Pressure, temperature, water content, and oxygen fugacity dependence of the Mg grain-boundary diffusion coefficient in forsterite
Pressure, temperature, water content, and oxygen fugacity dependence of the Mg grain-boundary diffusion coefficient in forsterite
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DOI：
10.2138/am-2018-6480
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发表时间：
2018-09
影响因子：
3.1
通讯作者：
H. Fei;S. Koizumi;N. Sakamoto;M. Hashiguchi;H. Yurimoto;K. Marquardt;N. Miyajima;T. Katsura
中科院分区：
文献类型：
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作者：
H. Fei;S. Koizumi;N. Sakamoto;M. Hashiguchi;H. Yurimoto;K. Marquardt;N. Miyajima;T. Katsura
本文测定了镁橄榄石团聚体中Mg的晶界扩散系数随压力（1atm，13 GPa）、温度（1100-1300 K）、含水量（<1-350 wt. %）、温度（1100-1300 K）和压力（1atm，13 GPa）的变化。ppm本体水）和氧逸度（10-18-10-0.7巴）。用二次离子质谱仪分析扩散剖面，用傅里叶变换红外光谱仪测定样品中的水分含量。Mg晶界扩散系数的激活体积、激活焓、水含量指数和氧逸度指数分别为3.9 ± 0.7 cm ~ 3/mol、355 ± 25 kJ/mol、1.0 ± 0.1和-0.02 ± 0.01。通过与Mg晶格扩散数据（Fei等人，2018年）比较，如果在上地幔条件下晶粒尺寸大于约1 mm，镁橄榄石中Mg的体扩散率以晶格扩散为主，而当晶粒尺寸为约1-100 μm时，有效晶界和晶格扩散率相当。
Abstract The Mg grain boundary diffusion coefficients were measured in forsterite aggregates as a function of pressure (1 atm and 13 GPa), temperature (1100–1300 K), water content (<1–350 wt. ppm bulk water), and oxygen fugacity (10–18–10–0.7 bar) using a multi-anvil apparatus and a gas-mixing furnace. The diffusion profiles were analyzed by secondary ion mass spectrometer, whereas the water contents in the samples were measured by Fourier transform infrared spectrometer. The activation volume, activation enthalpy, water content exponent, and oxygen fugacity exponent for the Mg grain-boundary diffusion coefficients are found to be 3.9 ± 0.7 cm3/mol, 355 ± 25 kJ/mol, 1.0 ± 0.1, and –0.02 ± 0.01, respectively. By comparison with the Mg lattice diffusion data (Fei et al. 2018), the bulk diffusivity of Mg in forsterite is dominated by lattice diffusion if the grain size is larger than ~1 mm under upper mantle conditions, whereas effective grain-boundary and lattice diffusivities are comparable when the grain size is ~1–100 μm.