ABSTRACT

Scanned cathodoluminescence imaging of deformation bands in porous quartzose sandstone of the Cambrian Hickory Sandstone in central Texas reveals a layered structure within the bands that records sequential stages in their development. Marginal zones of the bands have a distinct boundary with adjacent less-deformed sandstone. Within the marginal zone grains are prominently crushed, but grain fragments are separated by discrete opening-mode intragranular fractures such that particles derived from a common grain can be readily identified. The interior zone of larger bands (bands > 5-10 grain widths) manifests grain crushing that has proceeded to an extreme degree, producing a bimodal particle size distribution in which a few, large, unfractured 'survivor grains' (fine to medium sand-size) are surrounded by finely comminuted grain debris (coarse clay- to silt-size). Porosity loss by compaction and cementation is comparable in deformation bands and the adjacent less-deformed host sandstone. Grain volume loss through pressure dissolution is minor in both host rocks and deformation bands. A model of progressive band development is proposed in which bands initiate at a single crushed grain. Bands ultimately evolve from a planar zone dominated by grain crushing to a two-zoned band characterized by significant grain boundary sliding within the interior zone.