Geological melt studies under extreme conditions

如果我们要了解地球是如何形成的，岩浆是如何演化的，以及地球表面以下这些物质的化学和动力学行为，那么了解在地球深处发现的熔融岩石的行为是很重要的。我正在研究这种熔融材料。特别是，我在高压和高温下研究与地质相关的合成熔体（天然熔体太复杂）。我在加拿大光源（除其他外）使用复杂的x射线方法来专门研究Si和O等轻元素以及过渡元素的环境。这些元素构成了最常见的岩浆的主体，这些元素的原子环境的变化是自然熔体中发生的大部分物理和化学行为的原因。这包括晶体分馏、岩浆对流、火山喷发机制等过程，以及下地壳和上地幔的密度和粘度等特性的行为。由于在高温高压下进行实验的困难，我们对热熔融液体（如地质熔体）的了解非常有限。此外，几十年来，我们一直认为液体会随着压力和温度的变化而不断变化。然而，最近人们认识到，包括SiO2在内的许多液体都不是这样的。它们似乎经历了不连续的结构变化，并且可以以不止一种结构状态存在：它们可以作为离散的低密度和高密度液体存在。这类似于石墨和钻石等矿物，它们的成分相同，但结构不同，性质也截然不同。我建议研究在上地幔和下地壳的极端条件下，这些不同液态的结构是如何变化的。研究将在室内压力和温度以及上地幔的实际压力和温度特征（高达50 GPa和2000℃）下进行。我和我的学生将在加拿大光源和其他国际光源上使用不同类型的实验光束线来研究地质熔体和岩浆中常见的轻元素（Si， O, Al，碱和碱土）周围环境的性质。此外，我们将使用一种非常新的技术，这是唯一一种可以在高压下原位探测轻元素环境的方法。我们将研究这些具有地质意义的熔体的结构，包括模型玄武岩和花岗岩系统，这是地球上最常见的两种火成岩类型。这些研究的发现将极大地增强我们对地球最初是如何形成的，岩浆是如何以及为什么上升到地表的，以及火山爆发本身的性质的理解。此外，不同结构的液体具有不同的物理性质，如密度、粘度和扩散率，这可能会导致开发出具有以前未知性质的新型材料，这些材料可能具有商业应用价值。

Understanding the behaviour of molten rock (melts) under the conditions found deep in the Earth is important if we are to understand how the Earth formed, how magmas evolve, and the chemical and dynamical behaviour of such materials below the surface of the Earth. I am studying such molten materials. In particular I investigate geologically relevant synthetic melts (natural melts are far too complex) at high pressures and temperatures. I use sophisticated x-ray methods at the Canadian Light Source (amongst others) to specifically look at the environment of light elements such as Si and O as well as transition elements. These elements make up the bulk of most common magmas and changes in the atomic environment of these elements are responsible for much of the physical and chemical behaviours that occur in natural melts. These include processes such as crystal fractionation, magma convection, volcanic eruptive mechanism, as well as the behaviour of properties such density and viscosity in the lower crust and upper mantle. Our understanding of hot molten liquids such as geological melts has been very limited due to difficulties with doing experiments at high temperatures and pressures. In addition, for decades we have believed that liquids underwent continuous progressive changes with changing pressures and temperatures. However, it has recently been recognised that many liquids, including SiO2, do not behave this way. They appear to undergo discontinuous changes in structure and can exist in more than one type of structural state: they can exist as discrete low and high density liquids. This is akin to minerals like graphite and diamond that have the same composition but different structures and very different properties. I am proposing to investigate how the structure of these different liquid states change under the extreme conditions found in the upper mantle and lower crust. The studies will be carried out both at room pressures and temperatures and at the actual pressures and temperatures characteristic of the upper mantle (up to 50 GPa and 2000C). My students and I will use different types of experimental beamlines at the Canadian Light Source and other international based light sources to study the nature of the environment around light elements (Si, O, Al, alkalis and alkaline-earth) commonly found in geological melts and magmas. In addition, we will use a very new technique that is the only method that can probe the environment of the light elements in-situ at high pressure. We will study the structure of these melts of geological interest, including model basaltic and granitic systems, the two commonest types of igneous rocks on Earth. The findings of these studies will greatly enhance our understanding of how the Earth initially formed, how and why magmas rise to the surface, as well as, the nature of volcanic eruptions themselves. In addition, different structured liquids have differing physical properties such as density, viscosity and diffusivity, and this may lead to the development of new types of materials with previously unknown properties that could have commercial applications.