Electrical Investigation of Metal-Olivine Systems and Application to the Deep Interior of Mercury

1Zhou Zhang,1Anne Pommier
Journal of Geophysical Research, Planets (in Press) Link to Article [DOI: 10.1002/2017JE005390]
1University of California San Diego, Scripps Institution of Oceanography, Institute of Geophysics and Planetary Physics, La Jolla, CA, USA
Published by arrangement with John Wiley & Sons

We report electrical conductivity measurements on metal–olivine systems at 5 and 7 GPa and up to 1675°C in order to investigate the electrical properties of Core-Mantle Boundary (CMB) systems. Electrical experiments were conducted in the multi-anvil apparatus using the impedance spectroscopy technique. The samples are composed of one metal layer (Fe, FeS, FeSi2, or Fe-Ni-S-Si) and one polycrystalline olivine layer, with the metal:olivine ratio ranging from 1:0.7 to 1:9.2. For all samples, we observe that the bulk electrical conductivity increases with temperature from 10-2.5 to 101.8 S/m, which is higher than the conductivity of polycrystalline olivine but lower than the conductivity of the pure metal phase at similar conditions. In some experiments, a conductivity jump is observed at the temperature corresponding to the melting temperature of the metallic phase. Both the metal:olivine ratio and the metal phase geometry control the electrical conductivity of the two-layer samples. By combining electrical results, textural analyses of the samples, and previous studies of the structure and composition of Mercury’s interior, we propose an electrical profile of the deep interior of the planet that accounts for a layered CMB-outer core structure. The electrical model agrees with existing conductivity estimates of Mercury’s lower mantle and CMB using magnetic observations and thermodynamic calculations, and thus, supports the hypothesis of a layered CMB-outermost core structure in the present-day interior of Mercury. We propose that the layered CMB-outer core structure is possibly electrically insulating, which may influence the planet’s structure and cooling history.

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