GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 1-2
Presentation Time: 8:15 AM


LEVINE, Jamie S.F., POWELL, Nicholas E., CASALE, Gabriele and MARTIN, Claire P., Department of Geological and Environmental Sciences, Appalachian State University, 572 Rivers Street, Boone, NC 28608

The Toxaway Dome (TD), which straddles the North-South Carolina border, is an elongate northeast-southwest trending dome cored by the Grenville-aged Toxaway Gneiss and surrounded by the metasedimentary Tallulah Falls Formation. Fabrics along the eastern boundary of the TD are likely associated with motion along the Brevard fault, which marks the Blue Ridge-Piedmont boundary. However, the western edge of the TD is also characterized by a strongly developed S-C fabric, which decreases in strength with distance both east and west of the dome boundary. Mylonitic fabrics within both the Toxaway Gneiss and Tallulah Falls Formation are defined by quartz and feldspar, which can be used to determine conditions of shearing along the western dome boundary. Quartz has undergone fast grain boundary migration and rare chessboard extinction; feldspar contains well-developed subgrains, and bulging recrystallization, suggesting deformation occurred at 500-700 °C. Additionally, electron backscatter diffraction data from quartz grains are consistent with temperatures exceeding 500 °C. Quartz c-axis pole figures display pronounced point maxima close to the dome boundary and diffuse patterns inward and outward from the dome boundary, providing additional evidence for a western dome boundary shear zone. Garnet-biotite thermometry and garnet-biotite-muscovite-plagioclase thermobarometry from rocks of the Tallulah Falls Formation adjacent to the dome boundary record conditions of 640-700 °C and 0.6-0.8 GPa. The correlation between the temperatures recorded from garnet-biotite thermometry and those from the deformation conditions in quartz and feldspar suggest shearing occurred during peak metamorphism. Preliminary monazite data from two Tallulah Falls Formation samples, one adjacent to the dome boundary and one within a small hook-shaped exposure within the dome, record Alleghanian aged cores and rims. We suggest the Toxaway Dome experienced deformation and peak metamorphism at amphibolite-facies during the Alleghanian orogeny. Our interpretation suggests deformation conditions that are hotter than typically reported for Alleghanian deformation in this portion of the Blue Ridge.