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The electrical conductivity of garnet pyroxenite; implications for magmatic underplating

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Authors:Men Qingbo; Wang Qin; Bagdassarov, Nikolai; Xia Qunke; Fan Qicheng
Author Affiliations:Primary:
Nanjing University, School of Earth Sciences and Engineering, Nanjing, China
Other:
University of Frankfurt Frankfurt am Main, Germany
University of Science and Technology of China, China
Volume Title:Yanshi Kuangwuxue Zazhi Acta Petrologica et Mineralogica
Source:Yanshi Kuangwuxue Zazhi = Acta Petrologica et Mineralogica, 32(5), p.652-662. Publisher: Science Press, Beijing, China. ISSN: 1000-6524
Publication Date:2013
Note:In Chinese with English summary. 56 refs.; illus., incl. 2 tables
Summary:Garnet pyroxenite xenoliths from the Hannuoba Cenozoic basalt were formed by magmatic underplating in the uppermost mantle(40-45 km), and represent the crust-mantle transition zone. The electrical conductivity of sintered garnet pyroxenite WD958 was measured at 1.2GPa and 380-900°C, using a Solartron 1260 Phase-GainAnalyzer. The temperature dependence of electrical conductivity (σ)can be fitted by an Arrhenius equation: σ=σ0exp(-ΔH/kT), whereTisin Kelvin and k is the Boltzmann constant. Values of the preexponential factor (σ0) and activation enthalpy of electric conductivity (ΔH)of sample WD958 are 97.5 S/m and 1.27 eV, respectively. The water contents of minerals were analyzed using the Fourier transform infrared spectrometry. The average water content in clinopyroxene is 117×10-6H2O, whereas olivine is very dry (×10-6H2O) and the water content in garnet cannot be determined due to alteration. The laboratory-derived electrical conductivity of mantle minerals shows that the calculated conductivity using the Hashin-Shtrikman average can match the measured values by assuming a mixture of hydrogen-bearing clinopyroxene, dry garnet a dry olivine. This demonstrates the contribution of both small polaron conduction and proton conduction mechnisms to the bulk conductivity of garnet pyroxenite, and the sample can be regarded as a resistive matrix wi non-interconnected conductive inclusions. If the water partition equilibrium between minerals is preserved at t in situ depth (40-45 km), the electrical conductivity of garnet pyroxenite will be enhanced by 1 order magn tude and the proton conduction mechanism becomes predominant. For the lithosphere with a high geotherm gradient, the temperature at the Moho depth could reach 1000°C and garnet pyroxenite is characterized by hi conductivity. In contrast, under normal geothermal gradients, garnet pyroxenite shows conductivity as low spinel lherzolite. During magmatic underplating, therefore, the electrical crust-mantle boundary will vary wi temperature and water concentration.
Subjects:Basalts; Cenozoic; Crust; Electrical conductivity; Garnet pyroxenite; Igneous rocks; Inclusions; Mantle; Mohorovicic discontinuity; Plutonic rocks; Pyroxenite; Transition zones; Ultramafics; Underplating; Upper mantle; Volcanic rocks; Xenoliths; Asia; China; Far East; Hebei China; Hannuoba Basalt
Coordinates:N405000 N405000 E1145600 E1145600
Record ID:783798-7
Copyright Information:GeoRef, Copyright 2021 American Geosciences Institute.
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