The redox evolution of arc magmas: from the oxygenation of the Earth’s atmosphere to the genesis of giant hydrothermal ore deposits

Arc magmatism at subduction zones is responsible for much of the mass transfer of chemical elements between the Earths lower and upper spheres. Arc magmas are significantly more oxidized and richer in volatile elements than other voluminous magma types on Earth.

These characteristics promote the genesis of large magmatic-hydrothermal ore deposits and potentially also the build-up of the oxygen budget of the Earths atmosphere.

Despite its great significance, the origin of the higher oxidation state of arc magmas is still one of the most debated questions in petrology.

I will combine high-pressure-temperature experiments, field-based studies and computational simulations to obtain quantitative understanding of redox reactions taking place during magma genesis, differentiation and degassing.

Subsequently, I will apply this new knowledge to assess if arc magmatism may have been a key to the oxygenation of the Earths atmosphere, and to pinpoint the most prospective regions for the generation of giant ore deposits.

Most experiments will rely on revolutionary new instrumentation and methodologies, which I have recently developed or will develop as a part of the project.

For example, we will determine for the first time the speciation of sulfur in aqueous fluids in situ at magmatic temperatures and upper crustal pressures by using a prototype spectroscopic cell, so that its critical role in redox transfer and ore genesis can be quantified.

Similarly, the field-based studies will employ a new method to constrain the redox evolution of magmas with unparalleled precision, which will be developed experimentally by using a prototype high-pressure apparatus with a unique capability to control redox conditions.

In addition, these will also apply a powerful combination of novel and challenging analytical methods including the analysis of Au, Pt, Pd and Re concentrations and S isotope ratios in silicate melt inclusions in minerals to identify the key agents of magma oxidation.