The role of oblique arc-continent collision on the spatio-temporal evolution of stress in accretionary continental margins

Arc-continent collision is the process by which intra-oceanic arc crust is accreted to continental margins and the most important mechanism that enables the growth of the continental crust since Phanerozoic times. Modern examples of arc-continent collision show that collision is often oblique and that its different evolution stages, which involve episodes of lithospheric extension and compression, can vary in space and time in the trench-parallel direction. However, the way the collision obliquity affects the collision style and stress-strain evolution in the continent remains unexplored. We use 3D visco-plastic purely mechanical numerical models where we only vary the colliding arc obliquity to explore how it affects the collision and associated stress-strain evolution, using the UWGeodynamics code. We found that the obliquity of the colliding arc controls whether post-collisional extension is localized, or distributed in the trench-parallel direction by promoting slab-deformation and toroidal mantle flow. We interpret that the partitioning in stress into compression and extension in all simulations is caused by a gravity-driven flow, which equilibrates the buoyancy anomaly stored in the lithosphere during collision and episodes of lithospheric thickening. In our models, this gravity-driven flow applies a horizontal gravitational force (body force) directed from the collided arc towards the subducting plate (compressional) and the continental margin (extensional). Furthermore, our results show that all phases of arc-continent collision can coexist along the trench-parallel direction, as observed in Taiwan, Timor, and Papua New Guinea (PNG).