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

Abstract

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 VP and VS models reveal a strong low‐velocity anomaly from ∼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 VP and −5.5% for VS. A weaker, anomaly with a velocity perturbation of up to −1.0% VP and −2.5% VS continues to at least 400 km depth. This anomaly dips 30° 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 ∼200 km of the mantle and long‐lived volcanism. A high‐velocity anomaly, 1.2% VP and 1.9% VS, is located at ∼100 to 250 km depth southeast of Yellowstone and may represent a downwelling of colder, denser mantle material.