- Alteration of the oceanic lithosphere
As during geological storage of CO2, the alteration of the oceanic lithosphere leads to a net uptake of C. We work on better constraining the flux of carbon fixed during these reactions. Our approach is based on the analysis of carbon concentrations and isotopic compositions of altered basaltic samples. We have shown, for the first time, that more than 75% of the total C present in these rocks (away from veins) occur as organic compounds while carbonates represent less than 25%. We study the origin of such organic compounds, that could be formed either through biological or abiotic reactions (such as Fischer-Tropsch type) for the deepest samples. Analyses of various ages of the oceanic crust sections, as well as various spreading rates will help to build a global model for C uptake during alteration. This work has strong connections with the experimental section described below.
- Abiotic formation of hydrocarbons during alteration of oceanic crust
Recent oceanographic expeditions have revealed the abundance of ultramafic-hosted hydrothermal systems along the Mid-Atlantic ridge, where vents are characterized by the emission of large amounts of H2, CH4, and of complex carbon-bearing molecules formed during abiotic redox reactions. So far, however, the quantification of such production is only partially described and previous experimental works provide contrasted results.
Our interest is: (1) to better constrain the flux of CO2 which is transformed into reduced compounds with an effort on the condensed fraction and (2) to characterized both isotopically and mineralogically the different C compounds. We study here both natural samples, as well as experimental samples. This work is funded by the international DCO program (Deep Energy directorate).