Interaction between the northern Idaho-Wyoming thrust belt and bounding basement blocks, central western Wyoming

The curved east-facing salient of the Idaho-Wyoming thrust belt is a prime location to study well-dated interactions of foreland basement-cored uplifts and thrust belt development. Both field and fabric data, as well as analyses of twinned calcite, have been used to infer the deformation paths of rocks within the Absaroka, Darby, and Prospect thrust sheets as they approached the bounding foreland basement-cored uplifts. Each thrust sheet has a specific fracture pattern that maintains a constant orientation relative to the curvilinear strike of each thrust fault. Mean shortening directions computed from twinned calcite are layer-parallel, except in samples taken from sedimentary cover rocks of the basement uplifts, and mean compression and shortening axes are normal to local thrust strike. The joint and calcite fabric data indicate that the stress, strain, and presumably, deformation paths of each thrust sheet were normal to both the strike of the thrust fault, where it is exposed, and the base of the thrust ramp. Similarly, these data suggest that thrust sheet rotation, as much as 40° in a counterclockwise sense, took place as these thrust sheets approached the salient-bounding basement uplifts. South of Hoback Canyon, where there is no nearby basement uplift, a clockwise rotation of 36° is suggested. Interpretation of the thrust belt and Teton-Gros Ventre buttress tectonic history is based on deformation paths, cross sections, palinspastic maps, and well-documented timing relationships (Wiltschko and Dorr, 1983) of both terranes. Differential rotation and frontal imbrication are the primary responses of these thrust sheets to accommodate rotation into parallelism with the bounding basement uplifts.