Experimental investigation of volatile elements in mantle minerals and melts

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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).