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Published May 15, 2012 | Supplemental Material
Journal Article Open

Hot mantle upwelling across the 660 beneath Yellowstone


P-to-s receiver functions mapped to depth through P and S body-wave tomography models image continuous 410 and 660 km discontinuities beneath the area covered by USArray prior to the year 2011. Mean depths to the 410 and 660 km discontinuities of 410 and 656 km imply a mantle transition zone that is about 4 km thicker than the global average and hence has a slightly cooler mean temperature and/or enhanced water content. Compared to the mean 660 depth beneath this ~2000 km wide area, the 660 beneath the Yellowstone hotspot is deflected upward by 12–18 km over an area about 200 km wide. This is the most anomalous shallowing of the 660 imaged and its horizontal extent is similar to the area where P and S tomography image low-velocity mantle extending from the top of the transition zone to about 900 km depth. Together, these results indicate a high-temperature, plume-like upwelling extending across the 660. The depth of 410 km discontinuity beneath the Yellowstone region is within 5 km of the mean depth implying that the plume is vertically heterogeneous and possibly discontinuous. Tomography indicates a similar vertically heterogeneous thermal plume. The irregular plume structure may be intrinsic to the dynamics of upwelling through the transition zone, or distortion may be caused by subduction-induced mantle flow. Topography of the 410 and 660 confirms that subducted slabs beneath the western U.S. are highly segmented, as inferred from recent tomography studies. We find no evidence of regionally pervasive velocity discontinuities between 750 and 1400 km depth. The plume's depth of origin within the lower mantle remains uncertain.

Additional Information

© 2012 Elsevier B.V. Received 31 December 2011. Revised 13 March 2012. Accepted 15 March 2012. Available online 13 April 2012. Editor: P. Shearer. Seismic data were acquired from the IRIS DMC. We thank the investigators responsible for the FACES, CAFE, SIEDCAR, HLP, Big Horns, and Ruby Mountains PASSCAL arrays for data access. Discussions with Wei Leng, Fan-Chi Lin, and Victor Tsai are appreciated. We thank Nicholas Schmerr and Matt Fouch for constructive reviews, and Peter Shearer for editorial efforts. Seismic models can be obtained by contacting the corresponding author. This research was supported in part by the Gordon and Betty Moore Foundation. This is Caltech Tectonics Observatory Contribution #195. Additional support came from National Science Foundation grant EAR-0952194 to the University of Oregon.

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