Zhou Wen-Ge

A New Method for Experimental Determination of Compressional Velocities in Rocks and Minerals at High-Pressure

A transmission-reflection-combined new method is presented for measuring elastic velocities of rocks and minerals at elevated temperature and pressure, which resolves the problems of gradients of temperature and pressure existing in original sample assembly with a pyrophyllite cube. At room temperature and pressure up to 3 GPa, single-crystal quartz and eclogite were used to provide samples under test, respectively. The results of this work agree with the previous measurements very well within the error range. By the use of this new technique, more precise and reasonable data of elastic properties of rocks and minerals at elevated temperature and pressure can be achieved.

Sound Velocity in Water and Ice up to 4.2 GPa and 500 K on Multi-Anvil Apparatus

A new assembly for ultrasonic measurements of water and ice on multi-anvil apparatus has been designed, and the ultrasonic compressional wave velocities in water and ice up to 4.2 GPa and 500 K are achieved. The pressure of the sample is calibrated by the melting curve of ice VII and the transformation pressure of liquid to solid at ambient temperature. The continuous changing process of the sound velocity transforming from water into ice at high pressure is achieved, and the experimental results of sound velocities at high pressure at room temperature on the melting curve of water are consistent with the previous works by Brillouin scattering. It is believed that our new method of ultrasonic measurements of water is reliable, and worth being used for studying more liquids at high pressure.

Raman Investigation of BaWO4-II Phase under Hydrostatic Pressures up to 14.8 GPa

The BaWO4-II phase is synthesized at 5.0 GPa and 610°C with a cubic-anvil apparatus and identified by XRD. Raman scattering measurement is carried out to investigate the phase behaviour of a pure BaWO4-II phase (space group P21/n, Z = 8) under hydrostatic pressures up to 14.8 GPa at ambient temperature. In each spectrum recorded for this phase, 27 Raman modes are observed, and all bands shift toward higher wavenumber with a pressure dependence ranging from 3.8 to 0.2 cm−1/GPa. No pressure-driven phase transition occurs in the entire pressure range in this study. Our results indicate that the previously reported high pressure phase of BaWO4 at pressure above about 10 GPa and room temperature (Errandonea et al. Phys. Rev. B 73(2006)224103) is not the BaWO4-II phase.

Discovery of corundum in alkali basalt at high temperature and high pressure

Corundum megacrysts in alkali basalts are an important source of gems. However, the genesis of corundum megacrysts is still a controversial problem. Up to now, no experimental evidence has been acquired for the crystallization of corundum from basalt under high temperature and high pressure. With alkali basalt as the starting material in this experiment, the transformation of basalt into eclogite at the pressure of 3.5 GPa and the temperature of 1400°C was realized. In the experimental product, corundum has been discovered embraced in garnet.

Dehydration melting of solid amphibolite at 2.0 GPa: Effects of time and temperature

Two sets of dehydration-melting with a natural solid amphibolite, collected from North Himalayan structure zone, Tibet, have been carried out in multi-anvil apparatus at 2.0 GPa and 800–1000°C, for 12-200 h. One is keeping the pressure at 2.0 GPa and the annealing time of 12 h, changing the temperature (800–1000°C). The other is keeping the pressure at 2.0 GPa and temperature at 850°C, varying the annealing time (12–200 h). The products are inspected with microscope and electron probe. The results indicate that at 2.0 GPa, annealing time of 12 h, garnets, melts and clinopyroxenes occur in amphibolite gradually with increasing temperature and the chemical compositions of melt vary from tonalite to granodiorite, and then to tonalite. However, at 2.0 GPa and 850, with the annealing time increasing, the garnets, melts and clinopyroxenes also occur in amphibolite gradually and the chemical compositions of melt vary from tonalite to granodiorite. In both cases, melts interconnect with each other when the contents of melt are over the 5 vol.%. the viscosities of the melt produced in amphibolite at temperature higher than 850 are on a level with 104 Pa·s. The interconnected melt with such a viscosity may segregate from the source rock and form the magma over reasonable geological time. Therefore, it is believed that at the lower part of the overthickened crust, the tonlitic and granodioritic magma may be generated through the dehydration melting of amphibolite.

Phase Transition and EOS of Marmatite (Zn0.76Fe0.23S) up to 623 K and 17 GPa

In situ energy dispersive x-ray diffraction for natural marmatite (Zn0.76Fe0.23S) is performed up to 17.7 GPa and 623 K. It is fitted by the Birch–Murnaghan equation of state (EOS) that K0 and α0 for marmatite are 85(3)GPa and 0.79(16)×10−4 K−1, respectively. Fe2+ isomorphic replacing to Zn2+ in natural crystal is responsible for high bulk modulus and thermal expansivity of marmatite. Temperature derivative of bulk modulus (∂K/∂T)P for marmatite is fitted to be -0.044(23) GPaK−1. The unambiguous B3–B1 phase boundaries for marmatite are determined to be Pupper(GPa) = 15.50−0.016T(°C) and Plower(GPa)=9.94–0.012T(°C) at 300–623 K.

Garnet Growth in the Early Stage of Trachybasalt-Eclogite Transformation

Garnet growth in the early stage of the trachybasalt-eclogite transformation was observed at 2.0 GPa and temperatures of 860°C, 940°C and 1020°C for annealing times of 0.66-13.6 h. The grain size was determined optically to be increased with increasing annealing time. The growth rate decreased with increasing grain size. The garnet growth law was G2.46 = 5.65×10-15texp [-27.40×103/RT], where G represents the average grain size after annealing time t, R is the gas constant and T is the absolute temperature.

Ultrasonic P Wave Velocity and Attenuation in Pyroxenite Under 3.0 GPa up to 1170°C

Ultrasonic P wave velocity (VP) and quality factor (QP value, on behalf of attenuation) in pyroxenite were presented as functions of pressures (0.3-3.0 GPa) and temperatures (20-1170°C). The experimental results show that VP and QP depend upon pressure and temperature. VP and QP in pyroxenite increase more rapidly at the pressure 0.3-1.4 GPa than those at 1.4-3.0 GPa. As the temperature rising from 20°C to about 1170°C at the pressure 3.0 GPa, an almost linear decrease up to 11% in VP was observed, and QP drops from 243 at room temperature to 68 at 1170°C with decreasing 72%. The experimental data indicate that the pressure and temperature induced fabric changes and frictional sliding and dislocation in pyroxenite play a key role in wave propagation in rocks.

Evidence for Grain Boundary Transport from Impedance Spectroscopy of Gabbro at 1–2 GPa up to 890°C

Impedance spectra of gabbro were measured at 1–2 GPa and up to 890°C with applied frequency of 12 to 105 Hz. At temperatures below 680°C, only one impedance arc corresponding to the grain interior conduction process occurs. Owing to the grain boundary transport with increasing temperature, the impurities occur at the grain boundaries, resulting in the second arc corresponding to the grain boundary conduction process over the frequency range of 12 to 10 3Hz above 680°C, and the resistivities of the grain interior and the grain boundary conduction mechanisms add in series. The total conductivity of this rock is dominated by the grain interior conductivity and the impurities have no significant effect on the total electrical conductivities.