Slab Pull Drives IBM Trench Advance Despite the Weakened Philippine Sea Plate

The mechanism behind the significant Izu-Bonin-Mariana (IBM) trench advance is still controversial. We conduct slab subduction numerical models that reproduce the spatio-temporal tectonic evolution of the Philippine Sea region to investigate whether slab pull from the Ryukyu subduction zone can cross the weakened Philippine Sea Plate and act on the IBM trench. Model results show that the lithospheric strengthening and weakening effects cancel out each other during the rift stage so that the slab pull from the Ryukyu Trench can transmit through the weak fossil spreading centers and intra-arc rifts and drive the Izu-Bonin Trench's advance. In contrast, lithospheric weakening overwhelms lithospheric strengthening and impedes stress transfer in the back-arc spreading stage, suggesting that the slab pull cannot directly pull the Mariana Trench to advance at present. Our study indicates that extreme rheological parameters are not needed for the IBM trench advance, despite the Philippine Sea Plate is weakened. Understanding why IBM (Izu-Bonin-Mariana) has the globe's most significant trench advance affects not only our understanding of subduction dynamics and lithospheric deformation mechanisms, but also our knowledge on slab rheology, which is key to understanding many fundamental geodynamic questions. A number of models have been proposed to explain the IBM trench advance. These models can be broadly classified into two categories: one is single-slab subduction, and the other is double-slab subduction. Single-slab subduction models usually require extreme rheological parameters that seem inconsistent with those inferred from slab curvature and gravity observations, while double-slab subduction models need to consider whether the slab-pull force can transmit through the weak Philippine Sea Plate. The Philippine Sea Plate is strongly weakened due to extensive back-arc extensional deformations. We conduct numerical models that reproduce the first-order tectonic evolution of the IBM Subduction Zone to solve this dispute. The model results show that slab pull from the Ryukyu Trench can pass through the weakened Philippine Sea Plate and act on the IBM Trench. Thus, the IBM Trench advance does not require special rheological parameters as suggested by single-slab models. Slab pull can pass through the fossil young spreading centers and active intra-arc rifts, but not active spreading centersExtremely strong slabs or strong subduction-interface coupling are not needed to explain the IBM trench advanceThe Mariana Trench advance may be driven by the advance of the Izu-Bonin Trench at its north