Cataclastic Deformation Band Formation

Arrays of closely spaced (1-5 mm) sub-parallel cataclastic deformation bands are a common feature of faults in high porosity sandstones. The distribution of strain onto many low displacement bands is generally thought to require strain hardening within the deformation bands. This strain hardening model does not however account for widespread coalescing deformation bands and appears to have little support from laboratory data. The geometries and locations of many zones of deformation bands point to the role of fault geometrical complexities, rather than mechanical properties, in the formation of clusters of deformation bands. The geometric model is principally one of slip localisation by removal of fault surface irregularities and fault-rock weakening, a mechanism which is generally accepted for fault-zone development during brittle deformation for rock types other than high porosity sandstones.