The production of Barberton komatiites in an Archean subduction zone

Based upon their geochemical similarity, we propose that the 3.5 Ga Barbert on basaltic kornatiites (BK) are the Archean equivalents of modern boninite s, and were produced by the same melting processes (i.e. hydrous melting in a subduction zone). Tile Barberton komatiites also share some geochemical characteristics with boninites, including petrologic evidence for high magm atic H2O contents. Experimental data indicates that the Archean sub-are man tle need only be 1500-1600 degreesC to produce hydrous komatiitic melts. Th is is considerably cooler than estimates of mantle temperatures assuming an anhydrous, plume origin for komatiites (up to 1900 degreesC). The depicted mantle residue that generates the Barberton komatiites and BIC will be coo led and metasomatised as it resides beneath the fore-are, and may represent Dart of the material that formed the Kaapvaal cratonic keel.