Experimental contributions to the study of foliations in rocks: A review of research since 1960

Abstract

The classical conception of the cleavage problem is being succeeded by a new conception that recognizes the diversity of microstructures, grain-scale processes, strain histories, and geological conditions associated with cleavage development. Experiments are guided by, and to some extent have contributed to, the changes in this conceptual framework. Experimental attempts to induce slaty cleavage or crenulation cleavage directly in rock samples have not been very successful so far. More progress has been made by high temperature growth and deformation of synthetic layer-silicate aggregates, by annealing recrystallization of mica single crystals, and by room temperature deformation of salt-mica speciments. A major advantage of experiments is that the history of strains and displacements can be followed and the relations of these kinematic quantities to changes in the microstructure can be observed. This is not possible in study of naturally deformed rocks and it is beyond the reach of present theory, except for the simplest of microstructures. A few interesting directions for future experimental research are discussed briefly.