Electrical conductivity of dense hydrous magnesium silicates with implication for conductivity in the stagnant slab

Xinzhuan Guo, Takashi Yoshino

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Abstract

Electrical conductivities of dense hydrous magnesium silicates (DHMS), phase A, super-hydrous phase B (SuB) and phase D, were measured by means of impedance spectroscopy in the frequency range of 10-1-106Hz at temperatures up to 775, 700 and 700K and pressures of 10, 18 and 22GPa, respectively. For all phases, the increase in electrical conductivity (σ) with temperature follows the Arrhenian formula: σ=σ0exp(-(δH/kT)). The pre-exponential factors (σ0) and activation enthalpies (δH) of phase A, SuB and phase D yield values of 7.28±0.82S/m and 0.77±0.01eV, 292±48S/m and 0.83±0.01eV and 1342±154 and 0.75±0.01eV, respectively. Higher pressure DHMS phases show higher conductivity values. The electrical conductivities of phase D and super hydrous phase B are about two and one orders of magnitude higher than that of phase A in the same temperature range, respectively. Although the proton conduction is considered to be a dominant mechanism, there is no clear relationship between water content and conductivity. Rather the conductivity of DHMS phase is closely related to the ⋯O distance. The conductivity-depth profiles for a cold subduction zone were constructed based on the phase proportion predicted in the descending slab. The results show distinctly lower conductivity values than those geophysically observed beneath the northeastern China and the Philippine Sea, where the cold slab stagnates in the mantle transition zone. Consequently, the DHMS phases themselves cannot be a main contributor to enhance the conductivity in the stagnant slab. Dehydration of the stagnant slab would strongly enhance the conductivities in the transition zone beneath northeastern China and Philippine Sea.

Original languageEnglish
Pages (from-to)239-247
Number of pages9
JournalEarth and Planetary Science Letters
Volume369-370
DOIs
Publication statusPublished - May 1 2013

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Keywords

  • DHMS
  • Electrical conductivity
  • Phase A
  • Phase D
  • Stagnant slab
  • Super-hydrous phase B

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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