Earth is unique among known terrestrial planets in sustaining an oxygenated interior over geological time. This long-term “oxygen breathing” is driven by plate tectonics, whereby oxidised surface materials are recycled into the deep Earth at subduction zones. However, recent geochemical estimates indicate a fundamental imbalance: the redox capacity of subducting elements such as iron, sulphur, and carbon is not fully compensated by magmatism and volcanism. This implies a net deep-oxygenation of the planet, which remains poorly understood.
Current models generally assume that the redox state of subducting slabs evolves irreversibly with depth. Recent evidence challenges this assumption, showing instead that fluids released from different slab lithologies can mix and profoundly modify their oxidation states, as well as those of the residues transported into the mantle. Understanding these processes is essential to explain why arc magmas, produced above subduction zones, are the most oxidised magmas on Earth and to quantify the role of subduction in regulating Earth’s long-term redox evolution.
The OZ project aims to deliver the first quantitative, internally consistent framework for describing how oxygen and sulphur are transferred through subduction zones. By integrating high-pressure experiments, analyses of natural rocks, and thermodynamic and reactive transport modelling, the project seeks to determine the effectiveness of slab-derived fluids in oxidising the mantle wedge. The expected impact is a step change in our understanding of deep Earth cycles, with implications for planetary evolution, volcanic degassing, and the long-term stability of Earth’s surface environment.
