Geologic history of a portion of the eastern Blue Ridge, Southern Appalachians : Tray Mountain and Macedonia 7 1/2" quadrangles, Georgia

The eastern Blue Ridge of northeastern Georgia and southwestern North Carolina is underlain by rocks of the Tallulah Falls Formation, Coweeta Group, and Otto Formation, separated from the Ocoee Supergroup in the western Blue Ridge by the Hayesville fault. The study area encompasses portions of the Tray Mountain and Macedonia 7 1/2" quadrangles in northeast Georgia, and can be divided into three tectonic units. Tectonic unit 1 is the lowest, and includes the Otto Formation (mica schist and metasandstone) and intercalated amphibolite. It is bounded on the northwest by the Soque River fault. Tectonic unit 2, the next highest, comprises dominantly metasedimentary rocks of the Coweeta Group, underlain by possible Tallulah Falls Formation equivalents. The Coweeta Group can be divided into the Persimmon Creek Gneiss, Coleman River Formation, and Ridgepole Mountain Formation. Tectonic unit 3, the highest, includes an assemblage of garnetiferous mica schist, metasandstone, amphibolite, and hornblende gneiss, informally designated the Com Ridge formation. This unit is separated from tectonic unit 2 by the Shope Fork fault.

All of the sequences above, with the exception of the Persimmon Creek orthogneiss, are dominated by psammitic and pelitic rocks that originated as thick clastic sequences of greywacke with interbedded shale. Textural evidence indicates that the rocks experienced two episodes of prograde mineral growth, the first episode reaching sillimanite or kyanite grade, and the second garnet grade. These events may be correlated with the Taconic and Acadian orogenies. Subsequent retrograde metamorphism affected only rocks of tectonic unit 3. The rocks are no younger than early Paleozoic, constrained by the age of Taconic metamorphism in the southern Appalachians (430-470 m.y.).

Multiple deformation resulted in six recognizable folding phases; earlier flowage folds resulted in transposition of layering into a regionally penetrative foliation, later overprinted by flexural flow and flexural slip buckle folds. In the study area, the Shope Fork fault juxtaposes rocks of different metamorphic grade and cuts steep, northwest trending F5 folds, indicating some post-metamorphic movement. The Soque River fault, recognized primarily by truncation of stratigraphy, has an uncertain movement history.

The Coweeta Group lies within the core of a regionally extensive synclinorium, in a structurally similar position to that of the Alligator Back Formation of North Carolina and Virginia and the Murphy belt rocks in North Carolina and Georgia. Based on lithologic comparisons, the Coweeta Group cannot be positively correlated with these units. If equivalent to one or both, the Coweeta Group must represent a considerably different facies. In addition, petrography and heavy mineral analysis suggest that rocks of this portion of the eastern Blue Ridge had a different source area from that of the Ocoee Supergroup immediately to the west, within the Great Smoky thrust sheet.