EXHUMATION OF THE GRANITE MOUNTAINS, WY - INSIGHTS FROM THE BATTLE SPRINGS FORMATION

The Laramide Orogeny is characterized by basement-cored block uplifts and resulting intermontane basins that developed within the retroarc foreland basin of the Sevier fold-thrust belt. The Granite Mountains are an east-west trending mountain range in central Wyoming spanning approximately 150 km with peak modern elevations near 2.5 kilometers. Uplift and erosion of the Granite Mountains are documented by deposition of the Battle Springs Formation, a sequence of sedimentary rocks that accumulated on the southern flank of the uplift in the Great Divide Basin. While several Laramide structures in the region have been extensively studied, the exhumation history of individual ranges and the evolution of deformation during the Laramide Orogeny are not well-documented.

The Battle Springs Formation is composed of coarse-grained sandstone and cobble-boulder conglomerate dominated by leucocratic granite clasts derived from the Granite Mountains. The Battle Springs Formation is interpreted to have been deposited concurrently with active uplift of the Granite

Mountains. Six cobble-sized granitic clasts were collected from different stratigraphic positions from a 600-meter thick-section of the Battle Springs Fm. exposed in the Cooks Gap area of central Wyoming. LA-ICP-MS zircon U/Pb isotope data indicate that the granite clasts are Paleoproterozoic (ca. 2.5 Ga), consistent with rocks exposed in the core of the Granite Mountains. Zircons from the clasts have anomalously high uranium concentrations, which may be related to uranium roll-front located nearby. Preliminary apatite (U-Th)/He isotope analyses granite clasts yielded Oligo-Miocene dates, interpreted to be cooling ages. Additional (U-Th)/He data will be generated and used to construct time-temperature models of the cooling history of the Granite Mountains. The models and ages generated for this project will be compared to the results of previous low-temperature thermochronic studies of Laramide uplifts in the northern Laramide province.