LOW TEMPERATURE THERMOCHRONOLOGY FROM THE MITCHELL INLIER, CENTRAL OREGON

Despite its critical location near the juncture of the Basin and Range province, the northern Walker Lane, the Cascade volcanic arc and cratonic North America, thermochronologic data from central Oregon is extremely limited. The Mitchell Inlier hosts a regionally unique section of unmetamorphosed Cretaceous marine sediments that are apatite bearing. We sampled these units (Gable Creek and Hudspeth Formations) along with phyllite from the local Baker Terrane metamorphic basement in nine locations of varying structural relationships to the Mitchell Anticline, Mitchell Fault, and basal Cretaceous unconformity. The Mitchell Anticline is a NE-SW trending structure displaced by the east-west Mitchell Fault. The Mitchell Fault is an E-W trending structure that accounts for significant strike-slip separation, as well as major thickness changes in Cretaceous sedimentary units. The lack of published quantitative information constraining the regional thermal history means that no matter the extent or timing of potential post-depositional reheating and cooling the samples have experienced, new insights will be gained regarding the regional tectonic history and its relationship to western US cordilleran tectonics broadly. Hypothetical scenarios include a broad suite of potential admixtures of the following scenarios: some unreset samples since deposition in Cretaceous time (circa 100 Ma), pre-Clarno Paleogene resetting associated, Clarno associated thermal resetting in late Paleogene time, and Neogene heating associated with Columbia River Basalt lavas.