Identifying the Origin of the Newberry Hotspot Track

Mei Xue and Richard M. Allen
University of California Berkeley

Chapman Conference: The Great Plume Debate. Fort William, Scotland. August 2005.

Located in the northwestern United States, the Newberry hotspot track consists of a sequence of age-progressive volcanic domes and lava flows, showing a monotonic age progression from east to west ending at the Newberry Caldera. The northwest trending Newberry track crudely mirrors the better-known Yellowstone hotspot track. While located on the North American Plate, the Newberry track cannot be the product of plate motion over a stationary mantle source as its orientation is oblique to plate motion. Instead three end-member tectonic models have been proposed: (1) subduction counterflow, (2) gravitational flow along lithospheric topography, and (3) lithospheric faulting. Our preliminary SKS splits imply anisotropy primarily comes from the asthenosphere and that the anisotropy orientation does not vary with depth beneath the Newberry track. The first order observation is that the SKS splits are not aligned with the Newberry hotspot track as the subduction counterflow model or the gravitational flow model would require, indicating either the splits are not sensitive to mantle flow oriented along the track or the track is not the product of asthenospheric flow. Our splitting observations strongly argue for one layer of anisotropy, making the second explanation preferable. This leaves the lithospheric faulting model as the most likely causal process.