形状和速率。地质制图和相关的横截面提供了断层几何形状的估计。这种几何形状提供了一条可测试的路径，沿着这条路径，岩石从地下被移走并冷却到地球表面。主要研究人员将测试断层的几何形状控制着岩石中记录的一阶冷却年龄模式的假设，然后可以通过使用不同的断层几何形状将测量的冷却年龄与模拟的冷却年龄进行比较来验证这一假设。该方法将提供工作流程、方法和实例，说明断层几何形状（由地质剖面确定）和速率如何影响预测的冷却年龄。除了研究的科学目标外，该项目还通过为重要的STEM学科的研究生和本科生提供培训，为国民福祉和其他社会相关成果做出贡献，并为扩大地球科学中代表性不足的群体做出贡献。该项目为美国两个大学系统的研究基础设施的发展做出了贡献，并促进了美国、德国和尼泊尔科学家之间的国际合作。这项研究的结果将纳入课堂课程。作为该项目的一部分，主要研究人员正在开发一系列研究和教学模块，这些模块将为感兴趣的研究生和其他机构的研究人员提供在他们自己的领域和数据集上使用这种研究方法所需的技能，并允许教育工作者分配高级本科生和研究生的作业，教授压缩断层系统如何形成以及变形之间的关系。侵蚀和沉积。研究结果将通过同行评议的科学出版物、文献和在专业学会会议上的介绍加以传播；从项目中获得的数据将被归档到适当的社区支持的数据存储库中。将热时计与数值模拟相结合，在量化活动收缩板块构造环境中变形和侵蚀的速率、幅度和时间方面具有巨大的潜力。然而，对热时学数据的解释严重依赖于确定正确的热、运动学和侵蚀模型。了解断层的大小、几何形状和速率如何与挤压系统中的挖掘相关，需要定量地将断层滑动的几何形状和大小与侵蚀的分布和数量联系起来。在本项目中，主要研究人员认为，通过平衡的地质剖面可以最好地描绘褶皱冲断带的几何形状，并假设褶皱冲断带的几何形状，特别是滑脱中斜坡的位置和大小，控制着冷却时代的一级模式。为了解决这一假设，他们将应用二维热运动学和侵蚀模型来正演模拟平衡横截面，以量化推力带设置中的冷却历史。平衡截面提供了岩石和构造的运动序列，这是再现地表地质地图所必需的。主要研究人员将通过指定位移发生的年龄来测试这个运动学序列的有效性，并使用潜在速度矢量的范围来计算热传递、侵蚀和岩石冷却。将一套温度计记录的测量冷却历史与平衡截面的运动学预测相匹配，是对截面验证的额外支持。这项工作将检查提出的结构几何形状，岩石的冷却年龄和它们在尼泊尔中部和尼泊尔远西部的相互依存关系。在尼泊尔中部，有丰富的地质年代学/热年代学数据和最近的地图和截面解释。在尼泊尔遥远的西部，有详细的地图和越来越多的地质年代学/热年代学数据的截面解释。研究人员将利用这些已建立的和不断增长的数据集来验证我们的假设：1)评估平衡剖面的一系列允许几何形状（现场工作之前和之后），2)收集关键的现场观测（层理、叶理、解理）和必要的热年表样本，3)通过一套热时计建立复式和推力片的冷却历史，4)模拟时计对结构几何形状的依赖。位移路径和速率。该项目的智力价值包括研究温度计和运动学数据的敏感性和实用性，以计算推力运动的年龄和速率以及相关的挖掘。在尼泊尔使用这种方法，主要研究人员可以评估在空间和时间上缩短速率的范围，并确定喜马拉雅的长期缩短速率是恒定的还是可变的。这些方法/过程将可移植到世界各地的其他收缩系统，并将导致对造山系统的运动学、几何和速率的重新评估。

This proposal is aimed at understanding the structural, tectonic, and exhumation of a part of the Himalayan orogen in central and western Nepal. The principal investigators are investigating how fault magnitude, geometry and rate are related to uplift and exhumation in convergent margin plate tectonic systems where two continents are colliding. This research will allow the principal investigators to constrain both magnitude and age of faulting and gain insight into the geometry of these faults along a fundamental plate boundary between India and Asia in the Nepalese Himalaya, which will provide fundamental insights into how convergent plate margins evolve through time. This region is the site of large, destructive earthquakes that are a function of both geometry of the faults and the rates at which these faults move; thus, the research has the potential to further understanding in a region of active seismicity. This proposal combines thermochronometry (the age at which minerals cool) with numerical modeling to determine fault magnitude, geometry and rate. Geologic mapping and associated cross sections provide an estimate of fault geometry. This geometry provides a testable path along which rocks were displaced and cooled from the subsurface to the Earth's surface. The principal investigators will test the hypothesis that the geometry of faults controls the first-order pattern of cooling ages that are recorded in rocks, which can then be tested by comparing measured cooling ages to modeled cooling ages using different fault geometries. This approach will provide workflows, methodologies, and examples of how fault geometries, as determined from geologic cross sections, and rates impact predicted cooling ages. In addition to the scientific objectives of the study, the project is contributing to the national well-being and other socially relevant outcomes by providing for training of graduate and undergraduate students in an important STEM discipline, as well a contributing to the broadening of underrepresented groups in the earth sciences. The project it is contributing to the development of research infrastructure at two U.S. university systems, and is promoting international collaboration between U.S., German, and Nepalese scientists. Results from this research will be incorporated into classroom curricula. As part of this project, the principal investigators are developing a series of research and teaching modules that will provide interested graduate students and researchers from other institutions the skills needed to use this research approach for their own field areas and datasets, and allow educators to assign advanced undergraduates and graduate students assignments that teach the systematics of how compressional fault systems form and the relationships between deformation, erosion and deposition. The results of the research will be disseminated through peer-reviewed scientific publications literature and by presentations at professional society meetings; data obtained from the project will be archived in appropriate community supported data repositories. Combining thermochronometry with numerical modeling has an enormous potential to quantify the rates, magnitudes, and timing of deformation and erosion in active, contractional plate tectonic settings. However, the interpretations of thermochronometric data are critically dependent on determining the correct thermal, kinematic, and erosion models. Understanding how fault magnitude, geometry and rate are related to exhumation in compressional systems requires quantitatively linking the geometry and magnitude of fault slip to the distribution and amount of erosion. In this project, the principal investigators suggest that the geometry of fold-thrust belts is best delineated through balanced geologic cross-sections, and they hypothesize that the geometry of a fold-thrust belt, particularly the location and magnitude of ramps in the decollement, control the first-order pattern of cooling ages. To address this hypothesis they will apply a 2 dimensional thermo-kinematic and erosion model to forward modeled balanced cross sections to quantify the cooling history in a thrust belt setting. Balanced cross-sections provide the kinematic sequence of rocks and structures necessary to reproduce the mapped surface geology. The principal investigators will test the validity of this kinematic sequence by assigning ages over which displacement occurs, and use the range of potential velocity vectors to calculate heat transport, erosion, and rock cooling. Matching the measured cooling histories recorded by a suite of thermochronometers to that predicted by the kinematics of a balanced cross-section is an additional support for the validation of the cross section. This work will examine proposed structural geometries, the cooling ages of rocks and their interdependence in central Nepal and far western Nepal. In central Nepal, there is an abundance of geochronologic/thermochronologic data and recent maps and cross section interpretations. In far western Nepal, there are detailed maps and cross section interpretations with a growing body of geochronologic/thermochronologic data. The researchers will capitalize on these established and growing datasets to test our hypothesis by 1) evaluating a range of permissible geometries for balanced-sections (both prior to and following field work), 2) collecting critical field observations (bedding, foliation, cleavage) and necessary thermochronologic samples, 3) establishing the cooling history of duplexes and thrust sheets via a suite of thermochronometers, and 4) modeling the dependence of chronometers on structural geometries, displacement paths and rates. The intellectual merit of this project involves investigating the sensitivity and utility of thermochronometer and kinematic data for calculating the age and rate of thrust motion and associated exhumation. Using this approach in Nepal, the principal investigators can evaluate the range of shortening rates in space and time and determine if long-term shortening rates though the Himalaya are constant or variable. These methods/processes will be transportable to other contractional systems worldwide and will lead to a reevaluation of the kinematics, geometry and rates in orogenic systems.