The influence of Al2O3 on the H2O content in periclase and ferropericlase at 25 GPa

In this paper I present results of IR spectroscopic measurements of water solubility in Al-bearing periclase and ferropericlase (Mg# = 88) synthesized at 25 GPa and 1400–2000 °C. The IR spectra of their crystals show narrow absorption peaks at 3299, 3308, and 3474 cm−1. The calculated H2O contents are 11–25 ppm in periclase (Al2O3 = 0.9–1.2 wt.%) and 14–79 ppm in ferropericlase (Al2O3 = 0.9–2.9 wt.%). Ferropericlase contains more H2O and Al2O3 than periclase at 1800–2000 °C. I suggest that addition of Al2O3 does not influence the solubility of water in ferropericlase but can favor the additional incorporation of Fe2O3 into the structure. The incorporation of Fe3+ into ferropericlase increases water solubility as a result of iron reduction to Fe2+. It is shown that water has limited solubility in ferropericlase from mantle peridotite; therefore, ferropericlase cannot be considered an important hydrogen-bearing mineral in the lower mantle.