STRUCTURE OF THE MOUNT-RAYMOND TRANSVERSE ZONE AT THE SOUTHERN END OFTHE WYOMING SALIENT, SEVIER FOLD-THRUST BELT, UTAH

The Mount Raymond transverse zone (MRTZ) forms the east-west-trending boundary between the Wyoming salient of the Sevier fold-thrust belt an d the Uinta/Cottonwood arch in north-central Utah. Major faults in the zone dip 40 degrees to 45 degrees north. Our structural analysis indi cates that the MRTZ contains both contractional and extensional struct ures. The contractional structures (thrusts and related folds) initial ly formed as part of a southeast-verging, northeast-trending thrust sy stem. This system gradually curved and merged to the north with the ea st-verging Absaroka thrust system in the apex of the Wyoming salient. The contrast in trend between structures in the MRTZ and those in the apex of the Wyoming salient reflects the initial curvature of the sali ent. This curve formed because the stratigraphic sequence involved in thrusting thinned gradually southward, toward the axis of a proto-Uint a arch. The present east-west trend of the MRTZ developed during Laram ide uplift of the Uinta/Cottonwood arch, an event which tilted the fau lts into their present position. Cenozoic crustal extension subsequent ly reactivated segments of the MRTZ. In sum, the evolution of the MRTZ illustrates how post-thrusting processes can affect the map-view geom etry of thrust belts to create transverse zones.