Vol 517, No 2 (2024)

The results of U–Pb (ID-TIMS) geochronological studies of perovskite from kimberlite rocks of the Manchary pipe (Khompu-Mai kimberlite field, Central Yakutia) are presented. The U–Pb age estimate (472±1 Ma) indicates the Early Paleozoic age of formation of the Khompu-Mai field kimberlites and allows us to identify a new Aldan kimberlite subprovince within the Aldan anteclise.

The results of studying the quantitative, material, and morphometric composition of rock debris in sediments sampled by a box-corer on the Lomonosov Ridge (83° N), Arctic Ocean, during the Severny Polyus 41 expedition (AARI) are presented. Debris ≥1 cm was sampled from each lithological layer according to the description. The age model was created by lithostratigraphic correlation with previously dated cores. The content of debris on the eastern slope and the summit is significantly higher than on the western slope, which is explained by the higher sedimentation rate on the western slope after the deglaciation peak. The carbonate to igneous shift in rock composition and the increase in roundness with time indicate a higher input of Eurasian material in MIS 1.

The paper presents first data on isotopic U–Pb study (LA-ICP-MS method) of zircon from intrusive rocks of the Adyrtor intrusions – a group of small intrusives situated in the easternmost part of the deep-seated fault system of the “Nikolaev Line”. Here, these intrusions cut through one of the oldest (1.8-2.6 Ga) complexes of the basement rocks of Tien Shan (metamorphic rocks of the “Kuilyu suite”). These intrusive rocks belong to the high-potassic calc-alkaline to shoshonitic series, with some geochemical signatures also of anorogenic (A-type) magmatism. These intrusions are accompanied by skarn and porphyry W–Mo–Cu–Au mineralization. Together with the other Au, W and Cu deposits and occurrences, they are parts of the extended metallogenic belt of Tien Shan. The concordant isotopic U–Pb age data for zircon autocrysts indicate the crystallization of quartz syenite (330.7±4.3 Ma) and quartz monzonite (329.5±5.8 Ma) in the latest Early Carboniferous. The distinct W–Mo “specialization” of ore mineralization related to the intrusions studied is in agreement with post-collisional tectonic setting during their emplacement, despite of their older or similar age compared to the ore-bearing plutons in more western segments of the Middle Tien Shan, which corresponded to subduction-related setting. This supports the possibility of the ‘scissor-like” (from east to west) closure of the Turkestan paleoocean that resulted in the earlier cessation of subduction in the eastern Tien Shan compared to the western Tien Shan. The rocks also contain zircon xenocrysts with older (in the order of 1.7–2.6 Ga) age that is in agreement with the age of the host metamorphic rocks of the Tarim craton basement. This highlights the possibility of magma chamber development in the continental crust, together with the magma chambers in the metasomatically-enriched subcontinental upper mantle, the latter being common for high-potassic magmatism.

The present study shows that after the shutdown of the nuclear reactor at the Mining-and-Chemical Combine (MCC) of Rosatom in 2010, artificial radionuclides (⁶⁰Co, ¹³⁷Cs, ¹⁵²Eu, and ²⁴¹Am) are still detected in the bottom sediments (BS) of the Yenisei River in the MCC affected area. The paper, for the first time, reports results of the study comparing potential mobility of artificial radionuclides in the surface and lower layers of the Yenisei BS long after the shutdown of the MCC nuclear reactor. The mobility of radionuclides was estimated using the well-known procedure of sequential extraction of BS. A new finding is that potential mobility of ⁶⁰Co is higher in the lower (older) BS layers compared with the upper ones. Radionuclide ¹³⁷Cs is strongly bound with mineral solids of BS (approaching 100%) regardless of the time factor. The new data showing that ²⁴¹Am and ¹⁵²Eu retain their high potential mobility in the BS over long periods and that ⁶⁰Co potential mobility increases over time suggest potential bioavailability of these radionuclides in the Yenisei River ecosystem.

The results of detailed mineralogical and geochemical studies of precious metals from ultrabasic rocks of the Ariadne massif (Sikhote-Alin orogenic belt) are presented. The presence of several varieties of gold has been revealed, differing in different ratios of Ag, Cu and Hg. Isoferroplatin predominates among platinum minerals. The isotopic composition of ultrabasite sulfides corresponds to the mantle source, while basites are characterized by isotope–light sulfur, indicating the possibility of participation in the oreogenesis of crustal rocks. Isotope-carbon analysis of igneous rocks indicates the presence of derivatives of deep fluids and isotope-light biogenic matter of sedimentary rocks in them. These data show that mantle and crustal processes were involved in the formation of ore-bearing intrusions of ultrabasite-basites. The association of ilmenite, gold and platinum in ultrabasic basites, a derivative of these processes, can serve as a search criterion for the detection of industrially promising sources of strategic metals.

The reconstruction of the Early Paleozoic collision metamorphism of the Khan-Khukhei Block (Northern Mongolia) based on 3D modeling of thermal state of the crust and isotope dating is presented. The age of garnet-biotite schist from a metamorphic complex of the Khan-Khukhei Block of 517.4±7.4 Ma is determined for the first time. 3D modeling was conducted to compare this age of metamorphism with the available age determinations of (post-)collision granite formation in the range of 513–505 Ma. The model considers radiogenic heating at an increased value of heat release in the rocks of the thickened crust of the Khan-Khukhei block as the cause of the migmatization and formation of granitoid melts. Three-dimensional modeling was carried out for the first time for the thermal-dome type of metamorphism. The results provide a realistic conception of magma generation in typical collision settings in the absence of mantle magmatic heat sources. The time interval between metamorphism and the stage of anatectic magma formation is 5–12 million years.

Morphostructural analysis of the stream network of the south of the Far East has been carried out. It has been established that the latest vertical movements in the region were manifested against the background of an older, already formed and not fully eroded relief. Three stages of relief development are identified, reflecting neotectonic activity in the region: a) pre–Oligocene, characterized by a more intense uplift of the Bureinsky ridge, and less intense – the Sikhote-Alin ridge; b) Oligocene–Pliocene, characterized by the most intense vertical movements in the region during the period under review – late Eocene-Holocene; c) the Pleistocene is Holocene, during which a modern developed erosion-denudation relief was formed and no significant vertical movements occurred in amplitude. A map of the total amplitude of vertical neotectonic movements is constructed.

The features of the occurrence and propagation of transverse deformation waves in the elastic lithosphere – viscous asthenosphere system under non-isothermal conditions are studied in the approximation of a thin layer. In this case, the phase transition at the boundary of the layers, due to temperature and pressure disturbances, plays an essential role. The qualitative and quantitative properties of propagation of disturbances of thermomechanical fields have been studied in the long-wave approximation. It is shown that due to the energy supply from the non-isothermal asthenosphere, weakly attenuated wave packets can occur, which spread over thousands of km with a characteristic speed of about 100 km/year. This allows them to be considered as a possible trigger mechanism for the massive emission of methane from frozen sedimentary rocks into the atmosphere.

A method for recognizing infrasound acoustic signals for two types of sources based on the analysis of the shape of their wavelet spectra is proposed. The idea of constructing this form is based on the principal component method. Morphological image analysis methods are used to search for characteristic areas. The proposed method makes it possible to effectively solve the problem of multiclass classification of acoustic signals.

In the waters of the northeastern part of the Black Sea, new species of dinoflagellates have been noted for this area: Oxyhysis oxytoxoides, Spatulodinium pseudonoctiluca, Scaphodinium mirabile, Actiniscus pentasterias. These species, previously indicated only for the waters of Bulgaria, Romania, Turkey, Georgia, Ukraine and Crimea, have been found in the pelagial of the northeastern part of the Black Sea in the last decade: in the area from Abkhazia to the Kerch Strait.

The stress state of ice shelves using numerical modeling is studied. An ice shelf is modeled by an elastic plate floating on water and attached to the ice cover at a grounding point. An analytical solution for the elastic bending of the plate is obtained and it is shown that the maximum tensile stresses on the lower surface of the glacier near the grounding point can reach values of 5×10⁷ Pa, significantly exceeding the limiting strength values of the glacier. The fragmentation of a glacier that occurs when a glacier moves under conditions of constrained compression has been studied. It is shown that deformations of the ice plate are accompanied by the formation of zones of localization of inelastic deformations (ice ridges). A comparison was made of the calculated relief of the plate surface after localization of deformations with the pattern of hummocking of the Larsen Glacier, visible on satellite images.

The results of theoretical and experimental studies of convective vortex currents formed during ice melting, as well as physical modeling of the phenomenon of spontaneous rotation of an ice disk on the water surface, are presented. It is shown that the cause of the observed movements on the surface of initially quiescent water is a cellular convective flow generated by the process of ice melting at the lower boundary of the disk, and a new physical model of such rotation is constructed.

The research was carried out within the framework of the state agroecological monitoring program. The goal was to conduct an environmental assessment of chromium and nickel content in agroecosystems of the southwestern part of the Central Chernozem region using the example of the Belgorod region. All analytical studies were carried out in an accredited testing laboratory using generally accepted methods. During the research, it was found that the average gross content of chromium and nickel in the arable layer in leached chernozems is 19.8 and 24.5, in typical chernozems – 20.0 and 24.9, in ordinary chernozems – 20.9 and 26.6 mg/kg, respectively. The average content of mobile forms of chromium in the studied soils was in the range of 0.13–0.14, nickel – 0.37–0.41 mg/kg. Exceeding the levels of the approximately permissible amount of nickel and the maximum permissible concentration of mobile forms of these heavy metals in soils was not detected. In the agroecosystems of the Belgorod region, chromium and nickel are mainly supplied with organic fertilizers, but this does not pose a risk for soil contamination and crop production. The highest average chromium content (0.45 mg/kg) was observed in sunflower seeds, and the lowest (0.22 mg/kg) in corn grain. Soybean grain is characterized by an abnormally high nickel content (4.81 mg/kg), and the lowest concentration (0.63 mg/kg) is observed in corn grain.