INSIGHTS INTO THE PALEOGEOGRAPHY OF LAURENTIA DERIVED FROM U-PB AGES OF DETRITAL ZIRCONS IN MESOZOIC STRATA OF THE COLORADO PLATEAU

Individual U-Pb ages for 5199 detrital zircon (DZ) grains in 59 samples of Mesozoic sandstone from the Colorado Plateau, plus the contiguous High Plains and eastern Great Basin, provide insight into paleogeographic relations across southwest Laurentia. U-Pb ages were determined for ~100 DZ grains per sample by LA-ICP-MS using a beam diameter of 35µ, but ages >20% discordant or with analytical uncertainties >10% were rejected (average of 88 grain ages retained per sample). Middle Triassic fluviodeltaic facies (Moenkopi) and Upper Triassic fluvial facies (Chinle) of the southern plateau contain DZ populations derived dominantly from Proterozoic basement of SW Laurentia and either the Permian-Triassic East Mexico arc or the nascent Cordilleran arc within a provenance lying up-paleocurrent from the Colorado Plateau. Upper Triassic Chinle-Dockum sandstones from SSE-to-WNW paleodrainages crossing the High Plains and Colorado Plateau from headwaters in the Ouachita foreland contain more heterogeneous DZ populations that reflect recycling of detritus from the Ouachita orogen plus contributions of arc-derived DZ. Even more heterogeneous DZ populations in Jurassic eolianites are dominated by Paleozoic, Neoproterozoic, and Grenvillean grains blown southward across the Colorado Plateau from floodplains or deltas of transcontinental paleorivers heading in the Appalachian region, but also contain non-Appalachian DZ grains contributed by tributaries to the paleorivers during transit across the craton. Western plateau eolianites lack arc-derived grains, but eastern plateau eolianites contain admixed DZ derived ultimately from the East Mexico arc. Lower Jurassic fluvial facies displaying SSE-to-NNW paleocurrents contain DZ reflecting either mixture of East Mexico arc detritus with reworked eolian sand (Kayenta) or derivation largely from the Cordilleran arc assemblage (Springdale). Upper Jurassic and Lower Cretaceous fluvial and Upper Cretaceous fluviodeltaic facies derived from the west and southwest contain varied DZ populations that reflect both recycling of eolianite DZ, off the Sevier thrustbelt to the west and the Mogollon highlands to the south, and derivation from Proterozoic basement of the Mogollon highlands, together with variable admixtures of arc-derived DZ of Cordilleran origin.