Insight into the Evolution of the Eastern Margin of the Wyoming Craton from Complex, Laterally Variable Shear Wave Splitting

Author:

Birkey Andrew12ORCID,Ford Heather A.1,Anderson Megan3,Byrnes Joseph S.4,Bezada Maximiliano J.5,Shapovalov Maxim16

Affiliation:

1. Department of Earth and Planetary Sciences, University of California - Riverside 1 , Riverside, CA , USA

2. Department of Earth Sciences, University of Delaware 2 , Newark, DE , USA

3. Department of Natural Resources, Washington Geological Survey 3 , Olympia, WA , USA

4. School of Earth and Sustainability, Northern Arizona University 4 , Flagstaff, AZ , USA

5. Department of Earth and Environmental Sciences, University of Minnesota 5 , Twin Cities, Minneapolis , USA

6. Department of Geography, University of Oregon 6 , Eugene, OR , USA

Abstract

Abstract Dense seismic arrays such as EarthScope’s Transportable Array (TA) have enabled high-resolution seismic observations that show the structure of cratonic lithosphere is more heterogeneous and complex than previously assumed. In this study, we pair TA data with data from the Bighorn Arch Seismic Experiment and the Crust and lithosphere Investigation of the Easternmost expression of the Laramide Orogeny (CIELO) to provide unprecedented detail on the seismic anisotropic structure of the eastern margin of the Wyoming Craton, where several orogens emerged from nominally strong cratonic lithosphere during the Laramide Orogeny. In this study, we use the splitting of teleseismic shear waves to characterize fabrics associated with deformation in the Earth’s crust and mantle. We constrain distinct anisotropic domains in the study area, and forward modeling shows that each of these domains can be explained by a single layer of anisotropy. Most significantly, we find a fast direction in the southern part of the Powder River Basin, which we refer to as the Thunder Basin Block (TBB), that deviates from absolute plate motion (APM). This change in splitting behavior coincides with changes in other modeled geophysical observations, such as active source P-wave velocity models, potential field modeling, and seismic attenuation analysis, which all show a significant change moving from the Bighorn Mountains to the TBB. We argue that these results correspond to structure predating the Laramide Orogeny, and most likely indicate a Neoarchean boundary preserved within the lithosphere.

Publisher

GeoScienceWorld

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