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 applie d to three sections encompassing approximately 2 km of vertical relief along the Teton escarpment. The resulting data provide new insights o n the doming of the Precambrian-Cambrian unconformity and on the Teton exhumation/uplift history prior to the Miocene initiation of range-fr ont faulting. Each section exhibits successively younger fission-track ages with decreasing sample elevation. The majority of these dates ar e between 85 and 65 my. Mean track lengths decrease and the statistica l distribution of track lengths broadens with decreasing elevation. Th ese data indicate Late Cretaceous cooling and an inferred uplift of 1- 2 km. Younger dates (26-67 my) and typically broader track-length hist ograms characterize the northernmost section. Although mid-to-late Cen ozoic volcanic heat sources could have perturbed the northern section, modeling of two reasonable thermal sources indicates that such heat p erturbation 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 T etons involved both uplift and folding of the basement, rather than be ing restricted to compressional structures within the Phanerozoic stra ta. Consequently, deep-seated, basement-involved structures must have been active beneath the range in the Late Cretaceous. The fission-trac k data suggest that the most extensive, post-Cretaceous uplift occurre d in the northern part of the Teton Range and resulted in a southward tilt of 2-3-degrees between the northernmost and southernmost sections . To the extent discernable from the fission-track data, much of the a rching of the Precambrian-Cambrian unconformity occurred in the Late C retaceous and was rotated into its present position by differential fo otwall uplift during late Cenozoic extension.