Implications of U-Pb ages of detrital zircons in Mesozoic strata of the Four Corners region for provenance relations in space and time

Abstract

U-Pb ages for individual detrital zircons in sandstone record the ages of igneous source rocks in which zircon and accompanying quartz crystals formed because zircon U-Pb ages are not reset by either sedimentary or diagenetic processes. Ages of detrital zircons reflect ultimate sand sources in basement rocks but allowance must be made in provenance interpretations for potential recycling of resistant zircon grains from more proximate sources in sedimentary assemblages. Our database for Mesozoic strata in the Four Corners region includes 2213 concordant or nearly concordant U-Pb ages of detrital zircons from 24 samples (Triassic to Cretaceous). Chinle channel sands were derived largely from the Ouachita orogen where uplifted on the northern shoulder of the pre-Gulf of Mexico rift system, from which Ouachita-derived sand was carried westward by paleoriver systems ~1500 km long with headwaters in the Ouachita foreland. Southern tributaries of central Chinle paleorivers contributed detritus from Precambrian basement and the Cordilleran magmatic arc lying south of the Colorado Plateau. Eolian dune sands of Glen Canyon and San Rafael ergs were derived largely from pre-Atlantic rift highlands along the Appalachian belt, transported to deltas or floodplains in the northern Rocky Mountains region by a transcontinental paleoriver system ~2000 km long carrying Appalachian-derived sediment, and delivered southward to the Colorado Plateau ergs by the paleowinds recorded by dune crossbedding. Salt Wash (Morrison) and Burro Canyon (including Jackpile) fluvial sands were largely reworked from older Jurassic eolianites forming sedimentary cover over the Mogollon paleohighlands, but Westwater Canyon (Morrison), Cretaceous (Toreva-Gallup-Menefee ) fluvial and fluviodeltaic sands contain prominent components of detrital zircon derived from Proterozoic Mogollon basement and its sedimentary cover, and from the Mesozoic Cordilleran magmatic arc lying still farther south.