Том 509, № 2 (2023)

The Aj-Bogd massif, located in the Trans-Altai Gobi within the Hercynides of the Central Asian fold belt, is composed of rocks from two main intrusion phases. The rocks of the early phase are represented by two-feldspar granites. while the late phase is characterized by alkali-feldspar granites. During the reconstruction of the thermal history of these granites zircon was chosen as a mineral-indicator of the temperature regime of their formation. Two main approaches to using this mineral as a geothermometer have been proposed: the zircon saturation index and the zirconium-hafnium geothermometer. Both approaches demonstrate a similar thermal picture of the formation of granites from Aj-Bogd massif. Alkaline feldspar granites of the late intrusion phase crystallized at temperatures of 810–850°C while two-feldspar granites of the early phase formed at temperatures of 700–770°C. According to thermobarogeochemical studies of melt inclusions in zircon of late-phase alkali-feldspar granites, a similar temperature range of their formation was defined (825–850°C). All obtained data of the formation temperatures of studied granites from Aj-Bogd massif indicate a significantly higher (by 100–120°C) temperature of formation of alkali-feldspar granites compared to earlier two-feldspar granites. The significantly higher crystallization temperature of late alkali feldspar granites allow us to suggest the appearance of an additional heat source that could be mantle derived melts. The evidence of such melt participation in the formation of Aj-Bogd massif are mafic dikes that separate granites of two intrusion phases. The contrast temperature regime of the calc-alkaline and alkaline intrusion phases close in time was determined for the first time in this work.

The paper presents the results of U–Th–Pb geochronological studies of zircons from metamorphic rocks of the Amur group of the Synchyga Block of the Jiamusi continental massif. It is shown that the garnet-biotite-sericite schists of the Amur group have a primary sedimentary origin. The lower depositional age of the protolith can be determined by the age of the youngest zircons from group with Neoproterozoic ages ~832 Ma. The upper age boundary of protolith, apparently, corresponds to the age of metamorphic zircons ~533 Ma. Thus, the schists of the Amur group of the Synchyga Block are of Neoproterozoic in age rather than Early Precambrian, as was accepted earlier.

Experimental studies aimed at the modeling of interaction processes of sulfur-bearing metasomatic agents with mantle silicates and assessing the effect of sulfur concentration on olivine sulfidation were carried out in the Fe,Ni-olivine – sulfur system using the high-pressure multi-anvil apparatus BARS (1050 and 1450°C, 6.3 GPa, 40–60 hours, sulfur concentrations (Xs) 0.1, 2 and 6 mol. %.). It has been established that as a result of the recrystallization of Fe,Ni-olivine in a sulfur melt, Fe and Ni are extracted from olivine into this melt, and formation of Fe,Ni-sulfides (or sulfide melts) and low-iron, low-nickel silicates takes place. The key indicator characteristics of the olivine sulfidation process are determined depending on the temperature and sulfur concentration, including characteristic phase assemblages, regularities in the evolution of the chemical compositions of mineral and melt phases, and structural features of olivine crystals. It has been experimentally established that reducing sulfur-bearing metasomatic agents, even in minimal concentrations and at relatively low temperatures, are capable of dissolving and transporting mantle silicates and sulfides, and can play an important role in sulfide ore formation in the mantle.

In order to identify the source of copper, for the first time in world practice, the features of the Cu-isotopic composition of Pt–Fe minerals are characterized using the example of the Nizhny Tagil massif, the world standard of Ural-type zoned complexes. The chemical and isotopic composition of Pt-Fe minerals were determined by electron probe microanalysis, chemical sample preparation with selective separation of copper from the solution of the studied sample, and subsequent high-precision determination of the δ⁶⁵Cu value using multiple-collector inductively coupled plasma mass-spectrometry. The majority of platinum group minerals (PGM) from bedrock deposits of the Nizhny Tagil massif, represented by chromitites of the Alexandrovsky and Krutoy logs, are formed by Pt–Fe minerals, among which high-temperature ferroan platinum (Pt₂Fe) with inclusions of Os–Ir alloys and laurite (RuS₂) dominates. The concentrations of copper in the studied samples of ferroan platinum vary in the range of 0.4–1.4 wt. % Cu. The δ⁶⁵Cu values for Cu-bearing PGM vary in the range from –0.37 to 0.26‰. Secondary low-temperature PGM assemblage is represented by solid solutions of tetraferroplatinum (PtFe) – tulameenite (PtFe_0.5Cu_0.5) series. The concentrations of copper in these PGM vary in the range of 6.8–11.3 wt. %; the values of δ⁶⁵Cu are characterized by lighter isotopic compositions of copper that range from –1.15 to –0.72‰. The lightening of the Cu-isotopic composition in secondary Cu-bearing PGM compared with that in ferroan platinum (δ⁶⁵Cu = –1.01 ± 0.17, n = 8 and δ⁶⁵Cu = 0.03 ± 0.23, n = 7, respectively) is consistent with the secondary nature of isotopic variations, due to the evolution of the composition of the ore-forming fluid during the low-temperature formation of the tetraferroplatinum (PtFe) – tulameenite (PtFe_0.5Cu_0.5) series.

Within the Lena gold province, in addition to the well-known large-volume gold deposits of the “Sukhoi Log” type, such as Sukhoi Log, Verninskoye, etc. there are a number of objects that differ significantly in stratigraphic, mineralogical-petrographic, isotopic, geochemical characteristics and the volume of reserves. The most famous of them is the Necklace deposit. The article shows the main characteristics of the Ozherel’e deposit, highlighting its similar and distinctive features with deposits of the “Sukhoi Log” type. The results obtained in the course of mineralogical-petrographic and isotope studies do not give grounds for attributing the Necklace deposit to the “Sukhoi Log” genetic type.

The composition and age of subalkaline dolerites localized in chromite-bearing ultramafic rocks of the Rai-Iz massif are investigated. Dolerites are traced along tectonic zones inside ultramafic rocks and are not observed beyond their boundaries, spatially tending to deposits and occurrences of chromites.The studied dolerites are characterized by high concentrations of alkalis, TiO₂, P₂O₅, enrichment with large-ion lithophilic elements and Th; the amount of REE varies from 103.3 to 164.2 ppm; (La/Sm)_n = 1.3–1.7. The age of subalkaline dolerites was determined by the method ⁴⁰Ar/³⁹Ar (402.7 ± 3.8 million years). At this time, a deep metamorphic processing of ultramafic rocks of most of the Rai-Iz massif occurred with the formation of high-chromium chrome mineralization and the isolation of a vein series of subalkaline dolerites in the discharge zones.

U–Pb (ID-TIMS) geochronological studies of garnet from aillikites of the Kandalaksha dyke swarm (Kola alkaline province) were carried out. The obtained estimate of the U–Pb age of the garnet (374 ± 3 MA) coincides with the interval (373–377 MA) of the main stage of alkaline magmatism of the Kola province (LIP). This allows us to conclude that the formation of rocks of the dike complex of the Kandalaksha Bay and rocks of the phoidolite series of alkaline-ultrabasic massifs of this province is synchronous.

The possibility of identifying sources of terrigenous rocks based on geochemical data using a linear programming model is considered on the example of metasedimentary rocks of the Sakukan Formation of the Kemen Group of the Udokan Complex, Aldan Shield. It is shown that tonalite-trondhjemite gneisses (56.9%) and gneiss-granites (17.3%) of the Olekma complex, Paleoproterozoic granitoids of the Kuanda complex (7.6%) of the Chara-Olekma geoblock, metavolcanic rocks of the Fedorov Formation (15.4%) and gneiss-granites developed within it (1.8%) of the West Aldan megablock could be the sources of metasandstones of the Sakukan Formation. The results obtained are in good agreement with the Nd isotopic and geochronological data available for the metasandstones of the Sakukan Formation, which indicates the wide possibilities of identifying and searching for sources of terrigenous deposits using a linear programming model.

Using the results of instrumental observations carried out in the surface atmosphere, the response of the microbaric background, variations of the Earth’s magnetic and electric fields to the paroxysmal activity of the Stromboli volcano (October 9, 2022, Italy) is analyzed. It is shown that the active stage of a volcanic eruption was accompanied by the generation of an acoustic signal and pronounced variations in the geomagnetic and atmospheric electric fields at considerable distances both during the period of volcano activity and during the arrival of an infrasonic wave at the observation point. It was also noted that the volcanic eruption caused a response in the ionosphere in the form of a change in the critical frequency of the F₂ layer.

The instrumental monitoring reveals an autowave nature of ice deformation behavior prior to ice shocks. A few minutes or the first tens of minutes before the shock, this process shows an increase in the amplitude of oscillations, often with a multi-fold reduction in their period. An autowave dynamics of ice deformations is due to self-organization of a structurally heterogeneous ice environment under critical conditions. The self-organization ability of the deformation process is confirmed by the results of ice deformation time series processing by the structural function curvature analysis method (SFCAM) and by the Lomb-Scargle periodogram method. The results of seismic monitoring of ice showed that autowave processes are characterized by constant frequency of 0.1 Hz. Taking into account the ice deformation and microseismic fluctuation features preceding the ice shocks, spectral analysis was performed on the data of deformation and seismicity monitoring at the Buguldeika geodynamic polygon before the Kudara earthquake. According to the results, 14 hours before the earthquake the seismogram recorded a gradual increase in auto-oscillation amplitudes in the frequency range from 0.01 to 0.1 Hz. The maximum amplitude increase is 19.5 against the background.

The height distribution of dust aerosol in the surface layer based on measurements made in the summer of 2020–2021 in arid conditions on the territory of the Republic of Kalmykia is considered. For profiles of aerosol concentration under conditions of weak winds, a characteristic gradual slope with an index close to the value of –0.5. When the wind strengthens, the profile slope takes values closer to the degrees known for the conditions of saltation. –0.7…–1.0 (and steeper). The observed regularities can be explained by the character of motion of dust particles rising from the hot surface together with the surrounding warmed air volume, which is different for fine (<1 μm) and coarse (>1 μm) particle fractions.

An analysis of the variability of the winter surface temperature anomaly in the North Atlantic in decades of negative and positive values of the North Atlantic Oscillation Index is presented. It was found that in the decade with negative values of the North Atlantic Oscillation Index, the slope waters of the Gulf Stream system and Labrador Current waters decrease the temperature of the Gulf Stream at the mixing zone on the Scotia Peninsula shelf and in the area of the quasistationary anticyclonic vortex to a maximum. In the decade with positive values of the North Atlantic Oscillation Index, the temperature of the slope waters is close to the climate. Taking into account the increased speed of the Gulf Stream in the years with positive values of the North Atlantic Oscillation Index, the spreading of the surface ocean temperature anomaly over the North Atlantic water area occurs for a shorter time than in the years with its negative values.

The content of ions of the main salt composition and 50 dissolved trace elements (Li, Rb, Cs, Be, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn, Cd, Tl, Pb, Al, Sc, Ga, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ti, Zr, Hf, Th, U, F, B, Si, Ge, P, V, As, Sb, Cr, Se, Mo, W) in the waters of the Kolyma River mouth section the spring–summer flood decline and on the summer–autumn period was determined. A close positive correlation was established between the dissolved trace elements concentrations in the waters of the Kolyma River and of the rivers in the White and Kara seas catchment areas. Differences in the concentrations of dissolved trace elements in the river waters of the Russian Arctic are generally proportional to the ratio of their mineralization values.

Morphological properties of biogenic particles in the near-surface aerosol composition were studied by scanning electron microscopy in Moscow. We analyze the results of complex experiment conducted in 2019–2022 at the IAP RAS to study the variability of aerosol physico-chemical properties in a large city under various weather conditions. The main types of bioaerosol particles were determined, as well as their shape and size. For the first time, brochosomes were detected in the surface aerosol in Moscow during field aerosol observations.