RECOGNITION AND STRUCTURAL SIGNIFICANCE OF MACROSCOPIC QUARTZ VEINS IN THE CAROLINA TERRANE, CENTRAL SOUTH CAROLINA

The Neoproterozoic– Cambrian Carolina terrane (Ct) crops out prominently across central South Carolina. The Ct consists of interlayered metamorphosed volcanic, volcanogenic sedimentary, and sedimentary rocks that have undergone multiple deformations, including dextral strike-slip within the boundaries of the Late Paleozoic ductile-brittle Eastern Piedmont fault system (EPFS). First-pass geologic maps of the Ct focused on defining lithologic units and contacts and have established a regional stratigraphy and deformation chronology.

New 1:24,000-scale mapping of the Ct southwest of Lake Murray has identified prominent topographic features that are oriented subparallel and adjacent to lithologic contacts. Many of these topographic expressions are quartz veins and quartz-boulder trains that range from 10’s to 100’s m-wide and several km in length. Quartz veins are overprinted by multiple periods of crack-seal fabric and cataclasis. In the surrounding Ct rocks, an increased strain gradient is observed as the quartz veins are approached: fold frequency increases, fold hinges are tightened, compositional layering is transposed, and rocks are locally brecciated, cataclastic, or phyllonitic. Kinematic indicators such as asymmetric clasts, S-C fabrics, and fold vergence in sheared rocks predominantly indicate dextral slip. This suggests that the quartz veins were emplaced in zones of ductile deformation overprinted by brittle faults, and these areas are distinctly mapped at major lithologic contacts in Ct.

The coexistence of macroscopic–megascopic quartz veins (also known as quartz reefs) and brittle faults has been recognized in orogenic strike-slip fault systems. In these fault systems, the quartz veins mark the cores of individual fault zones. In the context of the Ct, the quartz reefs, brittle faults, and dextral structures are focused within gradational changes in Ct lithology, and may represent individual strands of the EPFS. Alternatively, they may represent older structures susceptible to brittle reactivation. Crosscutting relationships suggest that the brittle structures are the latest structures to form in the deformation chronology, and while their regional significance is still unclear, their recognition provides an important tool for mapping lithologic contacts in the Ct.