Advances in Understanding the Earth's Deep Interior From High-Pressure Experiments at Community-Based Synchrotron Facilities

The development of second- and third-generation synchrotron x-ray facilities has led to enormous growth and development in the field of high-pressure research that has dramatically improved our understanding of deep planetary interiors. In this talk, I will primarily focus on results from research conducted at the National Synchrotron Light Source and the GSECARS sector of the Advanced Photon Source. These synchrotron facilities have enabled entirely new classes of experiments that take advantage of the unique characteristics of the synchrotron beam including extremely high brilliance and low divergence, together with advances in beamline components. As an example of just one developing research area, the coupling of the brightest synchrotron x-ray diffraction beamlines with the most advanced systems for laser heating allow researchers to explore both simple and complex mineral systems under pressure-temperature conditions reaching up to those of the Earth's core-mantle boundary and beyond. For example, we have recently carried out a comprehensive study of the behavior of both SiO₂ and MgSiO₃ up to 120 GPa and 2500 K to understand the phase transitions occurring in these fundamental systems in the deep mantle. At conditions corresponding to the 660-km discontinuity and the top of the lower mantle, we have carried out the first in situ meausrements of the spinel- perovskite + periclase transition in the laser-heated diamond cell. Examples of other advances in high-pressure experimentation arising from the development of these facilities and the dynamic user community that has sprung up around them will be discussed. Examples of such advances include: mineral elasticity from coupled ultrasonic/synchrotron experiments, high-resolution crystal structure determination, stress/stain measurements of rheology and elasticity, viscosity and liquid structure determination, melting curves, and x-ray spectroscopies for determination of sound velocities, thermodynamic properties, and electronic structure. The future looks very bright for the continued rapid advancement of experimental capabilities using community-based synchrotron facilities, and some important future directions will be highlighted.