Application of IR and Raman spectroscopy for the determination of the role of oxygen fugacity in the formation of N-[ETH]!-[ETH]z-[ETH] molecules and complexes in the iron-bearing silicate melts at high pressures

• Published in: Geochemistry international Vol. 54; no. 13; pp. 1175 - 1186
• Main Authors: Kadik, A A, Koltashev, V V, Kryukova, E B, Tsekhonya, TI, Plotnichenko, V G
• Format: Journal Article
• Language: English
• Published: 01.12.2016
• Subjects: Fugacity; Glass; Infrared spectroscopy; Magma; Melts; Oceans; Oxygen; Silicates
• DOI: 10.1134/S0016702916130073
• ISSN: 0016-7029

Large-scale melting of the Earth's early mantle under the effect of global impact processes was accompanied by the generation of volatiles, which concentration was mainly controlled by the interaction of main N, C, O, and H gas-forming elements with silicate and metallic melts at low oxygen fugacity (fO sub(2)), which predominated during metallic segregation and self-oxidation of magma ocean. The paper considers the application of Raman and IR (infrared) Fourier spectroscopy for revealing the mechanisms of simultaneous dissolution and relative contents of N, C, O, and H in glasses, which represent the quench products of reduced model FeO-Na sub(2)O-Al sub(2)O sub(3)-SiO sub(2) melts after experiments at 4 GPa, 1550 degree C, and fO sub(2) 1.5-3 orders of magnitude below the oxygen fugacity of the iron-wustite buffer equilibrium (fO sub(2)(IW)). Such fO sub(2) values correspond to those inferred for the origin and evolution of magma ocean. It was established that the silicate melt contains complexes with N-H bonds (NH sub(3), NH sub(2) super(+), NH sub(2) super(-)), N sub(2), H sub(2), and CH sub(4) molecules, as well as oxidized hydrogen species (OH super(-) hydroxyl and molecular water H sub(2)O). Spectral characteristics of the glasses indicate significant influence of fO sub(2) on the N-C-O-H proportion in the melt. They are expressed in a sharp decrease of NH sub(2) super(+), NH sub(2) super(-)(O-NH sub(2)), OH super(-), H sub(2)O, and CH sub(4) and simultaneous increase of NH sub(2) super(-)(Si-NH sub(2)) and NH sub(3) with decreasing fO sub(2). As a result, NH sub(3) molecules become the dominant nitrogen compounds among N-C-H components in the melt at fO sub(2) two orders of magnitude below fO sub(2)(IW), whereas molecular [ETH]![ETH] sub(4) prevails at higher fO sub(2). The noteworthy feature of the redox reactions in the melt is stability of the [ETH]z[ETH] super(-) groups and molecular water, in spite of the sufficiently low fO sub(2). Our study shows that the composition of reduced magmatic gases transferred to the planet surface has been significantly modified under conditions of self-oxidation of mantle and magma ocean.