From seafloor spreading to subduction: Ridge-spreading inheritance modulates slab redox transfer

Subduction zones recycle redox-sensitive components into Earth’s interior, but how seafloor-spreading inheritance controls slab redox transfer remains poorly constrained. We combine two-dimensional open-system thermodynamic modeling with redox-budget calculations for two slab endmembers representing magma-rich fast- to slow-spreading and magma-poor ultraslow-spreading lithosphere under the same pressure–temperature evolution. Both generate sulfate-rich oxidizing fluids, yet their redox outputs differ markedly. The ultraslow-spreading endmember carries ~16% more incoming net oxidation flux but releases ~45% less at sub-arc depths under Channelized-Fluid-Extraction and ~25% less under Reactive-Transport formulations, while retaining a larger residual budget at 220 km. The largest single lithologic contributor to sub-arc source also shifts from mafic crust to hydrated mantle. This contrast persists without cross-layer reaction, showing that ridge-inherited architecture sets the baseline depth partitioning of oxidation capacity, while reactive transport redistributes sulfur and iron without reversing it. Oceanic-lithosphere construction therefore leaves a redox memory that influences where oxidation capacity is returned to the mantle, linking ridge tectonics to arc redox heterogeneity and deeper oxidant recycling.