Dynamic analysis of rough cleavage in the Martinsburg Formation, Maryland

Abstract

Deformation lamellae in detrital quartz and twin lamellae in vein calcite are common in greywacke beds in the upper portion of the Martinsburg Formation near Williamsport, Maryland. These features are a product of the same stresses that resulted in the formation of rough cleavage. Dynamic analysis of the deformation lamellae and the calcite twins indicates that the cleavage formed normal to the maximum principal stress. In limb samples, the intermediate principal stress is parallel to the fold axis and the least principal stress plunges steeply in the cleavage plane. In most hinge samples the intermediate and least stress axes could not be differentiated and together define the cleavage plane. The lamellae developed during a period of high differential stress that accompanied flattening of early-formed buckle folds. The abundance of deformation lamellae and their development synchronous with the cleavage, demonstrates that intracrystalline deformation may be an important mechanism in the formation of rough cleavage.