SGER: Interactions Of Hotspots and the Lithosphere: An Integrated Study of the Newberry Hotspot

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A crucial and unsolved question in global earth science is the relationship of hotspots toprocesses that occur in the mantle beneath them. The most prevalent model for the formation of hotspots is the mantle plume model (stationary deep-mantle source) and, consequently, many previous studies have focused on classic plume locations. The PI will address the cause of the Newberry hotspot track in Oregon which cannot be the product of a stationary mantle source. The three end-member tectonic models for the formation of the Newberry hotspot are: (1) gravitational flow along the base of the continental lithosphere due to the edge of the craton or plume related material, (2) counterflow associated with subduction of the Juan de Fuca plate, and (3) progressive lithospheric faulting at the northern boundary of the Basin and Range. The preliminary seismic data suggest that there is no flow of mantle material along the length of the Newberry hotspot. Rather, E-W oriented shear wave splitting observations, oblique to the volcanic progression, are observed regionally. These observations suggest that either hypotheses (1) and (2) need modification or that lithospheric processes (hypothesis 3) exert thedominant control. The PI will utilize datasets from seven existing seismic networks to investigate lithospheric and asthenospheric structure in the region. Tomographic imaging of the mantle will integrate teleseismic body-wave traveltimes with local surface-wave constraints. The preliminary seismic anisotropy study will be extended to include more stations and the larger datasets that are becoming available. The ultimate goal of the proposal is to characterize the lithospheric and asthenospheric processes beneath the Newberry hotspot. These processes can then be used as a complementary hypothesis to the mantle plume model, in order to objectively evaluate other hotspots. The proposed analysis of the existing data sets in Oregon will provide a mechanism to optimize Earthscope resources through planning of future experiments to coincide with thepresence of the USArray transportable array and the arrival of PBO equipment in the region.