Mineral and melt physics

The previous four years have been a period of enormous discovery, growth and diversification in the mineral physics community. To underscore this point, several highlights of the U.S. research effort can be listed from a wide range of fields. Relatively young experimental methods have quickly matured and come to produce exceedingly important results; a prime example of this is the measurement of the elastic moduli of the β and γ high-pressure phases of forsterite by Brillouin spectroscopy [Weidner et al., 1984; Sawamoto et al., 1984]. The technical capabilities of more established techniques have been considerably extended, with a spectacular example being provided by the attainment of a statically- maintained pressure of 550 GPa (5.5 Mbar) using a diamond anvil cell [Xu et. al, 1986]; this pressure far exceeds that in the center of the Earth! Moreover, existing static and dynamic high pressure technologies have been utilized in new and creative ways. A wide variety of spectroscopic methods are being used not only to measure the properties of materials, but also to precisely define the temperature and pressure conditions which are achieved within the small sample volume of a diamond anvil cell. The determinations of the melting points of Fe to 43 GPa [Boehler, 1986] and Mg.9Fe.1SiO3-perovskite to 60 GPa [Jeanloz and Heinz, 1984] are but two examples of how the diamond cell is being used to perform quantitative phase equilibrium measurements at ultrahigh pressures. Additional constraints on the phase relations of high-pressure silicates are being provided by calorimetric measurements of thermochemical properties [e.g., Akaogi et al., 1984]. Complementary to these efforts are dynamic measurements of the sound velocity [Brown and McQueen, 1986] and temperature [Lyzenga et al., 1983] during shock wave experiments. Both of these variables are sensitive to phase transitions and have been used to constrain the phase diagrams of Fe and SiO2, respectively, at pressures ranging to hundreds of GPa. Another new application of shock wave methods has been in the measurement of the pressure-density equation-of-state of silicate melts [Rigden et al., 1984], which gives experimental support to the interesting possibility of melts sinking, rather than rising, at depth in the mantle. Parallel to these experimental advances have been a series of theoretical efforts to model the equation-of- state and stability of high-pressure phases. First-principles calculations were recently performed to investigate the high-pressure equation-of-state of oxides [Hemley et al., 1985; Bukowinski, 1985], as well as structurally complex high-pressure silicates such as perovskites [Wolf and Bukowinski, 1986], and are in broad agreement with available experimental data on crystal structures and physical properties.