Assessing the geochemical signatures of abiogenically dominated methane sources

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Methane (CH4) and the higher hydrocarbons are of particular interest for society. The majority of naturally occurring hydrocarbons is assumed to derive from biogenic (thermogenic and microbial) sources. Unambiguous evidence for abiogenic reduction of CO2 to hydrocarbons within the Earth s crust has been lacking. Recently, we demonstrated the occurrence of abiogenic production of CH4 in three subduction-related bi-phase-hydrothermal systems of the Mediterranean region. These localities offer a great opportunity to study the abiogenic signature of these hydrocarbons in terms of the classical chemical and isotopic parameters, which are commonly used to distinguish thermogenic from microbial sources. Comparison of theoretical and empirical data with measured data will enable a) an estimate of the extent that biogenic sources contribute to overall hydrocarbon production in abiogenically dominated systems, and b) an assessment of the extent that abiogenically dominated sources might have been erroneously classified as biogenic. In search of new indicators for abiogenically dominated sources, we will investigate the factors that exert control on the occurrence of aromatic and unsaturated hydrocarbons in these volcanic-hydrothermal systems.