Investigating the role of lithospheric heterogeneity in localizing deformation during the Laramide Orogeny: Insights from seismic attenuation

Abstract:

Cratons, the ancient and stable cores of continental lithosphere, are considered to be protected from tectonic deformation by their strong, highly depleted mantle roots. Nevertheless, the Wyoming Craton underwent reactivation during the Laramide Orogeny, which resulted in a series of basement-cored uplifts that built the modern-day Rockies. The easternmost expression of this orogeny, the Black Hills in South Dakota, are separated from the main trend of the Rocky Mountains by a relatively flat region, that we refer to as the Thunder Basin (southern part of the Powder River Basin). Seismic tomography studies have indicated that a high velocity anomaly is present below the basin, extending to the depth of ~300 km and possibly representing a lithospheric keel. We investigate the hypothesis that the Thunder Basin acted as a rigid block transferring Laramide stresses east to the Black Hills by conducting seismic attenuation analysis. We utilize data from the CIELO seismic array, which extends from the Black Hills, across the Thunder Basin and into the Owl Creek Mountains, along with data from the BASE FlexArray deployment and the EarthScope Transportable Array. We analyze seismograms from deep teleseismic events and compare waveforms in the time-domain to characterize lateral attenuation variations. Measurements are combined to produce maps of teleseismic attenuation using linear and Bayesian approaches. Both procedures indicate that attenuation beneath the Thunder Basin Block is low, while it is high beneath the Black Hills. Furthermore, the Bighorn Mountains also correspond to a local high in attenuation while the Bighorn Basin is a local low, and the pattern is also observed elsewhere in the study area. We conclude that lateral variations in lithospheric strength, as evidenced by our seismic attenuation measurements, played an important role in the localization of deformation and orogenesis during the Laramide Orogeny.