MICROSTRUCTURAL AND KINEMATIC ANALYSIS OF DEFORMATION CONDITIONS WITHIN THE TALLULAH FALLS DOME

The Tallulah Falls Dome, located northwest of the Brevard Fault, is a prominent feature of the Eastern Blue Ridge and is composed of pervasively mylonitized metasedimentary rocks that record the complex deformation history of this part of the Southern Appalachians. This research focuses on understanding the structural history of the Tallulah Falls Dome and uses microstructural analysis to determine the conditions of deformation and the kinematic shear sense during dome formation. We determined the conditions of deformation by analyzing quartz and feldspar deformation fabrics, which are associated with mylonitization. Previous work indicates that the metamorphic grade of this region is upper-amphibolite facies with a greenschist facies overprint; however, we have found few examples of temperatures consistent with this greenschist facies overprint. Through microstructural analysis we have determined temperatures that fall primarily within the amphibolite facies and rarely the lowermost granulite facies. Quartz has undergone high-temperature (fast) grain boundary migration as evidenced by pinned micas in quartz, coarse grain sizes with amoeboid shapes, and the formation of quartz ribbons with high aspect ratios. Chessboard extinction is present in several samples, with coarse, equant grains of quartz, which provides evidence for uppermost amphibolite to lowermost granulite facies metamorphism. Feldspar grains provide evidence for a wider range in temperatures than quartz, and display incipient recrystallization, kinking, and occasional fractures. Foliation-parallel quartz ribbons are common and provide evidence for mylonitization at uppermost amphibolite facies conditions. We determined kinematic shear sense in mylonitic fabrics throughout the dome with analysis of S-C fabrics, mantled porphyroclasts, mica fish, and rotated garnets. Our observations of microstructures relating to metamorphic conditions, and kinematic shear sense support our conclusions that: 1) there is a complex pattern of shearing throughout the dome, and 2) widespread mylonitization occurred at uppermost amphibolite facies to lowermost granulate facies.