U-Pb dating of calcite veins reveals complex stress evolution and thrust sequence in the Bighorn Basin, Wyoming, USA

We report U-Pb absolute ages of calcite cements from a diffuse vein network documented in the Bighorn Basin (Wyoming, USA), where distinct systematic vein sets developed at the front of the thin-skinned Sevier orogen, during Laramide layer-parallel shortening, and during thick-skinned Laramide thrusting and folding. The U-Pb age distribution illustrates: (1) an outward (eastward) transmission of Sevier orogenic stress (from 89.7 ± 2.9 Ma [2σ] in the west, and from 75.3 ± 2.8 Ma in the east); and (2) an inward (westward) development of Laramide-related fracturing and folding (72 ± 3.0 Ma and 45.4 ± 1.8 Ma, respectively, in the east; 60.5 ± 4.6 Ma and 27.9 ± 1.1 Ma, respectively, in the west), which is in accordance with the known sequence of exhumation of the major Laramide basement arches. Our results also show that the stress related to Laramide compression first overprinted the stress related to Sevier compression in the sedimentary cover around major basement uplifts. This study highlights the utility of U-Pb calcite geochronology as a powerful tool for constraining complex sequences of deformation in orogenic forelands.