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 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) O6 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 H2O 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 H2O 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 H2O under lower mantle conditions, our study demonstrates that liebermannite could be an important host of H2O in these conditions. We propose that the relatively high H2O contents of ocean island basalts derived from deep mantle plumes are primarily related to deeply subducted continental sediments, in which liebermannite is the principal H2O carrier.

Electrical conductivity of metasomatized lithology in subcontinental lithosphere

“…The A sites are connected to each other to form channels along [001] direction that is likely to further facilitate the mobility of the Na + ions. Similar high electrical conductivity has been observed in liebermannite which also has tunnels that promote the migration of alkali cations (He et al, 2016;Manthilake et al, 2020). Also, fast ionic conduction in solid state has been observed in albite, where Na + ions undergo faster diffusion via the alkali ion cavities in the albite aluminosilicate framework (Hu et al, 2011).…”

Insights on the deep carbon cycle from the electrical conductivity of carbon-bearing aqueous fluids

“…The conductivity ( ) is expressed in S/m, temperature ( ) is in absolute temperature, is the pre-exponential factor in S/m, and is the gas constant in J K −1 mol −1 . We obtain the activation enthalpy and the pre-exponential factor following the combined electrical conductivity 43 , 44 . The notations , indicates distinct conduction mechanisms operating at different temperature intervals 45 (Table 1 ).…”

Some Remarks on the Electrical Conductivity of Hydrous Silicate Minerals in the Earth Crust, Upper Mantle and Subduction Zone at High Temperatures and High Pressures

“…In comprehensive comparisons with previously acquired electrical conductivity results on the hot-pressed sintering polycrystalline quartz reported by Bagdassarov and Delépine (2004) [113], synthetic polycrystalline anorthite reported by [60], as well as the pure aqueous fluid of sodium chloride with the 5% of weight percentage reported by Sinmyo and Keppler (2017) [114], one new origin for the explanation of high conductivity anomaly at the depth ranges from 70 to 120 km was put forward on the base of the released water-bearing fluid during the process of epidote dehydration at high temperature and high pressure. Furthermore, some recently reported electrical conductivity and elastic wave velocity results on hydrous halogen-bearing amphibole, glaucophane, Liebermannite, chlorite, and lawsonite from Manthilake et al [98][99][100][101][102] also confirmed that the dehydration of hydrous minerals will release a large amount of the water-bearing fluids, which can be used to reasonably explain the anomalously seismic and electrical transport behaviors in the region of hot subduction of deep mantle wedges.…”

“…It is well known that the electrochemical AC impedance spectroscopy method is one of most efficient technique to measure the electrical conductivity of hydrous minerals and rocks at conditions of high temperatures and high pressures [98][99][100][101][102][103][104][105][106]. Before we launched a complex impedance spectroscopy measurement, the AC signal voltage ranges from 10 mV to 3 V and the scanning frequency ranges from 10 −5 Hz to 3.2 × 10 7 Hz need to be predesignated by virtue of Z-Plot program in the complex impedance spectroscopy analyzer.…”

“…Hydrogen as a form of point defect dissolved in the crystalline structure of olivine can enhance several magnitude of orders in the electrical conductivity by virtue of the diffusion of some hydrogen-related defects [30]. Due to the complexity of the concentration and its corresponding mobility in the electric charge carrying species for these hydrogen-related defects, the electrical conductivity of hydrous single crystals along with [100],…”