Recycling reduced iron at the base of magmatic orogens

•Arclogite garnets have very low Fe3+/∑Fe compared to MORB and arc basalts.•Magnetite saturation is strongly suppressed in high pressure (>1 GPa) differentiation.•Differentiation pressure controls magma redox evolution by stabilizing/destabilizing garnet vs. magnetite.•The oxidized nature of continental crust may be a result of petrogenetic processes in magmatic orogens.