DEFORMATION OF THE SOUTH GRANITE MOUNTAINS FAULT SYSTEM: HOW CENOZOIC TECTONISM INFLUENCES MODERN FAULTING

The Cenozoic Tectonism that formed Wyoming’s Wind River Basin continues to influence modern deformation within the region. The South Granite Mountains Fault Zone, located adjacent to the Wind River Basin, is one of several Cenozoic faults in the region that exhibits evidence of continued Quaternary deformation. The South Granite Mountains formed during the Late Cretaceous Laramide orogeny (75-45 Ma). Subsequently, during the Eocene, the extensive downfaulting and downfolding caused the Precambrian Mountain core to collapse forming the Sweetwater Graben. Recent Quaternary deformation is expressed as fault scarps along the north side of the Granite Mountains. These features were originally studied in the 1980s but have received little attention since. In particular, the nature and style of faulting of this recent deformation was previously undocumented, and prior age estimates were broad. Recent data collected from similar faults in the northern Wind River Basin suggests active faulting occurs along reactivated Laramide thrust planes, this may also be true for the Granite Mountains region. This study applies new methodologies to assess the active tectonics and earthquake potential of the South Granite Mountains Fault Zone. Low-altitude aerial surveying using drones facilitate the measurement and analysis of fault scarp morphology. Shallow seismic reflection profiling (planned for summer 2021) will used to image the fault geometry to depths of approximately 400 - 500 meters, thus providing critical constraints on the geometry of the active fault. Application of scarp degradation models, in addition to new age constraints from pending results using terrestrial cosmogenic nuclides, will improve the estimation of the modern slip rate along the South Granite Mountains Fault Zone. A final component of this study involves the kinematic analysis of mesoscopic faults in the bedrock.