Melt inclusions and host olivine of Archean komatiites

Major, trace elements, H2O contents and hydrogen isotopes composition of melt inclusions and compositions of host olivine phenocrysts from komatiites of Barberton (3.3 Gyr), Belingwe (2.7 Gyr) and Abitibi (2.7 Gyr) greenstone belts. Using hydrogen isotopes, we show that the mantle sources of these melts contained excess H2O which implies that a deep mantle hydrated reservoir has been present in the Earth's interior at least since the Paleoarchean. The reconstructed initial hydrogen isotope composition of komatiites is significantly more depleted in deuterium than all surface reservoirs as well as typical mantle but resembles that in dehydrated subducted slabs. Together with a significant excess of chlorine and a temporal trend of Pb/Ce in the mantle sources of komatiites, these results argue that lithosphere recycling into the deep mantle, arguably via subduction, started before 3.3 Gyr.