Abstract
Analogue models have been used to investigate the influence of planar mechanical anisotropy on the orientation of shear fractures in an elastoviscous-brittle material. Multilayered models consisting of a mixture of plasticine, vaseline and preferentially-oriented paper flakes have been coaxially deformed for this purpose. The evolution of the orientation, length and connectivity of fracture sets has been systematically analysed with progressive coaxial deformation. The experimental results show that the orientation of fractures with respect to the deformation axes depends on the orientation of transverse anisotropy. Two symmetrical sets of shear fractures are formed in models with layering parallel to the extension axis X, while the fracture network is asymmetrical with respect to the deformation axes for cases with oblique anisotropy. The average dihedral angles between fracture sets are higher than 100 degrees, with the obtuse bisector between the two sets oriented perpendicular to layers. The stress fields calculated from fracture data differ from the boundary conditions applied by the deformation apparatus. This misorientation is related to the degree of anisotropy. In models with high oblique anisotropy both fracture arrays rotate in a dextral sense together with layers towards the X-axis, indicating that the presence of a strong anisotropy controls their evolution with progressive deformation. (C) 2011 Elsevier Ltd. All rights reserved.
| Original language | English |
|---|---|
| Pages (from-to) | 61-76 |
| Number of pages | 16 |
| Journal | Journal of Structural Geology |
| Volume | 34 |
| Early online date | 9 Nov 2011 |
| DOIs | |
| Publication status | Published - Jan 2012 |
Bibliographical note
This work was financed through the PhD grant BES-2003-0755 to EGR and research project CGL2004-03657, both funded by the Spanish Ministry of Education and Science. We thank J. Carreras and E. Druguet for discussions on various aspects related to this work, to P.D. Bons and M.W. Jessell for many valuable suggestions and to L.M. Castaño for her assistance during some of the experiments. We gratefully acknowledge N. Timms and A. Fagereng, whose constructive reviews greatly improved the manuscript, together with the editorial guidance of T.G. Blenkinsop. We would also like to thank G. Zulauf, F. Marques and D. Koehn for their comments to a previous version of the manuscript.Keywords
- shear fracture
- anisotropy
- layering
- fracture orientation
- stress field
- multilayer
- single-crystals
- deformation experiments
- vorticity analysis
- biaxial tests
- rock masses
- strain
- bands
- brittle
- fluid
- zones