Upper Mantle P-Wave Velocity Structure from Passcal Teleseismic Transects Across Idaho, Wyoming and Colorado

Inversion of teleseismic P-time residuals along two linear seismic arrays provides well-resolved inverse images of the upper mantle. Low velocity bodies beneath the Yellowstone Hotspot Track and the Grand Mesa volcanic field in western Colorado are similar in shape and magnitude. In the two places where our transects cross the 1.78 Ga Archean-Proterozoic Cheyenne suture, high velocities are imaged to 150 km. Beneath the Leucite Hills volcanic field in Wyoming a small upper mantle low velocity body is imaged. Whether these anomalies are lithospheric or asthenospheric in origin is poorly constrained, but the consistent high velocities beneath the Cheyenne suture suggest a lithospheric origin. Likewise, the lack of extension beneath the western Colorado volcanic fields suggests that a low-solidus lithosphere is being disturbed by a regional heating event.