Subduction zone studies have provided evidence for reduction of carbonates by reaction with hydrogen, resulting in hydrous mineral formation and the production of methane. While methane generation contributes to production of one of Earth's key biosignatures essential for the origins of life, few studies have recognized the implications of the contextual production of water. In Earth systems, water is assumed to be sourced from conventional reservoirs, e.g. seawater being recycled through plate tectonics. However, this “redox water” produced from molecular hydrogen and a potentially wide range of oxygen-bearing minerals is likely unaccounted for in Earth's availability of water.

These redox reactions can be investigated in association with several natural H2 reservoirs, whether in the continental crust, at mid-ocean ridges, along subducting slabs, in arc magmas, or even in the deep mantle. This work takes an experimental approach to investigate redox water formation.

Here we present preliminary results on H2-olivine reactions at 1GPa and 800 °C, P-T conditions compatible with lithospheric mantle conditions. End-loaded piston-cylinder double capsule experiments were conducted reacting San Carlos olivine (Fo92) and molecular H2 for approximately five days. Subsequent quadrupole mass spectrometry spectra show 0.83 µmol H2O, close to the 1 µmol amount predicted by thermodynamic modeling at the experimental conditions for the system olivine (Fo92)-H2. SEM-EDS and MicroRaman analyses on solid products will provide complementary mineralogical and chemical data to discern the reaction pathwaysof this water formation. Continued experimentation of potential H2 reactions with crustal and mantle rocks will help constrain maximum fluxes of redox water at varying P-T conditions, improving our understanding of the water budget on Earth and potentially on other planets.