Paleomagnetic evaluation of the Orocline Hypothesis in the central and southern Appalachians

Abstract

The axial traces of the major Appalachian folds change azimuthal direction from a NE‐SW orientation to a N‐S orientation in the area of the Pennsylvania Salient and swing back to a NE‐SW orientation in the vicinity of the Virginia Reentrant. All available paleomagnetic data from the folded Appalachians have been examined to test the Appalachian orocline hypothesis. Pre‐deformational site‐mean directions from suitable studies were rotated by the amount required to bring the strike of the sampled beds into coincidence with an average trend of the Central and Southern Appalachians (N35E). A comparison of clustering of site‐means before and after this correction, reveals that in all cases unbending of the arc causes site‐mean directions to disperse. This dispersal demonstrates that the curvature of the Appalachian orogen is to a very large degree a primary feature rather than a feature which resulted from the bending of initially straight fold axes. Copyright 1983 by the American Geophysical Union.