Thermochronological and Geochronological Constraints on Late Cretaceous Unroofing and Proximal Sedimentation in the Sevier Orogenic Belt, Utah

摘要

A source-to-sink analysis incorporating geochronometric and thermochronometric data from the Sevier fold-thrust belt (SFTB) and proximal synorogenic strata of the Canyon Range Conglomerate (CRC) and Indianola Group (IG) provides new insights into orogenic exhumation, erosional unroofing, and the interplay between thrusting and coarse clastic deposition in the Cretaceous Cordilleran foreland basin of western North America. Zircon (U-Th)/He ages from the Pavant and Nebo thrust sheets record significant Cenomanian cooling indicative of synchronous exhumation and thrusting along a large segment of the SFTB in central and northern Utah. Detrital zircon (U-Th)/He (DZHe) ages indistinguishable from depositional ages from the Cenomanian Dakota Formation and lower CRC also record rapid unroofing of the SFTB and synchronous deposition. DZHe data from wedge-top deposits of the CRC record two significant unroofing episodes: Albo-Cenomanian exhumation of the Pavant thrust and progressive unroofing of the Canyon Range culmination. For the IG, the presence of Paleozoic DZHe ages along with Paleozoic-Mesozoic DZ U-Pb ages in the Cenomanian Sanpete Formation suggests derivation from Paleozoic to Jurassic strata exhumed in the frontal Pavant and Nebo thrust sheets. After the Cenomanian episode of rapid exhumation, proximal foredeep strata recorded a widespread DZ provenance shift in the Turonian. Short DZHe lag time values from Campanian CRC and IG deposits reveal rapid exhumation of the SFTB during the Campanian. The synchroneity of major shortening and Campanian and Cenomanian changes in foreland basin architecture and provenance supports models proposing that active shortening in the fold-thrust belt coincides with coarse clastic influx in foreland basins.