Seismic imaging of the Newberry hotspot track

Mei Xue and Richard M. Allen
University of California Berkeley

AGU Fall Meeting 2005

Located in the northwestern United States, the Newberry hotspot track consists of a sequence of age-progressive silicic volcanic domes and lava flows, showing a monotonic age progression from east to west ending at the Newberry Caldera. While mantle plumes are often called upon to explain hotspot tracks, the Newberry hotspot track cannot be the product of plate motion over a stationary mantle source as its orientation is ~120 deg to plate motion, making it a good case study for alternative causal mechanisms of hotspot tracks. Four tectonic models have been proposed: (1) subduction counterflow, (2) gravitational flow along lithospheric topography, (3) lithospheric faulting, and (4) extension of Basin and Range. Our SKS splitting results imply that the Newberry hotspot track is not a product of asthenospheric flow as the subduction counterflow model or the gravitational flow model would require, leaving the lithospheric models the most likely causal processes. Our preliminary tomography results show low velocity residuals all along the Newberry track to a depth ~150 km, suggesting there is no migrating melt body in the asthenosphere beneath the region. This supports the conclusion from our SKS splits that the Newberry track is more likely a result of lithospheric processes.