Three-dimensional reference deformations and strain facies

Ln an attempt to categorize three-dimensional deformations, the concepts of kinematic axes, three-dimensional reference deformations, and strain facies are utilized. We have chosen 12 reference deformations, each being an idealized end-member of deformation involving a simultaneous combination of a three-dimensional coaxial component (constriction, flattening, or pure shear) and an orthogonal simple shear component. Velocity and displacement fields, infinitesimal deformation parameters, and finite deformation parameters can be calculated for each reference deformation, assuming steady-state deformation. There are three possibilities for the orientation of foliation and three possibilities for the orientation of lineation. depending on the relative contributions of the coaxial and non-coaxial components. The six emerging combinations of foliation and lineation orientations each give rise to a characteristic strain facies. Each of the strain facies is correlated to the reference deformations, and thus deformation parameters, which caused its formation. However, since the coaxial deformation component accumulates more effectively than the non-coaxial component, a change from one strain facies to another (i.e. a change in the orientation of lineation or foliation) is possible during steady-state deformation. The strain facies emphasize the boundary conditions of deformation and, together with the reference deformations, provide a framework for three-dimensional deformations. (C) 1999 Elsevier Science Ltd. All rights reserved.