Thermodynamic constraints on the formation of condensed carbon from serpentinization fluids

Vincent Milesi (1) , Thomas M. Mccollom , François Guyot (2)

1 IPGP - Institut de Physique du Globe de Paris
2 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie

Recent studies have identified carbonaceous material in serpentinite bodies, but whether these deposits have a biologic or abiotic origin remains uncertain. In this work, thermodynamic calculations were performed to examine the potential for abiotic condensed carbonaceous material to be produced from serpentinization-derived fluids under hydrothermal conditions. Calculation of reaction pathways during serpentinization of olivine showed that fluid compositions should equilibrate with condensed carbonaceous material, which controls the H₂ and CO₂ activities. Fluids from laboratory serpentinization experiments and from the Lost City and the Rainbow hydrothermal field are shown to be consistent with this model. The predictions indicate that carbonaceous material should be the dominant carbon product of CO₂ reduction in these hydrothermal settings, which would have significant implications for a number of processes, including the deep Earth carbon cycle by creating a pool of relatively immobile reduced carbon, the extent of H₂ production in ultrabasic environments, and mechanisms leading to abiotic reduced carbon compounds.

Mots clés: Serpentinization; Carbon; Organic compounds; Abiotic; Hydrogen; Thermodynamic modeling

Domaines: Planète et Univers [physics]

Vincent Milesi, Thomas M. Mccollom, François Guyot. Thermodynamic constraints on the formation of condensed carbon from serpentinization fluids. Geochimica et Cosmochimica Acta, 2016, 189, pp.391-403. ⟨10.1016/j.gca.2016.06.006⟩. ⟨insu-03581300⟩