Deep Earth’s Oxygen recycling at subduction Zones

ongoing

In contrast to other known terrestrial planets, the Earth's interior is oxygen-breathing through the sink of oxidised tectonic plates at convergent margins since the late Archean to Paleoproterozoic. Recent estimates suggest that the redox capacity of some key subducting chemical elements is not balanced on geological time scales by global magmatism and volcanism, thus implying a puzzling deep oxygenation of our planet. Although current models presume that the redox state of subducting slabs is irreversible, my most recent results demonstrate that mixing of fluids from different slab lithologies can dramatically change the redox capacity of such fluids and the deeply subducted residues. The OZ project will provide an unprecedented quantitative framework to account for such interactions in order to determine the effectiveness of subduction slab fluids to oxidise the mantle wedge and generate the most oxidised magmatism on Earth: arc magmatism. To achieve this ambitious goal, OZ will address four specific goals: (1) the experimental determination of the effect of oxygen (fO2) and sulphur (fS2) fugacity on the stability of critical mineral assemblages during the prograde metamorphic evolution of serpentinites by using a novel triple capsule buffering technique in high pressure experiments; (2) the determination of sulphur mobility at high pressure due to gradients in fO2 and fS2 by means of an original experimental capsule design with interconnected reservoirs representative of the heterogeneity of the slab; (3) the characterization of sulphide-oxide mineral associations in natural samples from exhumed paleo-subduction terranes to demonstrate the scales of fluid mixing in nature; and (4) the upscaling of these processes to subduction zones by using two types of equilibrium reactive transport models at the scale of the slab and the mantle wedge.