Numerical Models for Melt Segregation

熔体偏析的数值模型

• 批准号: 8720704
• 负责人: Frank Richter
• 金额: $ 11.65万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1988
• 资助国家: 美国
• 起止时间: 1988-03-15 至 1990-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8720704&HistoricalAwards=false
• 关键词: Numerical; Models; Melt; Segregation

This project addresses physical processes associated with melting and melt segregation in the mantle, and how these processes affect the geochemical properties of erupted lavas. It is a natural extension of earlier work on mantle convection in that there is a wealth of geochemical data with which to constrain and test various aspects of mantle dynamics, but in order to effectively use this data one must first understand how melts relate to their mantle source both physically and chemically. A two-dimensional finite element numerical code will be used to study a hierarchy of two-phase flow models involving melting and melt segregation: (i) Melt segregation and trace element fractionation from a chemically uniform source with spatially variable degree of melting. The purpose is to illustrate and understand the complexity, including time dependence, of the trace element concentrations in the "melts" segregating from such a source. (ii) Melt segregation and mixing from a source having heterogeneity in both chemistry and degree of melting. This model will be applied to the time dependent geochemical properties of lavas from Hawaii and also as a framework for modeling melt segregation for a source with ubiquitous heterogeneities, as seems to be required by the geochemistry of near-ridge seamounts. (iii) Models for melting and melt migration under midocean ridges. This type of model will be used to study the implications of crustal thickness and major element chemistry being quite insensitive to spreading rate while the variability of trace element ratios and isotopic ratios is related to the rate of spreading. The questions of how much melt erupts as opposed to underplating the otherwise depleted lithosphere is also considered.

该项目涉及与地幔中的熔融和熔体分离有关的物理过程，以及这些过程如何影响喷发熔岩的地球化学性质。这是早期关于地幔对流的工作的自然延伸，因为有大量的地球化学数据可以用来约束和测试地幔动力学的各个方面，但为了有效地利用这些数据，必须首先了解熔体在物理和化学上与其地幔来源的关系。用二维有限元数值程序研究了一系列涉及熔化和熔体分离的两相流动模型：(I)熔体分离和来自具有空间可变熔化度的化学均匀源的痕量元素分馏。目的是说明和理解从这种来源分离的“熔体”中的微量元素浓度的复杂性，包括与时间的相关性。(2)来自化学和熔化程度均不均匀的来源的熔体分离和混合。这一模型将应用于夏威夷熔岩的随时间变化的地球化学性质，并作为模拟无处不在的非均质源的熔体分离的框架，这似乎是近海脊海山的地球化学所要求的。(3)大洋中脊下的熔融和熔体迁移模式。这种类型的模型将被用于研究地壳厚度和主要元素化学对扩散速度相当不敏感，而微量元素比率和同位素比率的变异性为与传播速度有关。有多少融化的问题喷发，而不是以其他方式耗尽的岩石圈也被考虑在内。