Diffusion and partitioning of magnesium in quartz grain boundaries
Diffusion and partitioning of magnesium in quartz grain boundaries
复制标题
镁在石英晶界中的扩散和分配
DOI：
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发表时间：
2014
影响因子：
3.5
通讯作者：
E. Watson
中科院分区：
文献类型：
--
作者：
Jay B. Thomas;E. Watson
对Mg在石英晶界中的扩散进行了实验研究。由于Mg仅限于晶界，因此采用检测粒子法研究晶界扩散。通过将MgF2盘放置在石英岩盘上来组装扩散偶，该石英岩盘放置在含有铁橄榄石（Fe2SiO4）“检测器颗粒”的石英岩盘上。在扩散实验期间，Mg沿着中心石英岩的晶界向铁橄榄石石英岩扩散，在铁橄榄石石英岩处，Mg被并入铁橄榄石检测器颗粒中。从扩散源到铁橄榄石探测器颗粒的唯一运输途径是通过中央石英岩中的晶界。从扫描电子显微镜图像确定将Mg递送到铁橄榄石检测器颗粒的晶界的横截面积。使用铁橄榄石检测器颗粒的Mg含量来计算流过晶界的Mg的质量。在扩散实验过程中，辉石微晶成核和生长的中心石英岩从镁和铁，被运输沿着石英晶界。镁含量的微晶在整个石英岩线性变化，这表明稳态运输条件迅速建立在石英晶界。镁的浓度在辉石微晶成比例的浓度梯度在中央石英岩的晶界。晶界通量和线性浓度梯度被用来计算扩散耦合中的中心石英岩成分的晶界中的Mg的扩散。
Experiments were conducted to study Mg diffusion in quartz grain boundaries. A detector particle method was used to study grain-boundary diffusion because Mg was confined exclusively to the grain boundaries. Diffusion couples were assembled by placing a MgF2 disk against a disk of quartzite, which was placed against a disk of quartzite that contained fayalite (Fe2SiO4) ‘detector particles.’ During diffusion experiments, Mg diffused along the grain boundaries of the central quartzite toward the fayalite quartzite where it was incorporated into fayalite detector particles. The only pathway for transport from the diffusant source to fayalite detector particles was through the grain boundaries in the central quartzite. The cross-sectional area of the grain boundaries that delivered Mg to the fayalite detector particles was determined from scanning electron microscope images. The Mg contents of the fayalite detector particles were used to calculate the mass of Mg that fluxed through the grain boundaries. During the diffusion experiments, pyroxene crystallites nucleated and grew in the central quartzites from Mg and Fe that was transported along quartz grain boundaries. The Mg contents of the crystallites vary linearly throughout the quartzites, suggesting that steady-state transport conditions were rapidly established in the quartz grain boundaries. Magnesium concentrations in the pyroxene crystallites are proportional to concentration gradients in the grain boundaries of the central quartzite. Grain-boundary fluxes and linear concentration gradients were used to calculate diffusion of Mg in grain boundaries of the central quartzite component in the diffusion couples.