The Austell gneiss is located in the Piedmont 16 km west of Atlanta, Georgia, and 8 km northwest of the Brevard fault zone. This metamorphosed granite gneiss lies refolded in the nose of the Austell-Frolona antiform, a doubly plunging structure of regional extent. Subsequent to intrusion, the unit has undergone four episodes of deformation. The first and second generation folds (F1 and F2) are coaxial but not coplanar. The two later fold events were less intense and have little effect on local outcrop patterns in the study area. The age of the unit has been estimated to be greater than 325 m.y. but less than 365 m. y. The induced and remanent magnetic properties for at least six cores drilled at each of 10 sites within the Austell gneiss have been determined. The magnetic foliation for the unit is approximately parallel with field estimates for S1 foliation planes exhibited by mineral orientations within the body, indicating post-emplacement magnetic grain mobility. The stable remanent magnetization exhibited by the body was therefore probably acquired during or slightly after the F1 or F2 deformational events as a result of cooling from metamorphic temperatures (~600 ¿C), or, alternatively, from secondary magnetite grain nucleation and growth. A paleopole position calculated for these data without structural correlation, ϕ = 126.2, ϑ = 34.4, dp = 6.6, dm = 13.2, can be explained by magnetic acquisition in at least three possible geologic settings. From simple to complex, these are the following: First, since a large oval of confidence is observed for the unit and minor tilting can not be resolved, the data may be explained by magnetization of the Austell at its present site during cooling from metamorphic temperatures. Second, a northwestward thrust event may have resulted in bringing the Austell to its present location. Third, the data can be explained by two major translational events. The Austell may have initially been magnetized and then moved to the northeast by transcurrent strike slip faulting >1000 km into juxtaposition with the southern Appalachians, followed by thrusting of the unit to the northwest to its present location. In support of this last interpretation is the similarity between the paleopole for the Austell and paleopoles determined for the Maritime Provines of North America, which were suggested to have moved ~1500 km to the northeast during the mid to late Paleozoic. Against such an interpretation is the lack of geologic evidence in support of large-scale left-lateral strike slip faulting in the southern Appalachians. |