Collaborative Research: Quantifying crustal hydration effects in the Colorado Plateau from xenoliths

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

The Colorado Plateau in the western United States incorporates spectacular natural landscapes, such as Grand Canyon, Zion, and Arches National Parks. This region was at sea level 100 million years ago and now sits at an elevation of about 2 kilometers above sea level. However, the reasons why surface elevations in this region increased are not well understood. This project will investigate the viability of one of several proposed mechanisms that have generated considerable debate over the last several decades. Specifically, this research will address whether hydration of Earth’s crust by water derived from a subducted fragment of the Pacific oceanic plate reduced its density and caused the ground surface to rise. This is based on the same principles that govern how high blocks of wood with different densities will float in water. The results of this research could have far-reaching implications because causal mechanisms for high elevations in the broader Rocky Mountain region and High Plains (including Denver, the “Mile High City”) may be due to processes that also affect other mountainous regions such as the Andes. Common educational themes among all of the activities in this project include graduate and undergraduate education and training, international collaborations with researchers in France, and enhancement of underrepresented minority students in Earth science. This project will investigate the hypothesis that hydrous alteration changed the mineralogical makeup and associated density structure of the Colorado Plateau lower crust and contributed significantly to its 2 kilometers surface uplift via isostatic adjustment. This research will integrate new petrologic, geochronologic, and stable hydrogen isotopic studies of a suite of crustal xenoliths from the approximately 25-million-year-old Navajo Volcanic Field. A post-hydration (present-day) model of the central Colorado Plateau crust will be developed that incorporates new observations from xenoliths, and ensures compatibility with modern seismic and other geophysical data. This will be evaluated along with a pre-hydration model for the crust that is based on detailed xenolith analyses. Calculated differences in pre-and post-hydration model densities will be used to constrain the potential isostatic response to alteration. This project is jointly funded by the Tectonics program and the Petrology & Geochemistry program in the Division of Earth Sciences. 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.