GEOLOGIC MAPPING OF THE ANDERSON SOUTH 7.5-MINUTE QUADRANGLE, ANDERSON COUNTY, SOUTH CAROLINA

Mapping in the Anderson South 7.5-minute quadrangle, South Carolina, is leading to a better understanding of the structural geology of the area. This information, which is not available from previous mapping studies, will provide new insight into the potential of seismic hazard and local availability of groundwater.

The map area covers part of the Six Mile thrust sheet of the Inner Piedmont. An interlayered sequence of biotite gneiss, sillimanite mica schist, quartzo-feldspathic biotite gneiss, amphibolite gneiss, and augen gneiss is recognized. Northwest-verging, recumbent isoclinal folds with attenuated limbs deform the rock sequence. Isoclinal folds are refolded by northwest-verging, inclined closed folds and by northeast-southwest, doubly plunging antiforms. Two distinct bodies of silicified cataclasite delimit northeast-southwest striking fault zones. One body forms a prominent ridge, which includes Little Mountain, and comprises left- and right-stepping en echelon pods of silicified cataclasite. Unsilicified, inline faults (N72E/67NW) cut silicified cataclasite northeast of the Little Mountain radio tower. When traced southwest, both springs and right-lateral offset of the Little Mountain cataclasite ridge are found along strike of the inline faults. Elliptical-shaped pods of left-stepping en echelon cataclasite are found along strike of the other silicified cataclasite body, which is located to the north of Little Mountain. Zones of sub-parallel fractures ranging from N73-82E are present to the north and south of the two silicified cataclasite bodies. Springs are found along these fracture zones.

Integration of mapped relations identifies three periods of faulting. Arrangements of en echelon pods indicate that initial right-lateral movement was followed by left-lateral slip, which in turn was followed by right-lateral slip. Silicification did not occur during the younger periods of left-lateral and right-lateral slip. This progression agrees with recently identified patterns of brittle faulting on Pax Mountain, which is located north of the study area (Clendenin and Garihan, 2001).