Paleoarchean deep crustal hydration and oxidation induced by subduction-driven water recycling.

O (from 3.5 to 9.5 weight %) during 3.5 to 3.2 billion years ago. Thermodynamic-geochemical modeling shows that these magmas formed by water-fluxed melting of progressively enriched and oxidized mafic sources at similar pressures (0.9 to 1.3 gigapascals). Such extensive, secular deep crustal hydration and oxidation cannot be adequately explained by nonsubduction models. Instead, our findings underscore the indispensable role of subduction-driven water recycling in the origin of continental crust.