Research

Japanese

Theoretical Mineral Physics in Univ. Osaka

We conduct research to elucidate the internal structures of the Earth and other planets using first-principles calculations. Understanding the Earth's internal structure provides indispensable information for unraveling the evolutionary history of our planet. The Earth is thought to be composed mainly of a mantle made of silicate minerals and a core predominantly consisting of iron. From the surface to the core, the Earth experiences extreme variations in temperature (from 300 K to 5000 K) and pressure (from 1 to 365 Gigapascal), making it a highly challenging task to investigate the states of Earth’s constituent materials under such conditions, especially given their complex compositions.

Simulations based on first-principles electronic structure calculations have become one of the important approaches, alongside ultra-high-pressure experiments and seismic observations, for understanding the Earth's interior. Our group actively applies this method to predict the structures and physical properties of Earth- and planet-forming minerals under high-temperature and high-pressure conditions. In particular, our research covers a wide range of topics, including the structures and properties of minerals that transport volatile elements such as water to the deep Earth, minerals that retain water in the deep Earth, and the influence of impurity elements on the post-perovskite phase equilibrium in the lowermost mantle. The ability to investigate such a complex planetary system at the atomic level using quantum-mechanics-based simulations is one of the great attractions of this research.

In recent years, the computational power of modern computers has increased dramatically, and first-principles electronic structure calculations are expected to play an even more significant role in advancing our understanding of the interiors of the Earth and other planets. By fully leveraging this computational capability, we aim to conduct mineral simulations under extreme conditions that allow us to visualize the otherwise inaccessible interior of the Earth with high fidelity.

Based at the Department of Earth and Space Science, Graduate School of Science, Osaka University, we seek to establish an original research field at the interface between physics and Earth & planetary sciences.

Research Highlights

1. Structure and elastic properties of nominally anhydrous minerals (NAMs).

First principles investigation of the structural and elastic properties of hydrous wadsleyite under pressure, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, B02206, doi:10.1029/2008JB005841, 2009

Existence of water in the deep mantle may significantly affect the mantle dynamics, because the physical properties of mantle minerals such as atomic diffusivity, melting temperatures, and elasticity of the mantle constituent minerals are considerably changed by the presence of water. Many high pressure and temperature experiments have been conducted in order to know whether the mantle constituent mineral can retain water in the earth’s deep interiors It was reported experimentally that up to a few wt%H2O can be dissolved in wadsleyite and ringwoodite, which are believed to be the primarily component of the mantle transition zone. (e.g., up to ~2 wt% at 1000-1200°C, and ~0.5 wt% at 1600°C at the transition zone pressures (Ohtani et al. 2001)).

Therefore, if the hydrous minerals in subducting cold slab could transport water into the mantle transition zone, there is a possibility that significant amount of water is stored in wadsleyite and ringwoodite in the mantle transition zone. If such amount of water exists in wadsleyite and ringwoodite in the mantle transition zone, it should in principle be detected by the seismic observations. In order to determine the amount of water in the deep earth, the dependence of elastic moduli on water content of these minerals at high pressure conditionsas well as precise observation of seismic velocities is indispensable.

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