Structure, stratigraphy, and migmatization in the southwestern South Mountains, North Carolina

This thesis presents stratigraphic, structural, and geochemical data for parts of the Glenwood, Dysartsville, and Sunshine 7.5-minute quadrangles, which are located in the southwestern South Mountains of western North Carolina. The study area, roughly equal to one 7.5-minute quadrangle, is located within the Inner Piedmont geologic province of the southern Appalachians. Detailed geologic mapping confirms the presence of a stratigraphic sequence that is established in other portions of the Inner Piedmont. This stratigraphic sequence consists of the Talluluah Falls Formation and overlying Poor Mountain Formation. Mapping has also determined the eastern extent of the Dysartsville orthogneiss and revealed the presence of two disseminated bodies of previously unverified Walker Top orthogneiss in the southern Dysartsville and northern Sunshine quadrangles. Modal and chemical analyses indicate the Dysartsville orthogneiss ranges in composition from granite to tonalite, and the proposed Walker Top orthogneiss composition is granite to granodiorite. Several amphibolite and altered ultramafic bodies (xenoliths?) occur within the Dysartsville orthogneiss body. The structure within the study area is dominated by a series of tight recumbent folds, including the Cane Creek synform, the Buzzards Roost antiform, and the South Creek synform. The common limb between the Cane Creek Synform and the Buzzards Roost antiform is attenuated and cut by the Brindle Creek thrust. North of the study area the Brindle Creek thrust was interpreted to have approximately 5 km of displacement and is interpreted to increase southward into the study area. Foliations, lineations, and fold axes show little to no orientation variance across the Brindle Creek thrust, which is interpreted to indicate that thrusting was syn-peak metamorphism. An extensive migmatite lies only within the footwall of the Brindle Creek thrust constraining migmatization to be a pre-thrasting event. This migmatite displays outcrop-scale structures such as agmatite, opthalmite, schollen, and stromatite in disrupted Poor Mountain Formation rocks. Chemical analysis of leucosome shows a genetic link to the Dysartsville orthogneiss, because of similarities in composition. The genetic relationship between the leucosome and the Dysartsville orthogneiss could be the result of igneous injection during emplacement or they both were the result of partial melting during peak metamorphism.