日本地球惑星科学連合2014年大会

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セッション記号 S (固体地球科学) » S-MP 岩石学・鉱物学

[S-MP06_28PM2] Impact of volatiles on the processes of formation and evolution of the Earth's interior

2014年4月28日(月) 16:15 〜 17:45 411 (4F)

コンビーナ:*Mysen Bjorn(Geophysical Laboratory, Carnegie Inst. Washington)、Eiji OHTANI(Graduate School of Science Tohoku University 6-3 Aoba, Aramaki, Aoba-ku Sendai 980-8578)、Tatsuhiko KAWAMOTO(Univ. Kyoto Kyoto, 606-8502, JAPAN)、座長:大谷 栄治(東北大学大学院理学研究科地学専攻)

16:45 〜 17:00

[SMP06-09] In-situ characterization of carbon-speciation in silicate-C-O-H fluid and melt with temperature, pressure, and redox con

*MYSEN Bjorn1 (1.Geophysical Laboratory, CIW, USA)

キーワード:COH volatiles, fluid structure, melt structure, high pressure, high temperature, redox conditions

Speciation and partitioning of C-bearing volatiles species in and between silicate-saturated C-O-H fluids and (C-O-H)-saturated melts have been determined in-situ with the samples to pressures and temperatures of ~2GPa and 900oC, respectively. Structural characterization was conducted with vibrational spectroscopy of samples contained in externally-heated, hydrothermal diamond anvil cells. The redox conditions were controlled near that of the Fe+H2O=FeO+H2 (reducing, RED) and Ni+H2O=NiO+H2 (oxidizing, OX) equilibria, respectively. Melts are, therefore saturated in H2O, H2, and C-bearing species (redox dependent) and coexisting fluids saturated in silicate components. Solubility of volatile and silicate components depend on both temperature and pressure. The melt/fluid partition coefficients of the C-bearing species vary with redox conditions and temperature with the ∆HREDmelt/fluid = 44(7) kJ/mol and ∆HOXmelt/fluid = -70(32) kJ/mol. Pressure is a dependent variable and increases with increasing temperature. It is assumed no pressure effect of the partition coefficients.The solution equilibria under reducing and oxidizing conditions, respectively, were; (1) 2CH3-+H2O+Qn+1=2CH4+Qn and (2) 2CO32-+H2O+2Qn+1=HCO3-+2Qn, where the superscript, n, in the Q-species denotes number of bridging oxygen in the silicate species (Q-species). In the absence of H2O equilibrium (1) changes to CH3-+Qn=CH4+Qn+1. For oxidized carbon, there is an analogous expression expressing equilibrium between molecular CO2 and structurally bound CO32--groups. Under both oxidizing and reducing conditions, the abundance ratios, CH4/CH3- and HCO3-/CO32- increase with temperature. The enthalpy change associated with the species transformation does, however, differ for fluids and melts and also for oxidized and reduced carbon (∆H(1)fluid = -16(5) kJ/mol, ∆H(1)melt = -49(5) kJ/mol, ∆H(2)fluid=81(14) kJ/mol). For the exchange equilibrium of CH4 and CH3 species, the temperature-dependent equilibrium constant yields ∆H=34(3) kJ/mol.Reactions (1) and (2) involve changes in silicate polymerization where increasing abundance ratios, CH4/CH3- and CO32-/HCO3- lead to increased silicate melt polymerization. As a result of the relations between speciation of C-bearing species and melt and fluid structure, stable isotope (C and H) and element partition coefficients between melts and fluids, which depend on and silicate polymerization and silicate speciation, also vary with speciation of C-bearing species in silicate-C-O-H systems. Pressure, temperature, and redox control on the C-speciation also govern those (and other) properties.