USArray
A Continental-scale Seismic Observatory

Wallowa

Origin of the Columbia River Basalts and Uplift of the Wallowa Mountains                                                                                                                          

Principal Investigators and Institutions:

Eugene Humphreys, University of Oregon, EugeneStation Map

Funding Source:

NSF - Earthscope

Field Dates: 

9/2006 – 10/2008

Equipment Used:

20 broadband stations   

Data Status:

Archive ongoing 90% available

Network Code:

ZG

Description:

The Yellowstone hotspot initiated about 16.5 m.y. ago with a flood basalt eruption concentrated in NE Oregon. The origin of this event is not clear, nor is its overall effect on the lithosphere. This study will help us to understand how the Yellowstone hotspot began and the processes within the continental lithospheric. Several observations seem inconsistent with the plume hypothesis: there was no pre-eruptive uplift, magmatic fissuring occurred from a narrow but 700 km-long zone, and the main focus of magmatism occurred far off of the current Yellowstone hotspot track. This is a particularly suitable location for this study; nowhere else is there such a large, well-exposed, young and accessible area of continental growth interior to the continent.

The investigators will deploy 25-station teleseismic stations coordinated with the USArray deployment in the Wallowa area to image basic crustal and upper mantle structure in NE Oregon and nearby regions. This is the region from which the greatest basalt eruption occurred, and it is that which witnessed a remarkable uplift event that created a bull's eye pattern of relief with the Wallowa pluton at its center. The seismic investigation will be augmented with a focused set of geodynamic models to test a range of hypotheses in a manner that enforces mass and heat conservation and force balance under the constraints of realistic rheologic behavior.

The research plan of this proposal is designed to improve on the methods used to understand Earth processes by using geodynamic computer models to quantitatively relate hypotheses and a range of observations, and by studying a region with a teleseismic array of crustal-scale resolution embedded within a national array (USArray) of lithospheric-scale resolution. This project will prepare students and post-docs for the future through collaborations, participation in a diverse set of disciplines, and integration of the range of findings into consistent results.

Publications/ Abstracts

Gao, H, E. Humphreys, H. Yao, R. van der Hilst, Crust and lithosphere structure of the Northwestern U.S. with ambient noise tomography: Terrane accretion and Cascade arc development, Earth Planet. Sci. Lett., 304, 202-211, 2011.

Schmandt, B, E. Humphreys, Seismically Imaged Relict Slab from the 55 Ma Siletzia Accretion to Northwest USA, Geology, 39, 175-179, 2011.

Long, M. D., Gao, H., Klaus, A., Wagner, L. S., Fouch, M. J., James, D. E., & Humphreys, E. D., Shear wave splitting and the pattern of mantle flow beneath eastern Oregon, Earth and Planetary Sci. Lett., 288, 359-369, 2009.

Zandt, G., and E. Humphreys, Toroidal mantle flow through the western U.S. slab window, Geology, in review (accepted), 2007.

Nature 438, 842-845 (8 December 2005) | doi:10.1038/nature04313; Received 14 March 2005; Accepted 6 October 2005;A lithospheric instability origin for Columbia River flood basalts and Wallowa Mountains uplift in northeast Oregon,T. C. Hales1, D. L. Abt1,2, E. D. Humphreys1 & J. J. Roering1

American Geophysical Union, Fall Meeting 2007, abstract #T23A-1206, Seismic Imaging Beneath the Region of the Wallowa Mountains in Northeast OregonGao, H.; Humphreys, G.