DETRITAL CLAST THERMOCHRONOLOGY RECORDS THE EXHUMATION AND UNROOFING HISTORY OF THE SEVIER THRUST BELT OF NORTHEAST UTAH

Synorogenic sediment exhumed and eroded from thrust sheets provides a powerful record of the evolving deformational style and tempo of deformation in the thrust belt system. This study presents new zircon (U-Th)/He thermochronology of detrital sandstone clasts deposited in Aptian – Campanian synorogenic units of the Sevier foreland basin of northeast Utah. Provenance analyses including sandstone petrography and U-Pb geochronology link all clasts in this study to the Pennsylvanian – Permian Weber Sandstone indicating that all clasts were exhumed from a similar burial depth. We use measured cooling ages and thermal history modeling to evaluate the record of rock cooling throughout thrust belt evolution and propagation. Both the distribution of individual cooling ages and the modeled timing of Cretaceous cooling young upsection suggesting that there is a tight connection between actively exhuming structures and the thermal record of exhumation preserved in synorogenic foreland basin units. Aptian – Turonian units deposited during the deformation of the Willard thrust sheet consistently record a ~ 15 - 20 Myr lag time between exhumation and deposition. By the Campanian, lag times decrease to as little as ~ 0 Myrs reflecting faster rock exhumation associated with the exhumation of the Wasatch Anticlinorium. This study proves a powerful example of how synorogenic detrital thermochronology can track changes in rock exhumation throughout the deformational history of a thrust belt.