SIGNIFICANCE OF LATE EXTENSIONAL FAULTS IN THE SOUTHWESTERN APPALACHIAN EASTERN BLUE RIDGE

Two kinematically late-stage, en echelon left, rotational extensional faults, the Goodwater-Enitachopco fault (GEF) on the NW and Alexander City fault (ACF) on the SE, are significant components of the eastern Blue Ridge structural architecture in the southernmost part of the Appalachian orogen. These scissors faults, which dismember the Alleghanian thrust stack down dip via moderate latest Paleozoic (?) NW-SE extension, are offset ~20 km across strike, across a transfer zone, and have a ~25 km strike overlap. Displacement increases in opposite directions, with the GEF dying to the SW, and the ACF dying toward the NE. From a tip line ~35 km NE of the Gulf Coastal Plain onlap, displacement on the GEF increases to the NE, dropping the Wedowee Gp. down against various underlying units in the Ashland Supergroup, and locally across the low-angle structural base of the Ashland (the Hollins Line thrust) against the Talladega belt. At Millerville, the GEF cuts the underlying, far traveled, low-angle Hollins Line thrust at the base of the eastern Blue Ridge, placing the amphibolite facies Wedowee Gp. against the lower greenschist facies Talladega belt, eliminating the entire Ashland Supergroup, and requiring a normal displacement of >6 km. Here, the GEF also decapitates regional scale NW-SE-trending folds that fold much of the Alleghanian thrust stack, making this fault Permian or younger. Farther NE at Hightower, the GEF once again cuts the Hollins Line thrust, placing the Wedowee Gp. against the Talladega belt. Still farther, northeast of Yorkville, Georgia, this fault, mapped as the Allatoona fault, cuts up section in the hangingwall eliminating the Wedowee Gp., and down section in the footwall (Talladega belt). Consistent with down to the SE displacement, along the I-75 corridor near Cartersville, at the current surface level, the GEF comes within only a few 100 m of placing the Emuckfaw Fm. (structurally above the Wedowee Group) downward against foreland thrust belt rocks, eliminating most of the Ashland-Wedowee belt in the hanging wall and the Talladega belt in the footwall. The ACF extends SW along the SE flank of the Elkahatchee batholith an unknown distance beneath the Coastal Plain, but does not displace Upper Cretaceous units at the boundary. Together the GEF and ACF document latest Paleozoic collapse, extension, and exumation along the NW flank of the orogen.