SILURIAN-CARBONIFEROUS TECTONICS OF THE CENTRAL AND SOUTHERN APPALACHIANS

SHRIMP-RG studies of monazite confirm Famennian ID-TIMS monazite ages for upper amphibolite facies schists of the Inner Piedmont of Carolinas-Georgia. The absence of a S Appalachian Devonian clastic wedge, the presence of that wedge south of the NY Promontory, and extensive evidence of dextral shearing and sheath folding across a >30 km zone including rocks southeast and northwest of the Brevard zone compel the restoration of the terranes southeast of the BZ to the NY Promontory in the Late Devonian. Restored to that location, detrital zircon studies by Bream (2005) and Merschat (2009) on rocks of the Cat Square terrane (eastern Inner Piedmont) are interpreted in terms of a vast Wenlock-Ludlow Salinic successor basin complex (cf. CT Valley & Central ME synclinoria, Merrimack trough, Gaspé, La Poile Group) that covers the ca. 455 Ma Upper Ordovician Carolinian-Laurentian suture. Thus the original contact between the Cat Square terrane and underlying Tugaloo terrane is interpreted to be an unconformity. Petrography of “garnetiferous” schists along this feature (Brindle Creek fault) in SC shows complete retrogression of garnet to biotite, and no evidence for shearing following this event; U-Pb analysis of monazite from these schists yield ages at the Miss-Penn boundary (ca. 322 Ma). Coeval with the opening of the Cat Square basin is the magmatic expression of extension with lower crustal melts of the central Piedmont (424-414 Ma, e.g., Clouds Creek, Lake Murray gneiss, Newberry Granite, Fairmont Mill, Anderson Mill) followed by the 408-400 Ma subalkalic-alkalic gabbro-norites of the Concord-Mecklenberg suite. The Carboniferous central Piedmont shear zone juxtaposes Carolina terrane amphibolites with Cat Square basin schists and gneisses that postdate Carolinia’s accretion to Laurentia.