Evolution of slab-driven poloidal flow symmetry governs back-arc deformation rates

Subduction is considered the primary driver of plate tectonics, which is sometimes accompanied by back-arc spreading. Back-arc deformation on Earth exhibits substantial variability, ranging from compressional regimes in the Japan Sea to rapid spreading with rates up to 15 cm/yr in the Lau Basin. Even within a single subduction zone, back-arc basins can exhibit significant spatial and temporal variability in spreading rates along the trench. The mechanisms underlying this variability remain inadequately understood. To address this issue, we compiled global back-arc deformation rates and quantified slab area penetration into the deeper mantle. Additionally, we conducted a series of numerical simulations to elucidate the factors that govern back-arc deformation rate. Our global back-arc compilation and numerical models reveals a robust negative correlation between back-arc spreading rate and slab penetration into the deeper mantle, highlighting the initial stage of subduction as the peak phase of back-arc spreading. Furthermore, numerical simulations offer insights into the underlying dynamic mechanisms, demonstrating that slab-driven poloidal flow play a dominant role in governing back-arc deformation rates.