DETAILED GEOLOGIC MAPPING AND STRUCTURAL ANALYSIS OF A PORTION OF THE CENTRAL GEORGIA INNER PIEDMONT, AND A POSSIBLE FAULT IDENTIFIED WITH AEROMAGNETIC DATA

Detailed geologic mapping is being conducted in several 7.5-minute quadrangles in the central Georgia Inner Piedmont (IP), to investigate the geologic significance of a prominent aeromagnetic lineament. The lineament truncates a suite of curved magnetic anomalies, is interpreted as a fault, and is possibly the SW continuation of the Brindle Creek fault (BCF). This fault separates high-grade metasedimentary rocks of the western IP (Tugaloo terrane) from the Cat Square terrane (CSt). The BCF is interpreted as a large-scale SW-directed type-F thrust sheet and terrane boundary. The Tugaloo terrane consists of the Neoproterozoic to early Paleozoic(?) Tallulah Falls Fm. and the Mid-Ordovician Poor Mountain Fm., both intruded by Ordovician-Silurian granitoids. CSt rocks consist of Silurian-Devonian sillimanite-schist, biotite gneiss, amphibolite, and Devonian-Mississippian anatectic granitoids. Peri-Gondwanan, Laurentian, and 430 Ma zircons have been identified throughout the CSt, with one detrital zircon sample from the study area containing Laurentian and peri-Gondwanan zircons. Three distinct granitic units have been identified in the field area: 1) an early, strongly foliated, coarse megacrystic granitoid (Murder Creek); 2) a later, weakly foliated, coarse-grained granitoid; and 3) a weakly foliated, fine-grained granitoid that appears to be the youngest. At least five ductile and brittle deformational events have been recognized in the Inner Piedmont producing early recumbent folds, overprinted by later, more upright tight folds, then more open folds. Mesozoic brittle faults, traced by siliceous cataclasite and threshold quartz ductility mylonite, and diabase dikes, are present throughout the study area. A prominent siliceous cataclasite body traverses the field area trending ~030, and cross-cuts NW-SE trending diabase dikes. Map patterns suggest a relationship between the siliceous cataclasite and the threshold quartz ductility mylonites.