Geological melt studies under extreme conditions

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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.