Title
Chemical Reaction Between Metallic Iron and a Limited Water Supply Under Pressure: Implications for Water Behavior at the Core‐Mantle Boundary
Author
M. Nishi, Y. Kuwayama , T. Hatakeyama, S. Kawaguchi, N. Hirao, Y. Ohishi, T. Irifune
Year
2020
Journal
Geophysical Research Letters
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 FeO2Hx‐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 FeO2Hx 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.
Instrument
NRS-5100
Keywords
core‐mantle boundary, subducted plates, hydrous phases, iron core, iron oxide