HR: 08:20h
AN: V51F-02 INVITED    [Abstracts]
TI: Seismic and GPS constraints on the dynamics and kinematics of the Yellowstone volcanic field
AU: * Smith, R B
EM: rbsmith@mines.utah.edu
AF: University of Utah, Department of Geology and Geophysics 135 S. 1460 East, Salt Lake City, UT 84121, United States
AU: Farrell, J
EM: farrell@earth.utah.edu
AF: University of Utah, Department of Geology and Geophysics 135 S. 1460 East, Salt Lake City, UT 84121, United States
AU: Jordan, M
EM: mjordanphd@netscape.net
AF: University of Utah, Department of Geology and Geophysics 135 S. 1460 East, Salt Lake City, UT 84121, United States
AU: Puskas, C
EM: c.puskas@utah.edu
AF: University of Utah, Department of Geology and Geophysics 135 S. 1460 East, Salt Lake City, UT 84121, United States
AU: Waite, G P
EM: gpwaite@mtu.edu
AF: Michigan Technological University, Geol. & Mining Eng. & Sci. 1400 Townsend Dr, Houghton, MI 49931, United States
AB: The seismically and volcanically Yellowstone hotspot resulted from interaction of a mantle plume with the overriding North America plate. This feature and related processes have modified continental lithosphere producing the Yellowstone-Snake River Plain-Newberry silicic volcanic field (YSRPN) system, with its NE volcanically active Yellowstone volcanic field. The size and accessibility of the Yellowstone area has allowed a range of geophysical experiments including earthquake monitoring and seismic and GPS imaging of this system. Seismicity is dominated by small-magnitude normal- to oblique-slip faulting earthquake swarms with shallow focal depths, maximum of ~5 km, restricted by high temperatures and a weak elastic layer. There is developing evidence of non-double couple events. Outside the caldera, earthquakes are deeper, ~20 km, and capable of M 7+ earthquakes. We integrate the results from a multi-institution experiment that recorded data from 110 seismic stations and 180 GPS stations for 1999-2004. The tomographic images confirm the existence of a low Vp-body beneath the Yellowstone caldera at depths greater than 8 km, possibly representing hot, crystallizing magma. A key result of our study is a volume of anomalously low Vp and Vp/Vs in the northwestern part of the volcanic field at shallow depths of <2.0 km. Theoretical calculations of changes in P- to S-wave velocity ratios indicate that these anomalies can be interpreted as porous, gas-filled rock. GPS-measured episodes of caldera kinematics reveals uplift and subsidence of the caldera at decadal scales with average rates of ~20 mm/yr but much higher short-term rates of up to 70 mm/yr of accelerated uplift, 2004-2007. The stress field inverted from seismic and GPS data is dominated by regional SW extension with superimposed volumetric expansion and uplift from local volcanic sources. Mantle tomography derived from integrated inversion of teleseismic and local earthquake data constrained by geoid, crustal structure, discontinuity structure reveals an upper-mantle low P and S velocity body extends from 80 km to ~250 km directly beneath Yellowstone and then continues to 650 km with unexpected westward tilt to the west at ~60° with a 1% to 2% melt. This geometry is consistent with the ascent of the buoyant magma entrained in eastward return-flow of the upper mantle. Some remaining issues to be discussed are: 1) the interaction dynamics and magma path from the tilted plume to the lithosphere, 2) the transfer mechanism of mantle magma through the lithosphere into the upper crust, 3) how the high potential energy of the large 12 m+ geoid high drives the dominant extensional strain and concomitant crustal magma emplacement, 4) how the crustal magma interacts with the surface hydrothermal features, and 5) how stress interaction of faults and volcanic features behave at short- to decadal time scales.
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8419 Volcano monitoring (7280)
DE: 8434 Magma migration and fragmentation
DE: 8440 Calderas
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting