LITHOLOGIC AND STRUCTUAL RELATIONSHIPS IN THE CAROLINA TERRANE, DELMAR 1:24K QUADRANGLE, SALUDA COUNTY, SOUTH CAROLINA

The Carolina terrane is part of a Late Proterozoic–Cambrian peri-Gondwanan, oceanic island-arc system. Regional mapping shows that the remnants of this island-arc system extend from southern Virginia to Georgia. In South Carolina the system consists of a basal metavolcanic unit (Persimmon Fork Formation, ~552 Ma) overlain by a metasedimentary sequence (Emory Formation, ~535 Ma). Those early units are unconformably overlain by a metasedimentary sequence (Asbill Pond Formation) containing trilobites dated at 503 Ma. The metavolcanic and metasedimentary lithologies are metamorphosed to greenschist facies, and six deformation events have been documented across the terrane. Structural relationships record the terrane’s separation from Gondwana, accretion to Laurentia, amalgamation of Pangea, and the supercontinent’s subsequent break-up.

Geological mapping in the southern portion of the Delmar 1:24K quadrangle, Saluda County, South Carolina, has identified structural relationships corresponding to at least three of the defined events. The first event (Delmar, 535–503 Ma) is restricted to the Persimmon Fork and Emory Formations. Deformation produced steeply plunging isoclinal folds, and an axial planar cleavage. Localized zones of high shear strain are tentatively assigned to this event, because they have not been recognized in the overlying Asbill Pond Formation. The second event (Clarks Hill, 503–415 Ma) affects the Persimmon Fork, Emory, and Asbill Pond Formations. The undeformed Clouds Creek granite (415 Ma) that intrudes Asbill Pond rocks to the south constrains the Clarks Hill deformation age. Tight, moderately NE-SW plunging folds, an axial planar cleavage, and an intersection lineation modify earlier Delmar structures. The sub-parallel orientation of the cleavages suggests that the two fold generations are coaxial planar. The third event (Irmo deformation, 315–275 Ma) generates a disjunctive cleavage, steeply NE-plunging folds, and dextral faults. Quartz-filled tension gashes, diabase dikes, and brittle faults dissect earlier fabrics and are thought to be late Paleozoic (?) to Cenozoic in age.