ROTATION AND CONVERGENCE IN THE PENNSYLVANIA SALIENT, APPALACHIANS; CALCITE TWINNING AND MAGNETIC FABRIC ANALYSIS

The evolution of the Pennsylvania Salient in the central Appalachians remains a topic of discussion in large part due to conflicting kinematic and paleomagnetic data. Calcite twinning and AMS analyses applied to Cambro-Ordovician limestones along the Salient reveal tectonic signals that may help to better resolve the previously observed discrepancies. Although beset by complexities, paleostress directions inferred from calcite twin orientations show evidence of primary curvature for the major southern and central segment of the mountain belt, and suggests a small but significant clockwise oroclinal rotation of 20-25 degrees for the northern segment of the Salient. Furthermore, the inferred northwesterly compression direction implies oblique convergence of the continental margins and a sinistral sense of transpression. AMS results similarly show tectonically induced fabrics spanning a large portion of P'-T space (P' from 1.01 to 1.15 and T from -1 to 1), which usually but not always agree with inferred compression directions from calcite analyses. These differences may reflect complexities in the correlation such as multiple susceptibility contributors (diamagnetic calcite and paramagnetic clays inferred from the distribution of susceptibility values), multiple tectonic signals, differential timing of acquisition by deformation, and non-parallel stress fields. Future work will focus on Middle to Late Paleozoic units in order to characterize geometrical and spatial patterns.