The phase relationships and distributions of rare earth elements, Sc, Y and Li between aluminofluoride and aluminosilicate melts in the model granite system Si-Al-Na-K-Li-F-O-H at 700 °C, 1 and 2 kbar with a water content from 3 to 50 wt. %. were experimentally studied. Based on the obtained and available experimental data on phase relationships in a granite system saturated with water, fluorine and containing rare elements, a comparison was made with the parageneses of rare-metal cryolite-containing granites from three deposits in Eastern Siberia are Zashikhinsky, Katuginsky and Ulug-Tanzeksky. It has been shown that the processes of liquid immiscibility between granite and salt aluminofluoride melts, which manifest themselves at high contents of fluorine and lithium in the system, contribute to the accumulation of rare elements in salt cryolite-like melts. At a temperature of 700 °C and a pressure of 1 and 2 kbar, crystallization of the aluminofluoride melt occurs in the granite system, from which cryolite is formed. It is in association with cryolite and lithium micas that the considered natural objects contain minerals of rare and rare earth elements containing fluorine, such as pyrochlore, gagarinite, etc. As a result of a comparison of experimental and natural data, the hypothesis about the important role of liquid immiscibility in the formation of cryolite is confirmed. It is assumed that cryolite can serve as a reference mineral for rare metal-rare earth mineralization in granites with high lithium and fluorine content.

An Erratum to this paper has been published: https://doi.org/10.1134/S0016702924190030

Phase relations and the distributions of rare earth elements (REE), Sc, Y, and Li between aluminofluoride and aluminosilicate melts in the model granite system Si–Al–Na–K–Li–F–O–H were experimentally studied at 700°C, 1 and 2 kbar, and water contents of 3 to 50 wt

The results of study of the intrinsic oxygen fugacity (fO2) of various types of tektites from the European and Australasian scattering fields (moldavites, indochinites, philippinites, and australites) performed by the electrochemical method using an apparatus with two solid electrolytes are reported. The fO2 values of tektite glasses in the temperature range of 800–1050°C studied are between the fO2 of the iron–wustite and wustite–magnetite buffer equilibria. They demonstrate a significantly more reduced character of tektites in comparison with magmatic melts (volcanic glasses) of the crustal and mantle origin. Among the Australasian tektites, the widest fO2 variations are typical of indochinites including more diverse tektite species (Muong-Nong type and splat-forms), which are much closer to the hypothetical parental impact crater than philippinites and australites. At temperatures above that of complete melting (≥1000°C), fO2 for all tektite glasses is significantly higher than the fO2 values that correspond to the equilibrium of the metallic phase of iron with the silicate melt. It is assumed that the presence of microinclusions of metallic iron together with wustite, as well as magnetite and hematite in some tektites, is associated with nonequilibrium processes at different stages of tektite formation.

Deep seismic studies have revealed that low-velocity zones mainly occurred in the continental lithosphere at the depth of 100–150 km. Their origin has not been clearly explained yet. The article demonstrates the possible scale of Vp changes in crystalline rocks of different composition. The conclusions were made on the basis of the comprehensive analysis of the experimental data obtained by the authors. The compressional wave velocities in the temperature range from 20 to 800 °C, both in dry conditions (at pressure of 600 MPa) and in the presence of aqueous fluid (at pressure of 300 MPa) were measured. It is shown that the most significant decrease of velocities (by ~ 3 km/s) in the temperature range of 400–700 °C, corresponding to the deep waveguides of the lithospheric mantle, occurs under water pressure in ultramafic rocks enriched by olivine (dunites). Such decrease is due to rock structure changes caused by olivine serpentinization reactions. It is assumed that serpentinization and/or formation of similar hydrous minerals, which are stable in a wide range of PT-conditions in olivine-rich mantle rocks due to the influence of deep fluids, may cause low-velocities zones in the upper mantle at depths of about 100 km.

— A set of experiments was carried out in the system NaAlSi 3 O 8 –FeO–NiO–CoO–SiC–NaH 2 PO 4 at 1550°C, 4 GPa, and oxygen fugacity ( f O 2 ) 0.5–2.9 log. units below the iron–wüstite (IW) buffer to estimate how C–O–H components can affect Ni, Co, and P partition between silicate melt and a liquid metallic phase at redox conditions under which the metallic phase is segregated into melting products of the early reduced mantles of the Earth and other planetary bodies. It has been established that the Ni, Co, and P partition coefficients D (М) met/sil between silicate melts saturated with carbon and containing dissolved C–O–H volatiles (mainly in the form of OH groups, H 2 and CH 4 ) at relatively oxidized conditions ( f O 2 > IW – 1.5) correspond to D (М) met/sil values expected of metal–silicate melt equilibrium in volatile-free systems at analogous P , T , f O2 , and nbo/t parameters. Under more reduced conditions ( f O 2 ≤ IW – 2), the presence of C–O–H volatiles leads to a decrease in D (М) met/sil for Ni and P compared to that in “dry” melts. This difference increases with decreasing f O 2 and reaches ~0.5 and more than one order of magnitude for Ni and P, respectively, at f O 2 = IW – 2.9. The effect of volatiles on D (Co) met/sil is much weaker, and hence, a decrease in f O 2 leads to that D (Ni) met/sil and D (Co) met/sil converge. The Raman spectra of the experimental glasses and their SIMS analyses for hydrogen show that water content (OH + H 2 O) in the melts decreases with decreasing f O 2 , whereas the contents of CH 4 and complexes with C–H bonds significantly increases. The likely reasons for the decrease in D (М) met/sil under strongly reduced conditions may be changes in the structure of the silicate melts and the origin of complex compounds of siderophile elements with volatiles in these melts.

Longitudinal wave velocities ( V P ) in rocks were measured experimentally in dunite (olivinite) and serpentinite at a water pressure of 300 MPa and temperatures of 20–850°C. It is shown that the strong decrease in V P in dunite (by ~3 km/s) observed within the range of 400–800°C results from penetration of water into rock along microfractures and from the formation of hydrous minerals (mostly serpentine) along the boundaries of mineral grains as a result of water–olivine interaction. It is suggested that serpentinization or the formation of similar hydrous minerals in olivine-rich mantle rocks under the influence of deep fluids may result in the formation of zones of low-velocity elastic waves in the upper mantle at great depths (~100 km).

The contents and speciation of nitrogen, carbon, and hydrogen were determined in basalt–basaltic andesite melts in equilibrium with liquid Fe alloys at 1.5 Gpa, 1400°C, and oxygen fugacity (fO2) 1.4–1.9 log units below that of the Fe–FeO buffer (ΔlogfO2(IW) =–1.4 …–1.9). Experiments were carried out on a piston- cylinder type apparatus using welded Pt capsules in the presence of excess С (graphite). Starting mixture consisted of natural ferrobasaltic glass and silicon nitride (Si3N4) as nitrogen source in the system. Experimental quench products representing glasses with spherical inclusions of iron alloy were analyzed using electron microprobe, Raman, and IR spectroscopy. With increase of Si3N4 in the starting mixture and, respectively, decrease of fO2, silicate melt forming during experiments became depleted in FeO and enriched in SiO2. It was established that the nitrogen content in the glasses increases from 0.13 to 0.44 wt % with decrease of ΔlogfO2(IW) from–1.4 to–1.9, whereas C content in the first approximation remains constant within 1.18–1.13 wt %, while the total water content (ОН– + Н2О) determined by IR spectroscopy decreases from 4.91 to 1.20 wt %. The N (0.13–0.48 wt %) and C (0.75–2.26 wt %) contents determined in the Fe alloy show no clear correlation with fO2. The IR and Raman spectroscopic study of the glasses indicates the formation of molecules and complexes with bonds N–H (NH3, NH2 −, NH2 +, NH4 +), Н–О (Н2О, OH–), С–Н (СН4) as well as N2 and Н2 molecules in silicate melts. IR spectra also reveal the presence of complexes with С=О, С–N bonds and СО2 molecules. Obtained data are compared with results of previous studies on the solubility and speciation of N, С, and Н in the model FeO–Na2O–SiO2–Al2O3 melts in equilibrium with liquid iron alloys at 1.5 GPa (1400°C) and 4 GPa (1550°C) (Kadik et al., 2011, 2015).

The possible origin of the Moon’s metallic core at the precipitation of iron–sulfide phases during the partial melting of ultramafic material under various redox conditions was experimentally modeled by partially melting the model system olivine (85 wt %) + ferrobasalt (10 wt %) + metallic phase Fe 95 S 5 (wt %) in a high-temperature centrifuge at 1430–1450°C. The oxygen fugacity f O 2 was determined from the composition of the quenched experimental silicate melts (glasses). A decrease in f O 2 is proved to be favorable for the segregation of iron–sulfide melt from the silicate matrix. The metallic phase is most effectively segregated in the form of melt droplets, and these droplets are accumulated in the lower portions of the samples under strongly reduced conditions, at f O 2 ∼ 4.5–5.5 orders of magnitude lower than the iron–wüstite buffer.

An empirical computer model was developed to describe granite magma degassing and the partitioning behavior of Cl between melts and aqueous chloride fluids that formed during eutectic isobaric crystallization of magmas at pressures from 4 to 0.4 kbar and a temperature of 800 ± 25°C. This model is the extensions of the earlier model describing the decompression degassing of granite melts (Lukanin, 2015). The numerical modeling was performed for both closed-system conditions, when fluid remains in the system, and open-system conditions, when fluid is removed from the system. The results of numerical modeling revealed the main factors controlling the behavior of Cl during crystallization-induced degassing, such as the initial contents of Cl and H2O of the melts, pressure, and the degree of system openness. At high pressures (>1.6 kbar), isobaric crystallization is accompanied by a decrease in the concentrations of Cl in the melt (C Cl m ) and fluid phase (C Cl fl ). This tendency becomes even more pronounced in an open-system with increasing pressure and initial Cl content. A decrease in pressure in the range of 1.62–0.85 kbar results in a drastic change in the Cl behavior: the trend of C Cl fl and C Cl fl decrease dominating during crystallization at high pressures changes to the opposite. At low pressures (<0.85 kbar), the enrichment of the residual melts and released fluids in Cl leads at a certain stage of crystallization to the formation of a heterogeneous fluid consisting of two immiscible aqueous chloride phases, a waterdominated aqueous phase and a chloride-rich liquid (brine).

Based on available experimental data, a computer model was developed for the description of chlorine distribution between a magmatic melt of metaluminous granite composition and an aqueous chloride fluid phase formed during the decompression degassing of magma at pressures ranging from 5 to 0.5–0.3 kbar and temperatures of 800 ± 25°C. The model accounts for the dependence of fluid/melt Cl partition coefficient on pressure and Cl content of the melt. It allows the calculation of Cl and H 2 O redistribution between melt and fluid during the decompression degassing of magmas under both closed-system conditions, when fluid remains in the system, and open-system conditions, when the released fluid phase is completely of partly removed from the system. The results of numerical modeling revealed the influence of the initial Cl and H 2 O contents in melt and the degree of system openness on variations in the concentrations of these volatiles in aqueous fluid and melt during magma ascent toward the surface under near-isothermal conditions. The highest Cl concentrations of the fluid ( C Cl fl ) are attained at the early stages of decompression degassing at high pressures. With decreasing pressure, C Cl fl decreases at a rate that increases at increasing degree of system openness. During open-system degassing, the Cl content of melt ( C Cl m ) also decreases. In contrast, under closed-system conditions, C Cl m decreases initially with decreasing pressure, reaches a minimum, and then increases. If decompression degassing begins at P ≤ 1.0-1.25 kbar, C Cl m changes only slightly irrespective of the initial Cl content of the melt and the degree of system openness.

The solubility of all possible Zn and Pb species in aqueous chloride fluids was evaluated by means of thermodynamic simulations in systems ZnO(PbO)-aqueous solution of NaCl (KCl, NaCl + HCl) within broad ranges of temperature (600–900°C), pressure (0.7–5 kbar), and chloride concentrations, under parameters corresponding to the crystallization and degassing of granitoid magmas in the Earth’s crust. Our simulation results demonstrate that the addition of Cl to the fluid phase in the form of Na(K)Cl and HCl significantly increases the concentrations of Cl-bearing Zn and Pb complexes and the total concentration of the metals in the solutions in equilibrium with the solid oxides. In Zn-bearing fluids, the Zn(OH) 2 0 , ZnOH+, and Zn(OH) 3 − —hydroxyl complexes and the ZnCl 2 0 , and ZnCl+ chlorocomplexes, which are predominant at low Cl concentrations (CCl < 0.05–0.1 m) give way to ZnCl 4 2− with increasing CCl, which becomes the predominant Zn species of the fluid at CCl > 0.1–0.5 m throughout the whole temperature range in question and pressures higher than 1 kbar. For Pb-bearing fluids, the T-P-X region dominated by the Pb(OH) 2 0 , and Pb(OH) 3 − hydroxyl complexes is remarkably wider than the analogous region for Zn, particularly at elevated temperatures (≥700°C) in alkaline solutions. An increase in CCl is associated with an increase in the concentration and changes in the speciation of Pb chlorocomplexes: PbCl 2 0 → PbCl 3 − → PbCl 4 2− . The concentrations of Zn and Pb chlorocomplexes increase with increasing pressure, decreasing temperature, and decrease pH with the addition of HCl to the system. It is demonstrated that the solubility of ZnO at any given T-P-X in alkaline solutions with low chloride concentrations are lower than the solubility of PbO. The Zn concentration increases more significantly than with the Pb concentration with increasing CCl and decreasing pH, so that the Zn concentration in acidic solutions is higher than the Pb concentration over broad ranges of temperature, pressure, and Cl concentration. Chloride complexes of Zn (ZnCl 2 0 , and ZnCl 4 2− ) and Pb (PbCl 2 0 , and PbCl 3 − are proved to be predominant within broad T-P-X-pH ranges corresponding to the parameters under which magmatic fluid are generated. Our simulation results confirm the hypothesis that chlorocomplexes play a leading role in Zn and Pb distribution between aqueous chloride fluids and granitic melts. These simulation results are consistent with experimental data on the Zn and Pb distribution coefficients (D(Zn)f/m and D(Pb)f/m, respectively) between aqueous chloride fluids and granitic melts that demonstrated that (1) D(Zn)f/m and D(Pb)f/m increase with increasing Na and K chloride concentrations in the aqueous fluid, (2) both D(Zn)f/m and D(Pb)f/m drastically increase when HCl is added to the fluid, and (3) (D(Zn)f/m is higher than D(Pb)f/m at any given T-P-X parameters. The experimentally established decrease in D(Zn)f/m and D(Pb)f/m with increasing pressure (at unchanging temperature and Cl concentration) is likely explained by an increase in the alkalinity of the aqueous chloride fluid in equilibrium with granite melt and, correspondingly, a decrease in the Zn and Pb solubility in this fluid.

Для определения растворимости и возможных форм цинка и свинца в водно-хлоридных флюидах проведено термодинамическое моделирование в системах ZnO(PbO)–водный раствор NaCl (KCl, NaCl + HCl) в широком интервале Т (600–900°С), Р (0.7–5 кбар) и концентраций хлоридов при параметрах, соответствующих кристаллизации и дегазации гранитоидных магм в земной коре. Результаты моделирования показывают, что добавление Cl к водной флюидной фазе в виде Na(K)Cl и HCl приводит к существенному увеличению доли хлорсодержащих комплексов Zn и Pb, а также общей концентрации металлов в растворах, находящихся в равновесии с их твердыми оксидами. В цинксодержащих флюидах гидроксокомплексы Zn(OH) , ZnOH+, Zn(OH) и хлоркомплексы ZnCl , ZnCl+, преобладающие при низких концентрациях хлора (CCl 0.1–0.5 m во всем исследуемом интервале температур и давлениях выше 1 кбар. В свинецсодержащих флюидах Т–Р–Х область доминирования гидроксокомплексов свинца Pb(OH) , Pb(OH) значительно шире по сравнению с цинком, особенно при повышенных температурах (700°C) в щелочной среде. Увеличение CCl сопровождается повышением концентраций и сменой вида доминирующих хлоркомплексов свинца PbCl PbCl PbCl . Концентрация хлоркомплексов Zn и Pb возрастает с повышением давления, понижением температуры, а также с уменьшением рН при добавлении в систему HCl. Показано, что при данных Т–Р–Х параметрах растворимость ZnO в щелочных растворах с низкой концентрацией хлоридов ниже, чем PbO. C повышением CCl и понижением рН концентрация Zn по сравнению с Pb увеличивается более значительно и в кислых растворах в широком диапазоне Т–Р и CCl параметров она превышает концентрацию Pb. Сделан вывод о преобладании хлоридных комплексов цинка (ZnCl , ZnCl ) и свинца (PbCl , PbCl ) в широкой области Т–Р–Х и рН, соответствующих условиям формирования магматических флюидов. Результаты моделирования подтверждают предположение о ведущей роли хлоркомплексов при распределении Zn и Pb между водно-хлоридными флюидами и расплавами гранитоидного состава. Они согласуются с экспериментальными данными по коэффициентам распределения Zn и Pb (D(Zn)f/m, D(Pb)f/m ) между водно-хлоридными флюидами и гранитными расплавами, которые демонстрируют: 1) увеличение D(Zn)f/m и D(Pb)f/m c повышением в водном флюиде концентрации хлоридов Na и К; 2) резкое увеличение D(Zn)f/m и D(Pb)f/m при добавлении к флюидной фазе HCl; 3) более высокие значения D(Zn)f/m по сравнению D(Pb)f/m при данных Т–Р–Х условиях. Предполагается, что экспериментально установленный эффект уменьшения D(Zn)f/m и D(Pb)f/m с давлением (Т и CCl = const) обусловлен увеличением щелочности водно-хлоридного флюида, равновесного с гранитным расплавом, и соответственно уменьшением в нем растворимости цинка и свинца.