CONDITIONS OF DEFORMATION AND METAMORPHISM IN THE TOXAWAY DOME, EASTERN BLUE RIDGE

The Toxaway Dome (TD) is an elliptical gneiss dome located in the Eastern Blue Ridge of North and South Carolina, west of the Brevard Fault Zone. The TD is composed primarily of Toxaway Gneiss (TG), a Grenville-aged banded granitic gneiss. The dome is surrounded by the Tallulah Falls Formation (TFF), a suite composed of aluminous schist, metagraywacke, amphibolite, and quartzite, with portions of the TFF present in the interior of the dome. Doming of the TD has largely been attributed to multiple folding events but the presence of a shear zone along the western TD boundary suggests doming is at least in part related to faulting. We apply the garnet-biotite thermometer and the garnet-biotite-muscovite-plagioclase barometer to the TFF from directly on and west of the shear zone to offer new constraints on the pressure-temperature (P-T) conditions during the development of kinematic fabrics. We then compare these to deformation temperatures interpreted through analysis of dynamic recrystallization microstructures to relate peak P-T conditions to deformation conditions. Thermobarometric analysis of three TFF samples from west of the TD, two of which are from the shear zone on the western TD boundary, yielded peak temperatures ranging from 609 to 709 °C and pressures ranging from 6 to 8 kbar. This indicates the TFF reached mid to upper amphibolite-facies conditions at these locations. Due to the abundance of grain boundary migration and the presence of rare chessboard extinction in quartz as well as the presence of bulging recrystallization in plagioclase, deformation temperatures throughout the TD are 500 to 700 °C. The consistency between peak P-T conditions and deformation temperatures indicate that deformation occurred at peak P-T conditions. Because two of the TFF samples we analyzed in this study are located along the western TD boundary, this shear zone, and likely the overall dome structure, must have deformed at peak P-T conditions.