Paper No. 28-6
Presentation Time: 8:00 AM-12:00 PM
MICROSTRUCTURAL IMPLICATIONS ON CONDITIONS OF DOMING IN THE TOXAWAY DOME, EASTERN BLUE RIDGE
The Toxaway Dome (TD) is an elongate gneiss dome located west of the Brevard Fault Zone in the Blue Ridge of North and South Carolina. Its interior is primarily Toxaway Gneiss, a Grenville-aged banded granitic gneiss. The TD is mantled by the metasedimentary Tallulah Falls Formation, a small lens of which is also present within the southern region of the dome. We present data obtained from microstructural analysis to suggest new constraints on the conditions of doming. Deformation temperatures range from 500-700 °C both within and outside the dome, based on dominantly grain boundary migration and rare chessboard extinction in quartz as well as the presence of bulging recrystallization in plagioclase. The majority of samples record temperatures ranging from 550-650 °C but there is no clear spatial pattern given by the temperature data. Additionally, adjacent samples from inside and outside of the dome commonly show differing temperatures. Microstructural analysis of kinematic shear sense data indicates the presence of mylonitic fabrics in rocks along the boundary of the TD. These fabrics are not limited to the eastern boundary, which is in close proximity to the Brevard Fault, but are also found along the western boundary. Previous studies, based on detailed field observations, have suggested doming occurred as a result of polyphase folding. The presence of highly strained mylonitic fabrics along the western margin of the TD and the contrasting deformation temperatures across the boundary of the TD suggest faulting may have also contributed to doming. To further constrain the conditions of doming, we are conducting monazite geochronology to determine timing of mylonitic fabric formation as well as thermobarometric analysis to derive peak pressure and temperature conditions for the TD.