Graph showing the possible melting curve of hydrogen-bearing iron peroxide
Different scientific studies have calculated the melting curve of hydrogen-bearing iron peroxide (FeO2Hx) and estimated the core-mantle boundary temperature, some of which are plotted here. The study by Deng et al. [2019] suggests that FeO2Hx may be in a molten rather than solid state in the lowermost part of the mantle which may account for the anomalously low seismic velocities found in that zone. Credit: Deng et al. [2019], Figure 2
Source: Journal of Geophysical Research: Solid Earth

The core-mantle boundary is an area of complex thermal, seismic and chemical structure. Of particular interest are ultra-low velocity zones, areas of very low seismic velocities on the core-mantle boundary that may suggest melt is present. The identity of this melt, and its solid complement, is still an open question. Deng et al. [2019] suggest that the phase may be molten hydrogen-bearing iron peroxide (FeO2Hx), a pyrite-like structured, hydrated mineral. If true, ultra-low velocity zones would represent a significant reservoir for hydrogen in the mantle.

Citation: Deng, J., Karki, B. B., Ghosh, D. B., & Lee, K. K. M. [2019]. First‐principles study of FeO2Hx solid and melt system at high pressures: Implications for ultralow‐velocity zones. Journal of Geophysical Research: Solid Earth, 124, 4566– 4575.

—Stephen W. Parman, Editor, JGR: Solid Earth

Text © 2019. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.