Strain partitioning in an accretionary wedge, in oblique convergence : analogue modelling

Abstract

In subduction zones undergoing oblique convergence, strain partitioning is often expressed by an important deformation inducing strike-slip faulting. In accretionary wedges, parameters such as obliquity of the convergence and friction at the bottom of the wedge play an important role in the strain partitioning. The impact of these parameters is studied using sandbox experiments. Two backstop geometries have been designed to account for different geological settings. These experiments show that the wedge taper remains constant and close to [alpha] coulomb for variable obliquities. Measurements of critical tapers on the models suggest that the Coulomb wedge theory cannot be simply applied to determine parameters on wedges developed under oblique convergence. Parameters deduced from this theory are valid only when measured in the direction parallel to the convergence. In addition, the partition degree increases with the obliquity of the convergence, and strain partitioning occurs independently of the basal friction. We remark that the model morphology changes when an obliquity value, mainly, is exceeded. A transcurrent structure develops. The models show that oblique structures located above the velocity discontinuity are associated with strike-slip faults. Similar structures have been observed within the Hikurangi accretionary wedge (New Zealand).