STRUCTURE AND KINEMATIC GENESIS OF THE QUEALY WRENCH DUPLEX - TRANSPRESSIONAL REACTIVATION OF THE PRECAMBRIAN CHEYENNE BELT IN THE LARAMIE BASIN, WYOMING

Seismic and borehole data in the southern Laramie basin of southeaster n Wyoming outline a fault-bordered pop-up structure that is central to the Quealy wrench duplex and the site of the Quealy Dome oil field. T his contractional duplex formed at a restraining fault offset between two parallel, laterally extensive, northeast;ast-trending fault zones- the South and North Quealy faults. Spaced about 2 mi (3.2 km) apart, t hese parallel fault zones are interpreted as wrench straights, equival ent to the floor and roof thrusts of a duplex in a fold and thrust bel t, but described in map view rather than in cross section. The Quealy wrench duplex is comprised of three east-vergent, basement-involved th rust imbricates and a west-vergent, antithetic thrust, detached in Per mian shales. Duplex thrusts strike at high angles to the bordering Sou th and North Quealy fault zones. Measurements based on interpretive pi ercing-point evidence and fault-parallel, differential shortening indi cate: that net slip on the dominant South Quealy fault zone is dextral oblique. A component of dextral slip is also indicated on the North Qu ealy fault zone. The South Quealy fault and North Quealy/Overland faul t trends can be traced southwesterly into the footwall of the north-tr ending Arlington (basin-boundary) thrust and projected into the Precam brian Cheyenne belt of the Medicine Bow Mountains in the hanging wall of the Arlington thrust. It is proposed that the Quealy wrench duplex is a product of Precambrian shear zone reactivation along the Cheyenne belt under Permian and Laramide (Tertiary) transpression.