Abstract
AbstractHigh‐temperature ionic conductivity in olivine single crystals has been measured in the [100], [010], and [001] crystallographic orientations as a function of pressure from 2 to 10 GPa, temperature from 1450 to 2180 K, and H2O content from 20 to 580 wt. ppm using multianvil presses with in situ impedance analyses. The experimental results yield an activation energy, activation volume, and H2O content exponent of 250–405 kJ/mol, 3.2–5.3 cm3/mol, and 1.3 ± 0.2, respectively, for the high‐temperature ionic conduction regime. Olivine ionic conductivity has negative pressure and positive temperature dependences and is significantly enhanced by H2O incorporation. The [001] direction is more conductive than the [100] and [010] directions. The H2O‐enhanced ionic conductivity may contribute significantly to the electrical conductivity profile in the asthenosphere, especially in the regions under relatively high‐temperature and low‐pressure conditions.
Highlights
Olivine is the dominant mineral in the Earth's upper mantle
Our results demonstrate that olivine ionic conductivity is enhanced by H2O incorporation and may contribute significantly to the bulk conductivity of olivine under asthenospheric conditions
If using the Bell et al (2003) calibration, the absolute values of CH2O are higher by about 50%, the CH2O‐exponent for ionic conductivity reported in this study should remain the same
Summary
To understand the electrical conductivity profiles in the upper mantle, a series of experimental studies have been performed to measure the proton and small polaron conductivities in olivine (e.g., Du Frane et al, 2005; Dai & Karato, 2014a, 2014b; Poe et al, 2010; Wang et al, 2006; Xu et al, 1998; Yang, 2012) Their results suggest that the proton conduction is significantly enhanced by water incorporation. It may account for the magnetotellurically detected anomalously high and highly anisotropic electrical conductivity (10−1– 10−2 S/m) in the asthenosphere at 70–120 km depth beneath young plates near the East Pacific Rise (Baba et al, 2006; Evans et al, 2005), which cannot be explained by small polaron conductivity in dry olivine. Our results demonstrate that olivine ionic conductivity is enhanced by H2O incorporation and may contribute significantly to the bulk conductivity of olivine under asthenospheric conditions
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