Sub-arc mantle fugacity shifted by sediment recycling across the Great Oxidation Event

The chemical exchange between the atmosphere, crust and mantle depends on sediment recycling via subduction. However, it remains unclear how atmospherically-modified sediment may affect mantle oxygen fugacity through time. The Great Oxidation Event (GOE), amongst the most significant atmospheric changes on Earth, offers an opportunity to investigate changes in magmatism related to surface-mantle interactions. Here we identify a change of redox state of magmas across the GOE using the relative abundances of S6+, S4+ and S2− state in apatite inclusions hosted in 2.4-2.1 billion years (Gyr) old igneous zircons from the Mineiro Belt, Brazil. The host magmas record both intracrustal melting of juvenile crust and the involvement of recycled sediments in the sub-arc mantle wedge. Unaltered apatite inclusions reveal a change from reduced to more oxidised magmas from pre- to post-GOE during the early Proterozoic. We argue that this change is a direct result of deep subduction of oxidised sediments, and thus evidence of mantle-atmosphere interaction across the GOE. This suggests that the onset of sediment recycling in the Archaean provided atmospheric access to the mantle, and early ‘whiffs’ of oxygen may have already contributed to a major but localised increase of calc-alkaline magmatism and related ore deposits on Earth.