Modelling of non-cylindrical boudins
Final Report Abstract
Tablet boudins result from radial and concentric necks and/or fractures, which are forming almost simultaneously during single-phase pure flattening if the competent layer is perpendicular to the principal shortening axis, Z. Chocolate-tablet boudinage, on the other hand, can be produced by two phases of plane strain, with the Z-axis perpendicular to the layer, and the Y- and X-axis parallel to the layer and being exchanged from run to run. Viscous and brittle (extension fracture) boudins can be distinguished by their aspect ratio. In cases of extension-fracture boudinage, the boudin aspect ratio is close to 1. In cases of viscous boudinage and formation of pinch-and-swell structures, the aspect ratio is >> 1. Viscous and brittle (extension fracture) boudins can further be distinguished by the relation between layer thickness and boudin width. In cases of extension-fracture boudinage, this relation is linear, whereas under viscous conditions, this relation in non-linear. The shape of boudins is controlled not only by layer thickness, viscosity ratio between layer and matrix, and finite strain, but is also significantly controlled by the finite strain geometry (bulk flattening, plane or constrictional strain). Tablet boudins have yet not been described, and chocolate-tablet boudins have been described only in a few cases, from natural outcrops. The reasons might be that the characterization and evaluation of tablet and chocolate-tablet boudins requires geometrical analysis in three dimensions, which is a difficult task when such structures occur in nature . Further studies, particularly microfabric studies of natural boudins and surrounding matrix, are required to reveal the reasons for the difference in aspect ratio of natural and experimental boudins.
Publications
- 2011. Formation of chocolate-tablet boudins in a foreland fold and thrust belt: A case study from the external Variscides (Almograve, Portugal). J. Struct. Geol., 33, 1639-1649
Zulauf, G., Gutiérrez-Alonso, G., Kraus, R., Petschick, R., Potel, S.
(See online at https://doi.org/10.1016/j.jsg.2011.08.009) - 2011. Tablet boudinage of an anhydrite layer in rock-salt matrix: Results from thermomechanical experiments. J. Struct. Geol., 33, 1801-1815
Zulauf, J., Zulauf, G., Hammer, J., Zanella, F.
(See online at https://doi.org/10.1016/j.jsg.2011.09.006) - 2011. The origin of tablet boudinage: Results from experiments using power-law rock analogs. Tectonophysics, 510, 327–336
Zulauf, J., Zulauf, G., Kraus, R., Gutiérrez-Alonso, G.
(See online at https://doi.org/10.1016/j.tecto.2011.07.013) - 2012. Boudinage of anhydrite in rock-salt matrix: The impact of bulk finite strain geometry. In: Bérest, P., Ghoreychi, M., Hadj-Hassen, F. and Tijani, M. (Eds.), Mechanical Behavior of Salt VII, pp. 65-70. Taylor & Francis Group, London
Zulauf, G., Zulauf, J., Mertineit, M., Hammer, J.
