Hongsen Xie

Elastic and electrical properties of serpentinite dehydration at high temperature and high pressure

P-wave velocities (VP) and electrical conductivities (σ) in serpentinite, collected from Ailaoshan orogenic belt, Yunnan province, China, were measured at 2.0–3.5 GPa and high temperature with the pulse transmission–reflection combined method and impedance spectroscopy by the means of a multi-anvil pressure apparatus, the YJ-3000 press. VP decreased and σ increased markedly at temperature higher than about 560°C. It is argued that the onset of the dehydration of serpentine is the main cause for VP decreasing and σ increasing. Combining the present experimental data with the results of previous experiments, we were led to speculate that the formation of the low-velocity layer between the subducted slab and mantle wedge is closely related to the dehydration of serpentine.

In situ control of oxygen fugacity at high temperature and high pressure

A new technique to control oxygen fugacity in situ under high-temperature and high-pressure conditions has been developed. In this method a special sample assembly constructed of a reference buffer, yttrium-stabilized zirconia (YSZ) disks, a sample, and an oxygen reservoir was used. Through a driving voltage e0 between the sample and the oxygen reservoir, oxygen was moved from the reservoir into the sample, or from the sample into the reservoir. The rate of oxygen transport was adjusted by regulating e0 and the thickness of the YSZ disk d0. The oxygen fugacity in the sample and its variation during the process were monitored in situ by measuring the voltage between the sample and reference buffer. In this way the oxygen fugacity in the sample was controlled independently of temperature, pressure, and composition of the sample. We made experiments at 773–994 K and 1.0–4.0 GPa in the systems Cu-O, C-O, and Ni-O, and the results show that the technique is successful.

A simple external resistance heating diamond anvil cell and its application for synchrotron radiation x-ray diffraction

A simple external heating assemblage allowing diamond anvil cell experiments at pressures up to 34 GPa and temperatures up to 653 K was constructed. This cell can be connected to the synchrotron radiation conveniently. The design and construction of this cell are fully described, as well as its applications for x-ray diffraction. Heating is carried out by using an external-heating system, which is made of NiCr resistance wire, and the temperature was measured by a NiCr-NiSi or PtRh-Pt thermocouple. We showed the performance of the new system by introducing the phase transition study of cinnabar (alpha-HgS) and thermal equation of state study of almandine at high pressure and temperature with this cell.

In situ control of oxygen fugacity at high temperature and high pressure: A Ni‐O system

To control in situ oxygen fugacity in a sample at high temperature and high pressure, the oxygen pump that is usually used at ambient pressure was introduced into a high-pressure system in the present work. Inside the sample assembly, an oxygen buffer was used as an oxygen reservoir. By means of our high-pressure oxygen pump, oxygen could be pumped from the sample into the oxygen reservoir or from the reservoir into the sample at high temperature and high pressure. Meanwhile, the oxygen fugacity in the sample could be monitored in situ by inserting an oxygen sensor inside the sample assembly. Our experiments using Ni-O system show that the oxygen fugacity in the sample at high temperature and high pressure can be conveniently controlled and monitored in situ independently of temperature and pressure.

Electrical conductivity measurement of serpentine at high temperature and pressure

The electrical conductivity of serpentine is measured at 1.0–3.0 GPa and 300–870°C. The effect of frequencies on electrical conductivity measurement is analyzed. The conduction mechanisms of serpentine before and after dehydration are discussed. Our experimental results show that the electrical conductivity of serpentine increases significantly after dehydration of serpentine, through which highly conductive layers (HCL) can be formed in the Earth’s interior.

Conductivity of NaCl solution at 0.4-5.0 GPa and 25-500℃

NaCI-H2O is the most fundamental ternary system in geology. Until now, the measurements of electrical conductivity of NaCl solutions are still little at high pressures (> O.5 GPa) We measured the conductivity of 0.01 m NaCl solution at 0.4–5.0 GPa and 25-500°C. The results are consistent with that of Quist and Marshall (1968) at 0.4 GPa. The conductivity of NaCl solution increases with increasing temperature. The results also show that the conductivity of NaCl solution changes little with increasing pressure below 1.5 GPa and changes rapidly with increasing pressure above 1.5 GPa. The rapid increase of the conductivity of NaCl solution may play an important role in many geological processes (such as the genesis of ore deposits under hydrothermal condition) and other fields.

Note: Measurement method for sound velocity of melts in large volume press and its application to liquid sodium up to 2.0 GPa

Based on large volume press and conventional pulse-echo ultrasonic technique, we have overcome the difficulty in determining the length of liquid specimen under high pressure, and the sound velocity in liquid Na has been measured up to 2 GPa. The P-V data deduced by our sound velocity results through equation of state is in an excellent agreement with previous data directly determined by piezometer method. This new experimental technique is convenient and ready for use, being expected to advance investigation on thermodynamic properties of liquid metals and other melts under high pressure.

A method for experimental determination of compressional velocities in rocks and minerals at high pressure and high temperature

A new combined transmission–reflection 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 the original sample assembly with a pyrophyllite cube. At temperature up to 900°C and pressure up to 4 GPa, single-crystal quartz and serpentine were used as the samples tested. By the use of this new technique, more precise and reasonable data on elastic properties of rocks and minerals at elevated temperature and pressure can be achieved.

A broadband spectroscopy method for ultrasonic wave velocity measurement under high pressure

A broadband spectroscopy method is proposed to measure the ultrasonic wave phase velocity of Z-cut quartz under high pressure up to 4.7 GPa. The sample is in a hydrostatic circumstance under high pressure, and we can get longitudinal wave and shear wave signals simultaneously in our work. By fast Fourier transform of received signals, the spectrum and phase of the received signals could be obtained. After unwrapping the phase of the received signals, the travel time of ultrasonic wave in the sample could be obtained, and the ultrasonic wave phase velocity could also be resolved after data processing. The elastic constant of measurement under high pressure is also compared with previous studies. This broadband spectroscopy method is a valid method to get ultrasonic wave travel parameters, and it could be applied for elasticity study of materials under high pressure.

Experimental study of spinel-garnet phase transition in upper mantle and its significance

Experimental study of spinel-garnet phase transition was carried out using natural mineral and rock specimens from xenolith of mantle rocks in Cenozoic basalt as starting materials. From the result it was found that the condition of spinel Iherzolite-garnet Ihenolite phase transition (T = 1 100°C andP = 1.8–2.0 GPa) is consistent with theP-T equilibrium condition of the five-phase assemblage spinel/garnet Iherzolite in eastern China, suggesting that there may exist a spinel-garnet Iherzolite phase transition zone with the thickness of a few km to several ten km at the depth of 55–70 km in the continental upper mantle of eastern China. The depth of phase transition from spinel pyroxenite to garnet pyroxenite is found to be less than 55 km. Experiment results also show that water promotes metasomatism on one hand but suppresses phase transition on the other. Zoning of mineral composition was also discussed.