EGU21-752
https://doi.org/10.5194/egusphere-egu21-752
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

The ephemeral development of C' shear bands

Melanie Finch1,2, Paul Bons2, Florian Steinbach2, Albert Griera3, Maria-Gema Llorens4, Enrique Gomez-Rivas5, Hao Ran2,6, and Tamara de Riese2
Melanie Finch et al.
  • 1School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria, 3800, Australia
  • 2Department of Geosciences, Eberhard Karls University Tübingen, 72074 Tübingen, Germany
  • 3Departament de Geologia, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
  • 4Institute of Earth Sciences Jaume Almera (ICTJA-CSIC), Lluís Sol´e Sabarís s/n, E-08028 Barcelona, Spain
  • 5Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain
  • 6School of Earth Sciences and Resources, China University of Geosciences, Beijing, 100083, China

C' shear bands are common structures in ductile shear zones but their development is poorly understood. They occur in rocks with a high mechanical strength contrast so we used numerical models of viscoplastic deformation to study the effect of the proportion of weak phase and the phase strength contrast on C' shear band development. We employed simple shear to a finite strain of 18 in 900 steps and recorded the microstructure, stress and strain distribution at each step. We found that C' shear bands form in models with ≥5% weak phase when there is a moderate or high phase strength contrast, and they occur in all models with weak phase proportions ≥15%. Contrary to previous research, we find that C' shear bands form when layers of weak phase parallel to the shear zone boundary rotate forwards. This occurs due to mechanical instabilities that are a result of heterogeneous distributions of stress and strain rate. C' shear bands form on planes of low strain rate and stress, not in sites of maximum strain rate as has previously been suggested. C' shear bands are ephemeral and they either rotate backwards to the C plane once they are inactive or rotate into the field of shortening and thicken to form X- and triangle- shaped structures.

How to cite: Finch, M., Bons, P., Steinbach, F., Griera, A., Llorens, M.-G., Gomez-Rivas, E., Ran, H., and de Riese, T.: The ephemeral development of C' shear bands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-752, https://doi.org/10.5194/egusphere-egu21-752, 2021.

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