Magnetization of the Austell gneiss, northwest Georgia Piedmont.

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The Austell gneiss is located in the Piedmont 16km W of Atlanta, Georgia, and 8km NW 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 >325Ma but <365Ma. The induced and remanent magnetic properties for at least six cores drilled at each of 10 sites within the Austell gneis 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 (approx 600oC), or, alternatively, from secondary magnetite grain nucleation and growth. A paleopole position calculated for these data without structural correction, phi = 126.2, theta = 34.4, dp = 6.6, dm = 13.2, can be explained by magnetic acquisition in at least three possible geologic settings.-Authors

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Journal of Geophysical Research

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