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Electrical conductivity of enstatite as a function of water content: Implications for the electrical structure in the upper mantle
Baohua Zhang;  Takashi Yoshino;  Xiaoping Wu;  Takuya Matsuzaki;  Shuangming Shan;  Tomoo Katsura
2012
Source PublicationEarth and Planetary Science Letters
Volume357–358Pages:11-20
Abstract

The electrical conductivity of Ca-free aluminous enstatite with various water contents has been determined at a pressure of 3 GPa in a Kawai-type multi-anvil apparatus. Impedance spectroscopy was performed for both hydrogen-doped and -undoped samples in a frequency range from 0.1 Hz to 1 MHz to examine the effect of water on conductivity. Two conduction mechanisms were identified for hydrogen-undoped samples at temperature of 1000–1723 K and for hydrogen-doped samples at relatively lower temperature range of 500–900 K to minimize dehydration of samples. For the hydrogen-undoped samples, the activation enthalpy is around 1.9 eV at the higher temperatures range (>1300 K) suggesting that the dominant charge transfer mechanism is Fe2+−Fe3+ hopping (small polaron) conduction. For the hydrogen-doped samples measured below 900 K, the activation enthalpy decreases from 1.11 to 0.70 eV, and the conductivity values systematically increase with increasing water content, suggesting that proton conduction is the dominant conduction mechanism. Taking hopping conduction and water content dependence of activation enthalpy for proton conduction into account, all electrical conductivity data were fitted to the formula σ=σ0hexp(−Hh/kT)+σ0pCwexp[−(Hp0αCw1/3)/kT], where σ0 is pre-exponential factor, Cw is the water content in weight percent, H is the activation enthalpy, Hp0 is the activation enthalpy for proton conduction at very low water concentration, α is the geometrical factor, k is the Boltzmann constant, T is absolution temperature and subscripts h and prepresent hopping and proton conductions, respectively. Using the present results, a laboratory-based conductivity-depth profile in the Earth's upper mantle has been constructed as a function of water content. Comparison of our model with the currently available geophysical observations beneath the Eastern Pacific Rise indicates that hydrous aluminous enstatite cannot account for the high conductivity anomaly at the top of the asthenosphere as well as hydrous olivine.

KeywordElectrical Conductivity orthopyroxene waterupper Mantle
Indexed BySCI
Language英语
Document Type期刊论文
Identifierhttp://ir.gyig.ac.cn/handle/42920512-1/9474
Collection地球内部物质高温高压实验室
Affiliation1.Institute for Study of the Earth’s Interior, Okayama University, Misasa, Tottori-ken 682-0193, Japan
2.School of Earth and Space Science, University of Science and Technology of China, Hefei 230026, PR China
3.Laboratory for High Temperature & High Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China
4.Bayerisches Geoinstitut, Universitat Bayreuth, D-95440 Bayreuth, Germany
Recommended Citation
GB/T 7714
Baohua Zhang;Takashi Yoshino;Xiaoping Wu;Takuya Matsuzaki;Shuangming Shan;Tomoo Katsura. Electrical conductivity of enstatite as a function of water content: Implications for the electrical structure in the upper mantle[J]. Earth and Planetary Science Letters,2012,357–358:11-20.
APA Baohua Zhang;Takashi Yoshino;Xiaoping Wu;Takuya Matsuzaki;Shuangming Shan;Tomoo Katsura.(2012).Electrical conductivity of enstatite as a function of water content: Implications for the electrical structure in the upper mantle.Earth and Planetary Science Letters,357–358,11-20.
MLA Baohua Zhang;Takashi Yoshino;Xiaoping Wu;Takuya Matsuzaki;Shuangming Shan;Tomoo Katsura."Electrical conductivity of enstatite as a function of water content: Implications for the electrical structure in the upper mantle".Earth and Planetary Science Letters 357–358(2012):11-20.
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