Vol 69, No 4 (2024)

Olivine grains from the Seymchan pallasite were studied using optical microscopy, Raman spectroscopy and scanning electron microscopy (SEM). Olivine is characterized by the presence of hollow straight channels <1 µm wide and inclusions of hollow negative crystals of prismatic habit 1–2 µm thick. The channels are oriented parallel to [001] of olivine and developed along [001] screw dislocations. The elongation axes of negative crystals are also oriented parallel to [001]. In the channels, hollow segments alternate with segments filled with metallic iron. Negative crystals are crystallographically faceted voids in olivine; the largest of them contain inclusions of metallic iron. The rectilinear configuration and crystallographic orientation of the channels correspond to the characteristics of [001] screw dislocations, which allows us to consider [001] dislocations as channel precursors. The data obtained demonstrate for the first time the evolution of [001] dislocations in olivine as a result of the reduction of divalent iron during the interaction of olivine with the host FeNi metal. A model is proposed for the transformation of dislocations with the formation of channels and hollow negative crystals in Seymchan olivine in accordance with one of the reactions:

2Fe_host+ (Mg_1−nFe_n)₂SiO₄ = 2n[FeO]_host + [nSiO₂ + 2nFe⁰ + (1 − n)Mg₂SiO₄ + 2nv²⁻ + 2nv²⁺ ]_ol,

2Fe_host+ (Mg_1−nFe_n)₂SiO₄ = 2n[FeO]_host + [nMgSiO₃ + nFe⁰ + (1 − n)Mg₂SiO₄ + nv²⁻ + nv²⁺ ]_ol.

According to the model, at T > 1000°C the reduction process is accompanied by an increase in the concentration of Fe⁰ and associated vacancies (v^2- and + v²⁺) in dislocation zones. Voids in channels and in negative crystals are products of the annihilation of anionic and cationic structural vacancies having opposite charges. Phase association formed in this solid-phase transformation of olivine corresponds to the either OSI (olivine → SiO₂ + 2Fe⁰) or OPI (olivine → pyroxene + Fe⁰) buffer equilibrium. The results can be used for reconstruction of the thermal and shock histories of different types of pallasites.

Important problems of magma differentiation, formation of native metals and ore formation processes in the earth's crust are increasingly associated with the active participation of hydrogen. In this paper, new experimental data on the crystallization of andesite melts at high temperatures (900–1250°C) and hydrogen pressures (10–100 MPa) have been obtained, which clarify the possible role of hydrogen in the processes occurring in andesite melts in the earthʼs crust and during volcanism under strongly reduced conditions (f(O₂) = 10^–17–10^–18). In crystallization experiments, it was found that the crystal compositions (pyroxenes and plagioclases) formed in experiments on crystallization of andesite melt under hydrogen pressure closely correspond to the crystal compositions of lava flows of Avacha volcano in Kamchatka. This result can be considered as an experimental confirmation of the participation of hydrogen in the volcanic process.

New data on roméite (CaNa)Sb₂O₆F solubility in the NaF–H₂O system of P–Q type in a wide range of sodium fluoride concentrations (from 0 to 25 wt. % NaF) have been obtained. The concentration of antimony, in equilibrium with roméite and fluorite, in the range of NaF concentrations from 1 to 8 mol kg⁻¹ H₂O (25 wt. % NaF), is in the interval of 0.02–0.2 mol kg⁻¹ H₂O. According to the data obtained, the concentration of antimony in the L₁ and L₂ phases in the fluid immiscibility region of the NaF–H₂O system at 800°C, 200 MPa and f(O₂) = 50 Pa, specified by the Cu₂O–CuO buffer, is 0.4 and 2.1 wt. % Sb, respectively. For the first time, during these experiments, the formation of fluorite skeletal forms and an intermetallic compound Pt₅Sb of a hexagonal crystal system with lattice parameters (LP): a = b = 4.56(4), c = 4.229(2) Å, α = β = 90°, γ = 120° was established. Pentaplatinum antimonide is formed on the surface of Pt ampoules at 800°C, P = 200 MPa and f(O₂) ≤ 10^−3.47 Pa (Cu–Cu₂O buffer) in experiments on the incongruent dissolution of romeite, which causes a sharp decrease (more than 1000 times) the concentration of antimony in solution.

The analysis of the layer-by-layer dynamics of snow chemical parameters in one of the observation points in the Pechora-Ilych biosphere reserve (Yaksha village) in the winter period 2019–2020 was carried out. It is shown that the chemical composition of atmospheric precipitation is more affected by long-range transport of substances. The peculiarities of atmospheric circulation and the regions from which air masses are transferred determine the saturation of precipitation with certain chemical components. The calculation of the trajectories of reverse transport of air masses allowed us to show the regions where air masses can form that come to the research area, carry substances and potentially form the chemical composition of precipitation. It is shown that the calculation of trajectories allows us to estimate the regions that are sources of pollutants entering the atmosphere. In general, this method of studying the chemical composition of snow is very informative and allows you to better understand the factors of its formation.