Mid-mantle water transportation implied by the electrical and seismic properties of ε-FeOOH

Water in the mantle transition zone and the core-mantle boundary plays a key role in Earth's stratification, volatile cycling, and core formation. If water transportation is actively running between the aforementioned layers, the lower mantle should contain water channels with distinctive seismic and/or electromagnetic signatures. Here, we investigated the electrical conductivity and sound velocity of epsilon-FeOOH up to 71 GPa and 1800 K and compared them with global tomography data. An abrupt threeorder jump of electrical conductivity was observed above 50 GPa, reaching 1.24(12) similar to 10(3) S/m at 61 GPa. Meanwhile, the longitudinal sound velocity dropped by 16.8% in response to the high-to-low spin transition of Fe3+. The high-conductivity and low-sound velocity of epsilon-FeOOH match the features of heterogenous scatterers in the mid-lower mantle. Such unique properties of hydrous epsilon-FeOOH, or possibly other Fe-enriched phases can be detected as evidence of active water transportation in the mid-lower mantle. (C)2021 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.

Automated summary

Water in the mantle transition zone and the core-mantle boundary plays a crucial role in Earth's internal processes. This study investigates the electrical conductivity and sound velocity of a specific iron mineral and finds that it matches the characteristics of water channels in the mantle. This provides evidence for active water transportation in the mantle.