Vol 68, No 9 (2023)

This paper presents numerous new data on the geochemical composition of olivine, clinopyroxene, and leucite phenocrysts, as well as spinel inclusions in olivine and quench glass from lamproites of the Gaussberg Volcano (East Antarctica). Most of the olivine phenocrysts in the Gaussberg lamproites are high Mg varieties (Fo 89–91) with elevated Ni contents (up to 4900 ppm) and high Ni/Co ratios. According to the data of about 320 analyzes of clinopyroxenes, two groups of phenocrysts belonging to the diopside group have been established. Group I consists mainly of high-Mg varieties (Mg#>80), while group II clinopyroxenes are less magnesian (Mg# 52–80). The main difference between the clinopyroxenes of the two groups is manifested in the increased contents of Al2O3, FeO and reduced TiO2, Cr2O3, and NiO in the compositions of group II compared to group I, as well as different contents of trace elements, which may reflect their crystallization from different types of primary melts. According to the study of about 550 grains of leucite phenocrysts in Gaussberg lamproites, it was shown that they correspond to the ideal stoichiometry of leucite K[AlSi2O6] and are enriched in Na2O (0.05–0.35 wt %), but depleted in K2O (19.9–20.9 wt %) compared to with leucites from lamproites of other provinces. The BaO content reaches 0.3 wt %. %, SrO –0.04 wt. %. The iron content in most leucite phenocrysts varies within 0.7–1.2 wt % Fe2O3, with individual grains with low Fe2O3 contents (<0.5 wt %). In microlites of leucite in the groundmass and rims of phenocrysts, the iron content can reach 2.4 wt % Fe2O3, which may indicate more oxidized conditions at the time of lava eruption.
Based on the study of natural samples, existing experimental data and computational models, the order and conditions of crystallization of Gaussberg lamproites were restored. Crystallization proceeded in the following order: chrome spinel -> chrome spinel + olivine -> olivine + leucite (± chrome spinel) -> olivine + leucite + clinopyroxene (± chrome spinel). The near-liquidus association, represented by high-Mg olivine phenocrysts with inclusions of Cr-spinel, was formed in the temperature range from 1180 to 1250°C. Further crystallization of the melt with the formation of an association of olivine+leucite+clinopyroxene phenocrysts could occur at pressures below 2 GPa and temperatures of 1070–1180°C, corresponding to the presence of water in the magmatic system. Estimates of the redox conditions of crystallization of lamproites, obtained using different oxybarometers, vary in a wide range from QFM-0.5 to QFM+2.3.
Elevated Ni contents in liquidus olivines of Gaussberg indicate high nickel contents in the source. It is shown that the possible formation of ultraalkaline magmas in the region of Gaussberg Volcano occurred during the melting of the continental lithosphere, which was heterogeneous and included both the peridotite mantle and hydrous pyroxenite fragments.

The initial results of the experimental study of a hydrothermal system including lanthanides (Ln) and Fe oxides (magnetite and hematite) are presented. Ln concentrations in solutions and crystals were determined by ICP-MS and LM-ICP-MS, accordingly. The Ln distribution and cocrystallization coefficients obtained are interpreted as the maximal estimates of “true” values corresponding to structurally bound admixture. It is shown that Ln (except for Eu) are the compatible elements in hydrothermal magnetite; heavy Ln (beginning with Tb) are compatible in hematite. The pronounced tendency of the elevation of both coefficients with the Ln atomic number beginning from Gd-Tb was established. This is significant for using the ratio of light and heavy Ln as a typochemical guide for localization of the source of ore elements. The high-Ln-containing phases in associations with magnetite and hematite were obtained. These phases have oxychloride (without Fe) and oxyhydroxide (with Fe) composition and demonstrate the example of co-locating light and heavy Ln in the common space of hydrothermal system due to mutual crystallization of the phases selectively accumulating light and heavy lanthanides.

According to the results of GC-MS study of the composition and distribution of hydrocarbons (n-alkanes, isoprenoids, steranes, hopanes, polycyclic aromatic hydrocarbons (PAHs) and their alkyl homologues), the genesis, facies conditions of sedimentation, the degree of transformation of organic matter of bottom sediments and marching soils of the southwestern coast of the Barents Sea are characterized. The assessment of the toxicity levels of polyarenes on the biota inhabiting the tidal zones of the coast was carried out. Areas with increased anthropogenic load have been identified (littoral of the eastern Tana Fjord, the village of Kiberg, Abram Cape, the village of Mishukovo, the mouth of the Kulonga River, the apex part of the Yarnyshnaya Bay, Oscar Bay), indicating the unfavorable ecological state of the tidal zones of the Barents Sea coast.