PROVENANCE OF COLORADO PLATEAU PERMIAN AND JURASSIC EOLIANITES AS INFERRED FROM U-PB DETRITAL ZIRCON AGES

Detrital zircon grains (n=468) from Permian and Jurassic eolianites in Colorado Plateau ergs of southwest Laurentia fall into six age populations defined by discrete peaks on age-probability plots. The ergs received contributions of sand from all potential bedrock sources contiguous with Permian-Jurassic Laurentia and its orogenic-taphrogenic margins. Nearly half the detrital zircons were derived ultimately from Grenvillian (1315-1000 Ma), Pan-African (750-515 Ma), and Paleozoic (515-310 Ma) bedrock sources lying within or along the flank of the Appalachian orogen. Recycled origins for Appalachian-derived zircons, except from pre-orogenic Appalachian sediment cover or synorogenic flysch and molasse, are precluded either by regional geology or by available geochronology from other Laurentian sedimentary assemblages. Transcontinental Permian and Jurassic river systems evidently transported detritus of Appalachian provenance, from headwaters in the remnant Appalachian orogen (Permian) or the incipient Atlantic rift belt (Jurassic), westward across the subdued surface of the Laurentian craton to proximate sources for eolian systems in fluvial plains, deltas, and strandlines that lay up-paleowind from the ergs along or near the Cordilleran paleoshoreline north and northeast of the Colorado Plateau. Transport of Appalachian-derived detritus toward the Colorado Plateau was further aided 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 Archean (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), that delivered Appalachian-derived sediment to the proximity of the Colorado Plateau ergs.