STRUCTURAL, STRATIGRAPHIC, AGE, AND TECTONIC CONSTRAINTS ON THE NATURE OF THE BREVARD ZONE IN ALABAMA AND GEORGIA (USA)

The Brevard zone (BZ), marking the boundary between the Blue Ridge on its northwestern flank and western Inner Piedmont on the southeast, is a linear, orogen-parallel feature that stretches >700 km from Virginia to Alabama. With a width varying between 1 and 3 km, the BZ is characterized by rocks exhibiting varying degrees of deformation, including mylonitization and cataclasis, and exhibits evidence for prograde and retrograde metamorphism. Because the BZ spans a significant distance, workers studying the BZ in different regions have provided numerous interpretations for its kinematic and tectonic history. In recent years, the BZ of northeastern Georgia, South Carolina, and North Carolina has been interpreted as a Neoacadian orogenic channel accommodating significant crustal flow with over 200 km of orogen-parallel, dextral displacement. However, structural, stratigraphic, geochronologic and tectonic constraints from rocks at the southwestern end of the BZ in Alabama and western Georgia suggest limited displacement across its northwestern margin (Abanda fault), preservation of mappable stratigraphy internal to the BZ (i.e., Jacksons Gap Group) that likely formed in the same Ordovician-Silurian back-arc basin as rocks of the adjacent eastern Blue Ridge (Ashland-Wedowee-Emuckfaw belt), and a post-metamorphic origin for its southwestern boundary (Katy Creek fault). Accordingly, displacement models for the southwestern and northeastern ends of the BZ present conflicting interpretations for its history, kinematics and displacement magnitude. Here, we detail stratigraphic and structural relationships on either side of the Brevard zone in Alabama and Georgia, as well as petrologic and geochronologic constraints from plutons that cross the Brevard zone. In addition, we present the results of Rf-phi strain analysis of granitic plutons in the eastern Blue Ridge, BZ, and western Inner Piedmont to understand how strain is partitioned within and adjacent to the BZ in Alabama and Georgia.