First-Principles Molecular Dynamics Simulations of Silicate Liquids: Structure, Diffusion and Viscosity at Mantle Conditions

Louisiana State University, Baton Rouge LA

Investigators

Abstract

Magmatic processes are considered to play important role in the chemical and thermal evolution of the Earth. They are responsible for the origin and ongoing formation of the oceanic and continental crust. They may have played even more important role in the Earth?s earlier history when the accreting Earth may have been largely or completely molten ? so called the magma ocean. Melts are also thought to exist in the present day Earth at depths well below the shallow magma genetic zone, including atop the transition zone and the core-mantle boundary. These magmas and melts are essentially composed of silicate materials. To understand the origin and stability of these deep melts, and their role in the earliest evolution of the Earth and in the interpretation of seismic observations, knowledge about the physical properties of silicate liquids over relevant broad ranges of pressure, temperature, and composition is essential. Investigation of silicate liquids at extreme conditions of the Earth?s interior poses tremendous challenges. Here, we propose to apply a combination of first-principles parallel computation and visualization techniques to tackle this complex silicate liquid system. Our approach being parameter free provides the ideal complement to the experiments. To further promote our understanding of the role of silicate liquids in planetary evolution and magmatic processes, we plan to carry out the following specific activities: 1) Consider more compositions towards sampling natural melts (MgO-CaO-FeO-Fe2O3-Na2O-K2O-Al2O3-TiO2-SiO2 system) with/out volatiles (H2O and CO2) to calculate their densities, enthalpies, and structures as a function of pressure and temperature. 2) Investigate the transport properties of silicate melts through first-principles predictions of the self-diffusion and viscosity coefficients. 3) Continue the study of structure and compression mechanisms of silicate glasses as a way of gaining additional insight into the energetics underlying liquid structure, and in order to enrich contact with the extensive experimental literature on geologically relevant compositions in the vitreous state. 4) Visualize/analyze the massive simulation data to gain insight into the microscopic mechanisms of compression and transport phenomena. A unifying theme of this proposal is thus the intensive first-principles computer simulations of large systems that are necessary to explore realistic melt compositions, to accurately predict key transport properties, and to successfully capture the essence of glass structures. These results will allow us quantitatively understand the contrasts in density, diffusivity, viscosity, and bulk composition between molten silicates and their source regions, which control the generation and transport of magma and partial melts. The proposed research is essentially an exploitation of ideas and techniques of computational science to challenging problems in the investigation of Earth materials. This synergy will have impact on a number of fields including geochemistry, petrology, geophysics, computational materials physics, and scientific visualization. It will train graduate and undergraduate students, and postdoc for this multidisciplinary experience and expertise.