Chemical Reaction Between Metallic Iron and a Limited Water Supply Under Pressure: Implications for Water Behavior at the Core‐Mantle Boundary
Masayuki Nishi, Yasuhiro Kuwayama, Takeshi Hatakeyama, Saori I. Kawaguchi, Naohisa Hirao, Yasuo Ohishi, Tetsuo Irifune
Abstract
Abstract Water transportation to the deep lower mantle via plate subduction may induce a reaction between water and iron at the core‐mantle boundary. Recent experimental studies suggest that such a reaction may generate FeO 2 H x ‐rich domains, which can explain the seismic structures of the ultralow velocity zone in this region. In this study, the chemical reaction between metallic iron and a limited water supply at ~120 GPa was investigated using time‐resolved in situ synchrotron X‐ray diffraction measurements in combination with the laser‐heated diamond anvil cell technique. Contrary to the results of earlier studies, the formation of FeO instead of FeO 2 H x without intermediate phases was observed. Considering the unlimited availability of iron in the core and the limited water supply resulting from mantle downflow, the FeO‐rich layers consisted of Fe‐bearing ferropericlase and postperovskite, which must have locally cumulated at the bottom of the mantle simultaneously with hydrogen incorporation into the core.