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

Abstract

It is assumed in the theories of Earth formation that the composition of gases extracted by primary planetary magmas is formed by the large-scale melting of the early mantle, which occurred in the presence of a metallic Fe phase. The molten Fe metal and silicate materials underwent gravitational migration, which affected the fractionation of siderophile elements. Volatile compounds had to form simultaneously in the zones of large-scale melting of the early Earth; their compositions were controlled by interaction with silicate and metallic melts. This process remains poorly understood. A series of experiments was carried out in the system silicate melt (FeO-Na2O-SiO2-Al2O3) + liquid metallic Fe + C (graphite) + volatile components (N-C-H) at 1.5 GPa, 1400°C, and oxygen fugacity (fO2) 1.9 to 3.7 logarithmic units below the fO2 value of the IW buffer equilibrium for the investigation of the simultaneous dissolution of N, C, and H in iron-bearing silicate melts. The mechanisms of N, C, and H dissolution were elucidated using the Raman spectroscopy of glasses produced by quenching of reduced melts. It was established that melting in the T-F-fO2 stability range of the metallic phase results in the formation of species with N-H (NH3), C-H (CH4), and H-O (H2O, OH−) bonds and molecular N2 and H2 in silicate melts. Experimental investigations revealed a significant effect of pressure and fO2 on the partitioning of N between silicate melt and equilibrium metallic phase (DN = Nmetal/Nsilicate). At 1.5 GPa, 1400°C, and ΔlongfO2 (IW) values of −2.4 and −3.7, DN is 2.9 and 0.5, respectively.