CONSTRAINING EXHUMATION OF THE NORTH AMERICA CORDILLERA BY MULTIPLE LOW-TEMPERATURE THERMOCHRONOLOGY OF UPPER CRETACEOUS FORELAND BASIN DEPOSITS

Regional timing and exhumation of the North American Cordillera can be determined by detrital thermochronology of accessory minerals in foreland basin deposits, serving as a proxy for deformation and tectonics. We examined Middle to Upper Cretaceous foreland basin deposits from the Sevier fold and thrust belt located in northeast Utah and southwest Wyoming using the zircon (U-Th)/He (ZHe) and apatite fission track (AFT) low-T-thermochronological systems. ZHe ages of Quartzite clasts from the Lower Echo Canyon Conglomerate (88-86 Ma) derived from the Paleozoic and lower Mesozoic units of the Willard Sheet, suggest partial resetting during the Sevier orogeny of the zircon (U/Th)/He system with a large potential for radiation damage in the grains. AFT ages from the same clasts instead record Cretaceous ages resulting in short lag times in relation to their depositional age, owing to rapid exhumation. Furthermore, we analyzed five samples from the Upper Cretaceous distal foreland basin deposits for AFT analysis. AFT cooling ages show a younging trend up section, indicating that post deposition burial was not significant. The youngest age peaks in each sample plot within error of the deposition age. These preliminary results suggest that the source of clastic material in the distal foreland was exhuming rapidly and that significant recycling of material is absent. To distinguish exhumation ages from volcanic ages in these detrital samples, future work will focus on doubling dating using U-Pb LA-ICP-MS on the youngest apatite populations. Combined with previous work, this study completes a detailed multi-dating approach to understanding exhumation of the North American Cordillera from the Upper Jurassic to the Upper Cretaceous.