THREE-DIMENSIONAL KINEMATIC HISTORY OF THE WYOMING SALIENT OF THE SEVIER OROGENIC BELT

Mountain belts display curvature at a variety of scales, reflecting complex 3D displacement fields related to orogenic wedge properties and boundary conditions. To better understand origins of curvature, a collaborative effort is underway to determine the 3D kinematic history of the Wyoming salient of the Sevier orogenic belt. Regionally, the orogenic belt includes a metamorphic hinterland, a fold-thrust belt that deformed thick miogeoclinal to platform strata, and a foreland deformed by Laramide uplifts. Paleomagnetic and strain data from the Triassic Ankareh and Jurassic Twin Creek Formations in the fold-thrust belt record systematic kinematic patterns. Moderate counter-clockwise rotations (~10 to 30°) are widespread in the northern part of the salient, with larger (up to 50°) rotations in frontal thrust sheets that interacted with the Gros Ventre foreland uplift. Variable clockwise rotations and multiple fold phases occur in the southern part of the salient where thrust sheets interacted with the Uinta foreland uplift. Widespread early LPS produced minor folds, wedge faults, and cleavage subperpendicular to bedding, and cross striking veins record widespread, minor tangential extension parallel to structural trends. Principal shortening directions fan about the salient, reflecting a combination of initial curvature and vertical axis rotation of LPS fabrics. Shortening varies from generally <10% in frontal thrust sheets (increasing toward salient ends), to ~20% in more interior sheets. Backbone cross sections indicate ~150 to 200 km of shortening from major folds and faults (decreasing toward salient ends), with an additional ~30 to 50 km from LPS strain. Work is underway to assemble 3D reconstructions of the salient incorporating progressive rotations. A crustal scale section from the hinterland to foreland, integrating regional structural, geochronological, and sedimentological data, provides a basis for tectonic synthesis. Curvature in the Wyoming salient appears related to: primary thickness variations of the sedimentary wedge; differential shortening to maintain 3D orogenic wedge taper; interaction with Laramide foreland uplifts at salient ends; and linkage to a complex history of lower crustal thickening to upper crustal extension in the metamorphic core.