Two- and three-dimensional shape fabric analysis by the intercept method in grey levels

Patrick Launeau (1) , C.J. Archanjo (2) , David Picard (3) , Laurent Arbaret (3) , Pierre-Yves Robin (4)

1 LPGN - Laboratoire de Planétologie et Géodynamique de Nantes [UMR 6112]
2 Instituto de Geociências
3 ISTO - Institut des Sciences de la Terre d'Orléans
4 Department of Geology

The count intercept is a robust method for the numerical analysis of fabrics Launeau and Robin (1996). It counts the number of intersections between a set of parallel scan lines and a mineral phase, which must be identified on a digital image. However, the method is only sensitive to boundaries and therefore supposes the user has some knowledge about their significance. The aim of this paper is to show that a proper grey level detection of boundaries along scan lines is sufficient to calculate the two-dimensional anisotropy of grain or crystal distributions without any particular image processing. Populations of grains and crystals usually display elliptical anisotropies in rocks. When confirmed by the intercept analysis, a combination of a minimum of 3 mean length intercept roses, taken on 3 more or less perpendicular sections, allows the calculation of 3-dimensional ellipsoids and the determination of their standard deviation with direction and intensity in 3 dimensions as well. The feasibility of this quick method is attested by numerous examples on theoretical objects deformed by active and passive deformation, on BSE images of synthetic magma flow, on drawing or direct analysis of thin section pictures of sandstones and on digital images of granites directly taken and measured in the field.

Mots clés: Shape preferred orientation; Fabric; Structural geology; Intercepts; Image analysis; Shape preferred orientation

Domaines: Volcanologie; Milieux et Changements globaux

Patrick Launeau, C.J. Archanjo, David Picard, Laurent Arbaret, Pierre-Yves Robin. Two- and three-dimensional shape fabric analysis by the intercept method in grey levels. Tectonophysics, 2010, 492 (1-4), pp.230-239. ⟨10.1016/j.tecto.2010.06.005⟩. ⟨insu-00509163⟩