NEW EXPLORATION OF THE TECTONIC HISTORY OF THE APPALACHIAN INNER PIEDMONT IN CENTRAL GEORGIA: DEFINING THE EXTENT AND CHARACTERISTICS OF THE BRINDLE CREEK FAULT, TOWALIGA FAULT, AND CAT SQUARE TERRANE

The Inner Piedmont (IP) contains the largest area of high-grade metamorphism in the Appalachians, and is the Mid-Paleozoic Neoacadian orogenic core of the southern Appalachians. Detailed geologic mapping in the IP SE of Atlanta, GA, has been conducted to define the extent of the Brindle Creek fault (BCf) and Cat Square terrane (CSt). Three prominent ae­romagnetic lineaments were identified here in the IP. The northernmost lineament truncates a suite of curved magnetic anomalies, and may be the southern continuation of the BCf, the suture between the eastern Tugaloo terrane and the CSt. Map- and meso-scale patterns suggest the BCf is a southwest directed type-F thrust. The middle lineament is the dextral Alleghanian Towaliga fault (Tf), which extends from the IP in west-central GA to NE GA. The Tf is an earlier ductile fault, formed during post-Alleghanian regional metamorphism (garnet stable), that later underwent brittle reactivation. Based on our new field data, together with aeromagnetic data, the southernmost lineament is an independent thrust sheet, the Rex Haven fault (RHf), located in the CSt. Metamorphic grade along the RHf reaches sillimanite II grade, suggesting hot emplacement. The RHf has SW-directed transport. While foliations in the Rex Haven thrust strike N-S, the dominant surrounding foliations strike NE-SW.

A confined belt of NE-SW-trending granitoids spans the length of the field area. Three granitoids are located to this confined zone: a megacrystic granite with a fine- to medium-grained matrix, and poorly to well-defined foliation; a later medium- to coarse-grained granitoid with poorly defined foliation; and the youngest, which is fine-grained and poorly foliated. Presence of primary coarse muscovite indicates these granitoids are peraluminous, and correlation with similar granitoids in the North Carolina IP suggests that they may be anatectic.