BASIN AND CRUSTAL STRUCTURE OF THE BIGHORN MOUNTAIN REGION FROM TELESEISMIC RECEIVER FUNCTION AND SURFACE WAVE ANALYSIS: IMPLICATIONS FOR THE KINEMATICS OF LARAMIDE SHORTENING

Numerous studies propose shortening models for foreland arches, yet there has been a dearth of the detailed crustal-scale seismic imaging to test them. Proposed models predict different crustal and basin geometries.

The Bighorn Arch in northern Wyoming is an archetype of Laramide foreland arches and provides an excellent setting for the investigation of such structures. Two large Laramide foreland basins bound the arch, the Powder River Basin on its eastern flank and Bighorn Basin to the west. The Powder River Basin is deepest in the foredeep on its eastern edge, which bounds the Bighorn Arch, and shallows to the east. The foredeep of the Bighorn Basin is on its western edge and the basin thins eastward towards the Bighorn Arch.

The geometry of these basins relative to the geometry of lithospheric features (e.g., the Moho) provides a crucial test of the shortening kinematics of the Bighorn Mountains. We present passive source crustal imaging through the combination of teleseismic P wave receiver function and surface wave data. Our data was obtained from the Bighorns Arch Seismic Experiment (BASE) and EarthScope USArray Transportable Array (TA). We constrain P-wave velocity, S-wave velocity, and the depth of crustal interfaces (e.g., the Moho and basement sediment contact) in order to create 2D cross-sections through the Bighorn Basin, Bighorn Mountains, and Powder River Basin. We find that the Moho thins underneath the arch with no apparent crustal root or major fault offsets. The Moho deepens east of the range, distinctly different than the west-dipping basement-sediment contact in the Powder River Basin. Our results demonstrate that geometry of the sediment-basement contact is distinctly different from the geometry of the Moho. Combined geophysical and geological studies such as these are needed to resolve the link between the lower crust, Moho geometry, and surface deformation. The geometry and evolution of sedimentary basins provide important clues to understanding larger scale lithospheric tectonics. Our results imply that foreland basement-involved arches and their load-generated foreland basins are either independent of the underlying Moho geometry or related through complex processes such as a zone of detachment, a ductile lower crust processes, or lithospheric scale flexure.