SIGNIFICANCE OF LOW SYMMETRY FABRICS IN MAGMATIC ROCKS

The significance of low symmetry fabrics (monoclinic and triclinic) in magmatic rocks is studied using theoretical models describing the motion of rigid markers embedded in a slowly deforming ductile matrix. In agreement with Curie's Symmetry Principle, the development of these fabrics requires a non-coaxial strain-path. Simulations of monoclinic fabrics indicate that their characteristics depend on: (a) the strain regime and the amount of strain, and (b) the morphological composition of the population of rigid markers. Natural monoclinic fabrics contain precious information about the strain regime they result from: type of the non-coaxial strain-path involved (simple shear, non-coaxial flattening, etc.), orientation of its axes and sense of shear. The magnitude of the finite strain may eventually be estimated provided that the shape of the markers is precisely known.