Hydrous olivine unable to account for conductivity anomaly at the top of the asthenosphere
Hydrous olivine unable to account for conductivity anomaly at the top of the asthenosphere
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DOI：
10.1038/nature05223
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发表时间：
2006-10
期刊：
影响因子：
64.8
通讯作者：
T. Yoshino;Takuya Matsuzaki;S. Yamashita;T. Katsura
中科院分区：
文献类型：
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作者：
T. Yoshino;Takuya Matsuzaki;S. Yamashita;T. Katsura
大洋软流圈具有很高的电导率，在某些位置表现出高度的各向异性。在平行和垂直于板块运动的方向上，电导率分别为10-1和10-2S m-1量级，这不能用无水橄榄石的电导率来解释。但由于氢可以在地幔压力下结合到橄榄石中，所以这种观察结果被归因于橄榄石的水化作用，这可能通过质子迁移导致各向异性的高电导率。为了验证这一假设，我们报道了在500-1,500 K和3 GPa下，水对掺氢橄榄石和未掺氢橄榄石电导率及其各向异性的影响。在所研究的温度范围内，含水橄榄石比无水橄榄石具有更高的电导率和更低的活化能。然而，实验结果的外推表明，软流圈顶部的含水橄榄石的电导率应该是近各向同性的，仅为10-2S m-1量级。我们的数据表明，橄榄石的水化作用不能解释地球物理观测，相反，这可以用沿板块运动方向拉长的部分熔体的存在来解释。
The oceanic asthenosphere is observed to have high electrical conductivity, which is highly anisotropic in some locations,. In the directions parallel and normal to the plate motion, the conductivity is of the order of 10-1and 10-2S m-1, respectively, which cannot be explained by the conductivity of anhydrous olivine. But because hydrogen can be incorporated in olivine at mantle pressures,,, this observation has been attributed to olivine hydration, which might cause anisotropically high conductivity by proton migration,,,. To examine this hypothesis, here we report the effect of water on electrical conductivity and its anisotropy for hydrogen-doped and undoped olivine at 500–1,500 K and 3 GPa. The hydrous olivine has much higher conductivity and lower activation energy than anhydrous olivine in the investigated temperature range. Nevertheless, extrapolation of the experimental results suggests that conductivity of hydrous olivine at the top of the asthenosphere should be nearly isotropic and only of the order of 10-2S m-1. Our data indicate that the hydration of olivine cannot account for the geophysical observations, which instead may be explained by the presence of partial melt elongated in the direction of plate motion.