Multicomponent Diffusion in Silicate Melts

硅酸盐熔体中的多组分扩散

基本信息

批准号：
1524473
负责人：
Youxue Zhang
金额：
$ 41万
依托单位：
Regents of the University of Michigan - Ann Arbor
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2015
资助国家：
美国
起止时间：
2015-07-01 至 2019-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1524473&HistoricalAwards=false
关键词：
Multicomponent Diffusion Silicate Melts

项目摘要

Diffusion is a ubiquitous process originating from random motion of particles in a liquid, solid or gas. In simple systems, such random motion leads to a net mass transfer from a region of high concentration to one of low concentration. Although it is a microscopic process, diffusion plays a critical role in numerous macroscopic phenomena ranging from nutrient transfer in the human body, dispersal of pollutants, to a variety of igneous processes, such as explosive volcanic eruptions and igneous rock formation. For example, explosive volcanic eruptions begin with bubble growth, whose rate is controlled by the diffusion of gas molecules from the melt into the bubbles. Incidentally, bubble growth in melts is similar to the daily encountered bubble growth in beer, champagne and soft drinks. The more generalized diffusion concept has also been applied to understand the mean height of continents. Igneous rock formation is the collective effect of crystal growth in magma, in which diffusion plays an important role. A natural silicate melt typically contains many major oxide components, and hence the diffusion is multicomponent diffusion, more complex than diffusion in simple systems. The goal of this research is to understand multicomponent diffusion in silicate melts, which would advance the ability to interpret and quantify rates of such processes. One manifestation of the complications due to multicomponent diffusion is that an oxide component in silicate melts often diffuses from low concentration to high concentration, termed uphill diffusion. In the literature, diffusion in natural silicate melts is treated partially: If a component shows 'normal' diffusion behavior, meaning the flux is from high concentration to low concentration, it is quantified using the effective binary diffusion treatment. On the other hand, if a component displays uphill diffusion, researchers simply note the behavior, and then shy away from it without quantification. Such uphill diffusion is frequently encountered in experiments using silicate melts as well as in natural systems. As science advances rapidly and becomes increasingly more quantitative and predictive, it is time to confront the challenge of multi-component diffusion in natural silicate melts. The base melt composition chosen for this investigation will be similar to a mid-ocean ridge basalt, the most abundant terrestrial rock with a narrow compositional range. There are 8 major oxide components and the diffusion is described by a 7 by 7 diffusivity matrix. Glasses with appropriate compositions will be synthesized to form diffusion couples. High-temperature and high-pressure diffusion couple experiments will be carried out. The compositional profiles in the quenched glass will be measured using an electron microprobe. The data will be fit using the Levenberg-Marquardt algorithm to extract the diffusivity matrix. For verification, the obtained matrix will be used to calculate diffusion profiles in previous mineral dissolution experiments, and the calculated results will be compared with measured profiles. After verification, the diffusivity matrix will be applied to predict real diffusion in natural magmas during a variety of processes, including crystal growth and dissolution, magma mixing, and post-entrapment interaction between a melt inclusion and the host mineral. The results will be published and disseminated in scientific meetings and in teaching.

扩散是一个无处不在的过程，源自液体，固体或气体中颗粒的随机运动。在简单的系统中，这种随机运动导致从高浓度区域净大量转移到低浓度之一。尽管这是一个微观过程，但扩散在许多宏观现象中起着至关重要的作用。例如，爆炸性的火山喷发始于气泡的生长，其速率是由气体分子从熔体扩散到气泡中的。顺便说一句，融化中的气泡增长类似于每天遇到的啤酒，香槟和软饮料的泡沫增长。更广泛的扩散概念也已应用于了解大陆的平均高度。火成岩的形成是岩浆中晶体生长的集体效应，其中扩散起着重要作用。天然硅酸盐熔体通常包含许多主要的氧化物成分，因此扩散是多组分扩散，比简单系统中的扩散更复杂。这项研究的目的是了解硅酸盐熔体中的多组分扩散，这将提高解释和量化此类过程速率的能力。由于多组分扩散而引起的并发症的一种表现是，硅酸盐熔体中的氧化物成分通常从低浓度到高浓度扩散，称为上坡扩散。在文献中，自然硅酸盐熔体中的扩散被部分处理：如果组件显示出“正常”的扩散行为，则意味着通量从高浓度到低浓度，则使用有效的二进制扩散处理进行定量。另一方面，如果一个组件显示上坡扩散，研究人员只需注意行为，然后在没有量化的情况下回避它。在使用硅酸盐熔体以及自然系统中，在实验中经常遇到这种上坡扩散。随着科学的发展迅速并变得越来越定量和预测，现在是时候面对自然硅酸盐熔体中多组分扩散的挑战了。为此研究选择的基本熔体成分将类似于中山脊玄武岩，这是最丰富的陆地岩石，具有狭窄的组成范围。有8个主要的氧化物成分，扩散是通过7乘7扩散矩阵描述的。将合成具有适当成分的眼镜以形成扩散夫妇。将进行高温和高压扩散夫妇实验。将使用电子微探针测量淬灭玻璃中的成分曲线。数据将使用Levenberg-Marquardt算法拟合数据以提取扩散率矩阵。为了进行验证，所获得的矩阵将用于计算以前的矿物溶解实验中的扩散谱，并将计算结果与测量的曲线进行比较。经过验证后，将应用扩散率矩阵来预测各种过程中自然岩浆中的实际扩散，包括晶体生长和溶解，岩浆混合以及熔体融合和宿主矿物之间的沉积后相互作用。结果将在科学会议和教学中发布和传播。