Structural Petrology of the Baraboo Quartzite

Abstract

The microstructures of the Baraboo quartzite of Columbia and Sauk counties, Wisconsin, have been studied from oriented hand specimens, polished sections, and thin sections. Fabric axes, determined from the pole patterns of the deformation lamellae, vary consistently over the region and are not related to the bedding or the macrofoliation. Because of this variation, the deformation lamellae have been assigned to a deformation later than the major folding of the region. In addition, the character of the deformation lamellae themselves and the type of pole pattern have been used as a qualitative index of the intensity of the deformation. Microfractures are common features of the quartzite; they exhibit a strong preferred orientation and are geometrically related to the deformation lamellae. Quartz deformation bands are described, named, and correlated with bedding-plane shear. Quartz optic-axes fabrics are weak and difficult to interpret.