Mean kinematic vorticity of retrograde mylonite in the Brevard fault zone, South Carolina

The Brevard fault zone (BFZ) is one of the largest faults in the southern Appalachians, extending from Virginia to Alabama. It was originally recognized as a relatively narrow (1-3 km-wide) low-grade metamorphic belt, flanked by high-grade rocks on both sides. Recently, the concept of the BFZ has been expanded to include a wide (\u3e 10 km) shear zone exposed over much of the Inner Piedmont (IP) with high-grade metamorphism, indicating incipient A-subduction by the exotic Carolina superterrane of Laurentia and other Paleozoic terranes. Exhumation processes are reflected in the retrograde metamorphic gradient across the IP into the Blue Ridge. The main objective of this thesis is to delimit the relative contributions of pure and simple shear (kinematic vorticity) along strike within the retrograde mylonite in the study area (32 km²). Vorticity analysis is regarded as a useful approach in various tectonic settings to estimate pure/simple shear during noncoaxial progressive deformation. In the BFZ, feldspar porphyroclasts and other clasts were observed in the shear zone rocks, which were used to estimate mean kinematic vorticity (W[subscript m]). To improve data credibility, orientation of every sample was documented in detail and the vorticity data were plotted on the rigid grain net. Higher and lower W[subscript m] values were grouped. Results indicated that higher W[subscript m] values are associated with SW-directed crustal transport. Mesoscopic W[subscript k] values in the high-grade Neoacadian BFZ are substantially higher than W[subscript m] values in the early Alleghanian BFZ, a result of ductile deformation during the early Alleghanian orogeny. A triclinic deformation mechanism may have contributed to the W[subscript m] high-low patterns. Quartz c-axis patterns are similar to those from a previous study, and reveal a top-to-the-SW shear sense