The northern Inner Piedmont, southern Appalachians, USA: kinematics of transpression and SW-directed mid-crustal flow

Analysis of new and existing field, structural, petrologic, and geochronologic data in the northern Inner Piedmont (IP), southern Appalachians, provide insight into the processes and kinematics of Neoacadian (Late Devonian–Mississippian) crustal flow. The IP is characterized by 360–345 Ma middle to upper amphibolite facies metamorphism, gentle dip of the dominant S2 foliation, and curved L2 mineral lineation pattern. Recognized map-scale sheath folds are cored by Henderson Gneiss or outlined by Devonian granitoids, and record SW-directed axial elongations of 120–486%. Net Neoacadian fault displacement exceeds 400 km, with over 200 km associated with SW-directed, orogen-parallel flow. Map-scale sheath folds and mineral lineation patterns suggest that NW- and W-directed flow rooted to the east was deflected SW by an oblique buttress in the footwall beneath the Neoacadian Brevard fault zone. Kinematic vorticity estimates remain in the realm of sub-simple shear across the IP, and approaches simple shear in the Neoacadian Brevard fault zone. Curved IP flow paths provide a model for middle to lower crustal deformation and flow in ancient to active orogens like the Himalayas, including the possibility that the IP is an exhumed orogenic channel.