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

该项目旨在通过对岩浆化学演变的实验室研究，了解地壳形成的过程。岩浆分异过程改变了火成岩的化学成分，因此是地球上漂浮的大陆地壳（可能还有复杂的生命）的原因，它的细节仍然模糊不清。该项目将使用受控实验室实验来限制岩浆与共存晶体相互作用时发生的Mg、Fe和Li同位素比率的变化。这些数据将允许比较岩浆分异的不同模型;具体地说，这些数据将提供区分1）晶体从岩浆中的机械分离; 2）扩散和反应过程的分异的能力。由此产生的答案将影响我们对地球历史的理解，以及它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会对火成岩岩体内发生的化学分化做出重大贡献。需要评估的作用，扩散反应已刺激出现的数据表明，岩体保持热了很长一段时间，超临界H2O大大加快扩散速率。此外，质谱技术的发展现在允许直接识别扩散过程。锂、镁或铁等“非传统同位素”比率的空间变化提供了识别火成岩岩体内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得更快时，同位素梯度就会形成。拟议的工作将集中在高温高压实验室实验，旨在限制平衡和动力学条件下的部分熔融材料内的同位素分馏。此外，将开发扩散反应的数值模型，以预测各种条件下同位素比的梯度和幅度。将使用伊利诺斯大学新的MC-ICPMS设施进行实验和可能的侦察实地研究的同位素分析。使用磁化率（AMS）和电子背散射衍射（EBSD）的各向异性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晶粒尺度各向异性的发展。

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.