GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 237-32
Presentation Time: 9:00 AM-6:30 PM


BARKLEY, Morgan N. and HAWKINS, John F., Department of Geosciences, Auburn University, 210 Petrie Hall, Auburn, AL 36849,

The Alexander City Fault (ACF) is traditionally defined as a brittle-ductile strike slip fault propagating through the Eastern Blue Ridge (EBR), and serving as the contact between the Elkahatchee Quartz Diorite(EQD) and the Wedowee Group (WG). The trajectory and characteristics of this fault tends to become more enigmatic as it approaches the Alabama Coastal Plain. Detailed field mapping of a transect perpendicular to the contact of the EQD and WG in the Elkahatchee Creek, south of Alexander City, Alabama confirms this to be an intrusive contact rather than a fault emplacement. Shear fabric data (S and C) gathered along this transect from the EQD and WG have calculated slip lines that produce populations with concentrations at N33E, 11˚ and S27W, 05˚. These population’s local maxima aligns with S and C fabric data previously reported for ductile portions of the ACF. Interestingly, this trend aligns with S and C slip line data collected in the adjacent Our Town quadrangle lithologies, the Wedowee and Emuckfaw Groups and the Kowaliga Gneiss. These data locations are not interpreted to have been influenced by movement of the ACF and the S and C data are contributed to other regional shearing events. This proves to be an interesting correlation. With the contact being intrusive and slip line data showing strong correlations to other regional slip line populations that are not fault related, where does this leave the ACF? Data suggests that the ACF does not cross this study area as a ductile fault. Local S and C fabrics seen in the EQD and WG are not produced by ductile movement along the ACF, but rather other regional shearing events are responsible; however, this does not rule out a narrow brittle ACF propagating through this transect. Ongoing detailed field mapping along the ductile sections of the ACF will help to explain the interesting correlation between previously reported slip line data attributed to the ACF with other regional slip line data currently not connected with the ACF.