A discrete element model for orogenesis and accretionary wedge growth

Abstract

We develop a two-dimensional discrete element model to investigate the evolution of doubly vergent orogenic and accretionary wedges. This generates the localization of deformation across persistent structures as emergent phenomena unlike many continuum models that require predefined weaknesses to localize strain. The model is used to study how deformation processes evolve for two different boundary conditions, drawing strong comparisons with previous sandbox analogues and computational approaches. The deformational history of the modeled wedges is characterized by three stages defined by an evolution in the mechanisms available to accommodate shortening. The first stage develops a strong retrovergent thrust that initiates at the subduction point; the second stage shows a change in vergence of deformation as thin-skinned thrusting propagates into material carried on the subducting plate thus evolving a folded and thrusted prowedge; finally, a second shallower retrowedge develops in the overriding plate through accretion. This final stage is not present in all sand analogue modeling approaches, and defines a difference in the deformation style. Thresholds in geometry and size regulate the localization and style of deformation and hence the progression through the three stages. The wedges produced show periodicity in the modes of accretion to maintain a geometric form, with deformation localizing across structures that are internally reactivated. Thus prowedges and retrowedges are seen to oscillate about constant taper angles. Copyright 2005 by the American Geophysical Union.