Research | J Michael Brown

A focus on the other 99.9% of Earth

The Mineral Physics Group at the University of Washington is exploring properties of earth materials using a number of experimental and theoretical approaches WATCH SEMINAR HERE

NEW: Here is a link to Information concerning Local Basis Function Representations of Thermodynamic Surfaces

We use Impulsive Stimulated Light Scattering (ISLS) as a versatile tool to measure elastic properties, equations of state, and structural relaxation of solids and fluids in the diamond anvil cell and in conventional high pressure cells. Such data are prerequisite in efforts to understand processes occurring in the deep Earth. A few highlights of research are shown below. A list of publications is provided HERE.

Click for Selected Publications and Software (downloadable)

In the photo the pink, vaguely rectangular object is a single crystal of oxygen held at room temperature and 57 kbar, floating in supercritical fluid oxygen. The adjacent, colorless crystal is a piece of ruby, our pressure gauge. A platinum sphere, used to measure the viscosity of the fluid, is visible as a round, dark object. Several of the diamond facets can be seen around the perimeter

Our group was the first to report single crystal elastic constants for minerals over the range of pressures found in Earth’s upper mantle and transition zone. We pioneered measurements of elastic constants of the lower mantle mineral phase ferropericlase to 60 GPa (equivalent to a depth of almost 1500 km) through its electronic spin transition. The impact of this transition on the interpretation of mantle seismic velocities remains an active area of research. Sound velocities in ferropericlase through the high spin to low spin transition are shown. From J. C. Crowhurst, J. M. Brown, A. F. Goncharov, S. D. Jacobsen, Science, 2008. Note the dip in velocities as this mineral progresses through the spin transition.

Our group is the first to determine single crystal elastic constants of feldspars and amphiboles, the most abundant mineral groups in Earth’s crust. An innovative approach using both measurements of surface wave velocities and body wave velocities has allowed high precision measurements over the range of common chemistries found in Earth. These results are important contributions in efforts to better understand the nature of the middle and deep continental crust. Shown right (from Brown et al 2006) are surface wave velocities for albite as a function of propagation direction for six slices through a single crystal. The grey-scale background gives the expected amplitude of surface waves. The excellent fit of data to the highest intensities of surface waves gives confidence in the determination of all 21 elastic constants required for this symmetry system.

We are using measurements of sound velocities as a function of pressure, temperature, and chemical composition to determine the equation of state of fluids. In the case of aqueous solutions, we have extended determinations of mixing parameters into regimes found in deep hydrothermal systems on Earth and in Icy Worlds of the outer solar system. This work demonstrates that previously used extrapolations from lower pressure data give inadequate predictions at higher pressures. Selected figures from Vance and Brown 2013 are shown.

Posters below show some laboratory activity