ORIGIN OF CURVATURE IN THE TENNESSEE SALIENT FROM CALCITE TWINNING ANALYSIS AND PALEOMAGNETISM OF ORDOVICIAN CARBONATES

The Tennessee salient is an arcuate segment of the southern Appalachians that displays a curvature of nearly 60° from southern Virginia to northern Georgia. The origin of the curvature and any rotational history of this salient have remained largely unexplored. Samples for paleomagnetic and calcite twinning analysis were collected from limestones of the Ordovician Chickamauga Group to test whether remanence directions and paleostress orientations display evidence of consistent rotations along the the Tennessee salient. After the removal of a recent viscous magnetization, thermal demagnetization between 200°C and 450°C reveals a late Paleozoic characteristic remanence magnetization (ChRM) with shallow inclination to the south-southeast, similar to previous studies of limestones in the southern Appalachians. Application of the fold test indicates that the ChRM was acquired before tilting or during its earliest stages. Orientations of the structurally corrected ChRM's display no consistent variation in declination between limbs of the Tennessee salient and match the Late Paleozoic direction of stable North America. This result differs from preliminary paleostress orientations from calcite twinning analysis that indicate a coincident change of regional strike and layer-parallel, northwest to westerly compression directions. This pattern contrasts with previous calcite twinning results in the nearby cratonic interior cover sequence that show a uniform northwesterly compression direction. The systematically fanning paleostress orientations and uniform remagnetization direction in the thrust belt indicate oroclinal bending of the Tennessee salient prior to regional remagnetization of limestones in eastern North America and indicate a temporal separation of thrusting and folding in the Southern Appalachians, with thrusting primarily associated with curvature of the orogenic front.