Assessing Diffusive Differentiation During Igneous Intrusion Using Integrated Theoretical, Experimental and Field Studies

利用综合理论、实验和现场研究评估火成岩侵入过程中的扩散分异

• 批准号: 0609726
• 负责人: Craig Lundstrom
• 金额: $ 26.98万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-07-01 至 2009-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0609726&HistoricalAwards=false
• 关键词: Assessing; Diffusive; Differentiation; During; Igneous

This project seeks to understand the processes forming the Earth's crust through a laboratory study of how magmas chemically evolve. The magma differentiation process, which changes the chemical composition of igneous rocks and is thus responsible for buoyant continental crust (and probably complex life) on Earth, remains nebulous in detail. This project will use controlled laboratory experiments to constrain the changes in isotopic ratios of Mg, Fe and Li occurring as magmas interact with coexisting crystals. These data will allow comparison of different models of magma differentiation; specifically, the data will provide the ability to discriminate 1) mechanical separation of crystals from magma; from 2) differentiation by diffusion and reaction processes. The resulting answers will impact our understanding of the history of Earth and how it has chemically evolved through time.This project is designed to determine if diffusion-reaction processes, taking place in the presence of supercritical fluids and a thermal gradient, could contribute significantly to chemical differentiation occurring within igneous plutons. The need to evaluate the role of diffusion-reaction has been stimulated by the emergence of data showing that plutons stay hot for a long time and that supercritical H2O greatly accelerates diffusion rates. Additionally, technological developments in mass spectrometry now allow direct identification of diffusive processes. Spatial variations in the ratios of "non-traditional isotopes" such as Li, Mg or Fe provide the ability to identify diffusion-based processes occurring within igneous plutons because isotopic gradients develop when lighter isotopes diffuse faster than heavier isotopes. The proposed work will focus on laboratory experiments at high temperature and pressure designed to constrain the isotope fractionation within partially molten materials under both equilibrium and kinetic conditions. In addition, numerical models of diffusion-reaction will be developed to predict gradients and magnitudes of isotope ratios under a variety of conditions. Isotopic analyses for experiments and possible reconnaissance field studies will be conducted using the new MC-ICPMS facility at the University of Illinois. A pilot project using measurement of anisotropy of magnetic susceptibility (AMS) and Electron BackScatter Diffraction (EBSD) will allow us to determine if diffusion-reaction in the presence of a thermal gradient can also lead to the development of grain-scale anisotropy.

该项目旨在通过对岩浆化学演化的实验室研究来了解地壳的形成过程。岩浆分化过程改变了火成岩的化学成分，从而导致了地球上浮力的大陆地壳（可能还有复杂的生命），但其细节仍然模糊不清。该项目将使用受控的实验室实验来限制岩浆与共存晶体相互作用时Mg， Fe和Li同位素比率的变化。这些数据可以用来比较岩浆分化的不同模式；具体来说，这些数据将提供区分的能力：1)晶体与岩浆的机械分离；2)通过扩散和反应过程进行分化。由此得出的答案将影响我们对地球历史的理解，以及地球是如何随着时间的推移而化学演变的。该项目旨在确定在超临界流体和热梯度存在的情况下发生的扩散反应过程是否能够显著促进火成岩岩体内发生的化学分异。对扩散反应的作用进行评估的需要是由于一些数据的出现而引起的，这些数据表明，钚能长时间保持高温，超临界水能大大加速扩散速率。此外，质谱技术的发展现在可以直接识别扩散过程。Li、Mg或Fe等“非传统同位素”比例的空间变化提供了识别火成岩中发生的基于扩散的过程的能力，因为当较轻的同位素比较重的同位素扩散更快时，同位素梯度就会形成。该工作将集中在高温高压下的实验室实验，旨在限制平衡和动力学条件下部分熔融材料中的同位素分馏。此外，还将开发扩散反应的数值模型，以预测各种条件下同位素比率的梯度和幅度。实验的同位素分析和可能的实地侦察研究将使用伊利诺伊大学的新MC-ICPMS设备进行。利用磁化率各向异性（AMS）和电子反向散射衍射（EBSD）测量的试点项目将使我们能够确定在热梯度存在下的扩散反应是否也会导致颗粒尺度各向异性的发展。