GEODYNAMIC MODELS OF THE YELLOWSTONE HOTSPOT CONSTRAINED BY SEISMIC AND GPS IMAGING AND VOLCANO-TECTONIC DATA

Violent forces have produced the renowned scenery and the world's largest display of geysers at Yellowstone National Park. The energy responsible for these features is the Yellowstone hotspot, a coupled crust-mantle magmatic system. Moreover, the hotspot has had a profound influence on the tectonics and magmatic evolution of a much larger area of the western U.S., the Yellowstone-Snake River Plain-Newberry volcanic field (YSRPN), a 16 million year NE track of Cenozoic time-progressive volcanism of the Snake River Plain, and a complimentary NW trend of magmatism across the High Lava Plains to the Newberry caldera. The origin of this system has been variously ascribed to plume-plate interaction, lithosphere extension, return mantle flow, decompression melting, etc. Combined analyses of volcanic and tectonic data along with new geophysical and geodetic information provide a better understanding of the dynamics and kinematics of the hotspot. Our results reveal a +500m topographically swell centered on Yellowstone caldera. Regional GPS data shows secular deformation of up to ~4mm yr. SW extension across the caldera with decadal-scale uplift and subsidence at several mm/yr. Extension continues SW along the SRP and eastern Basin-Range at rates of ~2-3 mm/yr. Earthquake tomography reveals a mid crustal P- and S-wave low velocity body beneath the Yellowstone caldera that is interpreted as a crustal magma system. Using combined seismic, potential field and mantle discontinuity constraints, an upper-mantle plume has been imaged from ~50 km to ~650 km depth, dipping W at ~45° and originating ~150 km beneath the MT-ID border. Western US ESE mantle return-flow models are consistent with the orientation of the Yellowstone plume whose origin is at the base of the mantle transition zone at temperatures of +70°K. A deeper low velocity pillow underlies a much larger area of the western U.S. at mid-mantle depths and suggests that the plume may have initiated from this deeper source. Using the inclined plume-geometry, we suggest that SW plate motion carried the western U.S. across an energetic large plume-head associated with the Columbia Plateau basalt field and oceanic lithosphere, but was terminated by SW movement of the thicker continental lithosphere across the plume-head resulting in a less energetic plume-tail along the YSRP.