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Structural studies in the Wyoming-Idaho segment of the Cordilleran thrust belt have provided insight into the nature and origin of the broad, east-facing salient west and southwest of Jackson, Wyoming. Changes in the orientation of regional fracture patterns and compression directions determined by dynamic analysis of calcite twins both indicate that the thrust sheets rotated into the salient in a counterclockwise direction. Furthermore, both field observations and calcite twin data show that there has been a large amount of subhorizontal, strike-normal deformation in the Prospect thrust sheet in the Teton Pass area, where the Prospect and Cache Creek thrusts are in direct contact. Subsurface evidence from Teton valley and the Hoback basin dates the Cache Creek thrust as lder than the Prospect, Darby, and Absaroka thrusts.
Balanced cross sections drawn along deformation paths through the area show that movement on the Prospect thrust increases from less than 11 km (7 mi) near Victor, Idaho, to more than 37 km (23 mi) south of Jackson Hole. The fracture pattern and calcite twin data also show that the thrust sheets have rotated by as much as 40°. Palinspastic maps made by the sequential restoration of the cross sections show that prior to movement on the Prospect thrust, both the Darby and Absaroka thrusts curved gently to the northwest. As the Prospect sheet moved, it began to impinge upon the previously emplaced Teton-Gros Ventre uplift. The result was the rotation of the Prospect and piggyback Darby and Absaroka thrust sheets. The deformation due to this bending was taken up primarily by differen ial rotation of imbricate and main thrust sheets. An accurate understanding of the timing of these structural events relative to the timing of hydrocarbon generation and migration should be an essential factor in any exploration model of the area.
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