Copper recycling and redox evolution through progressive stages of oceanic subduction: Insights from the Izu-Bonin-Mariana forearc

•Oxidized hydrous boninites show low Cu contents and no clear slab addition of Cu.•Oceanic slabs from initial to mature subduction add little Cu to mantle wedge.•Slab materials added to the mantle wedge are generally reducing.•Hydrous slab melt-peridotite reaction is likely vital to produce oxidized arc magma.•The metasomatized mantle wedge is not enriched in Cu from the oceanic slab.