Temperature dependence and mechanism of hydrogen incorporation in olivine at 12.5–14.0 GPa | CU Experts

The concentration and incorporation mechanisms of hydrogen into (Mg, Fe)2SiO4 olivine have been studied under water saturated conditions at 12.5–14.0 GPa and 1100–2000°C. The hydrogen content of olivine (Fo90–Fo95) coexisting with enstatite and hydrous melt increases from about 4600 ppmw at 1100°C to a maximum of 6250 ppmw at 1200°C. Above 1400°C, the hydrogen content of olivine decreases non‐linearly, reaching 160–240 ppmw in the 1800–2000°C range where there is a high melt fraction and no enstatite. Polarized infrared spectra of the recovered olivines exhibit OH absorption bands in both the 3450–3650 cm−1 range (group I) and 3160–3450 cm−1 range (group II). Results indicate that hydration of olivine is associated with both Mg and Si site vacancies. Microprobe analyses of the samples show a clear deficit of Si in olivine. The water storage capacity of olivine is probably no more than 1.5–2.0 times less than wadsleyite at 1400°C and transition zone pressures.

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