U-PB AGES OF DETRITAL ZIRCONS IN CRETACEOUS STRATA OF THE COLORADO PLATEAU: PROVENANCE IMPLICATIONS FOR THE CORDILLERAN FORELAND BASIN

U/Pb ages for detrital zircons from Cretaceous strata of the Colorado Plateau shed light on provenance relations for the Cordilleran foreland basin. Samples studied include three from a widespread Lower Cretaceous fluvial blanket (Cedar Mountain and Burro Canyon Formations), three from lower Upper Cretaceous (Turonian) deltaic tongues (Ferron, Toreva, Gallup), and four from upper Upper Cretaceous (Campanian) fluvial to deltaic complexes (Castlegate, Wahweap, Menefee). Sampling strategy was designed to test for alternate derivation of sandy sediment from the Sevier thrust belt and the Mogollon highlands. Marine shoreface and shelf sandstones exposed basinward were not sampled to avoid any effects of longshore sediment redistribution by shoreface processes or marine currents. LA-ICP-MS analysis with a beam diameter of 35 microns was used to determine ages of ~100 zircon grains per sample, with a few grain ages from each sample rejected for >20% discordance or >10% uncertainty. Zircon populations in Turonian samples have prominent age peaks in the range of 1800-1600 Ma suggesting derivation in large part from Yavapai-Mazatzal basement of the Mogollon highlands, but contain few <250 Ma grains derived from the Cordilleran magmatic arc. Campanian samples from stratigraphic units in central Utah displaying paleocurrents implying derivation from the nearby Sevier thrust belt to the northwest contain grain populations largely recycled from Jurassic eolianites (Dickinson et al., this meeting) uplifted within the thrust belt, but no arc-derived zircon grains. Campanian samples from stratigraphic units displaying paleocurrents and facies trends indicative of sediment transport toward the northeast contain variable proportions (8%-48%) of arc-derived zircon grains (<250 Ma). Zircon age populations in the Lower Cretaceous Burro Canyon and Cedar Mountain Formations in the interior of the plateau reflect recycling of detritus from Jurassic eolianites of either the Sevier thrust belt or the Mogollon highlands, but contain few arc-derived grains. Ages of detrital zircons in Cretaceous strata of the Colorado Plateau imply that both the Sevier thrust belt and the Mogollon highlands contributed sediment to the adjacent Cordilleran foreland basin in complex patterns over time and space.