Hydrogenation of carbon at 5.5–7.8 GPa and 1100–1400 °C: Implications to formation of hydrocarbons in reduced mantles of terrestrial planets

C- and N-Bearing Species in Reduced Fluids in the Simplified C–O–H–N System and in Natural Pelite at Upper Mantle P–T Conditions

“…% ( Table 2) Note that the fluids synthesized in the graphite-bearing muscovite-C-O-H-N system likewise contained mainly light alkanes. As we showed before [18,19], heavier alkanes can form in experimental systems at higher pressures and temperatures, when Pt capsules are used instead of Au ones. Concentrations of heavier alkanes also become lower in fluids with lower H 2 O contents in the fluid [19].…”

“…The capsules were sealed by arc-welding prior to experiments. The capsule assembly details were described in our previous publications [10,19,20,38].…”

“…Much recent progress in experiments at mantle pressures and temperatures allows reconstructing the compositions of hydrocarbon fluids that form in different ways: By thermal decomposition of higher alkanes, aromatic compounds, and fatty carboxylic acids [8][9][10][11]; reaction of CO, CO 2 , and carbonate with FeO and H 2 O; or hydrogenation of carbon [7,[12][13][14][15][16][17][18][19][20]. Thermodynamic calculations and experimental data indicate that organic species, such as light alkanes, acids, and salts, e.g.…”

“…Thermodynamic calculations and experimental data indicate that organic species, such as light alkanes, acids, and salts, e.g. acetic acid and acetates, can be stable in the silicate mantle under the appropriate redox conditions [4,7,10,[12][13][14][15][16][17][19][20][21][22]. Specifically, light alkanes were found out [22] to be stable in a wide range of redox conditions in the presence of a lherzolitic mineral assemblage at 5.5-7.8 GPa and 1150-1350 • C. The discovery of hydrocarbons in diamonds from the mantle and in crustal alkaline rocks [5,17,[23][24][25][26][27]] supports this conclusion.…”

“…The abundance of CaSi-perovskite and Cr-poor majoritic garnets supports the formation of diamond in slabs within the transition zone or in the uppermost lower mantle. Our recent study [19] of HC generation by hydrogenation of different carbon sources in the presence of metal phases is another step forward in this field.…”