Surface Elevation History of the Northern North America Cordillera as Constraint for Eocene Tectonic and Climatic Boundary Conditions

山带发育过程中大尺度区域地形的发育反映了地壳和地幔深层的基本构造过程。利用各种地质和地球化学方法作为古海拔的代用物，这位研究人员和他的同事们认为，在大约5000万年前，落基山脉北部出现了一个广阔的高原（4到5公里高），并在大约4000万年前向南扩展到内华达州中部。内华达州和加利福尼亚州的数据支持这一模型，但数据有限的数据是模棱两可的。该项目旨在将古海拔数据的收集扩展到北部地区（华盛顿州西部、爱达荷州和蒙大拿州），以进一步测试该模型。如果数据不支持向南生长的观点，可能需要对北美科迪勒拉构造模型进行重大修订。该项目将通过以下方式促进预期的社会成果：1)妇女和代表性不足的少数民族充分参与STEM；(2)通过教师教育和推广K-12课程，改善STEM教育和教育工作者的发展；(3)通过公众外展提高公众科学素养和公众对STEM的参与；(4)通过研究生和本科生培训，培养多样化、具有全球竞争力的STEM劳动力；(5)通过国际合作，包括为研究生提供国际研究机会，增加了两国之间的伙伴关系。这项研究得到了构造学项目和美国国家科学基金会国际科学与工程项目的支持。了解山地带的地表高程历史是为构造模式和全球气候模式的边界条件设置关键约束的核心。先前的工作导致了北美科迪勒拉的隆起模型，该模型要求始新世高原从北向南生长，北落基山脉在~50 Ma时首先在不列颠哥伦比亚省达到~4至5公里的低纬度平均高度，并在~40 Ma时向南席卷到内华达州中部。然而，新的地质和地球化学证据表明，蛇河平原北部的地表高程历史与南部的地表高程历史有明显的对比。对于内华达州和加利福尼亚州来说，有充分的证据表明，白垩纪时期有一个中等高度的高原，在~40 Ma时经历了另一阶段的地表隆起，河流流经内华达州古大陆分水岭以西的低起伏高地，向东流经高起伏地貌。然而，在北部，观测到约50 Ma的较早阶段的地表隆起，但几乎没有证据表明存在广泛的始新世高地。如果这一证据是正确的，它将需要对地表海拔历史模型进行实质性的修改，并将提出北美北部科迪勒拉的其他构造模型，例如法拉龙板块的逐渐移除或板块窗口的形成。该项目旨在从华盛顿州西部、爱达荷州和蒙大拿州的盆地获取更多数据，以测试南部地区与北部地区之间的联系性质。该项目将采用：(1)与地质年代学研究相联系的沉积学研究，以确定年龄限制；2)火山玻璃、古土壤方解石、粘土矿物等稳定同位素研究以及团块同位素温度；3)水汽输送模型。

The development of large-scale regional topography during the development of mountain belts reflects fundamental tectonic processes that operate at deeper levels in the crust and mantle. Using a variety of geological and geochemical methods that act as proxies for paleoelevation, this researcher and colleagues suggested a broad high-standing plateau (4 to 5 km high) developed in the northern Rockies about 50 million years ago and grew southward into central Nevada by about 40 million years ago. Data from Nevada and California support this model, but data limited data are equivocal. This project aims to expand the collection of paleoelevation data to the northern regions (western Washington, Idaho, and Montana) to further test the model. Significant revisions to tectonic models of the building of the North American Cordillera could be required if the data do not support the southward growth idea. The project would advance desired societal outcomes through: 1) full participation of women and underrepresented minorities in STEM; (2) improved STEM education and educator development through teacher education and outreach to K-12 programs; (3) increased public scientific literacy and public engagement with STEM through public outreach; (4) development of a diverse, globally competitive STEM workforce through graduate and undergraduate student training; and (5) increased partnerships between through international collaboration that includes an international research opportunity for a graduate student. The research is supported by the Tectonics Program and NSF's International Science and Engineering program.Understanding the surface elevation history of mountain belts is central in placing critical constraints both on tectonic models and boundary conditions to global climate models. Previous work lead to an uplift model for the North American Cordillera that calls for north to south growth of an Eocene plateau with the northern Rockies reaching hypsometric mean heights of ~4 to 5 km first in British Columbia at ~50 Ma and sweeping southward into central Nevada at ~40 Ma. However, new geologic and geochemical evidence indicates that the surface elevation history north of the Snake River Plain contrasts markedly with its southern counterpart. For Nevada and California there is excellent evidence for a moderately high plateau in the Cretaceous that underwent another phase of surface uplift at ~40 Ma with rivers draining a low-relief highland west of the paleocontinental divide in Nevada and to the east across a high-relief landscape. To the north, however, an earlier phase of surface uplift at ~50 Ma is observed, but little evidence of a broad Eocene highland. If this evidence is correct, it will require substantial modification to surface elevation history models and would suggest other tectonic models for the northern North American Cordillera, such as piece-meal removal of the Farallon slab or the formation of a slab window. This project aims to obtain more data from basins in western Washington, Idaho, and Montana in order to test the nature of the connection between the southern region and regions farther north. The project would employ: (1) sedimentologic studies tied to geochronologic studies for age constraints; 2) stable isotopic studies from multiple proxies including volcanic glasses, calcite from paleosols, and clay minerals as well as clumped isotope temperatures; and 3) vapor transport models.