2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 2
Presentation Time: 2:05 PM


SMITH, Robert B.1, JORDAN, Michael1, PUSKAS, Christine1, WAITE, Greg2 and FARRELL, Jamie3, (1)Geology and Geophysics, University of Utah, 135 S. 1460 East, rm 702, Salt Lake City, UT 84112, (2)Seismology Branch, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, (3)Geology and Geophysics, University of Utah, 135 S. 1460 E, Room 706, Salt Lake City, UT 84112-0111, rbsmith@mines.utah.edu

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.