SINISTRAL SHEAR ZONES AND TERRANE BOUNDARIES IN THE EASTERN PIEDMONT OF SOUTH CAROLINA

In the eastern Piedmont of South Carolina, the Great Falls pluton is in close proximity to the Charlotte, Silverstreet, and Carolina terranes. This Neoproterozoic/early Paleozoic granitic pluton (~543±63 Ma Rb-Sr) contains inclusions of Carolina terrane porphyries and has an intrusive contact with the metadiorites, amphibolites, and biotite schists of the Charlotte terrane. Thus, the Great Falls granite is a stitching pluton, so a better age date is needed. To the south, a mass of greenschist facies metamorphosed Carolina terrane porphyry intervenes between the pluton and the eclogite-bearing gneisses of the Silverstreet terrane; this geometry suggests that the porphyry was thrust over the gneisses, and then the thrust sheet was folded by the Flint Hill antiform. Ductile sinistral shear zones of both N60E and N10E bearings cut the Great Falls pluton and the porphyries of the Carolina Terrane. The shear zones are only 50-100 m. wide, en echelon, and formed when the rocks were at greenschist facies conditions. Spaced dextral ductile shears are superimposed on the older sinistral shear zones that cut the Carolina Terrane and the Great Falls pluton. Dextral ductile shear zones also mark the roughly east-west boundaries between the Silverstreet and Charlotte terranes (Beaver Creek-Gaydens Creek shear zone) and the Carolina and the Silverstreet terranes (Chappells-Stoney Hill shear zone). Several authors have proposed that there was oblique sinistral convergence between outboard exotic terranes and Laurentia in the middle Paleozoic. The sinistral shear zones of the Great Falls area support the hypothesis that the Charlotte, Silverstreet, and Carolina terranes accreted at that time, and sustained superimposed dextral transpression in the late Paleozoic.