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Presented By: Earth and Environmental Sciences

Smith Lecture: Multi-scale Structures and Thermal Constraints at Earth's Core-mantle Boundary

Jennifer Jackson, Caltech

The large chemical, density, and dynamical contrast associated with the juxtaposition of a liquid iron-dominant alloy and an intimate mixture of silicates and oxides at Earth’s core–mantle boundary is associated with a wide range of complex seismological features. Interpretation of these multi-scale features and the dynamic processes that formed them requires, in part, knowledge of the thermoelasticity and melting properties of candidate phases. We will present recent nuclear resonant scattering measurements on iron-bearing phases and the application of these results to our understanding of Earth’s core and core-mantle boundary region [1-5]. Specifically, we will present nuclear resonant scattering and x-ray diffraction measurements to over 100 GPa and temperatures around 4500 K. The nuclear resonant inelastic x-ray scattering method provides specific vibrational information, e.g., the partial projected phonon density of states. The high statistical quality of the data in combination with a small x-ray focus size and in-situ x-ray diffraction permits accurate evaluation of the vibrational-related parameters of iron-bearing materials, such as the sound velocities, vibrational entropy and free energy, Grüneisen parameter, thermal pressure, and iron isotope fractionation quantities. Finally, we will present constraints on the temperature of the core-mantle boundary using a new method of melt-detection using synchrotron Mössbauer spectroscopy and a fast temperature readout spectrometer. Our approach is unique because the dynamics of the atoms are monitored prior to melting, while temperatures are determined accurately and precisely. We will discuss the implications of our results as they relate to the composition and dynamics of various structures near Earth’s core-mantle boundary.

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