Yingwei Fei

A major goal of petrological, geochemical and geophysical research is to completely describe the Earth's interior -- from the crust to the core -- to understand the physical and chemical conditions of the planet over time. Recent advances in high-pressure techniques allow scientists to explore the deep interiors of the Earth and other planets via simulations. Yingwei Fei is an expert in using high-pressure devices such as the piston-cylinder, the multianvil apparatus, and the diamond-anvil cell to simulate the high pressure and temperature conditions of planetary interiors. The multianvil apparatus allows scientists to simulate conditions ranging from 5 to 27 GPa. (The larger number is equivalent to a depth of 750 kilometers in the Earth, which is the uppermost part of the lower mantle.) While the diamond-anvil cell allows scientists to reproduce conditions as deep as the inner core, the multianvil apparatus is ideal for scientific investigations that require the analysis of relatively large samples to provide accurate phase equilibrium data.

One particularly vexing problem for earth scientists is the makeup of the Earth's core. Iron certainly is a major part; but what other elements are there? It has been proposed that sulfur (S), carbon (C), and oxygen (O) are the lighter alloying elements that reside there. Fei and postdoctoral fellow Jie Li are conducting experiments to investigate the nature of the core's lighter elements. Their experiments with the multianvil apparatus and the diamond-anvil cell have produced phase transformation and melting relations in the Fe-O-S-C system. This is an important step in understanding how these elements interact at high pressures and temperatures.

Fei and colleagues are also investigating the role of water and potassium in Earth's deep geological processes and the fate of subducted basaltic crust in the lower mantle. A subducted slab of oceanic crust contains significant amounts of water and potassium. What happens to the hydrous and potassium-bearing minerals at such depths? Many believe that hydrous phase transformations in subducted slabs play a large role in mantle processes, including magma generation, water recycling, and possibly the occurrence of deep-focus earthquakes. With the goal of elaborating these phase changes, Fei focuses on determining the stability fields of several dense hydrous magnesium silicates in the lower mantle. Fei and postdoctoral fellow Jürgen Konzett conducted a series of high-pressure experiments to address transport and storage of potassium in the Earth's upper mantle and transition zone. Postdoctoral fellow Wenjie Jiao and Fei, in collaboration with Department of Terrestrial Magnetism Staff Member Paul Silver, are developing a new multichannel acoustic emission data collecting system to detect acoustic emissions at high pressures and temperatures. This new system will allow them to test proposed physical mechanisms of deep earthquakes.

Much of what scientists learn about our Earth can be applied to other planets. Fei is collaborating with Research Scientist Connie Bertka in investigating the internal structure of the planet Mars. Since there is no seismic data for Mars, scientists must rely on models and high-pressure and temperature experiments. Fei and Bertka are developing a model of the Martian interior that starts with a chemical composition derived from Martian meteorites. On the basis of recent geophysical data from Mars Pathfinder, the two researchers found that C1 chondrite accretion models are not sufficient to explain the formation of Mars and the other terrestrial planets.

Fig. 7. This diagram shows the relation between mantle plumes and convection in the Earth's interior.