Forearc Spreading Cessation and Backarc Basin Evolution: Insights from Mariana Subduction System and Geodynamic Modeling

Evolutions of forearc and backarc spreading are related to processes of Subduction Initiation (SI). The unique evolution history of the Izu-Bonin-Mariana subduction system (IBM) provides a perfect example to investigate the relationships between forearc and backarc spreading with SI. The plate reconstruction model shows that the IBM initiated around 52 Ma, and the kinematics of the Pacific Plate changed around 47 Ma, providing horizontal velocity for forearc spreading cessation and backarc opening. Here, based on the plate motion history and the 2D thermomechanical models, we simulated the early stages of SI, as well as the evolutions of forearc and backarc spreading. We proposed a new model with a delayed convergence rate after similar to 5 Myr of SI, which can explain 1) the observed lithospheric forearc spreading cessation of the IBM; 2) the observed formation time of the Shikoku basin; and 3) the horizontally lying slab in the mantle transition zone after cessation of the backarc spreading of the IBM.