Folds and the strain ellipsoid: a general model

Kinematics of the Torcal Shear Zone: Transpressional tectonics in a salient-recess transition at the northern Gibraltar Arc

“…According to active folding models in monoclinic transpression, fold hinges track the maximum horizontal finite strain axis during progressive deformation (Tikoff and Peterson, 1998;Titus et al, 2007;Treagus and Treagus, 1981;Wilcox et al, 1973), which corresponds to the X-axis in simpleshear-dominated transpression and to the Y-axis in pure-sheardominated transpression (Fossen and Tikoff, 1993). The structural pattern suggests that transpression in the Valle de Abdalajís massif is pure-shear-dominated and thus the Y-axis is considered subparallel with fold hinges.…”

Mechanisms of flexural flow folding of competent single-layers as evidenced by folded fibrous dolomite veins

“…Ramsay, 1967;Fletcher, 1974;Shimamoto and Hara, 1976;Treagus and Treagus, 1981;Podladchikov, 1999, 2001;Schmid and Podladchikov, 2006;Hobbs et al, 2008Hobbs et al, , 2010Kocher et al, 2008;Huang et al, 2010;Schmid et al, 2010). Nevertheless, a number of ideal reference cases is put forward for the internal strain distribution in symmetrically buckled, competent, isotropic singlelayers within a viscous or power-law matrix.…”

StrainModeler: A Mathematica™-based program for 3D analysis of finite and progressive strain

“…With regards to the evolution of the fold hinges, two possibilities can be also envisaged: (1) the folds hinges form in the direction of the major axis of the finite whole-rock strain ellipse in (Osberg, 1975;Ramsay, 1980;Treagus and Treagus, 1981), and (2) the fold hinges form initially in the direction of the major axis of the whole-rock strain ellipse in the plane of the layer and subsequently rotate passively in agreement with the subsequent strain (Flinn, 1962;Sanderson, 1973;Ramsay, 1979;Jiang, 1999). An example of the differences between the paths obtained with these two evolution modes is shown in Fig.…”

“…They obtained equations that can be used to calculate the following: (i) the position and length of the principal axes of the strain ellipsoid at any stage of the deformation; (ii) the position and length of the principal axes of the strain ellipse in any plane at any stage of the deformation; (iii) the position and length of passive markers which initially coincided with the principal axes of the strain ellipse in a plane and then rotated passively; and (iv) the shear strain parallel to a plane or sheet. Treagus and Treagus (1981) developed methods to determine the orientation and length of the principal axes of the strain ellipse in layers oblique to the axes of the strain ellipsoid both in the case of known initial orientation and known deformed orientation. These methods were used to analyze the obliquity between the fold axes originated in the layer and the XY plane of the 3D deformation.…”