TIMING OF BRITTLE FAULTING ON PAX MOUNTAIN: A CHICKEN OR THE EGG QUESTION APPLICABLE TO PIEDMONT MAPPING

A northeast-trending ridge, known as Pax Mountain (PM), dominates the topography of the Tigerville 7.5-minute quadrangle, Greenville County, South Carolina. Pods of silicified cataclasite (PSC) crop out along the length of PM and pose a "chicken or the egg" question to geologists mapping in the Piedmont region. Conventional wisdom utilizes the PSC to define the position (chicken?) of the brittle Pax Mountain fault system, and mapping commonly portrays such brittle faults as continuous linear features. However, the PSC on PM are arranged in a right-stepping, en echelon pattern and, in places, are found in multiple, subparallel sets (Doar, 1998, SCGS, OFR-110).

To the south of PM, the Paleozoic Seneca fault also trends northeast across the quadrangle. The trace of this older thrust fault is used as a piercing point to identify younger fault separations, and our mapping shows that the Seneca fault is offset by both left- and right-lateral, subvertical, oblique-slip faults. These younger, unsilicified faults occur in inline sets that delimit other fault zones (egg?) adjacent to PM. Near the eastern terminus of PM, the trace of the Seneca fault turns abruptly to the north and is again offset by left- and right-lateral oblique-slip faults. Integrating these observations with the PSC patterns and with the kinematic indicators of Garihan and others (1990, South Carolina Geology, v. 33) shows: 1) an older, silicified Pax Mountain fault zone was reactivated and offset left-laterally and 2) subsequent reactivation offset both of those older fault zones right-laterally. Geologists should be aware of the "chicken or the egg" question because younger, unsilicified fault strands tend to occur in the vicinity of PSC in the Piedmont region. These younger, largely unrecognized fault strands may offset opposite motion, unsilicified faults and PSC, as well as older Paleozoic structures.