Experimental investigation of volatile elements in mantle minerals and melts

地幔矿物和熔体中挥发性元素的实验研究

• 批准号: RGPIN-2014-04969
• 负责人: Withers, Anthony
• 金额: $ 2.7万
• 依托单位: University of Western Ontario
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611355
• 关键词: Experimental; investigation; volatile; elements; mantle

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).

挥发性元素，如氢和碳，对地球内部的性质有根本影响，影响导致化学分化的熔融过程，地幔的对流活力，以及地幔岩石的导电性，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会导致大气的形成，从而对创造宜居世界产生影响。水通过俯冲循环进入地球深处，在那里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，人们对含水缺陷的确切性质知之甚少，这导致在预测地幔的流变性和解释物理测量方面存在不确定性。挥发物在溶解成硅酸盐液体时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物含量，但这些关系尚未在高压下进行系统研究。溶解挥发物的形态随化学环境的不同而不同，因此在低氧逸度条件下，如地球早期可能盛行的那样，H2成为主要的含水物种。为了知道有多少氢可以溶解在岩浆海洋中，以及这个过程可能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的溶解度的影响。 这项建议中描述的研究计划旨在1)表征地幔矿物中含水缺陷的性质，2)准确测量在高压和温度下合成的矿物的氢含量，以便限制地幔可能发生熔化的条件，3)系统地研究挥发性元素浓度对碳酸盐硅酸盐(金伯利岩)熔体粘度和电导率的影响，以及4)测量还原条件下挥发分在硅酸盐熔体中的溶解度，例如可能适用于早期地球或其他行星体。 在我的研究中，我使用了多种工具：高压仪器(将在WESTERN创建一个新的活塞缸实验室)、红外光谱分析(我的目标是创建一个优化的设施，用于研究实验产品，并培训我的学生使用偏振显微光谱技术)、核技术(通过现有的合作)和离子束技术(将作为学生项目开发，以建立在加拿大独一无二的分析能力)。