Multi-spectroscopic Investigation of Calcium in Silicate: Modification of Structure and Dynamics of Calcium in Silicate Melts and Glasses

Chemical and physical differentiation processes in the early history of Earth and other terrestrial planets were largely determined by the properties of silicate melts, such as density, elasticity, viscosity, elemental diffusivity and partition coefficients between melts and solids. All of these properties are primarily controlled by the structure of the melts. Studies of evolution in the structural, elastic, and/or inelastic properties of silicate melts give critical constraints on the differentiation processes. Although there has been an increasing number of theoretical and experimental studies, data corresponding to the actual conditions of the Earth's deep interior are scarce, and quantitative determination of silicate coordination in melts and glasses remains a challenge. In this presentation, we first report the structural evolution of wollastonite (CaSiO3) glass up to 70 GPa using a combination of experimental techniques including Raman and Brillouin spectroscopy as well as synchrotron X-ray diffraction. With increasing pressure, Raman vibrational modes of CaSiO3 reveal gradual modifications in the interconnectivity of the tetrahedral SiO4 network and change in coordination, resulting in several structural modifications at ~5, 20, and above 43 GPa. These changes are further corroborated by both Brillouin and X-ray diffraction results. Additionally, we report structural evolution of MgSiO3 and CaSiO3 melts up to 12 GPa (~3000 K) measured in a Paris Edinburgh press. Structural evolution in CaSiO3 melts in the Earth's deep interior will be discussed based on the combined glass and melt datasets.