Calculation of volume change in ductile band structures

Volume changes incurred during the development of ideal band structures (infinite shear zones) can be readily calculated if one knows the principal directions and principal ratios of total strain within, and adjacent to, the ideal band structures. The calculation is greatly simplified if one knows the directions and ratios of the strain that generated the band structures, or if the total strain of the host rocks is zero. In some natural deformation zones, apparent volume losses according to the band model, exceed 30% and may be unreasonably high. Further determinations of apparent volume change will help to judge the physical viability of the band model and its strict geometrical requirements. For example, the propagation of embryonic deformation zones may lead to total strain patterns that differ greatly from those of band structures.