DETRITAL ZIRCON U-PB GEOCHRONOLOGY OF PALEOZOIC STRATA IN THE GRAND CANYON, ARIZONA

U-Pb ages have been determined on detrital zircons from 26 samples of Paleozoic sandstone from the Grand Canyon. The resulting ages provide a rich record of Cambrian through Permian provenance and paleogeography. Cambrian strata (Tapeats and Bright Angel formations) yield mainly ~1.44 and 1.7-1.8 Ga ages that record derivation from basement rocks of the Yavapai Province exposed along the western flank of the Transcontinental Arch. The Devonian Temple Butte Formation was sourced further east, with a mix of Mazatzal and Yavapai source rocks, 1.34-1.40 Ga igneous rocks of the mid-continent region, and ~520 Ma rocks of the Amarillo-Wichita uplift. A few 400-420 Ma grains may have been shed from the northern Appalachian-Caledonian-Franklinian system. The Mississippian Surprise Canyon Formation records a major change in provenance, with predominantly 415-475 Ma and 1030-1190 Ma grains, as well as the pre-1.3 Ga ages present in underlying units. The younger grains are interpreted to have been shed from igneous rocks in the central Appalachian orogen, carried across the continent by rivers, wind, and coastal currents. Pennsylvanian strata of the Supai Group contain subequal proportions of 1.4-1.8 Ga grains derived from basement rocks exposed in the Ancestral Rocky Mountains and 410-465 and ~1070 Ma grains derived from igneous rocks in the Appalachians. Permian strata (Esplanade, Hermit, Coconino, Toroweap, and Kaibab formations) contain abundant Appalachian zircons, with the appearance of 270-370 Ma grains from the Alleghanian orogen first appearing within the Hermit Formation. Only one third of the zircons in Lower Permian strata have an age consistent with derivation from the Ancestral Rocky Mountains (most likely the Uncompahgre Uplift). Early Permian transport occurred in transcontinental river systems, facilitated by trade winds during low sea level and by coastal currents. With the young ages from all upper Paleozoic strata combined, age peaks of 270-370 Ma, 395-475 Ma, and 515-640 Ma are an excellent match for Alleghanian, Acadian-Taconic, and Penobscot-periGondwanan phases of magmatism along the Appalachian margin. Lag times of the youngest grains in these upper Paleozoic strata average ~25 Ma, which suggests relatively rapid exhumation and erosion of Appalachian source regions.