Deformation Processes At The Leading Edge Of The Sevier Fold And Thrust Belt Southwest Utah PDF Download

The Sevier thrust belt is one of the best-preserved thrust belts in the world and has been the focus of many studies attempting to understand the mechanics of deformation and erosion in thrust belts. The deformation history of eastward propagation of thrust sheets has been interpreted in part from the foreland basin which provides a record of synorogenic clastic material from 120 - 50 Ma. Previous studies have documented rates and kinematics of thrusting using thermochronology of rocks exposed in individual thrust sheets. However, we still do not understand the link between styles of deformation and exhumation rates. We use provenance analysis (sandstone petrography and U-Pb detrital zircon geochronology) to target synorogenic clasts eroded from the Pennsylvanian - Permian strata and deposited in the Cretaceous - Eocene Sevier foreland strata for zircon (U-Th)/He (ZHe) thermochronology. These clasts are derived from strata known to be exposed across all structures in the Sevier system and can be used to track exhumation across eastward propagating thrust sheets and the passively uplifting Wasatch Anticlinorium. Our ZHe cooling ages show a younging up-section which correlates to the eastward propagation of thrust sheets. ZHe distributions from clasts have one of three unique thermal histories, representing exhumation on specific a structural feature in the Sevier fold-thrust belt and Laramide including 1) exhumation at ~125 Ma on the Willard thrust which is observed in clasts deposited from 120 - 90 Ma (Kelvin, Frontier, and Henefer Formation), 2) exhumation at ~90 Ma on the Crawford thrust of clasts deposited from ~85 -75 Ma (Echo Canyon Conglomerate) and 3) exhumation at ~70 Ma possibly from the Uinta-Cottonwood Arch observed in clasts deposited from ~60 - 50 Ma (Wasatch Formation). We utilize lag time calculations to understand the relationship between deformation and exhumation related to orogenic steady state. We observe constant lag time trends from ~120 - 70 Ma and an increase ~70 - 50 Ma. Within individual thrust sheets, we observe a relationship between active thrust sheets which are associated with short lag times and Laramide structures which are associated with long lag times.