ULTRASONIC WAVE VELOCITY MEASUREMENTS IN SOLIDS UNDER HIGH PRESSURE USING SOLID PRESSURE MEDIA

An experimental technique to measure ultrasonic wave velocities of solids at pressures up to 50 kbar and temperatures up to 600°C using a new sliding-type, cubic-anvil, high-pressure apparatus is described. The sample assembly is designed to make the pressure distribution around a sample as hydrostatic as possible. Good agreement of the present data on a single crystal of MgO at room temperature with Spetzler's [1970] data indicates that the present technique can considerably extend the pressure range of ultrasonic wave velocity measurements. Compressional and shear wave velocities of a polycrystalline enstatite (MgSiO 3 ) were also measured to 40 kbar at room temperature. The results are in good agreement with those for a bronzite single crystal by Frisillo and Barsch [1972], but not with those for a bronzitite or pyroxenite by Christensen [1974] and by Wang [1974]. Shear wave velocities in Twin Sisters dunite have been determined to 50 kbar at room temperature and from 25–600°C at P = 48.5 kbar. These results encourage us to make further refinements of the present technique because of the potential for enabling us to determine seismic velocities of mantle minerals or rocks within a reasonable accuracy under upper mantle P-T conditions without any extrapolation.