How a volcanic arc influences back-arc extension: insight from 2D numerical models

Abstract

Abstract. Investigating plate tectonics through the lens of back-arc extension in subduction systems, this study introduces a 'hot region' on the overriding plate (OP) in 2D thermo-mechanical models, simulating the role of an arc. The models identified two extension locations on the OP: at the hot region (Mode EH) or surprisingly at a far-field location which is about 750 km from the trench (Mode EF). The study also found that extension could occur at the same far-field location without a hot region when the OP is young and thin, or the subducting plate (SP) is old and strong. Our models suggest that EH mode is common, occurring in many cases like Mariana Trough and Lau Basin, while the EF mode is rare, potentially occurring in scenarios like the Japan Sea. The primary driving mechanism in our models is poloidal flow beneath the OP, and the extension process is the competition of basal drag which thins the OP versus thermal healing which thickens it, and also a competition of thermal weakening at the hot region and at the far-field location. Increased trench retreat rates, facilitated by increased hot region temperature and width, encouraged this flow and consequently promoted back-arc extension.