USING EBSD AND MICROSTRUCTURAL ANALYSIS TO CONSTRAIN DEFORMATION CONDITIONS IN THE BLUE RIDGE

Across the Blue Ridge province there are many constraints on crystallization and metamorphic ages of rocks and peak pressure-temperature conditions of metamorphism, but conditions and timing of deformation itself are notably lacking. This is problematic for differentiating between the Taconic, Acadian, and Alleghanian orogenies, and better constraining the character of each of these events. Using detailed microstructural analysis, including determination of recrystallization regimes in quartz and feldspar, along with electron backscatter diffraction (EBSD) of quartz-rich samples can provide robust estimates on both the temperature conditions of deformation as well as the type of strain experienced by the rocks.

EBSD and microstructural analysis was conducted on three locations within the Blue Ridge; the Tallulah Falls Dome in northeastern Georgia, the Toxaway Dome, which straddles the North and South Carolina border, and along the Fries and Gossan Lead faults in northwestern North Carolina. Each of these locations records the presence of at least one high strain zone which preserves a mylonitic fabric that overprints all previous fabrics. Consequently these mylonitic fabrics are interpreted to record the final ductile deformational event in each location. In each of these locations microstructural observations from recrystallization fabrics in quartz and feldspar provide broad temperature constraints that agree with more precise estimates from quartz opening angle thermometry. Results from all three locations record greenschist-amphibolite facies conditions and are consistent with dominantly non-coaxial strain.