Dynamic Evolution of Back‐Arc Basins Affected by Double Subduction

Abstract Back‐arc basins are essential geological units, formation and development of which are controlled by subduction dynamics. In the previous modeling studies, evolution of back‐arc basins was widely investigated under single subduction scenarios, suggesting that development of a back‐arc basin is only influenced by the adjacent single subduction zone. However, natural observations show that in the case of face‐to‐face double subduction, such as the New Hebrides and Tonga subduction systems in the Southwest (SW) Pacific region, evolution of back‐arc basins is likely affected by double subduction. How double subduction affects back‐arc basin evolution remains enigmatic. Here, we use 2D thermomechanical numerical modeling to investigate the dynamic evolution of back‐arc basins affected by double subduction. Our results suggest that episodic back‐arc spreading could be induced by double subduction, i.e., back‐arc spreading is first retarded by the development of a second subduction and then promoted by its slab break‐off. The double subduction further enhances upwelling of the deep mantle, facilitating the material circulation between the shallow and deep mantle. The major parameters influencing double subduction and back‐arc spreading are the distance between the two subduction zones and slab ages. Our results provide a new perspective for interpreting the episodic back‐arc spreading and the enriched back‐arc basalts in the SW Pacific region, and suggest the importance of double subduction in the geodynamic evolution of this region.