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

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