EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Influence of initial preferred orientations on strain localisation and fold patterns in non-linear viscous anisotropic materials

Tamara de Riese1, Paul D. Bons1, Enrique Gomez-Rivas2, Albert Griera3, Maria-Gema Llorens4, and Ilka Weikusat1,5
Tamara de Riese et al.
  • 1Eberhard Karls Universität Tübingen, Tübingen, Germany (
  • 2Department of Mineralogy, Petrology and Applied Geology, University of Barcelona, Barcelona, Spain
  • 3Departament de Geologia, Universitat Autònoma de Barcelona, Barcelona, Spain
  • 4Institute of Earth Sciences Jaume Almera (ICTJA-CSIC), Barcelona, Spain
  • 5Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany

Deformation localisation in rocks can lead to a variety of structures, such as shear zones and shear bands that can range from grain to crustal scale, from discrete and isolated zones to anastomosing networks. The heterogeneous strain field can furthermore result in a wide range of highly diverse fold geometries.

We present a series of numerical simulations of the simple-shear deformation of an intrinsically anisotropic non-linear viscous material with a single maximum crystal preferred orientation (CPO) in dextral simple shear. We use the Viscoplastic Full-Field Transform (VPFFT) crystal plasticity code (e.g. Lebensohn & Rollett, 2020) coupled with the modelling platform ELLE ( to achieve very high strains. The VPFFT-approach simulates viscoplastic deformation by dislocation glide, taking into account the different available slip systems and their critical resolved shear stresses. The approach is well suited for strongly non-linear anisotropic materials (de Riese et al., 2019). We vary the anisotropic behaviour of the material from isotropic to highly anisotropic (according to the relative critical resolved shear stress required to activate the different slip systems), as well as the orientation of the initial single maximum orientation, which we vary from parallel to perpendicular to the shear plane. To visualize deformation structures, we use passive markers, for which we also systematically vary the initial orientation.

At relatively low strains the amount of strain rate localisation and resulting deformation structures highly depend on the initial single maximum orientation in the material in all anisotropic models. Three regimes can be recognised: distributed shear localisation, synthetic shear bands and antithetic shear bands. However, at very high strains localisation behaviour always tends to converge to a similar state, independent of the initial orientation of the anisotropy.

In rocks, shear localisation is often detected by the deflection and/or folding of layers, which may be parallel to the anisotropy (e.g. cleavage formed by aligned mica), or by deflection/deformation of passive layering, such as original sedimentary layers. The resulting fold patterns vary strongly, depending on the original orientation of layering relative to the deformation field. This can even result in misleading structures that seem to indicate the opposite sense of shear. Most distinct deformation structures tend to form when the layering is originally parallel to the shear plane.


de Riese, T., Evans, L., Gomez-Rivas, E., Griera, A., Lebensohn, R.A., Llorens, M.-G., Ran, H., Sachau, T., Weikusat, I., Bons, P.D. 2019. Shear localisation in anisotropic, non-linear viscous materials that develop a CPO: A numerical study. J. Struct. Geol. 124, 81-90.

Lebensohn, R.A., Rollett, A.D. 2020. Spectral methods for full-field micromechanical modelling of polycrystalline materials. Computational Mat. Sci. 173, 109336.

How to cite: de Riese, T., Bons, P. D., Gomez-Rivas, E., Griera, A., Llorens, M.-G., and Weikusat, I.: Influence of initial preferred orientations on strain localisation and fold patterns in non-linear viscous anisotropic materials , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13160,, 2020

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