DEFORMATION AND KINEMATICS IN THE TOXAWAY DOME, EASTERN BLUE RIDGE

The Toxaway Dome (TD) is composed of Grenville aged granitic gneiss, located northwest of the Brevard fault zone in the Eastern Blue Ridge of North and South Carolina. The dome is surrounded by metasedimentary rocks of the Tallulah Falls Formation (TFF). Previous authors suggest that the TFF unconformably overlies the dome, and that dome formation can be attributed to complex multiphase refolding of previous structures. However, the formation of gneiss domes elsewhere have been associated with faulting. This latter interpretation is consistent with some authors’ observations of a shear zone along the TD boundary. We use optical microscopy, electron backscatter diffraction (EBSD), and extensive field work to better determine the nature of the boundary and the possible role and conditions of faulting in the formation of the TD.

Deformation conditions can be constrained from quartz and feldspar recrystallization fabrics using optical microscopy and EBSD. Samples throughout the Toxaway Dome contain quartz that is elongate with pinned recrystallized quartz grains between layers of micaceous minerals, amoeboid grain boundaries, and grains with incipient chessboard extinction. These microstructures suggest fast grain boundary migration recrystallization in quartz. Feldspar grains in the Toxaway samples contain subgrains, undulose and patchy extinction, and serrated and finely recrystallized grain boundaries. These textures indicate bulging recrystallization in feldspar. The recrystallization textures seen throughout the dome and across the dome boundary suggest temperatures of deformation range between 500 - 650 °C.

Rock units within and immediately surrounding the Toxaway Dome have been mylonitized and contain kinematic indicators including, S-C fabrics, C’ fabrics, sheared garnet porphyroblasts, and feldspar porphyroclasts. Kinematic indicators throughout the area indicate a complex pattern of strain and are most consistent with the presence of a shear zone at the dome boundary that was active under amphibolite facies conditions.