GEOLOGIC MAPPING OF CAROLINA SLATE BELT ROCKS AT CLARK HILL RESERVOIR, WOODLAWN, GA QUADRANGLE

The Woodlawn, GA quadrangle lies near the GA-SC border and includes part of the shoreline of Clark Hill Reservoir. Greenschist facies rocks of the Carolina Slate Belt are well exposed along the shoreline of the reservoir. Recent drought conditions have resulted in very low lake levels, revealing extensive exposures that are normally not available for study. Geologic mapping was conducted in the south-central portion of the quadrangle, near Clay Hill Campground. A GPS survey was utilized to revise the 1:6000 topographic base map and accurately locate the low-water line.

Rocks within the Woodlawn quadrangle are predominantly volcanic and epiclastic rocks that have undergone greenschist facies metamorphism. Quartz diorite plutons and abundant quartz dikes and veins crosscut these rocks. The dominant metamorphic foliation strikes between 040 and 075, and dips steeply northwest. Contacts between units generally parallel the regional foliation, although compositional layering is locally discordant with respect to foliation. Compositional layering is locally folded by open, upright folds that trend northeast-southwest and have axial planes subparallel to regional foliation. Mafic rocks include greenstone layers and discordant dikes, and are characterized by the assemblage epidote-chlorite-actinolite-quartz-albite. Felsic volcanic rocks contain phenocrysts of quartz and plagioclase, and textures suggest the presence of relict pumice fragments in some exposures. Epiclastic rocks are predominantly mudstones and sandstones, which locally exhibit relict sedimentary structures. Field relationships suggest that epiclastic rocks interfinger with volcanic rocks throughout the area. Quartz diorite plutons intrude the volcanic and epiclastic units, and are weakly foliated. In the southern part of the map area, mylonitic fabric associated with the Modoc shear zone overprints regional greenschist facies metamorphic fabrics.