HR: 1340h
AN: T33A-1149    [Abstracts]
TI: Shear wave anisotropy beneath the Sierra Nevada range: Implications for lithospheric foundering and upper mantle flow
AU: * Badger, N B
EM: badgern@mailbox.sc.edu
AF: University of South Carolina, University of South Carolina, Columbia, SC 29208, United States
AU: Bastow, I D
EM: ian.bastow@bristol.ac.uk
AF: University of Bristol, Department of Earth Sciences, Bristol, BS81RJ, United Kingdom
AU: Owens, T J
EM: owens@seis.sc.edu
AF: University of South Carolina, University of South Carolina, Columbia, SC 29208, United States
AU: Zandt, G
EM: zandt@geo.arizona.edu
AF: University of Arizona, Department of Geosciences, Tucson, AZ 85721, United States
AU: Jones, C H
EM: cjones@cires.colorado.edu
AF: University of Colorado, Department of Geosciences, Boulder, CO 80309, United States
AU: Gilbert, H
EM: hersh@purdue.edu
AF: Purdue University, Department of Earth and Atmospheric Sciences, West Lafayette, IN 47907, United States
AB: Recent work asserts that the garnet-rich Sierra Nevada batholith root has undergone foundering since the early Cenozoic. The Sierra Nevada EarthScope Project (SNEP), undertaken to gain a better understanding of this phenomena, consists of a network of ~80 broadband seismometers spaced at ~25 km from ~37.0N to 40.5N. We use the Silver and Chan method to determine shear wave splitting parameters (dt and φ) for teleseismic SKS phases recorded at SNEP and US Array Transportable Array stations in the region. We find dt>1.1s and φ approximately in the E-NE direction over most of the batholith. Splitting of this magnitude cannot be accounted for solely in the crust, and our results, therefore, have significant implications for upper mantle flow beneath the region. At latitude ~39N to 40N, from the western Sierra Nevada range across our study area to central Nevada, we observe dt<1s at some stations. Smaller dt measurements in this region may be consistent with a vertically oriented anisotropic fabric resulting from asthenosphere upwelling into the slab window south of the southern edge of the Gorda-Juan de Fuca Plate. Such a flow pattern is also consistent with the circular pattern of splitting measurements that exist in the broader California and Western Nevada region. We observe subtle variations in splitting parameters as a function of backazimuth primarily at stations situated on the western foothills of the Sierra Nevada. These complexities may be indicative of either a two-layer or dipping layer structure beneath the batholith that may be associated with on- going lithospheric foundering beneath the Sierran range. Additionally, in the southern part of our study area, we note a reduction in dt for arrivals that sample the high V_p Isabella anomaly – an upper mantle downwelling thought to be a result of recent lithospheric foundering.
DE: 7203 Body waves
DE: 7218 Lithosphere (1236)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting