Crystallographic fabrics: a selective review of their applications to research in structural geology

Abstract

Abstract In this brief introductory review the potential geological use of crystallographic fabrics is illustrated by considering selected geological problems which, given appropriate conditions, may be investigated in plastically deformed rocks using fabric analysis. Quartz and calcite are taken as the main illustrative examples. Numerical fabric simulations indicate that the imposed strain path (strain symmetry, vorticity etc.) is reflected in the relationship between the fabric pattern, kinematic framework and finite strain axes. Although these fabric patterns are sensitive to the numerical model and combination of crystallographic slip systems chosen, many of the major fabric types have been observed in experimentally and naturally deformed rocks. The fabric pattern itself may contain important information on strain symmetry, orientation of fields of extension and contraction and operative slip systems. Similarly, the angular relationship between the fabric pattern and finite strain features (foliation and lineation) may provide information on shear sense and vorticity of deformation. Spatial transitions with decreasing grain size in naturally deformed rocks, from strongly defined fabrics to a complete lack of crystallographic preferred orientation, have been interpreted as indicating a switch to deformation mechanisms involving grain boundary sliding. Potential problems associated with using the absence of a fabric as an indication of grain boundary sliding (and by inference superplastic flow) are discussed. Experimental studies indicate that geometrical relationships between intracrystalline strain features and the crystal lattice of individual grains may be used to deduce palaeo-stress directions. Results of palaeo-stress analysis techniques based on such relationships are compared.