GPS-Derived Models of Intraplate Deformation of the Yellowstone Hotspot

The 800-km long Yellowstone-Snake River Plain (YSRP) is interpreted to be the track of the Yellowstone hotspot. It has experienced over 150 giant silicic volcanic eruptions in the last 16 Ma from magmatic sources derived from interaction of the N. American Plate with a mantle heat source. GPS measurements at more than 170 temporary stations and 10 continuous sites were made between 1987 and the present to assess the kinematic deformation field. The GPS observations cover a 800 by 600 km area affected by the volcanic system and are used to constrain kinematic and dynamic models. The present center of YSRP volcanic activity, at the Yellowstone Plateau, exhibits extensive earthquake activity and anomalously high rates of crustal deformation of ~4 mm/yr SW extension. In contrast, the hotspot track along the eastern Snake River Plain has much lower displacement rates of ~2 mm/yr SW extension. GPS-derived principal strain rate fields for the entire YSRP reveal rotation of the extensional strain axes from N-S to E-W at Yellowstone. This change corresponds to similar directions for tensional stress axes derived from focal mechanisms, post-caldera vent alignments, and active faults. The YSRP deformation field is compared with other geodetic, geologic, and seismic observations of the strain field for western North America to examine how it fits into the plate boundary framework. Finite-element models of the resolved deformation incorporate GPS rates, fault slip rates, volcanic features, seismicity, etc. These models suggest compression of the Snake River Plain, which apparently deforms as a single block within the resolution of the GPS data. Higher displacement rates at the Yellowstone caldera are likely due to local volcanic activity combined with with regional extension, for regional extension rates alone do not account for the observed rates. Volcanic acitivity has reworked the topography, enhanced heat flow, and modified lithosphere composition through melting and magmatic intrusions, and must be accounted for in geodynamic models. Key questions that will be addressed in the modeling are: What are the mechanisms for the rotation of strain axes at Yellowstone? How do the YSRP deformation rates and consequently stress rates fit into the western North America intraplate motions? What do the observed displacement rates imply about the mechanical properties of the YSRP lithosphere? and Can we resolve plume-plate interaction stresses at the earth's surface?