The Lithospheric Structure Beneath the High Lava Plains and the Owyhee Plateau, Oregon, USA, from Receiver Function Analysis
Date Issued
2014
Date
2014
Author(s)
Hou, Tung-Yuan
Abstract
The High Lava Plains and the Owyhee Plateau are located in the eastern Oregon, Pacific Northwest, USA. The Pacific Northwest has experienced continuous intraplate volcanism from the mid-Miocene to present, including the Columbia River flood basalts and the Steens Mountains flood basalts which erupted 16.6 Ma ago. In addition, there are two prominent age-progressive volcanic tracks, the Snake River Plain-Yellowstone and the High Lava Plains, both of which appear to have originated from near the Owyhee Plateau at approximately 12 Ma. Previous seismic studies have characterized the High Lava Plains with thinned crust, high Poisson’s ratio and low S-wave velocities in the crust and the uppermost mantle. In contrast, the Owyhee Plateau possesses thick crust with low Poisson’s ratio, and high intracrustal S-wave velocities, as well as distinct, albeit thin, mantle lithosphere. Recent ambient noise tomography and scattered-wave imaging reveal the presence of low velocity in the crust of the High Lava Plains and the high velocity layering in the Owyhee mid-crust. On the other hand, low velocities dominate the uppermost mantle. In this study, we perform detailed single station Ps receiver function analysis to better constrain the discontinuity structures within the High Lava Plains and the Owyhee lithosphere. We use teleseismic waveform data recorded at 115 High Lava Plains seismic array and 31 USArray Transportable Array broadband stations from 2004 to 2009. Our results show the coherent signals of low velocity discontinuity in the curst of the High Lava Plains, suggesting the presence of weakened crust and partial melt. We observe coherent signals of high velocity discontinuity at ~20 km depth beneath the Owyhee Plateau, possibly marking the upper bound of the high velocity layer imaged in previous studies, and suggesting that the Plateau represents an isolated block of older, and less modified, continental crust. Our results also reveal low velocity discontinuity in the uppermost mantle, at ~50 km depth beneath the High Lava Plains and ~75 km depth beneath the Owyhee Plateau. We interpret this low velocity discontinuity as the lithosphere-asthenosphere boundary (LAB), and thus both regions have relatively thin mantle lithospheres. We suggest that the origin of the High Lava Plans volcanic track is associated with the Cascadian back-arc extension, induced by the change of mantle flow field related to subduction processes.
Subjects
High Lava Plains
奧懷希高原
接收函數
不連續面
岩石圈構造
Type
thesis
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