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Characteristics of mantle fabrics beneath the south-central United States: Constraints from shear-wave splitting measurements

Stephen S. Gao^*,1, Kelly H. Liu¹, Robert J. Stern², G. Randy Keller³, John P. Hogan^,4, Jay Pulliam⁵ and Elizabeth Y. Anthony⁶

¹ Department of Geological Sciences and Engineering, Missouri University of Science and Technology, 129 McNutt Hall, Rolla, Missouri 65409, USA
² Geosciences Department, University of Texas at Dallas, 800 W. Campbell Road, Richardson, Texas 75080, USA
³ School of Geology and Geophysics, University of Oklahoma, 100 East Boyd Street, Suite 810, Norman, Oklahoma 73019, USA
⁴ Department of Geological Sciences and Engineering, Missouri University of Science and Technology,^, 129 McNutt Hall, Rolla, Missouri 65409, USA
⁵ Institute for Geophysics, University of Texas at Austin, J.J. Pickle Research Campus, 10100 Burnet Road, Austin, Texas 78758, USA
⁶ Department of Geological Sciences, University of Texas at El Paso, El Paso, Texas 79968, USA

New shear-wave splitting measurements at permanent broadband seismic stations in the south-central United States reveal the orientation and degree of polarization of mantle fabrics, and provide constraints on models for the formation of these fabrics. For stations on the stable North American craton, correspondence between observed polarization direction of the fast wave and the trend of Proterozoic and Paleozoic structures associated with rifts and orogenic belts implies a lithospheric origin for the observed anisotropy. The largest splitting times (up to 1.6 s) are observed at stations located in the ocean-continent transition zone, in which the fast directions are parallel to the Gulf of Mexico continental margin. The parallelism and the geometry of the keel of the craton beneath the study area suggest that asthenospheric flow around the keel of the North American craton, lithospheric fabrics developed during Mesozoic rifting, or a combination of these factors are responsible for the observed anisotropy on stations above the transitional crust.

Keywords: shear-wave splitting • seismic anisotropy • continent-ocean transitional crust • mantle flow • south-central United States