Deformation of erosive and accretive forearcs during subduction of migrating and non‐migrating aseismic ridges: Results from 3‐D finite element models and application to the Central American, Peruvian, and Ryukyu margins

Abstract

AbstractSubduction of aseismic oceanic ridges causes considerable uplift and deformation of the upper plate and may lead, for example, to the indentation of the forearc, the formation of marine terraces, or distinct fault patterns in the upper plate. Depending on the orientation of the ridge relative to the plate convergence direction, the ridge may either be stationary or migrate along the margin. Here we use three‐dimensional numerical models to investigate the tectonic evolution of forearcs affected by ridge subduction. In different experiments, we distinguish between migrating/non‐migrating ridges and accretive/erosive margins, respectively. Our results reveal that displacement and strain fields above migrating and non‐migrating ridges are asymmetric with respect to the ridge axis unless both ridge and plate convergence direction are perpendicular to the trench. As the asymmetric deformation pattern shifts along the margin through time, uplift caused by the underthrusting ridge is followed by subsidence when the ridge crest passed by, and regions initially experiencing shortening may subsequently undergo extension and vice versa. If the forearc comprises an accretionary prism, the ridge‐induced reentrant is larger than those in models with erosive forearcs and strain localizes in the frontal part of the wedge. Additional models with a setup adjusted to the Cocos and Gagua Ridges provide constraints on the onset of their subduction at the Central American and Ryukyu margins at ~2 Ma and 1 Ma, respectively. Displacement and strain fields from a model for the Nazca Ridge collision zone show good agreement with geological data from marine terraces and Quaternary faulting.