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

在山带发展过程中，大规模区域地形的发展反映了在地壳和地幔更深层次运作的基本构造过程。利用各种地质和地球化学方法作为古海拔的替代指标，这位研究人员和同事提出，大约5000万年前，落基山脉北部形成了一个宽阔的高海拔高原(4到5公里高)，大约4000万年前，它向南生长到内华达州中部。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，数据含糊不清。该项目旨在将古高程数据的收集范围扩大到北部地区(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增长的想法，可能需要对北美科迪勒拉建造的构造模型进行重大修订。该项目将通过以下途径促进预期的社会成果：1)妇女和代表性不足的少数群体充分参与STEM；(2)通过师范教育和K-12计划的推广，改进STEM教育和教育者发展；(3)通过公共外联，提高公众的科学素养和公众对STEM的参与；(4)通过研究生和本科生培训，发展一支多样化、具有全球竞争力的STEM劳动力队伍；以及(5)通过国际合作，包括为研究生提供国际研究机会，加强STEM和STEM之间的伙伴关系。这项研究得到了构造计划和NSF国际科学与工程计划的支持。了解山脉地带的地表高程历史是对构造模型和全球气候模型的边界条件施加关键约束的核心。前人的工作导致了北美科迪勒拉的隆升模型，该模型要求始新世高原由北向南生长，落基山脉北部在~50 Ma时首先在不列颠哥伦比亚省达到约4~5公里的平均高度，然后在~40 Ma向南扫入内华达州中部。然而，新的地质和地球化学证据表明，蛇河平原以北的地表高程历史与其南部的高程历史形成了鲜明的对比。对于内华达州和加利福尼亚州，有很好的证据表明，白垩纪有一个中等高的高原，在~40 Ma经历了另一阶段的地表抬升，河流从内华达州古大陆分水岭以西的低起伏高地向东穿过高起伏地貌。然而，在北面，观测到了约50 Ma的早期地表抬升，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，将需要对地表高程历史模型进行实质性修改，并将建议北美科迪勒拉北部的其他构造模型，如法拉隆板块的片状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得更多数据，以测试南部地区和更北部地区之间联系的性质。该项目将采用：(1)与年龄限制的地质年代学研究相联系的沉积学研究；(2)多个替代物的稳定同位素研究，包括火山玻璃、来自古土壤的方解石和粘土矿物以及聚集的同位素温度；以及3)蒸汽传输模型。

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.