Role of pre-existing topography and overburden on strain-partitioning of oblique doubly-vergent convergent wedges

Scaled sandbox modeling was used to analyze the three-dimensional aspects of strain partitioning along obliquely convergent margins that underwent a subduction polarity reversal event. In the experiments, the first phase of shortening produced a preexisting topography that affected wedge kinematics during the second phase. Increasing degrees of obliquity during the first shortening phase produced different amounts of inherited topography and overburden, giving way to different effects on wedge response during the second phase of shortening. During the second phase the models with an inherited heavy overburden show an anomalous orientation for Riedel shears predating the development of a margin-parallel strike-slip fault. These shears are oriented at an angle that is higher than kinematically predicted with respect to the subduction slot, suggesting a transient rotation of the stress applied by the obliquity of subduction. In contrast, experiments with a lighter overburden do not show this inconsistency. In addition, all the models displayed an unexpectedly high accretion rate during the second phase of shortening, which we interpret to be dependent on topographical slope breaks inherited after the first phase of shortening and the critical asymmetrical architecture of doubly vergent wedges.