TRIASSIC-JURASSIC REACTIVATION OF THE ALLEGHANIAN (PENNSYLVANIAN-PERMIAN) TOWALIGA FAULT, CENTRAL GEORGIA, APPALACHIANS

The Towaliga fault (TF) is a steeply dipping, Alleghanian, garnet grade, 070^o-trending dextral fault that bounds the NW flank of the Pine Mountain window (PMW) in the AL and GA southern Appalachians. It is traceable through the Inner Piedmont northeastward to near the GA-SC border on a 035^o trend. New detailed geologic mapping NE of the PMW has revealed that the TF contains rhomb-shaped bodies of siliceous cataclasite up to 2 km long and 0.3 km wide that indicate dextral reactivation (NW down) on this segment likely at the Triassic-Jurassic boundary coeval with diabase dike emplacement (~200 Ma). The fault underwent no normal-slip reactivation along the segment that bounds the PMW. Triassic-Jurassic timing of TF reactivation 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 belt of older 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. This fault, however, is not known to have been reactivated anywhere along its length from western GA to west of Winston-Salem, NC. Silicified cataclasites occur elsewhere in the southern Appalachians on non-reactivated Triassic-Jurassic faults. The presence of silicified cataclasites 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 models in which both plastic and brittle faulting mechanisms act concurrently. Normal (down-to-NW and SE) faults, and dextral reactivation of the TF, form a strain-compatible system of faults and diabase dikes in the Piedmont.