METAMORPHISM, KINEMATICS AND CRUSTAL FLOW OF THE SOUTHERN APPALACHIAN OROGENIC CORE: EVIDENCE FROM DETAILED GEOLOGIC MAPPING IN THE BRUSHY MOUNTAINS, NC

The southern Appalachian Neoacadian core is composed of Tugaloo terrane rocks of the western Inner Piedmont (WIP) and eastern Blue Ridge and Cat Square terrane rocks of the eastern Inner Piedmont (EIP). Recent detailed mapping in the NE Brushy Mountains NW of Winston Salem, NC has revealed important structural and petrologic relationships delimiting the timing and emplacement kinematics of the Cat Square terrane. The Brindle Creek fault (BCF) separates the WIP from the EIP. The Cat Square terrane is composed of sillimanite I and II, Silurian and Devonian aluminous schist and metagraywacke, and Devonian-Mississippian anatectic granitoids. These hanging-wall lithologies contrast with intensely migmatitic footwall rocks of Cambrian (?) Tallulah Falls/Ashe metasedimentary rocks, Middle Ordovician Poor Mountain metasedimentary and metavolcanic rocks, Ordovician Henderson Gneiss, and other Silurian and Ordovician granitoids. The BCF is folded at the northeastern end of the Brushy Mountains, exposing the ~427 Ma protomylonitic Brooks Crossroads pluton in the footwall and truncating map-scale, hanging-wall sheath folds cored by the ~366 Ma Walker Top orthogneiss. These relationships limit emplacement of the Brindle Creek thrust sheet to the Devonian-Mississippian boundary, consistent with ~360-350 zircon rims and intense deformation in the Devonian Rocky Face pluton of the south edge of the study area. New P-T estimates of metagraywacke core samples from the Vulcan 115 Quarry, range from 755°C to 875°C and 9.3 to 10.9 kbars. These estimates are consistent with previous work suggesting an upper amphibolite, sillimanite I and sillimanite II grade metamorphism. A map-scale crustal flow pattern is evident by mesoscopic sheath-fold axes, mineral stretching lineations, S-C fabrics, and rotated porphyroclasts that indicate a NW- and W- to SW-directed flow pattern reflecting dextral transport along the Neoacadian Brevard fault zone. This is probably related to Devonian-early Mississippian subduction of the Tugaloo and Cat Square terranes beneath the Carolina superterrane.