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<p>Electrical-conductivity anomalies in subduction zones are believed to be strongly connected with global water cycling, volcanism and seismicity. However, the causal atomic-scale processes related to conductivity of rock-forming minerals in subducting rocks are virtually unknown. Here, in situ simultaneous high-temperature Raman spectroscopy and resistivity measurements on riebeckite as a model Fe-rich amphibole in subduction zones show that (1) electronic small polarons, with high mobility along the <b>c</b>-axis of the amphibole structure, activate above 500&#xa0;K; (2) H<sup>+</sup> starts diffusing within the crystal above 650&#xa0;K, although electron transport <i>via</i> polaron hopping is still the dominant mechanism of charge transfer; (3) the anisotropy in the conductivity is enhanced with increasing temperature, emphasizing the dominant role of <i>e</i><sup>−</sup> over H<sup>+</sup> in causing the high conductivity (above 0.01&#xa0;S/m) of Fe-rich amphiboles. We show that conductivity data obtained <i>via</i> magnetotelluric measurements are best modelled by considering the effect of stress-driven alignment of amphiboles during plate motion. Our results thus link atomic- and Earth-scale conductivity processes, significantly improving our understanding of subduction processes.</p>

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The effect of anisotropic electrical conductivity of amphiboles on geophysical anomalies observed in subduction zones

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年4月24日

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  • Simone Bernardini,
  • Giancarlo Della Ventura,
  • Frank C. Hawthorne,
  • Augusto Marcelli,
  • Francesco Salvini,
  • Boriana Mihailova

摘要

Electrical-conductivity anomalies in subduction zones are believed to be strongly connected with global water cycling, volcanism and seismicity. However, the causal atomic-scale processes related to conductivity of rock-forming minerals in subducting rocks are virtually unknown. Here, in situ simultaneous high-temperature Raman spectroscopy and resistivity measurements on riebeckite as a model Fe-rich amphibole in subduction zones show that (1) electronic small polarons, with high mobility along the c-axis of the amphibole structure, activate above 500 K; (2) H+ starts diffusing within the crystal above 650 K, although electron transport via polaron hopping is still the dominant mechanism of charge transfer; (3) the anisotropy in the conductivity is enhanced with increasing temperature, emphasizing the dominant role of e− over H+ in causing the high conductivity (above 0.01 S/m) of Fe-rich amphiboles. We show that conductivity data obtained via magnetotelluric measurements are best modelled by considering the effect of stress-driven alignment of amphiboles during plate motion. Our results thus link atomic- and Earth-scale conductivity processes, significantly improving our understanding of subduction processes.