Abstract:

Carbon contents in reduced Martian basalts at graphite saturation were experimentally studied at 1400-1550 °C, 1-2 GPa, and logfO₂ of IW-0.4 to IW+1.5 (IW denotes the Fe-FeO buffer). The results show that carbon solubility in Martian basalts, determined by SIMS, is 20 to 1400 ppm, increasing with increasing fO₂. Raman and FTIR measurements on the quenched silicate glasses show that the dominant carbon species in Martian basalts is carbonate (CO₃^2-). The experimental data generated here were combined with literature data on similar graphite-saturated C solubility for mafic-ultramafic compositions to develop an empirical model that can be used to predict carbon content of graphite-saturated reduced basalts at vapor-absent conditions:

At IW+1.7 ≥ logfO₂ ≥ IW-1:

log(C, ppm) = -3702(±534)/T – 194(±49)P/T – 0.0034(±0.043)logXH₂O + 0.61(±0.07)NBO/T + 0.55(±0.02)ΔIW + 3.5(±0.3) (R²=0.89)

At IW-5.3 ≤ logfO₂ ≤ IW-1:

log(C, ppm) = 0.96(±0.19)logXH₂O – 0.25(±0.04)ΔIW + 2.83(±0.34) (R²=0.6)

in which T is temperature in K, P is pressure in GPa, is mole fraction of water in basalts,  is the oxygen fugacity relative to the IW buffer, and . This model was applied to predict carbon content in graphite-saturated mantle melts of the Mercury, Mars, and the Moon. The results show that graphite may be consumed during the production and extraction of some Martian basalts, and CO₂ released by volcanism on Mars cannot be an efficient greenhouse gas in the early Mars. The lunar mantle carbon may be one of the main propellant driving the fire-fountain eruption on the Moon; however, the mantle carbon may not be an important propellant for the explosive eruption on Mercury.

Li, Y., Dasgupta, R., Tsuno, K. (2017). Carbon contents in reduced basalts at graphite saturation: Implications for the degassing of Mars, Mercury, and the Moon. Journal of Geophysical Research – Planets 122. doi:10.1002/2017JE005289