Influence of oxygen fugacity on the solubility of carbon and hydrogen in FeO-Na2O-SiO2-Al2O3 melts in equilibrium with liquid iron at 1.5 GPa and 1400°C

Abstract

Equilibria in the model melt (NaAlSi3O8(80) + FeO(20))-C-H2 system were experimentally studied at ΔlogfO2(IW) from −2.2 to −5.6, a pressure of 1.5 GPa, and a temperature of 1400°C. The experiments were conducted in a piston-cylinder apparatus using Pt capsules. The low fO2 values were imposed during the experiments by adding 2, 5, and 7 wt % of finely dispersed SiC to NaAlSi3O8(80) + FeO(20) powder. The experimental products were investigated by electron microprobe analysis and Raman spectroscopy. The investigations showed that melting at 1.5 GPa and 1400°C in the stability field of a metallic iron phase produces silicate liquids containing both oxidized and reduced H and C species. Carbon and hydrogen are dissolved in the melt as C-H (CH4) complexes. In addition, OH− groups, molecular hydrogen H2, and molecular water H2O were observed in the melts. The proportions of dissolved C and H species strongly depend on oxygen fugacity. With decreasing fO2, the content of O-H species decreases and that of H-C species increases. The obtained data and previous results (Kadik et al., 2004, 2006) allow us to suppose a fundamental change in the character of magmatic transfer of C-O-H components during the evolution of the redox state of the Earth’s mantle in geologic time toward higher fO2 in its interiors.