Interference fold patterns in regional unidirectional stress fields: A result of local kinematic interactions

Folds are commonly found in association with ductile shear zones. However, superimposed folding contemporaneous with shearing is rarely reported. Here, we describe a macroscopic fold interference pattern with geometry intermediate between types 1 and 2 related to development of adjacent transcurrent shear zones. The interference fold pattern is located in a compartment bounded, on the eastern side, by an ENE-trending, dextral shear zone that connects with a NE-trending, sinistral shear zone, and, on the western side, by a NE-trending sinistral shear zone. A first folding episode produced NW-trending, SW-verging inclined folds and a later one NE-trending, upright folds. Folds of the first event are attributed to a local contractional strain field induced by the growth of the shear zones with opposed kinematics whereas the later folding episode and nucleation of the western shear zone reflects regional NW-SE contraction. Folding of a macro-scale NW-trending fold by NE-trending folds produced the fold interference structure. In contrast with most cases of types 1 and 2 fold interference patterns, in the present case no change on the orientation of regional stress axes is required.