Paleozoic structure of internal basement massifs, southern Appalachian Blue Ridge, incorporating new geochronologic, Nd and Sr isotopic, and geochemical data
Published:January 01, 2004
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Robert D. Hatcher, Jr., Brendan R. Bream, Calvin F. Miller, James O. Eckert, Jr., Paul D. Fullagar, Charles W. Carrigan, 2004. "Paleozoic structure of internal basement massifs, southern Appalachian Blue Ridge, incorporating new geochronologic, Nd and Sr isotopic, and geochemical data", Proterozoic Tectonic Evolution of the Grenville Orogen in North America, Richard P. Tollo, James McLelland, Louise Corriveau, Mervin J. Bartholomew
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A number of Grenvillian basement massifs occur in the southern Appalachian Blue Ridge. The largest are contained in the Blue Ridge anticlinorium, which extends northward from its widest point in western North Carolina to Maryland. The Tallulah Falls dome, Toxaway dome, and Trimont Ridge area contain small internal basement massifs in the eastern and central Blue Ridge of the Carolinas and northeastern Georgia. All are associated with Paleozoic antiformal culminations, but each contains different basement units and contrasting Paleozoic structure.
The Tallulah Falls dome is a broad foliation antiform wherein basement rocks (coarse augen 1158 ± 19 Ma Wiley Gneiss [ion microprobe, 207Pb/206Pb], medium-grained 1156 ± 23 Ma [207Pb/206Pb] and 1126 ± 23 Ma [207Pb/206Pb] Sutton Creek Gneiss, and medium-grained to megacrystic 1129 ± 23 Ma Wolf Creek Gneiss [sensitive high resolution ion microprobe, SHRIMP, 207Pb/206Pb]) form a ring and spiral pattern on the west, south, and southeast sides of the dome. Basement rocks are preserved in the hinges of isoclinal anticlines whose axial surfaces dip off the flanks of the dome. The Wiley Gneiss was intruded by Sutton Creek Gneiss. The Toxaway dome consists predominantly of coarse, banded 1151 ± 17 Ma and coarse augen 1149 ± 32 Ma (SHRIMP 206Pb/238U) Toxaway Gneiss folded into a northwest-vergent, gently southwest- and northeast-plunging antiform that contains a boomerang structure of Tallulah Falls Formation metasedimentary rocks in the core near the southwest end. The coarse augen gneiss phase constitutes a larger proportion of the Toxaway Gneiss toward the northeast. Field evidence indicates that the augen phase intruded the banded Toxaway lithology; U/Pb isotopic ages of these lithologies, however, are statistically indistinguishable. The Trimont Ridge massif occurs in an east-west–trending antiform west of Franklin, North Carolina, and consists of felsic gneiss that yielded a 1103 ± 69 Ma SHRIMP 207Pb/206Pb age.
An εNd-depleted mantle model age of 1.5–1.6 Ga permits derivation of all of these basement rocks (including most from the western Blue Ridge) from eastern granite-rhyolite province crust, except the Mars Hill terrane rocks, which yield 1.8–2.2-Ga model ages. The small Grenvillian internal massifs were probably rifted from Laurentia during the Neoproterozoic, and became islands in the Iapetus ocean that were later swept onto the eastern margin of Laurentia during Ordovician subduction and arc accretion. These massifs were additionally penetratively deformed and metamorphosed during the Taconian and Neoacadian orogenies.