SEISMIC TOMOGRAPHY OF THE COLORADO ROCKY MOUNTAINS UPPER MANTLE FROM CREST: LITHOSPHERE - ASTHENOSPHERE INTERACTIONS AND MANTLE SUPPORT OF TOPOGRAPHY

The CREST experiment (Colorado Rocky Mountains Experiment and Seismic Transects) integrated EarthScope USArray Transportable Array with additional stations to image the crust and mantle properties beneath the Colorado Rocky Mountains. A body-wave inversion of P and S wave arrival times recorded at 160 stations shows large Vp perturbations relative to AK135 of 7% and Vs variations of 8% across short (approaching tens of km) lateral distances. The previously identified broad low velocity upper mantle Aspen Anomaly is resolved into multiple features. The lowest Vp and Vs velocities in the region lie beneath the San Juan Mountains, which is clearly distinguished from low velocity features of the northern Rio Grande Rift and Jemez lineament, Aspen region, and below the Never Summer Mountains. We suggest that the San Juan anomaly, and a similar feature below the Latir volcanic field of northern New Mexico, are related to delamination and remnant heat (and melt) beneath these sites of extraordinarily voluminous middle-Cenozoic volcanism. We interpret a northeast-southwest grain in Vs structure parallel to the Colorado Mineral belt to depths near 150 km to be controlled by uppermost mantle Proterozoic accretionary lithospheric architecture. The Wyoming province and northern Colorado Plateau show high velocity features indicative of thick (150 km) preserved Archean and Proterozoic lithosphere, respectively. Overall, uppermost mantle velocity structure consistent with internfingered chemical Proterozoic lithosphere that has been, and possibly is presently being, replaced and magmatically modied by upwelling asthenosphere sourced as deeply as 410 km. One possible driving mechanism for this is interaction between upwelling hydration-induced partial meltand destabilized downwelling lithosphere. Tomographic imaging of mantle seismic velocity and crustal thickness results from the CREST experiment indicate that the highest elevations of the Colorado Rocky Mountains are substantially supported by the mantle. This, along with rich upper mantle seismic heterogeneity, indicate that mantle buoyancy and dynamics are central to the present day topographic support and recent geomorphic evolution of the region, and that relevant mantle influences could originate as deeply as the top of the transition zone.