Dynamic Evolution of Induced Subduction Through the Inversion of Spreading Ridges

Abstract

AbstractLithospheric weakness is essential in subduction initiation. Spreading ridges are divergent plate boundaries which may represent lithospheric weakness and promote subduction initiation. Natural examples of ridge‐inversed subduction along spreading ridges have been proposed (e.g., the Proto‐South China Sea subduction). Although, the dynamic evolution of ridge‐inversed subduction has been investigated by geodynamical numerical modeling previously, it remains obscure, especially the influence of the thermal state and geometries of spreading ridges on subduction initiation and dynamic evolution. We establish two‐dimensional thermomechanical coupled numerical models to simulate the dynamic evolution of forced subduction along spreading ridges, and quantify the influence of four major parameters on subduction development (i.e., the spreading rate and cooling age of spreading ridges, forced convergence rate and asymmetric ridge geometry). Our model results suggest the following findings. (1) The cooling age of spreading ridges and the forced convergence rate are the most important parameters controlling ridge‐inversed subduction initiation, and the thresholds of the two parameters are revealed, that is, subduction may easily initiate with a cooling age less than ∼20 Myr and a forced convergence rate lager than ∼4 cm/yr. (2) The spreading rate of ridges prior to forced convergence and asymmetric ridge geometries play a secondary role in subduction development. (3) Ridge‐inversed subduction of the Proto‐South China Sea along the Palawan spreading ridge was proposed geologically, and our numerical modeling results support this scenario.