CAREER: Investigations on the elastic and vibrational properties of mantle silicates and oxides

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Inferences of the mineralogy and chemical composition of Earth's deep interior depend on comparing accurate laboratory-measured properties of candidate phases with geophysical and geochemical observations, because our ability to directly sample the deep Earth is severely limited. This CAREER award investigates the effect of iron and aluminum on the elastic and vibrational properties of lower mantle silicates and oxides using national synchrotron facilities. Under the mentorship of the PI, students will use established synchrotron methods of micro x-ray diffraction and nuclear resonant inelastic x-ray scattering to obtain equations of state for mantle phases at unchartered pressure-temperature conditions. Typically, few students are able to experience research projects at such facilities due in part to limited accessibility and space constraints. Under the initiatives of this project, we will create a virtual beam-line by building on existing remote infrastructure at the synchrotron. Caltech's Summer Undergraduate Research Fellowships (SURF) program introduces students to research under the guidance of experienced research mentors at Caltech and the Jet Propulsion Laboratory. Undergraduate students from all over the country participate in a 10-week long SURF program over the summer. At the conclusion of the program, they submit a technical paper and give an oral presentation at SURF Seminar Day, a symposium modeled on a professional technical meeting. The proposed research agenda with its virtual beam-line offers a unique opportunity for an extended array of undergraduate and graduate students under the mentorship of the PI to apply state-of-the-art experimental techniques at multi-scale facilities and apply their results to geophysical phenomena. The effort to understand the origin of recently observed seismic complexities requires new and more accurate measurements of candidate lower mantle materials and is an active area of modern cross-disciplinary research. Typically, models of the deep Earth have been made by extrapolating mineral properties to relevant pressure-temperature conditions and comparing them with seismological determined compressional- and shear-wave velocities and density. However, several properties of deep mantle materials remain widely unknown due to experimental challenges. In an effort to overcome these obstacles, undergraduate and graduate students will use established synchrotron methods engaged with diamond anvil cells and laser heating technology to obtain equations of state for mantle silicates and oxides under relevant conditions. With the density determined from x-ray diffraction for these materials, the aggregate compressional and shear wave velocities, as well as the adiabatic bulk and shear moduli, will be determined from the measured partial phonon density of states. By creating a virtual beam-line to provide remote access to the proposed synchrotron experiments, more undergraduate and graduate students at Caltech will have access to synchrotron experiments. The students will publish their results in scientific journals and present their findings at national meetings. The data obtained will permit the evaluation of the effects of iron and aluminum on the sound velocities and elasticity of these materials in a previously unexplored pressure-temperatures sector and will put constraints on geodynamic simulations and whether observed seismological lateral variations are due to a chemical origin.