Boudinage and shearband boudins: A meso to micro-scale tool in structural analysis

A classification of boudinage and boudins is made presenting a simplified parametric description of boudin block geometry end-members. The most important shearband boudins parameters, ratios, microstructural domains and internal evolutions are described and interpreted. Shearband boudins are related to a large number of geological meso- and microstructures (e.g. pinch-and-swell, drawn or torn boudins, mica-fish, porphyroclasts, foliation boudinage, tectonic lozenges and C-S-C′). Several factors can control the asymmetric boudinage process, such as the obliquity of a competent layer, the orientation of an initial fracture, boudin axial ratio, the viscosity ratio between matrix and layer, flow type and shear strain. This review highlights the correlation of shearband boudins with other asymmetrically deformed structures and shows their geological relevance. Finally, this study presents a phenomenological framework for shearband boudins.