An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070292

Important problems of magma differentiation, formation of native metals, and ore-forming processes in the Earth’s crust are often related to 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 Earth’s crust and during volcanism under strongly reduced conditions ( fO_2 = 10–17–10–18). In the crystallization experiments, it was found out that the compositions of the crystals (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.

Using the original high-gas pressure unit (IHPV), experiments were conducted for the first time on the interaction of iron with methane at a temperature of 900°C and a pressure of 100 MPa. Complex methods (microprobe, Raman spectroscopy, chromatography, mass balance calculations) are used for a thorough analysis of fluid compositions and metallic phases formed in experiments. For the first time, experimental and theoretical quantitative data on the composition of the fluid and the composition of the fluid components dissolved in the metal were obtained. Unlike the previously studied Fe 3 C–H 2 system, in experiments, when Fe reacts with methane, there is an active interaction of carbon formed due to the pyrolysis of methane with iron up to the synthesis of Fe 3 C carbide. The experiments have shown that increasing pressure inhibits significantly hydrogen yield during methane conversion on metallic iron. Carbon saturation of iron with the formation of Fe 3 C is not complete within the entire volume of the metal during 24 h runs at 900°С. Employing molybdenum containers facilitates CH 4 decomposition.

We report new experimental data on the interaction of igneous melts with hydrogen at temperatures of 1100-1250 & DEG;C and hydrogen pressures of 1-100 MPa in strongly reducing conditions: fO2 = 10-12-10-14. The experiments were conducted using an original high-gas-pressure unit equipped with a unique device that provides long-term experiments at high temperatures and pressures of hydrogen. The experiments used natural samples of igneous rocks: the magnesian basalt of the Northern Breakthrough of the Tolbachik Volcano (Kam chatka) and the andesite of the Avacha Volcano (Kamchatka). On the basis of the experiments, the following features of the process of interaction of hydrogen with igneous melts have been established: (1) Despite the high reduction potential of the H2-igneous melt system, the reactions of hydrogen oxidation and complete reduction of oxides of metals of variable valence in the melt do not go to the end. The cessation of redox reactions in basaltic and andesitic melts is due to the formation of H2O in the melt, which buffers the reduction potential of hydrogen; (2) The initially homogeneous igneous melt becomes heterogeneous: The formed H2O dissolves in the melt and in the fluid phase (at first pure hydrogen), and melts of variable, more acidic composition and small metallic isolations of the liquation structure are formed; (3) The complex process of metal-silicate liquation in magmatic melts when they interact with hydrogen can be carried out at real magma temperatures in nature (& LE;1200 & DEG;C), significantly lower than the corresponding melting points of iron and its alloys with nickel and cobalt; (4) The structure and dimensions of the experimentally established metal isolations are consistent with natural data on the finds of small quantities of native metals, primarily iron and its alloys with nickel and cobalt, in igneous rocks of different compositions and genesis.

The paper presents the first experimental results on the chemical interdiffusion of major components (SiO 2, Al 2 O 3, Na 2 O, CaO, MgO, and FeO) and the CO_3^2- anion at interaction between basalt and kimberlite melts under moderate pressures. The research was carried out using a high gas pressure apparatus of original design at Ar or CO 2 pressures of 100 MPa and a temperature of 1300°C, with the use of the method of diffusion pairs. It is established that the rate of the oncoming chemical diffusion of all major components of melts (SiO 2, Al 2 O 3, Na 2 O, CaO, and MgO) and CO_3^2 - anion is almost identical at the interaction of model basalt and kimberlite carbonate-containing melts and is approximately one order of magnitude higher than the diffusion rate of these components at the interaction of melts in the more polymerized andesite–basalt model system. The latter is explained by the significantly lower viscosity of the boundary melt (Montana boundary), which is formed during the interaction of model basalt and kimberlite melts. The equal diffusion rates of CaO and the CO_3^2 - anion indicate that the CaCO 3 carbonate diffuses from kimberlite to basalt (both model and natural) melts by means of the diffusion of the end members. The pattern of the diffusion processes significantly changes when melt of natural magnesian basalt interacts with model kimberlite. Thereby calcite diffuses into magnesian basalt also by means of diffusion of the end members. The diffusion rates of all other components of the melts (SiO 2, MgO, and FeO) significantly increase. A weak exponential concentration dependence of all diffusing components is determined, with this dependence close to D ( i ) = constant.

In the experiments at 3.0–6.3 GPa and 1200–1350°C, it is found that under P–T parameters close to the conditions in ascending kimberlite magma, the carbonate melt enriched in potassium and volatiles is able to dissolve effectively the entire amount of xenogenic peridotite material that can potentially transport. As a result of this process, the melt is enriched in SiO2 (up to 30 wt %) and is transformed from carbonate to a kimberlite-like one. In the range of parameters studied, due to the high solubility of CO2 in the melt and the appearance of magnesite, an equilibrium fluid phase is not formed in the system. The interaction realized in the experiments may be the most important factor at the initial stage of magma evolution. The calculations performed in this work show that even after the dissolution of 30–50 wt % of lherzolite, the volatile-rich carbonate–silicate melt has a high degree of depolymerization (the ratio of the number of nonbridging oxygen atoms to the number of tetrahedrally coordinated ions (100NBO/T from 250 to 390) remains low-viscous (0.3–32.6 Pa s) and able to ascend to the surface rapidly. The obtained data indicate that immiscibility occurs between the potassium-rich carbonate–silicate and highly silicate melts only at 5.5 GPa and 1350°C and is likely to have a minor impact on the evolution of magma.

The paper presents the first experimental results on the chemical interdiffusion of major components (SiO2, Al2O3, Na2O, CaO, MgO, and FeO) and the $$\text{CO}_{3}^{2-}$$ anion at interaction between basalt and kimberlite melts under moderate pressures. The research was carried out using a high gas pressure apparatus of original design at Ar or CO2 pressures of 100 MPa and a temperature of 1300°C, with the use of the method of diffusion pairs. It is established that the rate of the oncoming chemical diffusion of all major components of melts (SiO2, Al2O3, Na2O, CaO, and MgO) and $${\text{CO}}_{3}^{{2 - }}$$ anion is almost identical at the interaction of model basalt and kimberlite carbonate-containing melts and is approximately one order of magnitude higher than the diffusion rate of these components at the interaction of melts in the more polymerized andesite–basalt model system. The latter is explained by the significantly lower viscosity of the boundary melt (Montana boundary), which is formed during the interaction of model basalt and kimberlite melts. The equal diffusion rates of CaO and the $${\text{CO}}_{3}^{{2 - }}$$ anion indicate that the CaCO3 carbonate diffuses from kimberlite to basalt (both model and natural) melts by means of the diffusion of the end members. The pattern of the diffusion processes significantly changes when melt of natural magnesian basalt interacts with model kimberlite. Thereby calcite diffuses into magnesian basalt also by means of diffusion of the end members. The diffusion rates of all other components of the melts (SiO2, MgO, and FeO) significantly increase. A weak exponential concentration dependence of all diffusing components is determined, with this dependence close to D(i) = constant.

New experimental data on interaction of synthetic iron carbide Fe3C with pure hydrogen were acquired in a unique in-house built IHPV, which allows long-lasting high-T runs under hydrogen pressure, in the temperature range T = 1273–1423 K and pressure P = 30–100 MPa. The run products consist of metal with a very low carbon content (0–2 ± 0.3 at %) and a fluid phase enriched in methane (CН4/(CH4 + H2) up to 0.37). Raman spectroscopy revealed peaks of hydrogen and disordered carbon in the metal product of one selected run, which indicates the possibility for both elements to enter the metal structure. Thermodynamic calculations at high P–T have shown that even in equilibrium with a methane-rich binary CН4–Н2 fluid, the metal should dissolve but a minor amount of C, while the H2 solubility can be rather high. Iron carbides can be stable only under conditions close to carbon saturation, when temperature does not exceed that of methane pyrolysis at a given P, and correspondingly, the hydrogen mole fraction in the fluid is very low.

The paper presents an original method developed by the authors for determining water content in highly polymerized rhyolite and rhyodacite glasses in melt inclusions. The method involves simultaneous determination of water content by two techniques: electron probe X-ray microanalysis (EPMA) and Raman spectroscopy, which are applied to mutual verify the results. The Raman spectroscopic technique was calibrated using a set of standard reference synthetic glasses of haplogranitic composition (SGS), containing 1.8 to 5.9 wt % water. The calibration was verified using a set of reference natural rhyolite obsidian samples (NRS) with water contents of 4.7 to 9.9 wt %. Two ratios were chosen as the calibrated parameters: (1) the area of the water and hydroxyl bands in the range of 2900–3800 cm–1 to the area of the silicate band vibration (Si–O and Al–O) in the range of 850–1200 cm–1 (Aw/As) and (2) the ratio of the intensities of the water band in the 3550–3560 cm–1 region and the 480 cm–1 band in the silicate vibration region (I3550/I480). As a result, the following calibration equations were acquired: $${{C}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}$$ = 0.8458 $$\frac{{{{A}_{w}}}}{{{{A}_{s}}}}$$ (σ) ± 0.17 wt % and $${{C}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}$$ = 11.494 $$\frac{{{{I}_{{3550}}}}}{{{{I}_{{480}}}}}$$ (σ) ± 0.21 wt %. Comparison of water concentrations in standard glasses determined by Raman spectroscopy using the Aw/As and I3550/I480 ratios and measured by X-ray microprobe analysis, showed a good consistency. Electron probe X-ray microanalysis was used to determine water content in glasses by recalculating the excess oxygen content. The method was tested on unheated glassy melt inclusions in minerals from dacitic and rhyolitic pumice from caldera eruption deposits of Okataina volcanic center, New Zealand; Kurile Lake, Kamchatka Peninsula; Vetrovoy Isthmus; and Lvinaya Past Bay of Iturup Island in the Kuriles Islands. The ability of using different Aw/As or I3550/I480 ratios makes it possible to minimize the effect of the overlaps of host-mineral bands in the low-frequency part of the Raman spectrum of the melt inclusions. We found out that the usage of the I3550/I480 ratio for melt inclusions in pyroxenes produces more reliable results than the use of the Aw/As ratio. At the same time, the Aw/As ratio is better to use for inclusions in quartz and plagioclase. Water content in the inclusions varies from 0.5 to 7.9 wt %. The proposed method can be routinely used for reliable measurements of water content in the glasses of melt inclusions no smaller than 10 μm, at water contents no lower than 0.5 wt %.

—New regularities of the viscosity of near-liquid felsic, medium, and mafic hydrous magmas have been established in a wide range of thermodynamic parameters and the Earth’s crust depths (1–30 km). The study was carried out using our new structural and chemical model of reliable predictions and by calculation of the viscosity of magmas of almost any composition. It is shown that these regularities are actually a quantitative physicochemical basis explaining the cause of the relative distribution of intrusive and effusive felsic and mafic rocks in the Earth’s crust. This confirms V.S. Sobolev’s idea of the relationship between the relative distribution of intrusive and effusive felsic, medium, and mafic rocks in the Earth’s crust and the laws of changes in the viscosity of hydrous magmas in a variable P–T field.

Paper provides a brief overview of the results of the established general regularities of the concentration, temperature, pressures and phase dependency of viscosity of the fluid-magmatic systems in connection with the anniversary of IEM RAS (50 years have passed since the establishment of this unique Institution). The study of the viscosity of such melts was carried out in the full range of compositions of natural magmas (acid-ultrabasic) in a wide range of fluid compositions (Ar, H2O, H2O + HCl, H2O + NaCl, H2O + HF, CO2, H2O + CO2, H2), and thermodynamic parameters of the earth’s crust and upper mantle (T = 800°–1950 °C, P = 100 MPa–12.0 GPa, Pfl= 10–500 MPa). The study of the viscosity of such melts was carried out in the IEM RAS in conjunction with the study of structural features of melts. The features of the unique equipment and techniques developed in the IEM RAS for such original studies are briefly considered. The possibilities and advantages of the developed structural-chemical model of reliable predictions and calculations of viscosity of fluid-magmatic systems in the full range of magma compositions from acidic to ultramafic at thermodynamic parameters of the earth’s crust and upper mantle are discussed. Some examples of successful application of the obtained experimental and theoretical results to natural processes are briefly considered.

Viscosity of magmatic melts is a key physical property that controls a variety of processes such as magma crystallization and differentiation, ascent and eruptions dynamics. Therefore, the physical-chemical model of forecasts and calculations of viscosity of magmatic melts is an actual problem of petrology and geochemistry. Here we present a unique model that for the first time allows reliable prediction of the viscosity of near-liquid magmatic melts in a full range of composition and conditions with high accuracy of the prediction (+/- 30% rel. for viscosity, and +/- 1.0% rel. for activation energy). The new model is an advanced version of the model proposed earlier. The basic equation used in this model to calculate the composition, temperature, pressure, and phase dependences of the viscosity of magmatic melts is a partly modified Arrhenian equation: eta(P)(T) = eta(o) exp(E-X(P)/RT) where eta(o) is the pre-exponential factor for the viscosity of melts at T -> infinity, (eta(o) = 10(-4.5) +/- 10(-0.1) Pa s); eta(P)(T) is the melt viscosity at given temperature, pressure and a volume content of crystals and bubbles in the melt (Pa s); T is the absolute temperature in K; E-X(P) is the activation energy of viscous flow (J/mol) depending on melt composition, including volatile components, and pressure; R = 8.3192 (J/mol K) is the gas constant. This model predicts the viscosity of near-liquid silicate and magmatic melts over nine orders of magnitude of viscosity (10(-1)-10(8) Pa s) and transforms about 3 decades of experimental study of silicate and magmatic melt viscosities.

New experimental data on interaction of basaltic melt with hydrogen at high temperature (1100-1250 degrees C) and hydrogen pressure (10-100 MPa) have been obtained to gain insight into the possible role of hydrogen in the processes occurring in basaltic melts in the earth's crust under reducing conditions (f(O-2) = 10(-13)-10(-15)). The experiments were carried out in a unique in house built internally heated pressure vessel (IHPV). This apparatus is equipped with an internal device, which allows long-term experiments under hydrogen pressure at high temperatures without losing hydrogen. Two types of experiments were carried out: 1 - kinetic experiments with isobaric quenching, 2 - crystallization experiments with subsequent isobaric quenching. It was found that, despite the high reducing potential of the H-2 - basaltic melt system, the hydrogen oxidation reactions and the Fe oxides reduction in the melt are not complete. Initially homogeneous basaltic melts become heterogeneous. H2O is formed in the fluid phase (initially consisted of pure hydrogen); H2O (0.34-0.9 wt%) also dissolves in the basaltic melts, and small metal blobs with an emulsion-like texture are formed in the melts at temperature significantly lower than the melting temperature of the metal phase (Fe). The texture and dimensions of the metal segregations resemble those reported from natural magmatic rocks. Some new features of the crystallization process of basaltic melt under very reducing conditions are also discussed. The assemblage of subliquidus minerals (olivine + clinopyroxene + plagioclase) formed in the crystallization experiment at T = 1100 degrees C, P(H-2) = 10 MPa with run duration 2 h, and their chemical compositions match closely those described in natural lavas (e.g. Kamchatka volcanoes). This result can be considered as an experimental confirmation of the participation of hydrogen in the magmatic process, which also corroborates with the composition of volcanic gases.

Many years ago, V.S. Sobolev suggested that the reason for the relative prevalence of intrusive and effusive rock masses in the earth’s crust lies in the regularities of viscosity of water-bearing magmas in a variable field of temperatures and pressures. Alas, in those years it was not possible to solve this problem on a quantitative physical-chemical basis, since experimental and theoretical studies of the viscosity of such melts at high pressures were just beginning. In the present work, new regularities of the viscosity of near-liquid water-bearing acidic magmas in a wide range of thermodynamic parameters and depths of the Earth’s crust (1–30 km) is established using the structural-chemical model of reliable and correct predictions and calculations of the viscosity of magmas of virtually any composition. It determined that these regularities really are a quantitative physical-chemical basis explaining the reason for the relative distribution of masses of intrusive and effusive rocks of acidic composition in the earth’s crust.

In continuation of our early works, an experimental study of the kinetics and interaction mechanisms in the hydrogen-basalt melt system at a hydrogen pressure of 100 MPa and temperature of 1250C carried out. It was found in kinetic experiments that, despite the high reduction potential of the H2-melt system, the hydrogen oxidation reactions and the complete reduction of Fe oxides in the melt do not go to the end. As a result, initially homogeneous basalt melt becomes heterogeneous: H2O is formed in the fluid phase; H2O is dissolved in the basalt melts, and a small metal separation of the liquation structure formed at a temperature significantly lower than the melting temperature of the metal phases (Fe, FeNiCo alloy). The structure and dimensions of the experimentally established metal separations agree well with the natural data on the findings of small amounts of the metal phase, primarily iron and its alloys with nickel and cobalt, reported from magmatic rocks of various compositions and origins.

В продолжение наших ранних работ проведено экспериментальное исследование кинетики и механизмов взаимодействия в системе водород−базальтовый расплав при давлении водорода 100 МПа и температуре 1250°С. В кинетических экспериментах установлено, что, несмотря на высокий восстановительный потенциал системы H 2 −расплав, реакции окисления водорода и полного восстановления оксидов Fe в расплаве не идут до конца. В результате первоначально однородный базальтовый расплав становится гетерогенным: во флюидной фазе образуется Н 2 О, а в базальтовом расплаве растворяется Н 2 О и образуются мелкие металлические обособления ликвационной структуры, сформировавшиеся при температуре, существенно меньшей температур плавления металлических фаз (Fe, сплав FeNiCo). Структура и размеры экспериментально установленных металлических обособлений хорошо согласуются с природными данными о находках небольших количеств металлической фазы, прежде всего железа и его сплавов с никелем и кобальтом, в магматических породах различного состава и генезиса.

The solubility of gold was measured in dry NaCl salt melt at 860 degrees C in closed systems with SiO2 (silica glass). The reactions do not occur in a closed system without oxidizer. Reaction of SiO2 with salt in the presence of an oxidizer (KClO4) results in the formation of water-soluble sodium silicates (a mixture of meta-, ortho-, and pyrosilicates). Gold mobilization by a salt melt is limited by the diffusion of Na in SiO2. In a closed system with the addition of a strong oxidizer (dry KClO4 salt), the solubility of gold increase with increasing amount of KClO4 and the saturation level is estimated to be similar to 3 wt % Au. For ampoule configurations used in our experiments, 5.5 g of gold dissolved per 1 g of KClO4. Only cheap, non-toxic reagents were used in our model experiments on gold dissolution in a salt melt, which did not require elevated pressures. The solubility of 30 g Au per 1 kg NaCl will eliminate geochemical problems associated with the compact leaching of gold ores using cyanide.