Paper No. 9
Presentation Time: 10:15 AM
U-PB, HF, AND AR/AR EVIDENCE FOR THE PROVENANCES OF JURASSIC NAVAJO SANDSTONE: ADDITIONAL SUPPORT FOR TRANSCONTINENTAL TRANSPORT
ALEINIKOFF, John N., U.S. Geological Survey, MS 963, Denver, CO 80225, COSCA, Michael A., USGS, Box 25046, Denver, CO 80225-0046, FANNING, C. Mark, Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia and YAXLEY, Greg M., Research School of Earth Sciences, Australian National University, Mills Road, Acton ACT, 0200, Australia, jaleinikoff@usgs.gov
The hypothesis of Mesozoic transcontinental (east to west) fluvial transport of sediments that were deflated and deposited in enormous ergs on the Colorado Plateau is supported by the occurrence of Neoproterozoic detrital zircons that likely were derived from rocks in the eastern US (Dickinson and Gehrels, 2003; 2009). Neoproterozoic crystalline rocks occur in accreted terranes of peri-Gondwanan origin in southern New England (Gander and Avalon) and the central/southern Appalachians (Carolina). In order to define the provenance(s) and processes of sedimentation, we used multiple methods of isotopic analysis, including: (1) U-Pb ages of detrital zircons and Ar/Ar ages of detrital K-feldspars from Early Jurassic Navajo Sandstone (NSs, from Zion National Park) and roughly coeval terrestrial sedimentary rocks from four Mesozoic basins (Hartford, Newark, Culpeper, and Deep River), and (2) Hf isotopes in Neoproterozoic zircons from NSs and Mesozoic basin samples, as well as in potential provenance rocks (both crystalline basement and Paleozoic cover rocks).
SHRIMP U-Pb ages of detrital zircons from the NSs have major populations in the Paleozoic (360-450 Ma), Neoproterozoic (550-620 Ma), and Mesoproterozoic (980-1200 Ma). These age groups also occur in detrital zircons from the Hartford basin rocks. The Newark basin sample lacks 1000-1100 Ma zircons, the Culpeper basin sample totally lacks Neoproterozoic zircons, and the Deep River basin sample contains few Mesoproterozoic zircons. The εHf values for Hartford basin Neoproterozoic zircons have the same range (-6 to 5) as most Neoproterozoic grains from the NSs and as crystalline rocks in southern New England. A few grains from NSs have higher εHf (7 to 11), similar to values from the Deep River basin and Carolina terrane crystalline rocks. Distribution of Ar/Ar total fusion cooling ages of single detrital K-feldspars from the NSs is most closely approximated by K-feldspar age data from the Hartford basin; compatibility decreases with distance to the south. These independent isotopic data sets suggest that the NSs sediments were primarily derived from the northern Appalachians, a major mountain range in the late Paleozoic due to Alleghanian (Himalayan-style) collisional tectonics. Lesser clastic input probably came from the southern Appalachians.
