Aluminum- and Iron-rich Perovskites and Post-perovskites and Earth's Deep Lower Mantle

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Understanding the deep interior of the Earth is a key ingredient in unraveling the processes involved in the origin and evolution of our planet. In addition, the geological activity that manifests itself so profoundly at the surface of the Earth has its ultimate origins in processes ongoing in the deep interior. Studying minerals under the extreme pressure-temperature conditions of the deepest Earth provides a means to test the limits of our understanding of basic physical and chemical properties of materials. The Earth's core-mantle boundary is particularly complex as it juxtaposes the churning liquid iron core against the hot but solid silicate minerals of the deep mantle at greater than a million times atmospheric pressure. In this work, we propose to recreate the conditions of Earth's deep mantle in the laboratory and study the detailed nature of the crystal structures that form under such conditions and their physical properties.The Earth's core-mantle boundary region (called D") is a thin layer (~200 km thick) lying just above the core that has long been of interest due to its unusual seismic properties. Perovskites (Pv) and post perovskites (pPv) are expected to be the major mineral phases of Earth's lower mantle and core-mantle boundary regions. Seismic evidence indicates the deep lower mantle exhibits considerable chemical heterogeneity and this may result from such phenomena as core-mantle interactions, partial melting in D", retained primordial material, or accumulation of subducting slabs. This chemical complexity will influence many key properties of the deep mantle including location and width of phase boundaries, density, sound velocities, element partitioning, and transport and thermal properties. In this project, the investigators will use synchrotron x-ray diffraction and scattering techniques to explore the behavior of iron- and aluminum-bearing perovskites and post-perovskites over a wide pressure range. They will synthesize a variety of phases at conditions up to 200 GPa and 2500 K and measure such properties as equations of state, compressibilities, phase boundaries, and Clapeyron slopes. This study of chemically complex systems at high pressures and temperatures will enable a better interpretation of seismically observed deep mantle structure in terms of the physical and chemical properties of realistic mineral assemblages. The proposed research will yield advances in understanding the geochemistry and thermoelastic properties of minerals of relevance for the Earth's deep mantle, and will impact the fields of mineral physics, geodynamics, seismology, and petrology.