Mathematical models of single-layer folding in shear zones and transpressional regimes

The problem of folding of layered rocks in shear zones and transpressional regimes is examined using a mathematical model to investigate the stability of viscous layered media during several basic types of deformations. Folding in shear zones is studied using a two-dimensional model of a layer embedded in a less competent medium undergoing simple shear. The medium is of infinite extent in the x-z plane with the layer at an angle ;The analysis indicates that the layer is identically unstable to infinitesimal fold-like perturbations for ;The second part of the analysis examines three-dimensional buckling and pinch-and-swell instabilities associated with wrench shearing and transpression. This analysis shows that a buckling instability is present in both wrench shear and transpression with the axes of the fastest growing buckling disturbances oriented perpendicular to the incremental shortening axis in the layer. In wrench shear, this results in folds with axes at 45...