Pre-subduction of the Caroline Plateau intensifies lithospheric hydration in the southern Mariana Trench

The subduction of oceanic plateaus significantly reshapes subduction systems, yet its impact on lithospheric hydration prior to subduction is not well understood. Here we investigate these processes as the Caroline Plateau approaches the southern Mariana Trench, using velocity models derived from wide-angle seismic lines. Our results from OBS2017-1 reveal that the crust of the subducting plate thickens from ~7.5 km beneath the trench axis to ~16.0 km at the outer rise, accompanied by reduced seismic velocities in the region between the toe of the plateau and the trench axis. These velocity reductions even exceed those observed beneath adjacent oceanic crust near Challenger Deep, indicating intensified hydration at the leading edge of the plateau, accompanied by a narrowing of the bending-related faulting zone. The simultaneous subduction of plateau and normal oceanic crust governs plate configuration, highlighting the role of oceanic plateaus in enhancing heterogeneous water percolation and modulating subduction dynamics. Seismic refraction profiling indicates that subduction initiation of the Caroline Plateau into the Mariana Trench has involved intense faulting and mantle serpentinization at the leading edge of the subducting oceanic plateau