MSA AWARD LECTURE: MINERALOGY AND CHEMISTRY OF THE EARTH'S LOWER MANTLE

Determination of a phase relationship and a chemical composition of the Earth’s lower mantle is a long-standing challenge in earth science. Advances in seismology have provided not only the global views of the internal structure of the earth but also the various anomalous seismic observations at the base of the mantle. However, the mineralogical model of lower mantle, which fully satisfies those seismological structure and observations, has not so far been well-established experimentally due to its extreme pressure and temperature condition.

Over the last decade, we have developed the in-situ synchrotron X-ray diffraction and the sound wave velocity measurement techniques under the relevant high-pressure and high-temperature condition to the lower mantle using laser-headed diamond anvil cell in order to overcome such an experimental hurdle. In-situ synchrotron X-ray diffraction measurement with laser-heated diamond anvil cell enables us to explore the phase transition/relationship in the lower mantle. The accurate knowledge of sound velocities of the lower mantle minerals under relevant high-pressure and -temperature (P-T) conditions is essential to constrain the mineralogy and chemical composition from seismological observations. With this combined measurement system, we revealed the phase transition/relationship and the elasticity of lower mantle phases up to pressure and temperature condition of the base of the mantle, which dramatically reshape our understanding of the Earth's interior and evolution.

Here we discuss on the dynamics at the Earth’s core-mantle boundary and new mineralogical model of the lower mantle, based on our new experimental results including the discovery of perovskite to post-perovskite phase transition in MgSiO₃ and the sound velocity data on lower mantle phases.