Release of CO2 in Cold Subduction Zones by Hydrous Carbonatitic Liquids

Abstract

AbstractThe release of CO2 from subducted slabs is an important process of the global carbon cycle. Previous studies have demonstrated that metamorphic reactions, carbonatitic melts, carbonate dissolutions, and hydrous carbonatitic liquids are effective CO2 recycling mechanisms in hot and warm thermal regimes, whereas the fate of subducted carbonates in cold subduction zones remains poorly understood. Here, we investigate the phase relations of subducted ophicarbonate at pressures beyond sub‐arc depths. The presence of complex quench textures indicates that hydrous carbonatitic liquids formed at temperatures as low as ∼850°C at depths of ∼300–440 km, which corresponds to cold thermal regimes. Water released by the decomposition of dense hydrous magnesium silicate phases can substantially affect the stability of subducted carbonates, which facilitates the formation of hydrous carbonatitic liquids. This provides a mechanism for scavenging CO2 from cold slabs and may promote the formation of metasomatized domains in the deep mantle.