Morphology of the Casper Mountain uplift and related, subsidiary structures, central Wyoming: Implications for Laramide kinematics, dynamics, and crustal inheritance

Abstract

The general east-west trend of the regional-scale, fault-related Cas per Mountain uplift in central Wyoming reflects a preexisting Pre cambrian fabric along which there was Laramide compressional re activation. Initial fault displacement on the south-dipping Casper Mountain fault zone probably predates displacement on the inter secting, northwest-trending, northeast-dipping Casper arch thrust that forms the northeastern border of the Wind River basin. Later phase, incremental, Laramide displacements occurred along both fault zones: left-oblique slip on the Casper Mountain fault zone, dip slip on the crosscutting Casper arch thrust. Basement-involved thrust generation of the subsidiary Laramide, northwest-trending Iron Creek and Emigrant Gap anticlines along the north (footwall) side of the Casper Mountain fault zone also occurred during this later phase Laramide deformation. Perturbation of far-field, northeast-southwest, Laramide max imum horizontal paleostress trajectories (s1) to local, nearly fault-normal orientation at Casper Mountain, together with strain par titioning, is proposed to explain the apparent coeval development of divergent hanging-wall and footwall, basement-involved, fault-related structures. This kinematic and dynamic interpretation may be applied conditionally to other east-west-trending Laramide up lifts in the central Rocky Mountain foreland province.