Abstract: Structure and Kinematic Genesis of the Quealy Wrench Fault Duplex: Product of Laramide Reactivation of Precambrian Shear Zones of the Cheyenne Belt in the Laramie Basin, Wyoming

Donald S. Stone

The Cheyenne belt is a series of northeast-trending mylonite zones described from the Medicine Bow Mountains of southwestern Wyoming. This belt has a complex deformational history with identifiable events in Archean through Proterozoic time (>2500 through 1700 Ma). It is interpreted as a collisional suture zone separating the Wyoming Archean province on the north from accreted Proterozoic island arc terrains on the south. In the Laramie basin, footwall to the Arlington thrust which borders the Medicine Bow Mountains on the east, subsurface studies indicate that northeast-trending faults in Phanerozoic rocks extend across the basin and probably reflect Precambrian shear zones of the Cheyenne belt that were variably reactivated under probable east-west directed principal horizontal s ress during several Phanerozoic deformational episodes.

A large seismic and borehole data base in the Quealy/James Lake area outlines a complex pop-up structure, which is interpreted as part of a left-stepping, dextral wrench fault duplex. This duplex is comprised of three west-dipping, north-northwest trending, basement-involved thrust faults, and one antithetic detachment (in Permian shales) thrust, confined between the east-northeast trending South Quealy and North Quealy fault zones. Along the south edge of the central Quealy pop-up, measurements based on differential shortening along either side of the South Quealy fault zone indicate that horizontal and vertical slip components are about equal (i.e., approx. 1 km). Laramide faulting and uplift produced the traps for oil accumulations in Cretaceous, Jurassic, and Permo-Pennsylvanian s ndstones in the Quealy oil field. Structural details are shown with maps, cross sections, and seismic profiles. Also, an interpretive, kinematic developmental sequence is diagrammed.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994