Experimental slip distribution in lentils as an analog for scaly clay fabrics

Abstract

Scaly fabrics are networks of anastomosing shear surfaces that are ubiquitous in deformed clay-rich sediments and fault gouges. Despite common occurrence, little is known about their behavior during deformation. It is not known whether they represent incremental slip on individual wavy shear surfaces, or whether multiple shear surfaces across a network deform simultaneously. We performed experiments on analog materials (oriented lentils) to observe the distribution of slip surfaces using a transparent shear box. We find that slip distributes through a network of anastomosing, transient slip surfaces that continually reorganize during shear. This is accompanied by local compaction and dilation so that volume changes caused by slip are balanced laterally between adjacent volumes. Lentils differ from equant granular materials because the shape inhibits grain rotation and facilitates interlocking. The self-perpetuating delocalization behavior of the system serves as a model for a conceptual understanding of how scaly fabrics deform and persist in natural clay-rich sediments and fault gouges.