ALLATOONA FAULT: CHARACTERISTICS AND EXTENT OF THE YOUNGEST THRUST IN THE APPALACHIAN BLUE RIDGE KINEMATIC SEQUENCE

The Allatoona fault (AF) is an internal, out-of-sequence Appalachian Blue Ridge fault extending >280 km, from near the Coastal Plain onlap in central AL to at least Dawsonville (DW) in N GA. Along its nearly linear trace it cuts obliquely through Blue Ridge tectonostratigraphy, metamorphic isograds, regional cross folds, and earlier thrusts, making it the youngest thrust in the kinematic sequence along the NW flank of this segment of the orogen. On the NW, the fault cuts Pennsylvanian or younger regional cross antiforms that cause significant orogenic curvature of older underlying thrust sheets, and is likely Permian in age. To the SE, however, rocks between the AF and Brevard zone maintain a nearly constant width resulting in a significant change in the orogen’s regional structural architecture. At the Mulberry Rock eyelid window in GA the AF has a horizontal net slip component of >17 km. From here, NE to DW, it carries the Dahlonega Gold Belt (DGB) in its immediate hanging wall, with older faults (Burnt Hickory Ridge and Chattahoochee) carried passively piggyback above the DGB. The extension of the AF NE of DW, however, is in debate. Recent mapping around the complex triple junction between the W, central, and E Blue Ridge provinces W of Dahlonega (DH), GA has revealed new evidence supporting the continuation of the AF NE of this intersection. For example, between DW and DH, internal DGB stratigraphy maintains its NE-trend, and the AF cuts both the structurally underlying “ancestral Allatoona” fault (AAF) carrying rocks correlated with the Otto Fm., and the Etowah River fault at the base of the Sally Free Mafic Complex. The latter two thrust sheets in the AF footwall are folded by the overturned NW-SE Sally Free synform, which is in turn decapitated by the AF. Although previous studies suggested that the Hayesville-Soque River fault (HSRF) to the NW postdated the AF, the regional Jasper antiform folds the Great Smoky thrust, the Murphy synclinorium, the AAF, and the HSRF, but is decapitated by the AF N of DW. Even though distinctive DGB units (ex. Canton and Univeter Fms.) were displaced 10’s of km NW along the AF and extend >110 km from type sections near Canton, GA, to at least Lake Burton, GA, 45 km NE of DH, previous interpretations place the DGB in the immediate footwall of the NW-dipping HSRF, with the AF apparently being excised by the HSRF.