Revisiting uplift in the Laramide Orogeny: Evidence for the Localization of Deformation by Variations in Lithospheric Strength from both Seismic Velocity and Attenuation
Abstract
The Rocky Mountains feature intermittent landforms, with mountains separated by relatively undeformed basins. Previous studies have suggested a connection between pre-Laramide crustal weaknesses and the localization of deformation. Although seismic tomography results reveal significant heterogeneity in the lithospheric mantle, the connection between deformation and deeper lithospheric structure has received comparatively little attention. In southern China and Iberia, thicker lithospheric blocks appear to be associated with undeformed regions. We investigate the possible connection between deformation, topography and lithospheric structure, in Wyoming and surrounding regions. Newly available data from local arrays, including the recent CIELO and FlexArray BASE experiment, enable us to construct a finer scale teleseismic P-wave velocity model than was previously available. The tomographic model is jointly interpreted with constraints on seismic attenuation from teleseismic t* measurements at the same stations. We find a moderate correlation between seismic velocity above 200 km, path integrated seismic attenuation, the abundance of seismicity and topography in the Laramide uplifts of Wyoming and South Dakota. Multiple small-scale anomalies in both velocity and attenuation spatially coincide with the basement-cored uplifts. The results imply the presence of colder and thicker lithosphere beneath the basins and warmer and thinner lithosphere beneath the mountain ranges. Given the modest amount of shortening across any individual range, we assume the lithospheric structure is not a consequence of contraction and existed Pre-Laramide. Therefore, localization of deformation is likely associated with pre-existing variations in lithosphere strength, which may have contributed to the formation of crustal weaknesses along which the uplift of ranges like the Bighorn Mountains and the Black Hills occurred.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.S45G..11Z