GEOLOGIC MAP PATTERNS IN THE WESTERN INNER PIEDMONT OF SOUTH CAROLINA AND ADJACENT NORTH CAROLINA

Our geologic mapping along the South Carolina-North Carolina state line between Landrum and Salem, South Carolina covers sixteen 7.5-minute quadrangles and provides a comprehensive view of the dominant regional trends of macroscopic folds and faults produced during polyphase Paleozoic and younger deformation. The different folding and faulting episodes have affected the distribution of Neoproterozoic-Paleozoic age, greenschist-amphibolite grade metamorphic rocks that are preserved in a thrust stack. This thrust stack consists of (NW to SE) the Eastatoee ductile fault separating the underlying Jocassee sheet from the Walhalla sheet, and the Seneca ductile thrust separating the Walhalla from the overlying Six Mile thrust sheet.

The dominant structural grain has a NE strike. Axial traces of macroscopic, NW-vergent, inclined-overturned isoclines strike NE in the western part of the region, consistent with an interpreted NW transport direction (Griffin, 1971). In the central and eastern parts, the inclined-overturned folds strike NW and are refolded by overprinting, SW-directed movement (Hatcher and Merschat, 2006). Southwest-vergent, ductile thrusting at greenschist conditions also places Walhalla sheet rocks over the Six Mile sheet rocks. Younger broad macroscopic folds strike consistently NE and refold older isoclines and previously folded ductile thrusts. Later faulting and erosion of this folding has resulted in Six Mile klippen being scattered across the map area. In contrast, although isoclinally folded, the low-angle Eastatoee fault retains a consistent NE strike across 5 quadrangles.

Brittle faults dominantly strike NE, NW, and E-W across the region and obliquely offset older fold and thrust patterns. NW striking, oblique-normal faults juxtapose different structural levels of the thrust stack, which invalidates simple linear projection of contacts as a mapping guide. In the eastern part, a progressive sequence of faulting has been determined on the basis of cross cutting fault relationships. In the central region, E-W faults consistently have left–lateral offsets of several kilometers.