Experimental investigation of volatile elements in mantle minerals and melts

挥发性元素，如氢和碳，对地球内部的性质有根本的影响，影响导致化学分化的熔融过程、地幔的对流活力和地幔岩石的导电性，这是地球内部的一种可测量的性质。此外，从行星内部提取挥发性元素导致大气的形成，因此对创造可居住的世界有影响。水通过俯冲到地球深处再循环，在那里它作为矿物晶格中的点缺陷储存在高压相中；正是这些含水缺陷的存在，解释了水对地幔物理性质的强烈影响。然而，含水缺陷的确切性质尚不清楚，这导致了预测地幔流变特性和解释物理测量结果的不确定性。当挥发物溶解成硅酸盐液体时，它们从地球内部释放出来。这些液体的粘度、密度和电导率取决于它们的挥发性含量，但这些关系尚未在高压下进行系统的研究。溶解挥发物的形态随化学环境的变化而变化，在低氧逸度的条件下，H2成为主要的含水物质，例如在地球早期可能普遍存在。为了了解岩浆海洋中H2的溶解量，以及这一过程如何影响行星的氧化还原演化，需要研究熔体结构对还原挥发性物质溶解度的影响。本提案所述的研究计划旨在1)表征地幔矿物含水缺陷的性质，2)精确测量在高压和高温下合成的矿物的氢含量，以限制地幔可能发生熔融的条件。3)系统地研究挥发性元素浓度对碳酸硅酸盐（金伯利岩）熔体粘度和导电性的影响；4)测量在简化条件下硅酸盐熔体中挥发物的溶解度，例如可能适用于早期地球或其他行星体。在我的研究中，我使用多种工具：高压仪器（将在西部大学创建一个新的活塞缸实验室），红外光谱（我的目标是创建一个用于研究实验产品的优化设施，并培训我的学生偏振微光谱技术），核能技术（通过现有的合作）和离子束技术（将作为一个学生项目开发，以创建一个在加拿大独一无二的分析能力）。

Volatile elements, such as hydrogen and carbon, have a fundamental influence on the properties of the Earth’s interior, affecting the melting processes that lead to chemical differentiation, the convective vigor of the mantle, and the electrical conductivity of mantle rocks, which is a measurable property of the Earth’s interior. Moreover, the extraction of volatile elements from planetary interiors leads to the formation of atmospheres and hence is influential in creating habitable worlds. Water is recycled through subduction into the deep Earth, where it is stored within high pressure phases as point defects in the mineral lattice; it is the presence of these hydrous defects that accounts for the strong influence of water on the physical properties of the mantle. The exact nature of the hydrous defects, however, is poorly understood, which leads to uncertainties in predicting the rheological properties of the mantle and in interpreting physical measurements. Volatiles are released from the Earth’s interior when they dissolve into silicate liquids. The viscosity, density and electrical conductivity of those liquids depend on their volatile content, but these relationships have yet to be investigated systematically at high pressure. The speciation of dissolved volatiles varies with chemical environment, such that H2 becomes the dominant hydrous species under conditions of low oxygen fugacity, such as may prevail in the early Earth. In order to know how much H2 could dissolve in a magma ocean, and how that process may affect the redox evolution of a planet, the effect of melt structure on the solubility of reduced volatile species needs to be investigated. The research program described in this proposal aims 1) to characterise the nature of hydrous defects in mantle minerals, 2) to measure accurately the hydrogen contents of minerals synthesised at high pressure and temperature, in order to constrain the conditions under which melting may occur in the mantle, 3) to investigate systematically the effects of volatile element concentrations on the viscosity and conductivity of carbonated silicate (kimberlitic) melts and 4) to measure the solubility of volatiles in silicate melts under reduced conditions, such as may apply to early Earth or to other planetary bodies. In my research I use multiple tools: high pressure apparatus (a new piston cylinder lab will be created at Western), infrared spectroscopy (my aim is to create a facility that is optimised for studying experimental products and train my students in polarised micro-spectroscopic techniques), nuclear techniques (through existing collaboration) and ion beam techniques (which will be developed as a student project to create an analytical capability that will be unique within Canada).