Crustal Structure beneath the High Lava Plains of Eastern Oregon and Surrounding Regions from Receiver Function Analysis

Crustal Structure beneath the High Lava Plains of Eastern Oregon and Surrounding Regions from Receiver Function Analysis, Figure 1 Figure 1.
Map of Moho depth derived from H-k stacking analysis. Single station results (colored circles) are smoothed over a 10 x 10 km 20 grid using splines under tension with a tension factor of 0.3 using the Generic Mapping Tools 30 [Smith and Wessel, 1990]. Red colors denote shallower Moho; blue colors denote deeper Moho; gray regions represent areas of limited sampling in this study. Black solid lines denote5 km contours. 87Sr/86Sr isopleths of 0.704and 0.706 (“.704” and “.706” lines) denoted by black dashed lines. Geologic provinces include Cascade volcanic arc (CM), Blue Mountains (BM),High Lava Plains (HLP), Columbia River basin (CRB), Snake River Plain (SRP), Idaho batholith (IB), Owyhee Plateau (OP), Modoc Plateau (MP), and Great Basin (GB).
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We analyze teleseismic P-to-S receiver functions to image crustal structure beneath the High Lava Plains (HLP) of eastern Oregon and surrounding regions. The coverage from 206 broadband seismic stations provides the first opportunity to resolve small scale variations in crustal composition, thickness, and heterogeneity. We utilize both Hκ stacking and a new Gaussian-weighted common conversion point stacking technique. We find crust that is ≥ 40 km thick beneath the Cascades, Idaho Batholith, and Owyhee Plateau, and thinner (~31 km) crust beneath the HLP and northern Great Basin. Low Poisson’s ratios of ~0.250 characterize the granitic Idaho Batholith, while the Owyhee Plateau possesses values of ~0.270, typical of average continental crust. The Owyhee Plateau is a thick simple crustal block with distinct edges at depth. The western HLP exhibits high average values of 0.295, expected from widespread basaltic volcanism. Combined with other geological and geophysical observations, the areas of high Poisson’s ratios (~0.320) and low velocity zones in the crust beneath north-central and southern Oregon are consistent with the presence of partial melt on either side of the HLP track, suggesting a central zone where crustal melts have drained to the surface, perhaps enabled by the Brothers Fault zone. Thicker crust and an anomalous N-S band of low Poisson’s ratios (~0.252) skirting the Steens Mountain escarpment is consistent with residuum from a mid-crustal magma source of the massive flood basalts, supporting the view of extensive mafic under- and intraplating of the crust from Cenozoic volcanism.
</p><p>References
</p><p>Eagar, K.C., M.J. Fouch, D.E. James, R.W. Carlson, and the High Lava Plains Seismic Working Group, Crustal structure beneath the High Lava Plains of Eastern Oregon and surrounding regions from receiver function analysis, submitted to J. Geophys. Res., June 2010.
</p><p>Acknowledgements: This work would not have been possible without high quality seismic data provided through the hard work of the TA and the Seismic Experiment teams (http://www.dtm.ciw.edu/research/HLP), and the services of the IRIS DMC. As always, the IRIS PASSCAL program provided world-class technical field supp4o3r ̊Nt. A special thanks goes to Jenda Johnson, whose contributions to the project have been innumerable and immeasurable, and Steven Golden for providing field and data support. We would also like to acknowledge the work and productive discussions on the crustal evolution with the other PIs of the HLP project, including Anita Grunder, Bill Hart, Tim Grove, Randy Keller, Steve Harder, and Bob Duncan. This research was supp41o ̊Nrted by National Science Foundation awards EAR-0548288 (MJF EarthScope CAREER grant), EAR- C’0507248 (MJF Continental Dynamics High Lava Plains grant) and EAR-0506914 (DEJ/RWC Continental Dynamics High Lava Plains grant).</p>

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