Slab pull drives IBM Trench advance despite the weakened Philippine Sea Plate

Abstract

The Izu-Bonin-Mariana (IBM) subduction zone has one of the most significant advancing trenches on Earth, but the mechanism responsible for its trench advance remains in dispute. Slab pull from the Ryukyu subduction zone may have provided the main driver for this significant trench advance. However, it is unclear whether this slab-pull force can transmit through the weak zones, such as the young Shikoku and Parece Vela basins, the active Izu-Bonin rifts, and the continuous spreading Mariana Trough, and then act on the IBM trench. To figure out this issue, we conduct slab subduction numerical models to reproduce the spatio-temporal tectonic evolution of the Philippine Sea Plate. Model results show that the stretching rate of 2.5 cm/yr during rifting/spreading represents the critical threshold for the transmission of slab pull. Additionally, 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. We suggest that the Mariana Trench advance is driven by the continuous Izu-Bonin Trench advance from the north, which is supported by the fact that the Mariana Trench is further east than the Izu-Bonin Trench and that the IBM trench advance rate decreases southward.