Uplift and thermal history of the Teton Range (northwestern Wyoming) defined by apatite fission-track dating

In order to determine the pattern and timing of exhumation and uplift in the Teton Range, fission-track analysis of apatites has been applied to three sections encompassing ~ 2 km of vertical relief along the Teton escarpment. The resulting data provide new insights on the doming of the Precambrian-Cambrian unconformity and on the Teton exhumation/uplift history prior to the Miocene initiation of range-front faulting. Each section exhibits successively younger fission-track ages with decreasing sample elevation. The majority of these dates are between 85 and 65 my. Mean track lengths decrease and the statistical distribution of track lengths broadens with decreasing elevation. These data indicate Late Cretaceous cooling and an inferred uplift of 1-2 km. Younger dates (26-67 my) and typically broader track-length histograms characterize the northernmost section. Although mid-to-late Cenozoic volcanic heat sources could have perturbed the northern section, modeling of two reasonable thermal sources indicates that such heat perturbation is unlikely. Instead, it appears that this section and the lower parts of the more southerly sections, which also exhibit broad track-length distributions, resided in the partial annealing zone for a considerable span of the Tertiary. The Laramide deformation in the Tetons involved both uplift and folding of the basement, rather than being restricted to compressional structures within the Phanerozoic strata. Consequently, deep-seated, basement-involved structures must have been active beneath the range in the Late Cretaceous. The fission-track data suggest that the most extensive, post-Cretaceous uplift occurred in the northern part of the Teton Range and resulted in a southward tilt of 2-3 ° between the northernmost and southernmost sections. To the extent discernable from the fission-track data, much of the arching of the Precambrian-Cambrian unconformity occurred in the Late Cretaceous and was rotated into its present position by differential footwall uplift during late Cenozoic extension.