Failure mode transition in brittle boudinage: Effects of cohesion, confining pressure, and layer thickness

Boudins are ubiquitous periodic structures that form during layer-parallel extension of competent material embedded in less competent material. They can have a wide range of geometries, depending on paleo-rheological conditions. This makes them a powerful tool in interpreting the time–temperature and deformation history of a rock package. Consequently, multiple field and modeling studies have described their geometries as well as explored the boundary conditions for their formation. Inspired by previous findings in modeling and field studies, we test the hypothesis that boudin end member geometries, such as pinch-and-swell, domino, torn, and shear band boudins, can be realized with purely brittle–elastic behavior of the boudinaged layer embedded in a viscous matrix. For this purpose, we designed a parametric Discrete Element Modeling study in which different failure modes in the brittle material are achieved by varying the layer thickness, material cohesion and the layer parallel confining stress. We show that the different boudin geometry is a first order result of the failure mode, fracture mechanics in the brittle layer and the associated post failure behavior. Our models confirm previous findings that block rotation of boudins may be associated with coaxial deformation. Our models indicate a failure mode transition exits between torn and drawn boudins. These results may help us better understand the evolution of boudins and thus help interpret natural examples such as the boudin trains in Naxos, Greece.