DIGITAL GEOLOGIC MAP OF THE NORTHERN INNER PIEDMONT, NC-SC-GA

Detailed 1:24,000 to 1:250,000 scale geologic mapping has been conducted in the Inner Piedmont (IP) during the past fifty years, and has newly been compiled into a 1:100,000 digital geologic map in Adobe Illustrator ^TM and georeferenced using Map Publisher. ^TM The map extends northeast from Gainesville, GA to the Sauratown Mountains, NC and from the Brevard fault zone to the central Piedmont suture. Primary data sources are detailed 7.5 minute geologic maps, and USGS publications.

This compilation of macro- and mesoscale data makes it possible to address key questions about stratigraphy, fault kinematics and mechanics, terrane boundaries, and 3D crustal flow within the IP. The IP here is a gently to moderately dipping stack of W-verging thrust sheets. The Brindle Creek fault, a terrane boundary, separates Laurentian affinity metasedimentary sequences and Ordovician granitoids of the western IP from younger metasedimentary sequences and Devonian-Mississippian granitoids of the eastern IP/Cat Square terrane. Thrust sheets of the NC western IP in ascending stacking order are the Marion, Tumblebug Creek, Sugarloaf Mountain and Mill Spring thrust sheets. These thrust sheets contain distinct packages of Cambrian(?) Tallulah Falls and Chauga River Formations intruded by Ordovician granitoids and overlain by the Middle Ordovician Poor Mountain Formation. Suspect rocks of the eastern IP comprise the Brindle Creek thrust sheet, the largest and highest IP thrust sheet that consists of a sequence of Siluro-Devonian aluminous schist and metagraywacke intruded by Devonian granitoids. Crystalline Type-F thrust sheets of the IP nucleated plastically at peak metamorphic conditions in a transpressional zone related to NW-directed, oblique convergence of the Carolina terrane during the Neoacadian, ~350 Ma. Map-scale sheath folds and mineral lineation patterns indicate that NW-directed flow rooted in the eastern IP is deflected to the SW by strong constrictional flow along the primordial Brevard fault zone throught western NC, SC and northeast GA.