Paper No. 1
Presentation Time: 1:05 PM


GEHRELS, G.E.1, PECHA, Mark2, DICKINSON, William R.2, KARLSTROM, Karl E.3, DOE, Michael F.4 and BLAKEY, Ronald5, (1)Geosciences, Univ of Arizona, Tucson, AZ 85721, (2)Department of Geosciences, University of Arizona, Tucson, AZ 85721, (3)Department of Earth and Planetary Science, Univ of New Mexico, Northrop Hall, Albuquerque, NM 87131, (4)Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401, (5)Geology, Northern Arizona University, Box 4099, Flagstaff, AZ 86011,

Detrital zircons from a variety of Paleoproterozoic through Eocene sedimentary units of southwestern North America have been analyzed for U-Pb ages and Hf isotope compositions. Ten main phases of sediment provenance are apparent: (1) 1.8-1.7 Ga (Vishnu and equivalents) = turbidites sourced from 1.85 and 2.5 Ga Mojave province and/or adjacent Archean-cored cratons; (2) 1.49-1.44 Ga (Defiance-Blackjack basins) = local basement plus ~1.5 Ga grains derived from outboard magmatic arcs (now in Australia?); (3) 1.33-1.10 Ga (Unkar & Apache) = Grenville clastic wedge plus local basement and ~1.4 Ga granites; (4) 0.8-0.74 Ga (Chuar) = reworking of Grenville clastic wedge plus input from local basement during Rodinia rifting; (5) Cambrian = reworking/removal of Grenville clastic wedge (forming Great Unconformity) plus local basement and scattered ~510 Ma granites; (6) Ordovician = blanket of quartz sand from the northwestern Canadian Shield; (7) Devonian-Mississippian = influx of sediment from peri-Laurentian orogens (Antler highlands to the west, Franklinian orogen to the north, Caledonian-Appalachian orogen to the east); (8) Pennsylvanian-Permian = transport (mostly aeolian?) from Caledonian-Appalachian-Ouachita orogens; (9) Triassic-Jurassic = variable input from local basement sources, Appalachian-Ouachita orogen, and outboard Cordilleran arcs; and (10) Cretaceous-Eocene = arc-derived sediment plus recycling from Cordilleran thrust belt and then Laramide basement uplifts. Sediment dispersal patterns were controlled by interactions between tectonics (e.g. continental configurations), paleogeography (e.g. peri-cratonic orogens), paleo-sea level, and paleoclimate (e.g. aridity, wind patterns). Hf isotopes record significant crustal growth at 1.8-1.6 Ga (Mojave-Yavapai-Mazatzal provinces), a mix of crustal growth and reworking at 1.45-1.35 (mid-continent granite-rhyolite provinces) and 1.3-1.0 Ga (Grenville Orogen), 700-400 Ma crustal growth along the Franklinian margin and crustal reworking in the Appalachian and Caledonian orogens, and mostly crustal reworking, with little crustal growth, in Cordilleran magmatic arcs during the past 300 Ma.