U–Pb ages of detrital zircons from Permian and Jurassic eolian sandstones of the Colorado Plateau, USA: paleogeographic implications

Abstract

Detrital zircon grains (n=468) from eolian sandstones of Permian and Jurassic sand seas on the Colorado Plateau of southwest Laurentia fall into six separable age populations defined by discrete peaks on age–probability plots. The eolian sands include significant contributions from all Precambrian age belts of the Laurentian craton and all key plutonic assemblages of the Appalachian orogen marking the Laurentia–Gondwana suture within Pangaea. Nearly half the detrital zircon grains were derived ultimately from Grenvillian (1315–1000 Ma), Pan-African (750–500 Ma), and Paleozoic (500–310 Ma) bedrock sources lying within or along the flank of the Appalachian orogen. Recycled origins for Appalachian-derived grains, except for temporary residence of synorogenic detritus in the Appalachian foreland basin or in deformed Ouachita flysch and molasses along tectonic strike, are precluded by regional geology and known geochronology from other Laurentian sedimentary assemblages. We infer that transcontinental Permian and Jurassic river systems transported detritus of Appalachian provenance westward across the subdued surface of the Laurentian craton, for deposition as proximate sources for eolian systems feeding the ergs, on unconsolidated fluvial plains, deltas, and strandlines that lay up-paleowind along or near the Cordilleran paleoshoreline north and northeast of the Colorado Plateau. The postulated river systems headed in the remnant Appalachian orogen (Permian) or the incipient Atlantic rift belt (Jurassic), and additional transport of the Appalachian-derived detritus toward the Colorado Plateau was achieved by longshore drift of sediment southward along the Cordilleran paleoshoreline under the influence of prevailing trade winds in the Permian–Jurassic tropics. Only a quarter of the eolianite detrital zircons were derived or recycled from Mesoproterozoic (1470–1335 Ma) and younger Paleoproterozoic (1800–1615 Ma) basement of the Ancestral Rocky Mountains province adjacent to the Colorado Plateau. The final quarter of eolianite detrital zircons were derived from older Paleoproterozoic (2200–1800 Ma) and Archaean (3015–2580 Ma) basement of the Laurentian shield, or recycled from its sedimentary cover. Both Laurentian shield and Ancestral Rockies detritus may have entered the same transcontinental river systems (through tributary streams), or the same Cordilleran strandline system (by longshore drift), responsible for the delivery of Appalachian-derived sediment to positions near the Colorado Plateau ergs. As Colorado Plateau ergs received contributions from all the potential bedrock sources contiguous with Permian–Jurassic Laurentia and its orogenic–taphrogenic margins, detrital zircon studies of analogous ancient erg deposits elsewhere may help test reconstructions of Rodinia and other ancient paleocontinents by providing proxy records of the full age ranges of bedrock sources distributed across the surfaces of entire landmasses.