Simultaneous determination of elastic and structural properties under simulated mantle conditions using multi-anvil device MAX80

Abstract

An ultrasonic interferometry high-pressure set-up for elastic wave velocity measurements under simulated Earth's mantle conditions has been developed. A DIA-type multi-anvil apparatus MAX80 permanently located at HASYLAB, Hamburg, Germany for X-ray diffraction (XRD) under in situ condition was equipped for simultaneous ultrasonic measurements. Two of the six anvils were equipped with lithium niobate P- and S-wave transducers of 33.3 MHz natural frequency. The pressure and temperature limits of the high-pressure apparatus were not reduced as a side effect of the modification. The ultrasonic configuration allows all kinds of interferometric measurements with compressional and shear waves. In addition to the classical ultrasonic interferometry the newly developed data transfer function technique (DTF), first described in [J. Phys. Condens. Matter 14 (2002) 11337], is discussed in detail to give the readers the chance to use this valuable and important new method . The results for natural San Carlos olivine up to 3 GPa pressure are compared with published data of several authors. The data for hot-isostatic-pressed anorthite solved discrepancies between published high-pressure and normal-pressure data for polycrystalline anorthite leading to v p = 7.28 km/s, v s = 3.93 km/s at ambient conditions and dv.,/dp = 0.027 km/s GPa, dv s /dp = 0.001 km/s GPa. The obtained data sets correspond to published results within the accuracy of the method . As an example for unquenchable phase transitions we measured the elastic wave velocities at the high-pressure clinoenstatite (MgSiO 3 , HCEn) –low-pressure (LCEn) transition at high pressure, high temperature conditions in conjunction with in situ XRD. For ultrasonic interferometry experiments LCEn powder synthesized at ambient pressure was hot-isostatic-pressed at 0.4 GPa and 1400°C for 2 h in MAX80 to obtain low-porosity samples. The elastic wave velocities v p and v s of the CEn sample were measured in situ using the classical interferometric technique as well as the recently developed ultrasonic data transfer function (DTF) technique for the elastic wave velocities as a function of pressure at 700°C. To compare the results, v p and v s were measured at 6.7 and 7.5 GPa using both interferometric techniques. The results correspond within the limits of less than 1% .