THE ALLATOONA FAULT: MAP PATTERNS AND GEOLOGIC CONSTRAINTS

The map trace of the Allatoona fault (AF), that separates the Western Blue Ridge (WBR) and Eastern Blue Ridge (EBR) in western and central Georgia, runs nearly straight as an arrow for much of its length. But what happens at its terminations, and what factors control how we depict this on a geologic map? North of the Mulberry Rock antiform in western GA, the AF corresponds to a distinct lithologic and metamorphic break, and is marked by ductile shearing and retrograde metamorphism. South of this area and across the state line into Alabama, however, pervasive imbricate faulting, and stratigraphic uncertainties complicate delineation of the AF. Various interpretations of its map pattern include: 1) the AF is continuous with the Hollins line fault that separates the EBR from the Talladega belt in Alabama; 2) the AF is continuous with the Goodwater-Enitachopco fault, which cuts the Hollins line thrust and has been interpreted as a normal fault; 3) the AF and the Hillabee shear zone, that separates the Hillabee Greenstone from Laurentian margin rocks of the Talladega belt, represent essentially the same structural level, although perhaps as parts of a broader fault zone rather than one discrete fault; and 4) the AF loops back into Georgia, framing a large window into WBR units. This presentation will illustrate the different interpretations, and consider constraints on the map pattern and relationships with other faults.