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

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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.