[S-MP06_28PM1] Impact of volatiles on the processes of formation and evolution of the Earth's interior

[SMP06-02] Influence of H2 fluid on the stability of MgSiO3 enstatite in the upper mantle condition

*Ayako SHINOZAKI¹, Hiroyuki KAGI¹, Hisako HIRAI², Hiroaki OHFUJI², Taku OKADA³, Satoshi NAKANO⁴, Takehiko YAGI² (1.GCRC, The university of Tokyo, 2.GRC, Ehime university, 3.ISSP, The university of Tokyo, 4.NIMS)

Keywords:enstatite, H2 fluid, upper mantle, laser heated diamond anvil cell

C-O-H fluids affect the phase relation and melting of silicate minerals in the mantle of the Earth. The mantle is expected to become progressively reduced with increasing depth, so that H₂ fluid is considered to exist in the deep mantle with H₂O fluids. In this study, influence of H₂ fluid on stability and phase relation of enstatite, which was the secondary most abundant mineral in the upper mantle, was examined using a laser heated diamond anvil cell. In this presentation, we will report the results of MgSiO₃-H₂ system, which is non-iron-bearing system. After heating at 3.1-13.8 GPa and about 1500-2000 K, decomposition of enstatite and formation of forsterite (Mg₂SiO₄), periclase (MgO) and coesite/stishovite (SiO₂) were observed from XRD measurements. The presence of H₂ fluid were observed from Raman spectra even after the heating. Since the studied P-T range is in the stability field of orthoenstatite and high pressure clinoenstatite under dry condition, the decomposition reaction observed in the present study was presumably induced by H₂ fluid. Formation process of these silicate phases were evaluated by observation of quench texture of the recovered samples using SEM and TEM.