HR: 0800h
AN: V51B-0554    [Abstracts]
TI: New Seismic Constraints for the Yellowstone Hotspot
AU: Dueker, K G
EM: dueker@uwyo.edu
AF: Department of Geology and Geophysics University of Wyoming, Dept. 3006 1000 University Ave., Laramie, WY 82071 United States
AU: * Schutt, D L
EM: schutt@uwyo.edu
AF: Department of Geology and Geophysics University of Wyoming, Dept. 3006 1000 University Ave., Laramie, WY 82071 United States
AU: Yuan, H
EM: yuan@uwyo.edu
AF: Department of Geology and Geophysics University of Wyoming, Dept. 3006 1000 University Ave., Laramie, WY 82071 United States
AU: Fee, D
EM: fee@uwyo.edu
AF: Department of Geology and Geophysics University of Wyoming, Dept. 3006 1000 University Ave., Laramie, WY 82071 United States
AB: A synthesis of recent University of Wyoming studies of the Yellowstone Hotspot is presented; this includes teleseismic body wave tomography, transition zone discontinuity structure, and surface wave tomography. Our primary conclusion is that the Yellowstone Hotspot is not a purely "top driven" system. This conclusion is supported by the following constraints. First, the P-wave tomography shows a 120 km diameter low velocity pipe that is reliably imaged to extend from beneath the current hotspot location at Yellowstone Park down to 410 km depth. Below this depth, resolution of a continuation of this pipe is equivocal. It is worth noting that the pipe is tilted about $10\deg$ towards the NW. Translation of the velocity anomalies into temperature suggests a $150-200\deg$ anomaly. Second, imaging of discontinuity topography on the 410 discontinuity finds a 15-20 km depression in the 410 that is spatially well correlated with the low velocity pipe at 410 km depth. Translation of this 410 depression into its corresponding thermal field suggests a $150-200\deg$ anomaly. However, while the 660 km discontinuity does show significant topography, there is no corresponding upwarp of the 660 consistent with extension of the low velocity pipe through the 660. In addition, stacks of the radial component receiver functions intermittently require a 4-6% negative velocity discontinuity at 720 km. Tangential component receiver functions show similar magnitude arrivals from both 660 and 720 km depth. Modeling suggests that dipping layers are not creating this tangential energy and instead an anisotropic layer between 660-720 km is required. Third, Rayleigh wave tomography reveals that the Yellowstone hotspot track is underlain by extremely slow mantle between 60-120 km depth (i.e., 12% lower than the minimum velocity found under Hawaii). This mantle is significantly slower than a normal adiabatic profile would predict, and significant partial melting is indicated. The depth extent of the low velocity zone indicates the solidus is crossed at a mean depth of 104 km. Assuming an anhydrous solidus, this depth implies mantle temperatures $100\deg$ in excess of a normal mantle adiabat. Integration of these new results suggests that the Yellowstone hotspot is a transient thermal upwelling. We speculate that this upwelling is nucleated from super-adiabatic mantle ponded below the 660 km discontinuity in the uppermost lower mantle.
DE: 8180 Tomography
DE: 9350 North America
DE: 7255 Surface waves and free oscillations
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 7218 Lithosphere and upper mantle
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting