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The Electrical Conductivity of Liebermannite: Implications for Water Transport Into the Earth's Lower Mantle
Author(s) -
Manthilake Geeth,
Schiavi Federica,
Zhao Chengcheng,
Mookherjee Mainak,
Bouhifd Mohamed Ali,
Jouffret Laurent
Publication year - 2020
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2020jb020094
Subject(s) - mantle (geology) , subduction , geology , transition zone , geochemistry , tectonics , paleontology
Liebermannite (KAlSi 3 O 8 ) is a principal mineral phase expected to be thermodynamically stable in deeply subducted continental and oceanic crusts. The crystal structure of liebermannite exhibits tunnels that are formed between the assemblies of double chains of edge‐sharing (Si, Al) O 6 octahedral units, which act as a repository for large incompatible alkali ions. In this study, we investigate the electrical conductivity of liebermannite at 12, 15, and 24 GPa and temperature of 1500 K to track subduction pathways of continental sediments into the Earth's lower mantle. Further, we looked at whether liebermannite could sequester incompatible H 2 O at deep mantle conditions. We observe that the superionic conductivity of liebermannite due to the thermally activated hopping of K + ions results in high electrical conductivity of more than 1 S/m. Infrared spectral features of hydrous liebermannite indicate the presence of both molecular H 2 O and hydroxyl (OH − ) groups in its crystal structure. The observed high electrical conductivity in the mantle transition zone beneath Northeastern China and the lower mantle beneath the Philippine Sea can be attributed to the subduction pathways of continental sediments deep into the Earth's mantle. While major mineral phases in pyrolitic compositions are almost devoid of H 2 O under lower mantle conditions, our study demonstrates that liebermannite could be an important host of H 2 O in these conditions. We propose that the relatively high H 2 O contents of ocean island basalts derived from deep mantle plumes are primarily related to deeply subducted continental sediments, in which liebermannite is the principal H 2 O carrier.