Shortening episodes in the Sevier hinterland within the larger context of the Cordilleran retroarc thrust system: Insights from the Cretaceous Newark Canyon Formation in central Nevada

Abstract:

Documenting the spatio-temporal progression of deformation within fold-thrust belts is critical for understanding orogen dynamics, and sedimentary basins associated with upper-crustal shortening can provide important records of deformation timing. In the North American Cordillera, the geometry, magnitude, and timing of shortening across a broad region of Nevada known as the ‘Sevier hinterland’ have been difficult to characterize due to limited exposures of syn-contractional sedimentary rocks and overprinting of Cenozoic extension. To elucidate the depositional and deformational history of the Sevier hinterland, we present new geologic mapping, stratigraphic divisions, U-Pb detrital zircon geochronology, and clast composition data from three separate exposures of the Cretaceous Newark Canyon Formation (NCF), a synorogenic sedimentary unit in central Nevada. In the Cortez Mountains, NCF deposition is bracketed between ~120 and ~106 Ma, and is hypothesized to be related to thrusting or folding in the proximal region to the west. In the southern Fish Creek Range, NCF deposition is bracketed between ~130 and ~100 Ma, and was likely related to motion on an east-vergent thrust fault exposed on the western flank of the range. In the central Pancake Range, NCF deposition is bracketed between ~129 and ~66 Ma, and post-dated large-scale, east-vergent folding. We incorporate these timing constraints into a compilation of deformation episodes in the Sevier hinterland. Late Jurassic (~165-155 Ma) shortening, which largely post-dated shortening in the Luning-Fencemaker thrust belt in western Nevada and pre-dated initial deformation in the Sevier fold-thrust belt to the east in Utah, is interpreted to represent diffuse, low-magnitude deformation that accompanied eastward migration of the basal Cordilleran décollement. Cretaceous (~130-75 Ma) hinterland shortening, which includes deformation associated with NCF deposition in central Nevada, was contemporaneous with shortening in the Sevier fold-thrust belt to the east. This is interpreted to represent long-duration strain partitioning between foreland and hinterland positions in the Cordilleran thrust belt during continued coupling above the basal décollement and the progressive westward underthrusting of thick North American lower-middle crust.