STRUCTURE OF SOUTHERN APPALACHIAN BLUE RIDGE INTERNAL MASSIFS OF GRENVILLIAN BASEMENT

The Tallulah Falls dome (TFD), Toxaway dome (TD), and Trimont Ridge massif (TRM) are all internal basement massifs in the eastern and central Blue Ridge of the Carolinas and NE Georgia. All are associated with antiformal culminations but each contains different basement units and Paleozoic structure. The TFD is a broad antiformal structure wherein basement rocks (coarse augen 1.158 Ga Wiley Gneiss, medium-grained 1.156 Ga Sutton Creek Gneiss and medium grained to megacrystic 1.050 Ga Wolf Creek gneiss) form a swirl pattern on the N, E, and S sides of the TFD. Basement rocks are preserved in the hinges of isoclinal aniclines whose axial surfaces dip N, E, and S toward the flanks of the dome. Wiley Gneiss is intruded by Sutton Creek Gneiss. The TD consists predominantly of coarse, banded 1.150 Ga Toxaway Gneiss folded into a NW-vergent, SW and NE-plunging antiform that contains a boomerang structure of Tallulah Falls Formation metasedimentary rocks in the core. Some coarse augen gneiss (resembling Wiley Gneiss) intrudes the banded Toxaway lithology. The Trimont Ridge massif occurs in an E-W-trending antiform west of Franklin, NC, and contains an orthopyroxene-bearing felsic gneiss that yielded a SHRIMP age of ~1.050 Ga. These Grenvillian basement massifs were once part of a larger mass that was probably connected to Laurentia. They were rifted as fragments from Laurentia during the Late Proterozoic where they possibly were islands in the Iapetus ocean that were swept up during Ordovician subduction and arc accretion and emplaced onto the eastern margin of Laurentia. These massifs were additionally penetratively deformed and metamorphosed during the Acadian (Neoacadian?) event.