Kinematics and timing of orogen-parallel flow, Grouse Creek Mountains, Utah
Alternating contractional and extensional events in orogenic belts play a significant role in dynamically adjusting crustal thickness during regional contraction. Distinguishing between these two contrasting kinematic regimes is not only important for understanding the tectonic setting but also provides insights into the dynamics of evolving orogenic wedges. The earliest pervasive fabric, D1, in the Grouse Creek Mountains of northwest Utah is interpreted to have played an integral role in accommodating such a dynamic adjustment. It is interpreted that focused crustal thickening led to differences in gravitational potential energy along strike, facilitating an episode of mid-Cretaceous synconvergent orogen-parallel extension. The D2 event is a previously undocumented deformational event in the Pennsylvanian-Permian Oquirrh Formation and overprints the earlier D1 fabric. D 2 is characterized by an axial planar cleavage, S2, associated with east-verging north-northeast-trending large-scale folds at Marble Peak, South Hill and the Rosebud area, and is interpreted to record a top-to-the southeast contractional event.