Abstract

The Canyon Range, Pavant, Paxton, and Gunnison thrust systems in central Utah form the Sevier fold-and-thrust belt in its type area. The Canyon Range thrust carries an ∼12-km-thick succession of Neoproterozoic through Triassic sedimentary rocks and is breached at the surface by the Neogene extensional Sevier Desert detachment fault. The Pavant, Paxton, and Gunnison thrusts carry Lower Cambrian through Cretaceous strata and have major footwall detachments in weak Jurassic rocks. The Canyon Range thrust was active during latest Jurassic–Early Cretaceous time. The Pavant thrust sheet was emplaced in Albian time, formed an internal duplex beneath the Canyon Range during the Cenomanian, and then developed a frontal duplex during the Turonian. The Paxton thrust sheet was initially emplaced during the Santonian, and subsequently formed the Paxton duplex during the early to mid-Campanian. Some slip on the Paxton system was fed into a frontal triangle zone along the Sanpete Valley antiform. The Gunnison thrust system became active in late Campanian time and continued to feed slip into the frontal triangle zone through the early Paleocene. The Canyon Range and main Pavant thrust sheets experienced long-distance eastward transport (totaling >140 km) mainly because they are composed of relatively strong rocks, whereas the eastern thrust sheets accommodated less shortening and formed multiple antiformal duplexes in order to maintain sufficient taper for continued forward propagation of the fold-and-thrust belt. Total shortening was at least 220 km. Upper crustal thickening of ∼16 km produced crust that was >50 km thick and a likely surface elevation >3 km in western Utah. Shortening across the entire Cordilleran retroarc thrust belt at the latitude of central Utah may have exceeded 335 km. The Late Cretaceous paleogeography of the fold-and-thrust belt and foreland basin was similar to the modern central Andean fold-and-thrust belt, with a high-elevation, low-relief hinterland plateau and a rugged topographic front. The frontal part of the Sevier belt was buried by several kilometers of nonmarine and shallow-marine sediments in the wedge-top depozone of the foreland basin system. The Canyon Range thrust sheet dominated sediment supply throughout the history of shortening in the Sevier belt. Westward underthrusting of a several hundred-kilometer-long panel of North American lower crust beneath the Cordilleran magmatic arc is required to balance upper-crustal shortening in the thrust belt, and may be petrogenetically linked to a Late Cretaceous flare-up of the magmatic arc as preserved in the Sierra Nevada Batholith.

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