PROPERTIES OF MINERALS AT EXTREME PRESSURES AND TEMPERATURES, AND NATURE OF THE DEEP EARTH

Professor Bass is a geophysicist whose research is largely involved with understanding the chemical composition, structure, and thermal structure of Earth’s deep interior. Of particular interest is the Earth’s mantle, a thick stony layer with its base at 2900 km depth (the core-mantle boundary), and an upper surface at 8 km depth under the oceans and 40 km depth beneath continents. Most of what is known about the deeper parts of the mantle comes from seismology, in the form of how fast seismic waves travel and the mantle’s density at various depths. Interpreting this information in terms of chemical composition or temperature requires laboratory measurements on the right kinds of minerals under conditions similar to those at depth. However, the pressures and temperatures in the Earth are incredible, with a pressure at the base of the mantle of about 1.3 million times that at the surface and probable temperatures of a few thousands of degrees Celsius. These conditions are difficult to achieve in the laboratory. In addition, minerals in the mantle are present as exotic, highly dense phases that are obtainable only in very small quantities.

During his Center appointment, Professor Bass will work on new techniques for measuring physical properties of minerals at high pressures and temperatures. Much of this work will involve the use of diamond-anvil high-pressure cells and laser-induced heating. He will measure the velocities of sound waves (seismic velocities) using spectroscopic techniques. One of these is a laser light-scattering technique called Brillouin spectroscopy, which has been in use in his lab for mineralogical studies for more than a decade. Other techniques involve the inelastic scattering of x-rays. Accurate measurements using such x-ray-based methods have just recently become possible with instrumentation developed at such synchrotron x-ray sources as the Advanced Photon Source at Argonne, Illinois. Bass will collaborate with experts at synchrotron facilities to adapt such methods for work on miniscule samples under mantle pressures and temperatures.