Mg lattice diffusion in iron-free olivine and implications to conductivity anomaly in the oceanic asthenosphere
Mg lattice diffusion in iron-free olivine and implications to conductivity anomaly in the oceanic asthenosphere
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DOI：
10.1016/j.epsl.2017.12.020
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发表时间：
2018-02-15
影响因子：
5.3
通讯作者：
Katsura, Tomoo
中科院分区：
文献类型：
--
作者：
Fei, Hongzhan;Koizumi, Sanae;Katsura, Tomoo
利用多砧仪和二次离子质谱仪在深度剖面模式下测量了无铁橄榄石团聚体中Mg晶格扩散系数作为压力从1到13 GPa，温度从1100到1300 K，体积含水量从1到350 wt. ppm的函数。用傅里叶透射红外光谱仪对样品中的水分含量进行了分析。结果表明：Mg晶格扩散系数随温度和含水量的升高而增大，随压力的增大而减小；活化能为250 +/- 30 kJ/mol，水含量指数为1.2 +/- 0.2，活化体积为4.3 +/- 03 cm(3)/mol。由于镁晶格扩散根据能斯特-爱因斯坦关系控制橄榄石中的离子电导率，由于压力负校正和含水量正校正，上地幔的离子电导率在海洋软流层顶部出现最大值，这很好地解释了在年轻海洋板块下方类似70-120 km深度观测到的高电导率异常。(C) 2017 Elsevier B.V.版权所有
Mg lattice diffusion coefficients in iron-free olivine aggregates were measured as a function of pressure from 1 to 13 GPa, temperature from 1100 to 1300 K, and bulk water content from less than 1 up to 350 wt. ppm using multi-anvil apparatus and secondary ion mass spectrometer in depth profiling mode. The water contents in the samples were analyzed by Fourier transmission infrared spectrometer. The results show that Mg lattice diffusion coefficient increase with increasing temperature and water content, and decrease with pressure. The activation energy, water content exponent, and activation volume are 250 +/- 30 kJ/mol, 1.2 +/- 0.2, and 4.3 +/- 03 cm(3)/mol, respectively. Since Mg lattice diffusion controls the ionic conduction in olivine based on the Nernst-Einstein relation, the ionic conductivity in the upper mantle appears as a maximum at the top of oceanic asthenosphere due to the negative correction for pressure and positive correction for water content, which well explains the high conductivity anomaly observed at similar to 70-120 km depth beneath young oceanic plates. (C) 2017 Elsevier B.V. All rights reserved.