ROLE OF THE YELLOWSTONE HOTSPOT IN WESTERN US DEFORMATION AND LITHOSPHERIC STRESS

Intraplate tectonic deformation of the western US extends ~1200 km across the Basin-Range extensional province between the stable plate interior and the San Andreas and Cascade plate boundaries. The Yellowstone-Snake River (YSRP) volcanic field occupies a large part of the eastern BR. Contemporary tectonism is characterized by extraordinarily high heat flow, rapid crustal deformation, and a well-defined belt of high seismicity and active faulting surrounding the YSRP. To evaluate the kinematics of this active system, GPS surveys have been made at the Yellowstone-Snake River Plain, 1987-2003, including continuous GPS monitoring starting in 1996 to the present. These data show that the Yellowstone caldera has had episodes of rapid uplift and subsidence along with ongoing SW extension across the entire Yellowstone Plateau at rates up to 4.4 mm/yr. The eastern Snake River Plain motion experienced smaller rates of 2.4 mm/yr to the SW from 1995-2000 implying a zone of intraplate compression between these two areas. To evaluate the role of the hotspot in the large-scale tectonic framework, we have incorporated these data with a compilation of GPS data for the entire western US. The combined GPS data were supplemented by late Quaternary fault slip rates. The combined data were used to construct regional kinematic velocity and strain fields using block and continuous deformation models. Regional stress fields were then estimated for the geoid and crustal buoyancy and compared with the strain field to obtain determine the average effective lithospheric viscosity for appropriate constitutive parameters. The overall kinematics show that the YSRP accommodates NE-SW extension in the western interior with SW flow down a topographic potential gradient from the hotspot swell, while the Basin-Range tectonic province is characterized by E-W to NW extension. Zones of rapid deformation were identified from their lower effective viscosities, including the Yellowstone Plateau and Wasatch fault zone at the eastern margins of the western US. Effective viscosity decreased from east to west, reflecting the high deformation rates at the North America plate boundary.