Xie Hongsen

Impedance spectroscopy analysis on electrical properties of serpentine at high pressure and high temperature

The electrical conductivity of serpentine is measured and the microscopic conductance mechanisms are investigated with impedance spectroscopy at 2.5–4.0 GPa and 220–780°C. The results show that the electrical conductivity is strongly dependent on the frequencies used, and that only arc I, which reflects grain interior conductance, occurs and dominates the whole conductance processes over 12-105Hz at high pressure before dehydration. The arc II, which indicates the grain boundary process, begins to occur at the initial stage of dehydration. After dehydration, due to the presence of highly conductive networks of free water, the electrical conductivity is not dependent on frequencies any longer and the total electrical conductivity is dominated by process of ionic conductance of free water in interconnected networks. Dehydration of serpentine enhances pronouncedly the total electrical conductivity, through which highly conductive layers (HCL) may be formed in the earth’s interior.

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.

Experimental study to confirm the existence of hydrocarbon under high pressure and temperature of deep lithosphere

Pyrolysis of lignite was conducted at high temperatures from 400 to 700 °C and high pressures of 1 and 3 GPa in a closed system in order to investigate pressure and temperature effects on organic matter maturation. The data indicated that the total yield of liquid hydrocarbons decreased with increasing pressure and the maximum of production was obtained at a higher temperature. The alkanes show more mature characteristics with increasing temperature at a given pressure, conversely, high pressure significantly hinders the thermal evolution of geological organic matter. The experimental results also demonstrated that the relative abundance of high molecular weight hydrocarbons may exist under the conditions of the lower lithosphere, which not only breaks through the traditional concept that alkanes mainly present at stage of “oil window”, but also enhances the possibility to find the oil in the high temperature and pressure areas.

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.

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.

Evolutive characteristics of aromatics under high pressure and temperature of deep lithosphere

Pyrolysis of lignite in closed systems was conducted at temperatures from 400 to 700°C and pressure from 1 to 3 GPa in order to investigate the evolutive characteristics of aromatics and the effects of pressure and temperature on the maturation of organic matter under the extreme conditions. The total yield of liquid hydrocarbons decreased with increasing pressure and the aromatics shows more mature with increasing temperature at a given pressure. The data indicate that high pressure significantly suppresses the thermal evolution of geological orgnaic matter especially at lower temperature, but favors the cyclization, polymerization and aromatization of pyrolysate. The pressure effect on maturation of organic matter is nonlinear. Therefore, it can be inferred that sediment organic-matters in the subducted slab could be retained in the deep lithosphere, and the results are also significant for understanding the accumulation and preservation of petroleum in deep reservoirs.

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.

In-Situ Resistivity Measurement of ZnS in Diamond Anvil Cell under High Pressure

An effective method is developed to fabricate metallic microcircuits in diamond anvil cell (DAC) for resistivity measurement under high pressure. The resistivity of nanocrystal ZnS is measured under high pressure up to 36.4 GPa by using designed DAC. The reversibility and hysteresis of the phase transition are observed. The experimental data is confirmed by an electric current field analysis accurately. The method used here can also be used under both ultrahigh pressure and high temperature conditions.

Elastic Behaviors of Bulk Metallic Glass Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 Investigated by Using Ultrasonic Technique

The acoustic velocity, attenuation, and their pressure dependence of a bulk metallic glass Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 have been measured under pressures up to 0.5 GPa at room temperature using the pulse echo overlap method. The sample was prepared from melt by quenching into liquid nitrogen. Bulk modulus, Youngs modulus, shear modulus, and Poissons ratio were derived, other elastic properties and vibrational anharmonicity were also discussed.

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.