Age, paleomagnetism, and tectonic significance of the Elberton Granite, northeast Georgia Piedmont

The Rb/Sr whole rock age of 350±11 m.y., the remanent magnetism (RM), and petrology of samples from 21 sites within the granitic Elberton pluton (NE Georgia) have been determined. Two partially conflicting estimates of tectonic rotation are developed and evaluated. The first, based on the orientation of the magnetic foliation within the body and its reorientation, assuming an originally horizontal upper granite contact and coincident magnetic fabric, requires a post emplacement rotation of 30°–35° down to the SE about a N‐NE axis. The second, based on reorienting the body so that the pole determined for the granite before tilt correction (ϕ = 120.3; θ = 54.7; dp = 2.2; dm = 4.5) becomes coincident with an independently reported mean 350 m.y. B.P. paleopole (ϕ = 120; θ = 47), indicates a postemplacement rotation for the body of ∼15° down to the NW along a E‐NE axis. While these tilt estimates are different, they do have two very important points in common, namely, that the strike of rotation is similar and the magnitude of rotation is small. We conclude from these data that no major structural reorientation or relocation of the Elberton granite is necessary to produce a pole position consistent with the 350 m.y. Rb/Sr whole rock age. We suggest that the tilting of the granite (if any) that may have occurred resulted from uplift of the Inner Piedmont, with the Elberton pluton isolated within a rigid crustal block bounded by NE‐SW trending faults moving in response to that uplift. Our interpretation of these data is not consistent with a post 350 m.y. major continental collision event, with concurrent large‐scale thrust fault motion, involving the Southern Appalachians of North America. This conclusion is reinforced by tectonic analyses based on the regional gravity gradient and on oxygen isotopic data reported for late orogenic granites in the Southern Piedmont.