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Abstract. Analysis of a deployment of broadband sensors along a 500-km-long line crossing the Yellowstone hotspot track (YHT) has provided 423 in-plane receiver functions with which to image lateral variations in mantle discontinuity structure. Imaging is accomplished by performing the converted wave equivalent of a common midpoint stack, which significantly improves resolution of mantle discontinuity structure with respect to single-station stacks. Timing corrections are calculated from locally derived tomographic P and $ wave velocity images and applied to the Pds (where d is the depth of the conversion) ray set in order to isolate true discontinuity topography. Using the one-dimensional

The high water storage capacity of minerals in Earth's mantle transition zone (410- to 660-kilometer depth) implies the possibility of a deep H2O reservoir, which could cause dehydration melting of vertically flowing mantle. We examined the effects of downwelling from the transition zone into the lower mantle with high-pressure laboratory experiments, numerical modeling, and seismic P-to-S conversions recorded by a dense seismic array in North America. In experiments, the transition of hydrous ringwoodite to perovskite and (Mg,Fe)O produces intergranular melt. Detections of abrupt decreases in seismic velocity where downwelling mantle is inferred are consistent with partial melt below 660 kilometers. These results suggest hydration of a large region of the transition zone and that dehydration melting may act to trap H2O in the transition zone.

The correspondence between seismic velocity anomalies in the crust and mantle and the differential incision of the continental-scale Colorado River system suggests that signifi cant mantle-to-surface interactions can take place deep within continental interiors. The Colorado Rocky Mountain region exhibits low-seismic-velocity crust and mantle associated with atypically high (and rough) topography, steep normalized river segments, and areas of greatest differential river incision. Thermochronologic and geologic data show that regional exhumation accelerated starting ca. 6-10 Ma, especially in regions underlain by low-velocity mantle. Integration and synthesis of diverse geologic and geophysical data sets support the provocative hypothesis that Neogene mantle convection has driven long-wavelength surface deformation and tilting over the past 10 Ma. Attendant surface uplift on the order of 500-1000 m may account for ~25%-50% of the current elevation of the region, with the rest achieved during Laramide and mid-Tertiary uplift episodes. This hypothesis highlights the importance of continued multidisciplinary tests of the nature and magnitude of surface responses to mantle dynamics in intraplate settings.

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Inversion of a new data set of teleseismic P‐wave travel‐times from three PASSCAL seismic deployments around the Yellowstone hotspot reveals a 100 km diameter upper mantle plume that extends from the Yellowstone volcanic caldera to 500 km depth and dips 20° to the northwest. A monotonic decrease in the velocity perturbation of the plume from −3.2% at 100 km to −0.9% at 450 km is consistent with a uniform thermal anomaly of 180°C. Where the plume crosses the 410 km discontinuity, previous research shows a depression in the 410 km discontinuity consistent with a warm plume (Fee and Dueker, 2004). Additionally, a region of high velocities extends to 250 km beneath the Wind River basin in NW Wyoming that may represent a convective downwelling of the lithosphere.

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