Structure, Thermoelasticity and T race-Element Hosting Properties of High-Pressure Silicate Minerals

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

The investigators propose to further develop an efficient and reliable atomistic model of crystals in order to study thermoelastic and geochemical properties of complex silicate minerals. They have developed a model that relies on density-functional theory and parametric covalent corrections, which in turn compete with inter-ionic charge transfer in attaining structural and electronic equilibrium. In terms of the accuracy of predicted equations of state and elastic wave velocities, this approach competes successfully with the far more computer intensive methods based on first principles. The above model stands to have a broad impact on deep planetary physics research. The method effectively bootstraps high quality low-pressure elasticity data into deep Earth conditions, thus greatly enhancing the data's utility. The investigators will use the model to examine the effects of temperature, crystal structure and the presence of relatively low-abundance components like Al, Ca and Fe3+ on the thermoelastic properties of silicate perovskites, garnets, various SiO2 phases, and other minerals composed of MgO, SiO2, CaO, Al2O3, and FeO that may be present in the lower mantle and D'' zones. In previous studies of the microscopic mechanisms by which Al is incorporated into perovskites, the investigators found that Al-bearing perovskites might be good hosts for rare gases and other "incompatible" elements. They will therefore also examine the effects of pressure on the compatibility of rare gases in some of these minerals, as well as their diffusivities within them. Adding non-equilibrium thermodynamic considerations, they hope to shed light on the mechanisms by which these gases might be sequestered deep in the Earth, and thus help account for the "missing rare gases," one of the outstanding geochemical issues. The model approach has the intellectual merit of yielding new practical tools for the study of microscopic geochemical processes, in addition to the physical processes, that need to be understood in order to reconcile and interpret the separate inferences drawn form seismology, geochemistry and geodynamics.