Paper No. 16
Presentation Time: 1:00 PM-5:00 PM
AN UPDATE ON INVESTIGATIONS OF THE BREVARD ZONE AND RELATED STRUCTURES IN ALABAMA
The Brevard zone (BZ) is a polyphase Appalachian fault zone with portions representing a potential terrane boundary, and other portions confined to a discrete structural zone, cross-cutting lithologies and terranes. In Alabama, it corresponds to the boundary between the eastern Blue Ridge (EBR) and Inner Piedmont/Dadeville Complex (IP/DC) terranes. Exposures contain eight poorly understood problems unique to the Alabama segment of the fault zone: (1) faults encapsulate a lithologic package of distinctly lower-grade (greenschist vs middle amphibolite-facies) and lower-strained package of metapelites and metasiliciclastics that include metaconglomerates and other primary sedimentary structures called the Jacksons Gap Group (JGG); (2) zones of retrograde mylonite/phyllonite interlace the JGG rather than penetratively affecting the entire package of rocks; (3) the JGG conspicuously contains no igneous intrusions, which are bountiful in its encapsulating terranes; (4) retrograde strain is mainly accommodated within phyllitic, particularly graphitc, units; (5) the Abanda fault is a ductile shear zone that forms the base of the JGG/BZ separating it from the higher-grade EBR (beneath); (6) the Katy Creek fault is a syn-metamorphic fault that forms the upper boundary of the JGG/BZ and separates it from the higher-grade IP/DC (above); (7) cataclastic zones of uncertain origin splay out from the Abanda fault to merge with the Alexander City fault zone (ACFZ), an internal EBR fault; and (8) the EBR, BZ/JGG, and the IP/DC are all folded by the late-stage Tallassee synform. We present a digital collage of detailed 1:24K geologic maps of the BZ throughout Alabama and report field, structural, petrographic and isotopic investigations relating to the development of the BZ and its related structures. This poster is in conjunction with a companion abstract and poster which similarly treats the BZ in Georgia to form a better understanding of the BZ in its most southernwestern exposures.