Thermomechanical Characteristics of the YNP/SRP Region

The Snake River Plain/Yellowstone system is one of the most prominent and unique thermotectonic regions in North America. The unique characteristics of the strength of the heat source and its extensive effect on the structure of the crust have resulted in a unique region that has distinct thermal and strength characteristics compared to adjacent crustal regions (the Northern Basin and Range, the Northern Rocky Mountains and the Middle Rocky Mountains). These properties evolve with time in a systematic way as the heat source moves to the east. The unique crustal behavior and the extensive modification of the crust along the trend are related to the large scale vertical and horizontal deformational behavior, and the bow of earthquakes around the eastern 1/2 of the feature. The thermal and mechanical effects of the modification of the crust are examined based on the observed geothermal and geophysical data by use of numerical thermal models that explore a range of crustal thermal behavior that might be associated with the region based on a family of thermal configurations. The models are characterized by a large mafic chamber with a large overlying silicic magma chamber. The temperatures are modeled based on the time progression of the hot spot. The combination of the higher than background temperatures and the compositional modification of the crust, result in a rapidly evolving modification of the crustal behavior in time and space in and around the feature. Initially the crust is very weak because of the high temperatures. As the area cools the compositional modifications began to dominate the crustal behavior. At longer times the center of the feature becomes stronger and denser than its surroundings and sinks. The uncertainly is primarily how extensive the mafic chamber is outside of the SRP feature as that is one control on the lateral extent of the effects. The behavior is illustrated by the models. The discontinuities in deformation observed geologically and by GPS studies can be explained by a combination of the strength discontinuity at the boundary, lateral thermal evolution, and loading effects.