NEW GEOCHRONOLOGICAL CONSTRAINTS ON THE DEPOSITION OF THE HUNTINGTON FORMATION, OLDS FERRY TERRANE, AND IMPLICATIONS FOR THE EVOLUTION OF THE BLUE MOUNTAINS PROVINCE

The volcanic and volcaniclastic Huntington Formation constitutes the bulk of the Olds Ferry terrane of the Blue Mountains province, but has received little attention in terms of chronostratigraphy and geochemistry. The Huntington Formation consists of basaltic to rhyolitic arc volcanic and volcaniclastic rocks with the majority being intermediate in composition. The lower Huntington Formation comprises massive mafic lavas and volcaniclastic breccias while the upper Huntington Formation contains more felsic volcanics along with intercalated sedimentary layers. A Late Triassic age has been assigned to the Huntington Formation based on fossils found in intercalated limestone lenses of the upper Huntington. New U-Pb zircon geochronological data from volcanic rocks of the uppermost Huntington Formation suggests that arc activity may have lasted well into the Early Jurassic. These new data eliminate the need for an east-west time-transgression in Izee basin sedimentation (the “Megasequence-2” overlap assemblage of Dorsey and LaMaskin, 2007). This persistence of volcanism into the Early Jurassic also contrasts with the apparent cessation of volcanic activity in the Wallowa arc in the earliest Late Triassic, with implications for the nature and timing of the assembly of the Blue Mountains province.

Dorsey and LaMaskin, 2007, Am. J. Sci., in press.