ABSTRACT

This project integrates available data on the tectonic and physiographic evolution of the Colorado Plateau to test a geodynamic model for the Tertiary history of this region. The centerpiece of this model is the idea that the Colorado Plateau is underlain by compositionally distinct mantle lithosphere that is depleted in basaltic components. In this scenario, intrinsic chemical buoyancy of the lithosphere may explain the enigmatic tectonic coherence and stability of the Colorado Plateau. The geodynamic implications of this idea are being explored by comparing numerical model results constraints derived from many diverse datasets, including: Tertiary magmatic patterns, heat flow, seismic velocity variations, xenoliths, rock exhumation, and rock and surface uplift. This research includes explicit consideration of possibly differing tectonic histories of the edges vs. the middle of the Colorado Plateau. The primary goal of this project is to shed light on two of the most puzzling aspects of the Tertiary evolution of the Colorado Plateau - the timing and mechanism of its rock and surface uplift and its relative tectonic stability during a time when vigorous magmatism and active deformation affected the rest of the western United States. The mechanism and timing of the uplift of the Colorado Plateau is a long-standing puzzle that has challenged some of the best geologists, including J.W. Powell, C. Dutton, and G.K. Gilbert. This project develops a new idea for the history of the region, namely that the uplift of the Colorado Plateau is intimately related to the chemical structure of the North American plate and is governed by intense heating and igneous activity that affected the plate since removal of the subducted Farallon plate beneath it. This idea will be tested using physics-based models and comparing results with observations from a range of disciplines. If this new idea is consistent with a wide variety of data, then the geologic community may have a robust and viable solution to the long-standing problem of the uplift of the Colorado Plateau. The project is providing important training for a graduate student in building quantitative models of the Earth and is broadening participation of underrepresented groups in the earth sciences. The computer models and programs developed in this research will be available to the wider geologic community.

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