OBSERVATIONS ACROSS MAJOR FAULT ZONES IN THE SOUTHERNMOST EXPOSED APPALACHIANS AND THEIR TECTONIC IMPLICATIONS

We report on the southernmost exposures of three fundamental Appalachian fault zones, from structurally lowest progressing upward and westward, the Towaliga fault zone (TFZ), Stonewall Line, and Brevard zone. The TFZ separates Pine Mountain window (PMW) Grenville basement and attached miogeoclinal cover from the Opelika Complex (OC), which traditionally is correlated with the Inner Piedmont (IP) terrane. The Stonewall Line separates the metasedimentary and metaplutonic OC from the overlying metavolcanic/metaplutonic Dadeville Complex, which also is considered part of the IP. We use SHRIMP RG (USGS-Stanford) U-Pb isotopic data from zircons separated from PMW Grenville basement to compare and contrast them with zircons from metaquartzites of the PMW cover, the Brevard zone, and from the nonmetamorphosed, Laurentian, Wiesner Formation to characterize the provenance of the sedimentary protoliths and their basements. We examine zircons from ‘xenoliths' within the PMW Grenville gneisses to explore whether these might have sourced Early Proterozoic (2.0 - 2.4 Ga) zircons within the stratigraphically overlying Hollis Quartzite, perhaps indicating a Gondwanan origin. The southern Appalachian master decollement passed over the Pine Mountain massif but in our study area has been excised by the younger TFZ. Metasedimentary protoliths, plutonic rocks, metamorphic features, and 40Ar/39Ar and U-Pb isotopic data indicate that the OC more closely resembles the eastern Blue Ridge (EBR) rather than the IP. Thus, here the Stonewall Line appears to be the boundary between the EBR and the IP. Our mapping indicates that the OC wraps around the hinge of the Tallassee synform, projecting beneath a thin veneer of Coastal Plain sediments, to connect with documented EBR units. Discrete, ‘late-stage,' shears mark the southern continuation of the Brevard trend to the Coastal Plain onlap. ‘Early-stage' Brevard zone lithologies and fabrics appear to have been folded by the Tallassee synform, projecting into the Stonewall Line. The ‘early-stage' Brevard history, which elsewhere has been obscured by intense, ‘late-stage' retrogressive movements, therefore, appears to be physically separable in this area.