Host: Abstracts of Annual Meeting of the Geochemical Society of Japan
Pages 172-
We proposed a method to estimate redox state of mantle from CO/CO2 ratio of fluid inclusions in mantle minerals. We analyzed Raman spectra of a fluid inclusion in a mantle xenolith. This shows prominent CO2 peaks with a weak CO peak. The relative ratio of CO to CO2 is 0.0114 in Raman intensities, corresponding to 0.021 as molar ratio. Considering the pyroxene geothermometric value of 980°C, the oxygen fugacity of the fluid can be calculated to around QFM-0.7 in log unit. The major element composition of chromian-spinel is comparable to the oxygen fugacity of QFM-0.6 in log unit, which is well consistent with the value from CO/CO2 ratio. The CO/CO2 ratio of a mantle xenolith would be applicable as a probe for mantle redox.
