Microscopic observation of intact granitoids reveals that different kinds of deformation microstructures within mineral grains result from various processes; deformation microstructures due to microcracking, microfaulting, microfolding, recovery and recrystallization. Some samples of intact granitoids exhibit only the undulose extinctions of quartz, plagioclase and biotite, while the others show abundant deformation microstructures, indicating that they contain many submicron-sized apertures in them. These deformation microstructures may be important as a possible cause of diffusivity and permeability of intact granitoids.
Water pathways within intact granitoids are detected in an experiment based on the capillarity of a KMnO₄ solution. The EPMA images show that MnO₂ is present on the polished surfaces of orthoclase, plagioclase and biotite grains after the experiment. MnO₂ occurs in three ways : on grain-boundaries and/or intragranular cracks, in clustered submicron-sized pores, and dispersed on plagioclase and biotite grains. These modes of occurrence suggest that water pathways in intact granitoids are not only grain-boundaries and/or intragranular microcracks, but may also be mineral grains themselves that are permeated with submicron-sized apertures possibly having formed in deformation microstructures.
It follows that deformation microstructures should be most apparent at sites where abundant submicron-sized apertures are present. There are differences of deformation grade even in intact granitoids. This means that some intact granitoids include relatively few deformation microstructures, whereas others include many deformation microstructures. Since deformation microstructures are possible pathways for water, it is very likely that the diffusivity and permeability of a granitoid sample correlates with the nature and abundance of its included deformation microstructures. These microscopic observations and experiment suggest that deformation microstructures, as well as microcracks, should be studied much more thoroughly with regard to the diffusivity and permeability of intact granitoids.