REDUCTION OF CO2 DURING SERPENTINIZATION OF OLIVINE AT 300-DEGREES-C AND 500 BAR

CO2 reduction processes occurring during experimental serpentinization of olivine at 300 degrees C and 500 bar confirm that ultramafic rocks can play an important role in the generation of abiogenic hydrocarbon gas. Data reveal that conversion of Fe(II) in olivine to Fe(III) in m agnetite during serpentinization leads to production of H-2 and conver sion of dissolved CO2 to reduced-C species including methane, ethane, propane, and an amorphous carbonaceous phase, Hydrocarbon gases genera ted in the process fit a Schulz-Flory distribution consistent with cat alysis by mineral reactants or products. Magnetite is inferred to be t he catalyst for methanization during serpentinization, because it has been previously shown to accelerate Fischer-Tropsch synthesis of metha ne in industrial applications involving mixtures of H-2 and CO2. The c arbonaceous phase was predominantly aliphatic, but had a significant a romatic component. Although this phase should ultimately be converted to hydrocarbon gases and graphite, if full thermodynamic equilibrium w ere established, its formation in these experiments indicates that the pathway for reduction of CO2 during serpentinization processes is com plex and involves a series of metastable intermediates.