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The Electrical Conductivity of Liebermannite: Implications for Water Transport Into the Earth's Lower Mantle

Abstract : Liebermannite (KAlSi3O8) is a principal mineral phase expected to be thermodynamicallystable in deeply subducted continental and oceanic crusts. The crystal structure of liebermanniteexhibits tunnels that are formed between the assemblies of double chains of edge‐sharing (Si, Al) O6octahedral units, which act as a repository for large incompatible alkali ions. In this study, we investigate theelectrical conductivity of liebermannite at 12, 15, and 24 GPa and temperature of 1500 K to track subductionpathways of continental sediments into the Earth's lower mantle. Further, we looked at whetherliebermannite could sequester incompatible H2O at deep mantle conditions. We observe that the superionicconductivity of liebermannite due to the thermally activated hopping of K+ions results in high electricalconductivity of more than 1 S/m. Infrared spectral features of hydrous liebermannite indicate the presenceof both molecular H2O and hydroxyl (OH−) groups in its crystal structure. The observed high electricalconductivity in the mantle transition zone beneath Northeastern China and the lower mantle beneath thePhilippine Sea can be attributed to the subduction pathways of continental sediments deep into the Earth'smantle. While major mineral phases in pyrolitic compositions are almost devoid of H2O under lowermantle conditions, our study demonstrates that liebermannite could be an important host of H2O in theseconditions. We propose that the relatively high H2O contents of ocean island basalts derived from deepmantle plumes are primarily related to deeply subducted continental sediments, in which liebermannite isthe principal H2O carrier.
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Submitted on : Thursday, November 26, 2020 - 8:15:31 AM
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Manthilake et al. 2020 JGR-Pla...
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Geeth Manthilake, Federica Schiavi, Chengcheng Zhao, Mainak Mookherjee, Mohamed Ali Bouhifd, et al.. The Electrical Conductivity of Liebermannite: Implications for Water Transport Into the Earth's Lower Mantle. Journal of Geophysical Research : Solid Earth, American Geophysical Union, 2020, 125 (8), ⟨10.1029/2020JB020094⟩. ⟨hal-02933235⟩



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