<p>Subduction transports oxidized material into Earth’s interior. The Mariana subduction zone is a representative example of modern plate tectonic regimes and provides a comprehensive set of geological, geochemical and geodynamical data. Here we use thermomechanical–thermodynamic numerical methods to simulate redox dynamics and fluid-melt release along a Mariana-type subduction setting in two dimensions, allowing comparison between our model and long-term oxidation events in the Mariana arc. Our findings demonstrate two main mechanisms of subduction-related mantle oxidation. First, sulfide oxidation during subduction enables fluids to carry substantial redox budgets into the sub-arc mantle. Partially hydrated mantle emerges as the primary fluid contributor, followed by altered oceanic crust. Secondly, oxidized iron-rich (Fe³⁺) partial melts extracted from slab-top sediments and altered oceanic crust exert a dominant influence on back-arc mantle oxidation. The majority of oxidized material is carried into the deeper mantle with subducted slabs. Our work demonstrates that with the advent of modern plate tectonics and efficient lithospheric recycling, oxidized material carried by Mariana-type subduction zones has had a global impact on Earth’s mantle redox evolution and our planet’s oxygenation.</p>