Abstract
Upper mantle fabric, as detected by shear wave splitting measurements, records lithospheric strain history that may be related to past tectonic events. We present SKS (core‐refracted shear wave) splitting measurements taken around the western Great Lakes, North America: the Archean Superior Province (SP) and surroundings. We analyze 40 sites in the USA and 5 in Canada and outline a region of strong anisotropy corresponding to a high‐velocity zone in tomographic models, which we dub the Western Superior Mantle Anomaly (WSMA) and interpret to represent a preserved fabric from accretion of the SP. To the southwest of the WSMA, we locate a region of rotated fast direction corresponding to a linear low‐velocity feature observed by tomography and which may represent a failed branch of the Mid‐Continent Rift. Further south, within the Minnesota River Valley Terrane, the split times drop to near zero, suggesting isotropic lithosphere resulting from vertical (diapiric) rather than horizontal tectonic processes.
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