Water partitioning at 660 km depth and evidence for very low water solubility in magnesium silicate perovskite

Water partitioning experiments were performed in MgO ± FeO ± Al 2 O 3 ‐SiO 2 ‐H 2 O systems at 24 GPa and 1400°C and 1750°C in the multi‐anvil press. In high‐temperature experiments, water was not detected in near‐infrared spectra of perovskite. In samples synthesized at 1400°C, in Al‐free systems, (Mg,Fe)SiO 3 perovskite coexisting with hydrous ringwoodite contained 1–2 ppm wt H 2 O. The partition coefficient D ringwoodite/perovskite of water between perovskite and ringwoodite varies between ∼1050 and 1400. In the presence of aluminium at 1400°C, perovskite coexisted with superhydrous phase B. Raman analysis of the samples reveals the presence of superhydrous phase B and brucite as small inclusions in the perovskite, explaining the peaks near 3690, 3410 and 3350 cm −1 , frequently seen in the infrared spectra of aluminous perovskites, but which are absent in perfectly clear regions. Consequently, the water solubility in aluminous perovskite appears to be very low. The partition coefficient D magnesiowüstite/perovskite varies between 60 and 75 in Fe‐ and Al‐bearing systems, respectively.