Earth Materials

The Mystery of Iron Oxide shows the importance of studying iron in minerals using the latest methods that allow inclusion of temperature as well as pressure, opening up many avenues for further investigation:

• How does the metallisation of FeO extend into (Mg,Fe)O solid solutions (ferropericlase and magnesiowustite)?
• How does iron in perovskite and post-perovskite behave? Do they also metallise?
• How does this effect the major phase diagram for the deep Earth, the ternary SiO₂-MgO-SiO₂?
• Do correlations affect the properties of crystalline iron under Earth’s inner core conditions?
• How do other transition metal ions behave in minerals at high pressures and temperatures in the Earth?
• Do electronic and magnetic transitions change element partitioning from trends inferred from lower pressure and temperature experiments?

We will compare our results with experiments, working closely with experimentalists, and with results of more approximate methods such as LDA+U to understand better the range of validity of such approximations. We will compute quantities that are particularly amenable to high-pressure diamond anvil studies, such as optical properties, so that optical measurements can be interpreted more easily, and used as probes of high pressure high temperature electronic transitions.

Properties of C-H-O fluids

This project will also address the behaviour of carbonated H₂O-CO₂ and H₂O-CH₄ fluids under conditions of subducted slabs and the mantle wedge. We use a variety of methods, including first-principles molecular dynamics to obtain accurate equations of state, phase diagrams, dielectric constants, and diffusivities. We are particularly interested in the molecular speciation of CHO fluids. Very little is known about the properties of fluids under these conditions but some exploratory work has been carried out. This work should give insights into slab dewatering, hydration and transport of fluids from the slab and formation of diamonds and kimberlites.