Formation of regional cross-fold joints in the northern Appalachian Plateau

Abstract

Fold-axis-parallel elongation associated with the development of arcuate fold and thrust belts is proposed as a causal mechanism for syn-orogenic cross-fold joints. Such a mechanism can be coupled with other joint-propagation models, providing a widely applicable resolution to the enigmatic origin of regional systematic joints. The fold-axis-parallel elongation model is compatible with kinematic indicators as recorded by a sequence of cross-fold joints and related deformational fabrics in the central and northern Appalachian Plateau. Modeling of an arcuate tectonic boundary subjected to normal compressive loading demonstrates that tangential tensile stress can be large enough to initiate cross-fold joints on the convex side of the tectonic boundary. Simulated stress trajectories from boundary element modeling bear a strong resemblance to the stress trajectories inferred from the regional cross-fold joint patterns in the central and northern Appalachian Plateau. Modeling also displays a cratonward decrease in both the tangential stress and the tangential strain. Such a decrease is consistent with the deformation styles observed in the central and northern Appalachian Plateau.