Deep Earth’s Oxygen recycling at subduction Zones

Projektinformationen

OZ

ID Finanzhilfevereinbarung: 101088573

DOI

10.3030/101088573

EK-Unterschriftsdatum 6 März 2023

Startdatum 1 Dezember 2023

Enddatum 30 November 2028

Finanziert unter

• European Research Council (ERC)

Gesamtkosten

€ 2 000 000,00

EU-Beitrag

€ 2 000 000,00

Koordiniert durch

AGENCIA ESTATAL CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS
Spain

Periodic Reporting for period 1 - OZ (Deep Earth’s Oxygen recycling at subduction Zones)

Berichtszeitraum: 2023-12-01 bis 2026-05-31

Zusammenfassung vom Kontext und den Gesamtzielen des Projekts

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.

Arbeit, die ab Beginn des Projekts bis zum Ende des durch den Bericht erfassten Berichtszeitraums geleistet wurde, und die wichtigsten bis dahin erzielten Ergebnisse

The project addresses four tightly linked objectives. First, novel high-pressure experimental strategies were developed to quantify how oxygen and sulphur fugacity control mineral stability during the metamorphic evolution of serpentinites, key water-rich rocks in subducting slabs. New in situ methods now allow direct measurement of iron redox states in hydrous minerals at the micrometre scale, significantly improving accuracy relative to previous approaches.

Second, innovative experimental designs demonstrated that strong redox gradients can induce complete mobilisation of sulphur during slab dehydration. These experiments provide the first direct evidence that sulphur transfer at depth is intrinsic to redox conditions rather than limited by kinetic constraints.

Third, state-of-the-art chemical and isotopic analyses of sulphide–oxide assemblages in natural rocks from exhumed subduction zones revealed that fluid mixing occurs at multiple spatial scales and exerts first-order control on redox conditions during metamorphism. These observations directly link experimental predictions with geological reality.

Finally, the project developed new thermodynamic and computational tools that upscale mineral-scale redox processes to the scale of entire subduction systems. These models now allow systematic evaluation of oxygen transfer between slabs and the mantle wedge under realistic pressure–temperature conditions.

Fortschritte, die über den aktuellen Stand der Technik hinausgehen und voraussichtliche potenzielle Auswirkungen (einschließlich der bis dato erzielten sozioökonomischen Auswirkungen und weiter gefassten gesellschaftlichen Auswirkungen des Projekts)

The OZ project moves beyond the state of the art by demonstrating that the redox evolution of subducting slabs is dynamic, reversible, and strongly controlled by fluid mixing and sulphur mobility. It establishes, for the first time, a quantitative link between mineral-scale redox reactions, fluid chemistry, and the generation of oxidised arc magmas. The project also introduces new methodologies for in situ redox quantification and large-scale thermodynamic modelling, both broadly applicable to deep Earth research.

These results open new research directions and provide a robust framework for future experimental and modelling studies. The tools and concepts developed are expected to be adopted widely by the geoscience community, supporting further integration into global models of Earth’s chemical and redox evolution.