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P-to-S Receiver Function Imaging of the Crust Beneath the High Lava Plains of Eastern Oregon

EAGAR, K.C., Arizona State University, Tempe, AZ, keagar@asu.edu; FOUCH, M.J., Arizona State University, Tempe, AZ, fouch@asu.edu; JAMES, D.E., Carnegie Inst. of Washington, Washington, DC, james@dtm.ciw.edu; CARLSON, R.W., Carnegie Inst. of Washington, Washington, DC, rcalson@ciw.edu

We analyze teleseismic P-to-S receiver functions to image crustal structure beneath the High Lava Plains (HLP) of eastern Oregon and the surrounding Pacific Northwest region. The high-density broadband seismic array in the area provides an opportunity to constrain, in high-resolution, variations in regional bulk crustal composition, Moho depth, and crustal anisotropy by applying the H-k stacking method to receiver functions from 209 individual stations. Our results reveal relatively thin crust beneath the HLP and northern Great Basin that thickens dramatically below the Cascade volcanic arc and Idaho Batholith. Poisson's ratios are more scattered but generally show higher values than average continental crust throughout the HLP. Although the crust beneath HLP is generally thin everywhere, receiver functions also reveal localized small-scale complexities such as a dipping or diffuse Moho or anisotropic layers. The Owyhee Plateau seems to have a distinctive crustal signature, characterized by thick crust and receiver functions that adhere well to the H-k stacking assumptions of a flat-lying, isotropic, homogeneous crust. The transition from the HLP to the Owyhee Plateau occurs over short distances and coincides approximately with the Sr87/Sr86 0.706 line, which delineates cratonic North America to the east from younger terranes to the west. Our results suggest a fundamentally different crustal evolution of the HLP in response to widespread magmatism relative to surrounding terranes, especially the Owyhee Plateau, which seems to have escaped significant Cenozoic modification. The high Poisson's ratios of the HLP crust may suggest mafic underplating and high, near melting, temperatures in the crust, consistent with the occurrence of rhyolitic volcanism across the HLP.

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Last Modified: 2011 Aug 10

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