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2003 Seattle Annual Meeting (November 2–5, 2003)

Paper No. 4
Presentation Time: 8:55 AM

CHARACTERIZATION OF THE LATE PALEOZOIC ALLEGHANIAN OROGEN BY DETRITAL ZIRCONS FROM THE SYNOROGENIC CLASTIC WEDGE


BECKER, Thomas1, THOMAS, William A.1, SAMSON, Scott D.2 and GEHRELS, George E.3, (1)Department of Geological Sciences, Univ of Kentucky, 101 Slone Bldg, Lexington, KY 40506-0053, (2)Department of Earth Sciences, Syracuse Univ, Syracuse, NY 13244, (3)Department of Geosciences, Univ of Arizona, Tucson, AZ 85721-0077, tpbeck2@uky.edu

Early stages of the late Paleozoic Alleghanian orogeny in eastern North America are recorded by coarse, texturally immature, quartz-rich clastic deposits in the lowest Pennsylvanian strata of the Appalachian basin. Paleobotanical correlations document substantial temporal and spatial variability of initial Pennsylvanian-age clastic deposition within the Appalachian foreland basin, suggesting a complex early Alleghanian tectonic history that resulted in localized topography.

To characterize the crustal components of the orogen, we obtained U-Pb ages of detrital zircons (six samples by LA-ICP-MS and one by SHRIMP) from the following basal Pennsylvanian strata along the Appalachians: (#1) Tumbling Run Member/Pottsville Formation, east-central Pennsylvania (n=26) 389-555, 915-1498, 2564 Ma; (#2) Pottsville Formation, south-central Pennsylvania (n=77) 389-460, 548, 666, 874-1579, 1650, 1830, 2262, 2628 Ma; (#3) Lee Formation, southern West Virginia (n=61) 916, 965-1488, 2112 Ma; (#4) Lee Formation, western Virginia (n=59) 425, 897-1194, 1282, 1406-1863, 2134, 2653-2780, 2923 Ma; (#5) Sewanee Conglomerate, eastern Tennessee (n=41) 385-415, 435-465, 900-1350, 1460-1540, 1700-1820, 2690-2755 Ma; (#6) Raccoon Mountain Formation, northwestern Georgia (n=69) 365-499, 612, 990-1489, 1677-1844, 2369, 2558, 2763-2815 Ma; (#7) Straven Conglomerate Member/Pottsville Formation, central Alabama (n=36) 931-1229, 1323-1423, 1505-1514, 1626-1644, 1817, 2880 Ma.

All seven samples contain zircons that correspond in age to mid-Proterozoic Laurentian basement (874-1500 Ma). Zircons in most samples (except #3) also represent older components of the Laurentian craton, likely recycled from craton-derived detritus in Iapetan synrift deposits (1500-1863 and 2369-2923 Ma). Ages of Iapetan synrift igneous rocks (548-555 Ma) and/or Taconic and Acadian plutons (365-499 Ma) are represented in all but two samples (#3 and #7). None of the detrital zircons have synorogenic Alleghanian crystallization ages. In samples #2, #3, #4, and #6, a few detrital zircons suggest sources from accreted peri-Gondwanan terranes (612, 666, 2112-2262 Ma). These results demonstrate that the early phases of the Alleghanian orogeny were dominated by crustal rocks of Laurentian affinity.

Session No. 148

T114. Isotopic Determination of Sediment Provenance: Techniques and Applications
Tuesday, 4 November 2003: 8:00 AM-12:00 PM
Geological Society of America Abstracts with Programs. Vol. 35, No. 6, September 2003, p.389
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