LOW-TEMPERATURE THERMOCHRONOLOGICAL CONSTRAINTS ON THE TIMING, MAGNITUDE, AND SPATIAL EXTENT OF LATE CRETACEOUS COOLING WITHIN THE ENIGMATIC TETON-GROS VENTRE UPLIFT

The modern topography of the Teton Range, formed as a consequence of mid-Miocene to recent exhumation along the Teton normal fault, obscures the structural and topographic expression of the Cretaceous basement-involved Teton-Gros Ventre uplift.. Previously published apatite fission-track cooling ages from basement rocks of the Teton Range were interpreted to record Late Cretaceous exhumation of the Teton-Gros Ventre uplift in the hanging wall of the northeast-dipping Cache Creek thrust. To evaluate the spatial extent, timing, and magnitude of Cretaceous cooling in the Tetons, we used low-temperature thermochronology (zircon and apatite U-Th/He; ZHe and AHe) to reconstruct the ~300-50˚C thermal history of Archean basement rocks in an ~40 km long transect through the hanging wall of the Cache Creek thrust. Samples from the northern part of our transect, in the most distal positions relative to the trace of the Cache Creek thrust, yielded single crystal ZHe dates of ~6-62 Ma with effective uranium (eU), a proxy for radiation damage, values of 353-6341 ppm, exhibiting a negative-slope date-eU trend that is qualitatively consistent with radiation damage effects on ZHe dates. In contrast, AHe dates from these rocks are ~51-79 Ma, with eU values of 11-66 ppm; these AHe data show no correlation between AHe date and eU and display a date inversion relative to the ZHe data. Farther south and closer to the Cache Creek thrust, ZHe dates are ~19-116 Ma (eU 100-2071 ppm) and also display a negative date-eU trend. Across the entire range, the ZHe date-eU trend has a high-eU (2300-6341 ppm) ‘pediment’ at ~10 Ma, related to the recent Miocene-recent exhumation. The high-eU composition of the analyzed zircons likely contributed to the young measured ZHe dates because significant radiation damage can create pathways for helium loss, leading to younger measured dates. Ongoing thermal history modeling will allow us to identify time-temperature histories consistent with the observed data and preserved geologic record, providing insights into the cooling history of the Cretaceous Gros-Ventre uplift.