T148 Isotopic Determination of Sediment Provenance: Techniques and Applications

Tuesday, 4 November 2003
8:00 AM - 12:00 PM

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

Paper number: T148-4
Program: Technical Sessions
Time: 8:55 AM – 9:10 AM

Authors

Abstract

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.