Remagnetization in the Tennessee salient, Southern Appalachians, USA: Constraints on the timing of deformation

The Appalachian fold-thrust belt is characterized by a sinuous trace in map-view, creating a series of salients and recesses. The kinematic evolution of these arcuate features remains a controversial topic in orogenesis. Primary magnetizations from clastic red beds in the Pennsylvania salient show Pennsylvanian rotations that account for about half of the curvature, while Kiaman-aged (Permian) remagnetizations display no relative rotation between the limbs. The more southern Tennessee salient shows a maximum change in regional strike from similar to 65 degrees in Virginia to similar to 10 degrees in northern Georgia. Paleomagnetic results from thirty-two sites in the Middle to Upper Ordovician Chickamauga Group limestones and twenty sites from the Middle Cambrian Rome Formation red beds were analyzed to constrain the relative age of magnetization as well as the nature of curvature in the Tennessee salient. Results from three sites of the Silurian Red Mountain Formation were added to an existing dataset in order to determine whether the southern limb had rotated. After thermal demagnetization, all three sample suites display a down and southeasterly direction, albeit carried by different magnetic minerals. The syn-tilting direction of the Chickamauga limestones lies on the Pennsylvanian segment of the North American apparent polar wander path (APWP), indicating that deformation was about half completed by the Late Pennsylvanian. The Rome and Red Mountain Formations were also remagnetized during the Pennsylvanian. Both the Chickamauga limestones and Rome red beds fail to show a correlation between strike and declination along the salient, suggesting either that the salient was a primary, non-rotational feature or that secondary curvature occurred prior to remagnetization, as it did in Pennsylvania. Moreover, remagnetized directions from the Red Mountain sites show no statistical difference between the southern limb of the salient and the more northeasterly trending portion of the fold-thrust belt in Alabama. Thus, all of the studied units in the Tennessee salient are remagnetized and show no evidence for rotation. This confirms that remagnetization was widespread in the southern Appalachians and that any potential orogenic rotation must have occurred prior to the Late Pennsylvanian. (C) 2009 Elsevier BY. All rights reserved.