Electrical conductivity of amphibole-bearing rocks: influence of dehydration |
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Authors: | Duojun Wang Yingxing Guo Yingjie Yu Shun-ichiro Karato |
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Institution: | (1) Key Laboratory of Computational Geodynamics, Graduate University of Chinese Academy of Sciences, Beijing, 100049, China;(2) Department of Geology and Geophysics, Yale University, New Haven, CT, USA |
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Abstract: | We investigated the electrical conductivity of amphibole-bearing rocks under the conditions of the middle to lower crust.
Alternating current measurements were performed in the frequency range of 10–106 Hz in a cubic-anvil high-pressure apparatus at 0.5–1.0 GPa and 373–873 K. The electrical conductivity of these rocks is weakly
temperature dependent below ~800 K with modest anisotropy and relatively low conductivity (~5 × 10−3 S/m at ~750 K with the activation enthalpy of 64–67 kJ/mol). However, the electrical conductivity starts to increase with
temperature more rapidly above ~800 K (activation enthalpy of 320–380 kJ/mol). The infrared spectroscopy observations indicate
that dehydration occurs in this high temperature regime. The observed high activation enthalpy and the reproducibility suggest
that the enhanced conductivity is not due to the direct effect caused by the generation of conductive fluids. Dehydration
of amphibole is associated with the oxidation of iron (from ferrous to ferric), and we suggest that the increased conductivity
associated with dehydration is caused by oxidation. This effect may explain high electrical conductivity observed in some
regions of the continental crust. |
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