The Plume-slab Interaction beneath Yellowstone Revealed by Multiple-frequency Tomography

The Plume-slab Interaction beneath Yellowstone Revealed by Multiple-frequency Tomography, Figure 2 Figure 2.
Great-circle cross sections of the velocity structure under the Yellowstone Caldera (YC) and the eastern Snake River Plain (SRP). The black dot and 0° represent the location of the Yellowstone Caldera and the mid-point of the great circle arc. In the cross-section views, each grid along the arc represents 1°. Labels S1, S2, N2, SG identify the same subduction structure as in Sigloch et al. [2008] and Tian et al. [2009].
<p>S-velocity structure under the Yellowstone region is obtained from multiple-frequency tomography of a mixed data set of shear waves and Love waves. In this study, we used a total of 211440 data measurements measured from 36344 seismic wave- forms, and over 95% of the waveforms are from IRIS. A strong slow anomaly (Y0) with large velocity gradient is observed under the Yellowstone Caldera (Figures 1-2), reaching ~200 km depth. Y0 connects to a slow anomaly (Y1) in the transition zone, which is centered at ~1° north of Y0 (Figure 2AA’). To the southwest, Y0 abuts a belt of strong slow anomalies (SR0) under the eastern Snake River Plain. Down in the lower mantle, a plume-shaped conduit (Y2) is observed with its top directly under Y1. The plume comes from south, tilting ~40° from vertical, reaches as deep as 1500 km, but spreads out at 700–1100 km depth. The spreading of SR2 can be explained either if the 660-km discontinuity acts as a barrier, or if the slab fragment S1 [Sigloch et al., 2008; Tian et al., 2009] acts as a barrier for the uprising Y2 (Figure 1b). Y2 might have distorted in two ways in response to the barrier. Part of Y2 might have navigated its path around S1 and found its way up through the slab gap, and the other part of Y2 might have smeared southwestward along the base of S1 and formed SR2. Though much of this explanation is speculative, it is clear that we witness a complex interaction between upwellings and downwellings in this part of the mantle. The very high resolution we obtained under the Yellowstone region would not be possible without the USArray, one of the densest networks in the world. The eastward movement of the USArray will make it possible to image detailed structure under the central and eastern US with similar resolution.
</p><p>Sigloch, K., N. McQuarrie, and G. Nolet (2008), Two-stage subduction history under North America inferred from finite-frequency tomography, Nature Geoscience, 1, 458–462.
</p><p>Tian, Y., K. Sigloch, and G. Nolet (2009), Multiple-frequency SH-wave tomography of the western U.S. upper mantle, Geophys. J. Int., 178, 1384–1402.
</p><p>Acknowledgements: NSF grants EAR-0309298, EAR-0105387, and EAR-0809464.</p>


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