CAREER: The Fall of Mountains: Reconstructing Extensional Collapse in the North American Cordillera from the Surface Record

自从刘易斯和克拉克从大陆分水岭眺望落基山脉以来，北方山脉看似无穷无尽的高山和深谷一直在游客中引发好奇。这项研究的目的是了解这种戏剧性的景观是何时形成的，以及山脉是如何分崩离析的，这一过程今天在美国西部仍然活跃。首席研究员和她的学生们正在使用在火山灰中保存了数百万年的古代雨水来测量爱达荷州，蒙大拿州和怀俄明州过去5000万年的海拔，结合随着时间的推移填充山谷的沉积物的年龄，以重建北方落基山脉和盆地和山脉的造山和崩塌的历史。通过这个项目，研究人员的目的是增加所有级别的学生对地球科学的可及性。学生受益于研究生和本科生研究项目的直接支持，为本科课程开发广泛访问，动手调查Google Earth活动，以及通过STEM Access和TRIO-实习计划招募的代表性不足的高中生的暑期实习。该项目支持扩大代表性不足的群体在STEM领域的代表性，通过早期职业女性地球科学家研究员和她的学生的直接研究支持，并通过Tuff Talk播客，通过与地球科学领域成功女性的互动访谈，为广大受众提供远程指导，辅导和专业发展。这项研究还使用了地球化学和年龄测定分析技术的新组合，目的是完善这些方法。高海拔地区对区域水文，全球气候，沉积物的侵蚀和沉积以及许多其他地球过程都有巨大的影响。造山带在地壳缩短或地幔拆沉结束后仍能维持高地形，尽管岩石圈具有高重力位能和热弱化。虽然对隆升时间的估计最近变得普遍，但我们缺乏造山带崩塌的精确地表记录，即使是在研究得很好的北美科迪勒拉山脉。测量地表下降的时间和速度，以及它对侵蚀和盆地沉积的影响，可以为我们提供深入了解这种延伸的驱动因素，以及原始造山带的成因和结构。本研究的总体目标是重建整个北美科迪勒拉的新生代地形演化，包括时间，规模和机制的表面降低，砾岩沉积和排水重组，从而产生一个整体模型的造山带崩溃表示在表面记录。首席研究员和她的学生通过将创新的、广泛分布的稳定同位素代用材料与精确的辐射年龄相结合，量化地表地形的变化，并使用同位素全球气候模型来解释这些数据，以捕捉海拔随时间的变化。将古高程测量与新的物源、折返和沉积物滞后时间数据（来自盆地记录）相结合，以确定延伸的开始，并测试表面变形是否产生广泛的砾岩沉积。结果被用来区分各种潜在的机制造山塌陷，并开发一个模型之间的相互作用，和表面表达，核心复杂的形成，板回滚，岩浆活动。通过多个实地和分析数据集的结合以及结果的整合，项目小组对北美科迪勒拉地表下降的进展以及启动范围广泛的延伸和岩石圈减薄的必要条件有了新的认识。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The seemingly endless chain of high mountains and deep valleys of the northern Rocky Mountains has sparked wonder in visitors since Lewis and Clark looked across it from the continental divide. The goal of this research is to understand when this dramatic landscape formed and how mountains fall apart, a process that is still active in the western U.S. today. The principal investigator and her students are using ancient rainwater, preserved for millions of years in volcanic ash, to measure elevations from the past 50 million years across Idaho, Montana, and Wyoming, combined with the ages of sediments that have filled the valleys over time, to reconstruct the history of mountain building and collapse in the northern Rocky Mountains and Basin and Range. Through this project, the researcher aims to increase accessibility to geoscience for students of all levels. Students benefit from direct support for graduate and undergraduate research projects, development of widely accessible, hands-on investigative Google Earth activities for undergraduate courses, and summer internships for high school students from underrepresented groups, recruited via STEM Access and TRIO-Inspire programs. The project supports to broadening of representation of underrepresented groups in STEM fields through direct research support of an early career female geoscientist researcher and her students, and through the Tuff Talk podcast, which provides distance mentorship, coaching, and professional development to a broad audience through interactive interviews with successful women in Earth science. This research also uses a novel combination of analytical techniques in geochemistry and age dating, with the goal of refining these methods.Elevated regions have an outsized influence on regional hydrology, global climate, erosion and deposition of sediment, and many other Earth processes. Orogens can maintain high topography well after the end of crustal shortening or mantle delamination, despite high gravitational potential energy and thermal weakening of the lithosphere. Although estimates of the timing of uplift have recently become common, we lack precise surface records of orogen collapse, even in the well-studied North American Cordillera. Measuring the timing and pace of surface lowering, and its effects on erosion and basin sedimentation, can provide us with insights into the drivers for that extension, and into the genesis and structure of the original orogen. The overall objective of this research is to reconstruct the Cenozoic evolution of topography across the North American Cordillera, including the timing, magnitude, and mechanisms of surface-lowering, conglomerate deposition, and drainage reorganization, thereby generating a holistic model of orogen collapse as expressed in the surface record. The principal investigator and her students quantify changes in surface topography by combining an innovative, widely distributed stable isotope proxy material with precise radiometric ages, and interpreting those data using an isotope-enabled global climate model to capture changes in elevation over time. Paleoelevation measurements are integrated with new provenance, exhumation, and sediment lag time data from the basin record to determine the onset of extension and test if surface deformation generated widespread conglomerate deposition. Results are used to discriminate between various potential mechanisms for orogenic collapse and to develop a model for the interactions between, and surface expressions of, core complex formation, slab rollback, and magmatism. Through the combination of multiple field and analytical datasets and the integration of findings, the project team is gaining a new understanding of the progression of North American Cordilleran surface lowering and the conditions necessary to initiate range-wide extension and lithospheric thinning. The proposal is supported in part by co-funding by the Division of Earth Sciences Education and Human Resources Program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.