Abiotic Methane in Continental Serpentinization Sites: An Overview

Until 2008 methane in land-based serpentinized peridotites (MSP) was considered to be an unusual and rare occurrence of abiotic gas. Today, reports of MSP are increasing for numerous localities worldwide in low temperature settings in ophiolites, orogenic massifs or intrusions. CH4 emanates from focused seeps, hyperalkaline water springs or through diffuse seepage from the ground, typically along faults. MSP has a combination of stable C and H isotope composition that is different from that of biotic methane; it is likely produced by Fischer-Tropsch Type reactions between CO2 (or other C compounds) and H2 (from serpentinization) at low temperatures (typically <100 °C) and its carbon is fossil, 14C free, which does not derive from the more recent C dissolved in the hyperalkaline waters. MPS is more common than previously assumed; it may have played a key role in the origin of life, may fuel microbial life in igneous rocks on Earth and other planets, and can be an additional source of gas in atypical petroleum systems hosting ultramafic rocks.