Formation of Carbon and Hydrogen Species in Magmas at Low Oxygen Fugacity

Studies of iron-bearing silicate melt ( ferrobasalt) þ iron metallic phase þ graphite þ hydrogen equilibria show that carbon and hydrogen solubilities in melts are important for the evolution of the upper mantle. In a series of experiments conducted at 37GPa and 1520---1600C, we have characterized the nature (oxidized vs reduced) and quantified the abundances of C- and H-compounds dissolved in iron-bearing silicate melts. Experiments were carried out in an anvil-with-hole apparatus permitting the achievement of equal chemical potentials of H2 in the inner Pt capsule and outer furnace assembly. The fO2 for silicate melt---iron equilibrium was 232 004 log units below iron---wüstite (IW). The ferrobasalt used as starting material experienced a reduction of its iron oxides and silicate network. The counterpart was a liberation of oxygen reacting with the hydrogen entering the capsule. The amount of H2O dis-solved in the glasses was measured by ion microprobe and by step