Equation of State and Phase Boundary of Post-Perovskite

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Intellectual Merit. The discovery of the phase transition in Mg-silicate perovskite (Pv) to a new phase (post-perovskite, PPv) at lowermost mantle conditions has influenced the interpretation of seismic observations and the understanding of the dynamic role of this region of the Earth's interior. Because there are discrepancies between recent experiments and theoretical calculations regarding the PPv transition, new and more sophisticated experimental work is needed. The PI's recently conducted XRD measurements on (Fe0.1Mg0.9)SiO3-PPv to 136 GPa captured the complete transformation from Pv+PPv mixture to pure PPv at in situ high P-T, which enables reliable determination of the phase boundary. This work also makes possible an accurate determination of the equation of state (EOS) for PPv. Further work is proposed to for pure and Al-bearing Mg-PPv. Combined work on pure, Fe-bearing, and Al-bearing Mg-Pv, the proposed measurements will allow self-consistent evaluation of density and compressibility across the PPv transition - thereby defining phase relations for the lower mantle.Broader Impacts. A long term goal is to understand the structure and dynamics of the mantle using experimental approaches, and taking advantage of rapid developments in synchrotron XRD techniques to study important geophysical problems. The most significant educational activity of this proposal is to provide research opportunities in mineral physics to MIT undergraduate students who will participate in the proposed project during summer. This project will also support Ph.D. research of K. Catalli. The outcome of the proposed research will also be incorporated into courses at MIT, "Structure of Earth Materials", "Introduction to Mineral Physics", and "The Core-Mantle Boundary", for undergraduate and graduate students.