Experimentally developed folds in a material with a plannar mineral fabric

Abstract

The experimental development of folds in a foliated wax/mica aggregate having an anisotropy value (( N 1/ Q 1) ∗ ∗ The coefficients N 1, and Q 1 are, respectively, the maximum and minimum principal values of the compressive stiffness of the material. of between 5 and 10 is compared with a theoretical model of finite fold development in statistically homogeneous anisotropic continua described by Cobbold (1976). A pure shear deformation with the compression parallel to the foliation of the model material resulted in the formation of a train of four folds which became chevron in form. The average foliation orientation during the development of these folds for the most part was in agreement with the theoretical predictions for chevron folds in a material with N 1/ Q 1 between 5 and ∞. Some of the mechanical effects of anisotropy predicted by the theoretical model were clearly demonstrated experimentally such as rapid fold amplification and the development of angular profiles at low and intermediate limb-dips.