ORIGIN OF A MAJOR APPALACHIAN TRANSVERSE ZONE AND INFLECTION IN OROGENIC CURVATURE: CONSEQUENCE OF AN OBLIQUE RAMP INHERITED FROM A RIFTED-MARGIN TRANSFORM FAULT

The inflection between opposing curves (salients and recesses) of orogenic belts is commonly marked by a transverse zone containing an array of along-strike contrasts (e.g., cross-strike discontinuities) in structure and stratigraphy. Curvature is especially distinctive along the west flank of the Appalachians in Georgia where a thin-skinned transverse zone, designated as the Cartersville transverse zone, separates the Alabama recess and Tennessee salient, and extends across the entire width of the deformed Laurentian cover sequences. The most notable feature in this zone is a large oblique hanging-wall ramp within the frontal metamorphic allochthon (western Blue Ridge-Talladega belt) formed during Alleghanian collision and subsequent thrusting. The basal décollement steps several km's stratigraphically upward across the ramp to the southwest, from Proterozoic basement and its overlying Late Proterozoic rift sequence (Tennessee salient) into basal Cambrian and younger units (Alabama recess). This ramp resulted from the displacement of the western Blue Ridge-Talladega belt metamorphic allochthon against an inherited, east facing continental margin transform fault that initially separated rifted margins of upper and lower plate affinities, resulting in variations in basin geometry that existed across the transverse zone prior to Paleozoic deformation, and likely contributing to orogenic curvature. Translation of the frontal allochthon over the ramp caused deflection of the tectonic transport trajectory resulting in major cross folding and rotation of earlier structures and associated out-of-plane deformation that propagated across the foreland, producing an array of structures aligned into the transverse zone. The model from Thomas's 1977 paper for the Late Proterozoic rift-transform architecture and its genetic relationships with current Appalachian salients and recesses provides the context for this study.