Late-stage Laramide reactivation of Precambrian structures: evidence for ~N-S Laramide shortening along the southeastern margin of the Wind River Mountains, Wyoming
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Deformation along the southeastern margin of the Wind River Mountains during the late stages of the Laramide orogeny is a result of local ~N-S Laramide shortening, which is in contrast to the regional NE-SW shortening typical in the Laramide orogen. The shortening resulted in the reactivation of Precambrian brittle structures that are concentrated north of the region where the trend of the Wind River thrust changes from its typical NW-SE trend to a more E-W trend. The Spring Creek fault (SCF) is an ENE-trending feature that extends from the Archean core of the range across Paleozoic and Mesozoic units deformed in Sheep Mountain anticline (SMA). Laramide reactivation of the Spring Creek fault produced reverse, south-side-up offset and steep to overturned sections of the Tensleep Sandstone and Madison Limestone on the hanging wall of the fault. The Beaver Creek thrust (BCT), just south of the Spring Creek fault, is a largely E-W trending, northerly dipping Laramide fault that terminates at the Spring Creek fault. It is the controlling fault along the southern margin of the Schoettlin Mountain anticline (ScMA), which is cored by Archean granitic gneiss. Results from mapping, structural analysis, fracture analysis, and 2D seismic experiments all show consistent late-stage ~N-S Laramide compression throughout the area. The ~E-W orientations of the Beaver Creek thrust and the Spring Creek fault, parallel to the ~E-W trace of the Wind River thrust to the south, are interpreted as late-stage hanging wall deformation above the Wind River thrust.