Second, the magnitude of the stress inhomogeneity operative when the mineral segregation formed is, as the present results show, proportionately reduced the more prominently developed the segregation, for comparable bulk strain. When there is no segregation, because of sluggishness of transport or kinetics, all other things being equal, the pressure shadow has maximal magnitude. In the present case, that quantity is the local interfacial normal stress. The same reviewer also pointed out that the present formulation involves the somewhat paradoxical choice of concentrating dissolution, transport, and precipitation at the boundaries of objects boudins, porphyroblasts, and folded layers the dimensions of which are several orders of magnitude larger than the grain scale. This idea has also occurred to me and to others.
Observations are generally in support of transport at the larger scale, as in the present models.
Of course, in the case of boudin separation, there is no alternative. The suggestion is that large, continuous surfaces behave differently from grain interfaces. As the reviewer suggested, this may have substantial importance in treating all types of transport in rock. Clearly, interconnected cracks will dominate in fluid flow if the grain-scale permeability is sufficiently low. In diffusive transport, intergranular surfaces may be substantially tighter than larger surfaces.