VP and VS structure of the Yellowstone hot spot from teleseismic tomography:: Evidence for an upper mantle plume

[1] The movement of the lithosphere over a stationary mantle magmatic source, often thought to be a mantle plume, explains key features of the 16 Ma Yellowstone - Snake River Plain volcanic system. However, the seismic signature of a Yellowstone plume has remained elusive because of the lack of adequate data. We employ new teleseismic P and S wave traveltime data to develop tomographic images of the Yellowstone hot spot upper mantle. The teleseismic data were recorded with two temporary seismograph arrays deployed in a 500 km by 600 km area centered on Yellowstone. Additional data from nearby regional seismic networks were incorporated into the data set. The V-P and V-S models reveal a strong low-velocity anomaly from similar to 50 to 200 km directly beneath the Yellowstone caldera and eastern Snake River Plain, as has been imaged in previous studies. Peak anomalies are - 2.3% for V-P and - 5.5% for V-S. A weaker, anomaly with a velocity perturbation of up to - 1.0% V-P and - 2.5% V-S continues to at least 400 km depth. This anomaly dips 30 degrees from vertical, west-northwest to a location beneath the northern Rocky Mountains. We interpret the low-velocity body as a plume of upwelling hot, and possibly wet rock, from the mantle transition zone that promotes small-scale convection in the upper similar to 200 km of the mantle and long-lived volcanism. A high-velocity anomaly, 1.2% V-P and 1.9% V-S, is located at similar to 100 to 250 km depth southeast of Yellowstone and may represent a downwelling of colder, denser mantle material.