Unconventional water and hydrous mineral formation from dry minerals and H₂ fluids

Water availability in the lithosphere has been crucial to the geological evolution of Earth as well as the emergence and persistence of life. The global geological water cycle associated with plate tectonics has been understood as a system controlled by the presence of oxygen and hydrogen, either in fluids and melts or bound within mineral structures. However, recent work on H₂ production in the lithosphere indicates that a water mass equivalent to about 25 to 50% of global annual water inputs into subduction is converted to H₂ every year. This H₂ can be decoupled from the water cycle and potentially lost to space over geological timescales. Here, we show that the interaction of H₂-rich fluids with oxygen-bearing minerals results in the formation of unconventional redox water. This influences the residence time of hydrogen in Earth's interior and offers previously unidentified perspectives on how hydrous fluids, minerals, and melts may form in initially dry geological reservoirs.