Nadezda Chertkova

Primary inclusions in natural diamonds provide unique information about deep-seated mantle minerals and fluids. Findings of the VI and VII modifications of H2O-ice as inclusions in diamonds show the presence of aqueous fluids at different depths in the diamond-bearing mantle (Kagi et al., 2000; Tschauner et al., 2018). In this work, we apply various experimental techniques for the investigation of mineral associations and H2O phases, captured as inclusions in diamonds, in the pressure range from 4 to 8 GPa and at temperatures from 500 °C to 1250 °C. In situ observations using diamond anvil cell (DAC) technique revealed crystallization of ice VII in association with ilmenite and olivine minerals upon cooling from 890 °C at 4 GPa, in agreement with the data, obtained from natural samples by Tschauner et al. (2018). Heating of this assemblage to 1200 °C at 6 GPa results in the formation of another mineral association, which includes ilmenite, pyroxene and clinohumite. Obtained experimental results can be used to reconstruct the pressure and temperature conditions of mineral and fluid inclusions capturing upon diamond growth and transfer in the lithosphere.  This work was supported by grant No. 20-77-00079 from the Russian Science Foundation.

Rapid development of in situ experimental techniques provides researchers with new opportunities to model geological processes, which take place deep in the Earth’s interior. Raman spectroscopy is considered a powerful analytical tool for investigation of the samples subjected to high pressures in a diamond anvil cell, since in such experiments phase assemblages can be determined in real time using measured Raman spectra.In this study, we describe experimental methods for in situ observation and spectroscopic analysis of fluids and minerals, which constitute environment for diamond growth, at the upper mantle pressure conditions. Experiments were conducted in the externally heated, “piston-cylinder” type diamond anvil cell at pressures exceeding 6 GPa and temperatures up to 600 degree C. Phase relationships and fluid speciation were monitored during experiments to reconstruct the environment and mechanism of inclusions formation. Compared to other analytical tools, commonly used in combination with diamond anvil cell apparatus, Raman spectroscopy offers several advantages, such as short sample preparation time, non-destructive characterization of the phases observed in the sample chamber and relatively short measurement time.This work was supported by grant No. 20-77-00079 from the Russian Science Foundation.

Using an external heating system, specifically designed for the lever-type diamond anvil cell, we investigated for the first time the phase relationships in the C₂H₂O₄ system at temperatures exceeding 850°C and pressures up to 6.5 GPa. In situ Raman spectroscopy was applied for the characterization of structural features of observed high-temperature phases, which transformed to the black carbon-rich material upon quenching and decompression. Results of this work give insights on the pressure-induced polymerization process of organic compounds at high temperatures.

This work is devoted to the study of one of the largest caldera eruptions of the Kurile-Kamchatka island-arc system that occurred on the island of Iturup. The object of investigation of this work are phenocrysts of quartz and plagioclase from dacite pumice of the Isthmus of the Isthmus, which is located on the island of Iturup. The purpose of this work is to determine the water content in the melts that participated in the caldera eruption of the Vetrovoy Isthmus and the patterns of their changes during the crystallization of magma. In the course of the work, the following were carried out: 1) adaptation and calibration of the Raman spectroscopy method for determining water in rhyolite melt's inclusions glasses in quartz and plagioclase from pumice stone; 2) determination of composition and estimation of water content in melt inclusions in quartz and plagioclase according to x-ray spectral analysis; 3) establishment of the regularities of the change in the water content during the evolution of the magmatic melt; 4) evaluation of fluid pressure by comparison with experimental data

Polycrystalline, cubic 13C diamond was synthesized from amorphous carbon in the Kawai-type multianvil apparatus at 21 GPa and at a temperature greater than 2350ºC. The polycrystalline diamond was homogeneous with a small grain size (10–20 μm) and a sharp Raman peak, and thereby was suitable as a pressure sensor for the experiments in a hydrothermal diamond anvil cell. Pressure- and temperature-dependence of the Raman shift of the synthesized 13C diamond was investigated in situ at simultaneous high pressures and high temperatures in the hydrothermal diamond anvil cell, using the ruby fluorescence line, quartz Raman shift and H2O phase transitions as pressure references. It was observed that the frequency shift with pressure is independent of temperature and vice versa up to 500ºC and 4.2 GPa. The present study indicates that the 13C diamond Raman shift can be used for pressure determination with an accuracy better than ±0.3 GPa under the conditions examined.