EFFECTS OF THE YELLOWSTONE HOTSPOT AND ITS MANTLE PLUME ON THE WESTERN U.S. INTERIOR

The Yellowstone hotspot resulted by interaction of a mantle plume with the overriding North America plate that has influenced a large part of the western U.S. producing the 16 Ma old Yellowstone-Snake River Plain-Newberry volcanic field (YSRPN) and much of the surrounding region. We integrate results from seismic imaging, kinematics from GPS observations, tectonics and volcanic patterns and rates, and geodynamic modeling of the lithosphere-asthenosphere system. Tomography reveals an upper-mantle low- P and S velocity body that tilts west ~60° and extends to the base of the lower mantle transition zone at 650 km that is interpreted as the Yellowstone plume. The westward tilt is modeled by buoyant magma ascending in eastward return flow of the upper mantle. Using the inclined plume geometry we extrapolated the Yellowstone mantle source southwestward ~800 km as a plume-head at the oceanic-continent lithosphere boundary that was centered beneath the Columbia Plateau basalt field (LIP) at 16 Ma. Dynamic models show that shear stresses coupling of the lithosphere-asthenosphere boundary is small and likely not capable of producing asymmetry of surface topography or tectonics. Alternately the buoyancy forces from the mantle plume produce large deviatoric vertical stresses centered on the Yellowstone geoid,+15m, anomaly that significantly enhances lithospheric extension. New analyses of the regional gravity field, constrained by tomographically imaged lithospheric structure, is used to construct models thermal structure and crustal strength models (rheology) that inherently effects tectonic style, volcanism and rates of faulting. Integrated geodynamic models thus suggest that deformation of the YSRP during its 16 Ma history is driven principally by gravitational stresses produced by the high topography of the Yellowstone geoid anomaly, the topographically high Yellowstone Plateau and from interaction of the North America with the adjacent plates and the mantle discontinuities.