Determining the timing and rates of fault slip within fold-thrust belts, relations between foreland thrusting and crustal thickening in metamorphic hinterlands, and relations between thrust loading and foreland basin subsidence are critical for understanding evolution of mountain systems along convergent plate boundaries. This study will combine detailed thermochronology studies and structural analysis of thrust sheets and sedimentary rocks in associated basins to determine timing of initiation and duration of faulting, fault slip rates, and erosion histories of two "dominant" thrust sheets in the Sevier fold-thrust belt, the Willard thrust sheet in northern Utah and the Wheeler Pass thrust sheet in southern Nevada and adjacent California. These thrust sheets provide an exceptional opportunity to quantify fault slip and thermal histories as they are well exposed, have large displacements (20-50 km), exhibit significant (>5 km) structural relief, and contain rocks suitable for application of thermochronology methods. Three sampling strategies will be used to elucidate thermal, erosion, and fault slip histories: multiple thermochronometers (muscovite and K-feldspar 40Ar/39Ar, zircon and apatite fission track, and zircon U-Th/He that cover a range of closure temperatures from 400° to 100°C) will be combined to determine temperature-time paths for individual locations in thrust sheets; variations in cooling ages along vertical transects through thrust sheets will be completed to constrain exhumation rates; and variations in ages along horizontal transects in the fault slip direction across thrust sheets will be used to estimate fault slip rates. Thermochronologic data will be compared with thermal models for a range of fault geometries constrained by structural analysis, boundary conditions, and erosion histories constrained by analysis of sediments shed from thrust sheets and deposited in associated foreland basins. Results will improve understanding of the poorly defined timing of initiation of thrusting in the Sevier belt, temporal correlations between shortening in the fold-thrust belt and the complex tectonic history of the metamorphic hinterland, and along strike variations in emplacement of the dominant thrust sheets that were key mechanical components in development of the Sevier belt. The application of multiple thermochronometers using detailed sampling schemes will serve as a case study for on how to robustly estimate thermal histories in thrust systems, which is critical for understanding hydrocarbon maturation and targeting potential hydrocarbon accumulations. The project is a collaborative effort between researchers at the University of Nevada-Las Vegas and Weber State University. As part of the project, graduate students and undergraduate students from both universities will conduct collaborative research and communicate results through scientific meetings and publications, providing significant scientific training. The work may also contribute to understanding/exploration for hydrocarbon and mineral resources in the Great Basin.
