NEW GEOCHRONOLOGICAL CONSTRAINTS ON THE TIMING OF DEPOSITION IN THE COON HOLLOW AND WEATHERBY FORMATIONS, AND CORRELATIONS BETWEEN THE WALLOWA AND OLDS FERRY TERRANES, BLUE MOUNTAINS PROVINCE, NORTHERN U.S. CORDILLERA

New U-Pb zircon ages for volcanic tuffs within the sedimentary onlap assemblages overlying the Wallowa and Olds Ferry volcanic arc terranes of the Blue Mountains province provide evidence for an earlier connection between the terranes than has previously been recognized. Tuffs collected from the Coon Hollow Formation (Pittsburg Landing, Wallowa terrane) and the Weatherby Formation and underlying Huntington Formation (Dennett Creek, Olds Ferry terrane) have been dated by high-precision CA-TIMS U-Pb geochronology. Two tuffs from within the lower Weatherby Fm. in Dennett Creek near the abandoned mining town of Mineral, ID are early Middle Jurassic (~174 Ma) and late Early Jurassic (~181 Ma), respectively, which is younger than previous estimates for the age of this section. These samples, along with a rhyolite and andesite (~187 and ~188 Ma respectively) at the top of the underlying Huntington Fm., help constrain the surprisingly short duration of the unconformity separating the Huntington and Weatherby Formations. We correlate this unconformity with that present at the base of the transgressive sandstone and mudstone unit in the Coon Hollow Fm. based on new data from a ~197 Ma welded tuff (Red Tuff unit) below this unconformity. The Red Tuff unit of the lower Coon Hollow Fm. is tentatively correlated with deposits of the upper Huntington Fm. The scarcity of fossil control until fairly high in the upper Coon Hollow Fm. allows for the possibility that this section is correlative with the lower Weatherby Fm. New U-Pb zircon geochronology from volcanics in the lower Huntington Fm. yields an age of ~220 Ma and allows for the tentative age correlation of these strata with Norian strata in the Wallowa terrane (Martin Bridge Limestone and Hurwal Formation) that are not present at Pittsburg Landing. New ages from volcanic tuffs in the sedimentary onlap assemblages of the Coon Hollow and Weatherby Formations allow these to be correlative without the need for time-transgressive sedimentation and provide evidence for a connection between the Wallowa and Olds Ferry terranes by Early Jurassic time. New geochronological age constraints from the Olds Ferry terrane show that the more profound unconformity in this section is not at the base of the Weatherby Formation, but is within the Huntington Formation.