Multicomponent diffusion in silicate melts using eigen-component approach

使用特征分量方法在硅酸盐熔体中进行多组分扩散

• 批准号: 2314724
• 负责人: Youxue Zhang
• 金额: $ 47.5万
• 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: 2023
• 资助国家: 美国
• 起止时间: 2023-07-01 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2314724&HistoricalAwards=false
• 关键词: Multicomponent; diffusion; silicate; melts; using

This project will investigate diffusion of all major oxides (defined to be more than one weight percent) in dry natural silicate melts using a new approach. In the past, researchers could only successfully and quantitatively study the diffusion of oxides in natural silicate melts with monotonic, or flat, concentration profiles. But what about oxides with non-monotonic profiles? The goal of this project is to develop an easier way to quantify diffusion of all major oxides in dry silicate melts. One application of the new method will be the modeling of the mixing of two magmas. Preliminary results show that such mixing may result in unexpected high concentrations of some metals. Such high concentrations may lead to ore formation. Hence, one of the practical applications is to explain previously unexplained ore formation, and to predict possible locations of ore deposits. Other applications of the new method include more accurate quantification of crystal growth and dissolution rates. This research will also solve a major theoretical problem in high-temperature geochemical kinetics. This project will investigate multicomponent diffusion in dry natural silicate melts using eigen-component approach. Multicomponent diffusion in silicate melts is fundamental to mass transport in igneous processes and is also one of the most difficult experimental and theoretical problems facing geochemical kineticists. Multicomponent diffusion is often encountered in natural silicate melts but not treated due to the level of difficulties in terms of both theory and especially experiments. This team has extracted a diffusion matrix in basaltic melts at three different temperatures, and roughly verified that the diffusion eigenvector matrix in basaltic melts is roughly independent of temperature. They now hypothesize that the diffusion eigenvector matrix is also roughly independent of melt composition in dry melts. They are now further improving the eigenvector matrix and hope to verify that the eigenvector matrix is invariant with composition. In the eigen-component approach, plots of “concentrations” of eigen-components (rather than oxide wt% or mole fractions) versus distance will be made. If their hypothesis is correct, then using the eigenvector matrix, all eigen-component plots would be monotonic, and diffusion eigenvalues (i.e., diffusivity for the eigen-components) will be obtained from fitting the eigen-component profiles. If some eigen-component plots in some experiments show nonmonotonic profiles, within the framework of our hypothesis, it would mean inaccuracy of the eigenvector matrix, and hence the need to improve the eigenvector matrix. To complete the investigation of multicomponent diffusion in a melt, a couple of well-designed experiments at each temperature and pressure will be enough to determine all eigenvalues, and hence the full diffusion matrix. This team's hypothesis and new approach will contribute to the fundamental understanding of diffusion in natural silicate melts. The success of the proposed work will remove one difficult problem from the list of geochemical kineticists and allow future geochemists to realistically predict diffusion-controlled processes, such as magma mixing, mineral growth and dissolution, and post-entrapment interaction between a melt inclusion and its host mineral. They will build and publish an online resource to compute multicomponent diffusion profiles. This would enable interested students and scientists to use multicomponent diffusion in their research of geological problems. This planned online calculator will help facilitate the use of their results by the petrological and geochemical community.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

该项目将使用一种新的方法研究干燥天然硅酸盐熔体中所有主要氧化物（定义为超过1重量%）的扩散。在过去，研究人员只能成功地和定量地研究氧化物在天然硅酸盐熔体中的扩散与单调的，或平坦的，浓度分布。但是对于非单调分布的氧化物呢？该项目的目标是开发一种更简单的方法来量化干燥硅酸盐熔体中所有主要氧化物的扩散。 新方法的一个应用将是两种岩浆混合的模拟。初步结果表明，这种混合可能会导致某些金属的意外高浓度。如此高的浓度可能导致矿石形成。因此，实际应用之一是解释以前无法解释的成矿作用，并预测可能的矿床位置。新方法的其他应用包括更准确地量化晶体生长和溶解速率。该研究也将解决高温地球化学动力学中的一个重大理论问题。本计画将利用本征成份法探讨天然矽酸盐熔体中多组份之扩散。硅酸盐熔体中的多组分扩散是岩浆过程中物质输运的基础，也是地球化学动力学家面临的最困难的实验和理论问题之一。天然硅酸盐熔体中的多组分扩散是经常遇到的问题，但由于理论和实验上的困难而没有得到处理。该团队在三种不同温度下提取了玄武岩熔体中的扩散矩阵，并粗略验证了玄武岩熔体中的扩散特征向量矩阵大致与温度无关。他们现在假设，在干熔体中，扩散特征向量矩阵也大致与熔体成分无关。他们现在正在进一步改进特征向量矩阵，并希望验证特征向量矩阵是不随组合而变的。在本征组分法中，将绘制本征组分的“浓度”（而不是氧化物重量%或摩尔分数）与距离的关系图。如果他们的假设是正确的，那么使用特征向量矩阵，所有特征分量图将是单调的，并且扩散特征值（即，本征分量的扩散率）将通过拟合本征分量分布而获得。在我们的假设框架内，如果某些实验中的某些特征分量图显示非单调分布，则意味着特征向量矩阵不准确，因此需要改进特征向量矩阵。为了完成熔体中多组分扩散的研究，在每个温度和压力下进行几个精心设计的实验就足以确定所有的特征值，从而确定完整的扩散矩阵。该团队的假设和新方法将有助于对天然硅酸盐熔体中扩散的基本理解。这项工作的成功将为地球化学动力学家们解决一个难题，并使未来的地球化学家们能够真实地预测扩散控制的过程，如岩浆混合、矿物生长和溶解，以及熔融包裹体与其寄主矿物之间的包裹后相互作用，他们将建立并发布一个在线资源来计算多组分扩散剖面。这将使感兴趣的学生和科学家能够在地质问题的研究中使用多组分扩散。这个计划中的在线计算器将有助于促进岩石学和地球化学界使用他们的结果。这个奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。