EXTENT, KINEMATICS, AND MESOZOIC REACTIVATION OF THE ALLEGHANIAN TOWALIGA FAULT, CENTRAL GEORGIA APPALACHIANS

The Towaliga fault (TF) is a steeply dipping, Alleghanian, garnet grade, dextral fault that bounds the NW flank of the Pine Mountain Window (PMW) in the AL and GA Appalachians. It trends along the NW flank of the PMW, then changes to 035^o in the Inner Piedmont NE of the PMW, and may end near the SC border. The change in trend occurs at the NE end of the PMW, which may have acted as a buttress during Alleghanian emplacement. Detailed geologic mapping NE of the PMW has revealed that the TF contains isolated, rhomb-shaped pods of siliceous cataclasite up to 2 km long and 0.3 km wide that indicate dextral reactivation on this segment, and normal (?) reactivation along the PMW segment, likely during the Triassic-Jurassic (~200 Ma). End-member fabrics present in these pods range from multiply brecciated quartz-rich rocks to undeformed vein quartz. Timing of reactivation of the TF is confirmed by ~200 Ma diabase dikes that are both truncated by cataclasite bodies and by other diabase dikes that cut the fault. The TF truncates a zone of crosscutting granitoid plutons that lie to the NW. Farther NW is the Brindle Creek fault, a suture that separates the Tugaloo (NW) from the Cat Square (SE) terranes. Although the orientation of this fault is similar, nowhere along its length from western GA to west of Winston-Salem, NC, has reactivation been observed. The presence of silicified cataclasite across the southern and central Appalachian orogen, independent of ductile faulting, along with the spatial relationships between diabase dikes and cataclasite, suggests brittle faulting post-dates earlier, higher-temperature ductile faulting, as opposed to both mechanisms forming coevally in a predominantly ductile regime. A tentative relationship exists between the siliceous cataclasite and low-temperature (~350 ⁰C) quartz mylonites that are abundant in the Inner Piedmont. In the southern Appalachians, only the Brevard fault exhibits significant reactivation, but only during the Paleozoic.