Том 508, № 2 (2023)

The paper is based on geological and geophysical data obtained during 53-th expedition of the research vessel “Akademik Nikolaj Strakhov”. We analyze the structure of Mid-Atlantic Ridge segment, 400 km long in the North Atlantic (between 48° and 51.5° N). According to our studies, this segment is characterized by specific structures formed during the formation of the oceanic crust with reduced basaltic melts supply, which, with going extension in the rift valley, leads to tectonic outcropping of deep lower crustal and mantle rocks. Such processes, called “dry” spreading, were previously unknown in the North Atlantic.

Upper Muna kimberlite field) showed that the crust at different levels is composed of pyroxene, garnet-pyroxene crystalline schists and garnet-pyroxene gneisses. Exsolution textures in pyroxenes and amphiboles, granat rims around grains of ilmenite and pyroxenes indicate that the mineral associations of crystalline schists were formed during cooling at constant pressure. Р–Т equilibrium parameters indicate that garnet-pyroxene crystalline schists are present in the middle crust (P = 7–8 kbar), while garnet-pyroxene gneisses can be considered as rocks of the lower crust (P = 9–10.1 kbar). For the first time, sodalite was found in xenoliths of crystalline schists, which indicates the presence of brines with a high concentration of NaCl at the final stages of rock cooling. The determination of the U–Pb age of zircons testifies to the Neoarchean (2.7 Ma) tectono-thermal event, accompanied by the melting of the crust. In the garnet–pyroxene gneisses, the 1.9 stage is weakly manifistated. The obtained data confirm the earlier conclusion about the vertical and lateral heterogeneity of the crust of the Yakutsk diamondiferous province and the absence of dependence between the degree of crust reworking and spatial location relative to the main collision zones of the Siberian craton.

For the first time, based on the data of the study of fluid inclusions, the PTX parameters of the formation of gold mineralization of the Taimyr-Severozemelsky orogen were established. The temperature of formation of gold ores covers the range from 310 to 105°C, the pressure was not lower than 110–96 MPa. The ore-forming fluids were characterized by NaCl + KCl + H₂O + CO₂ + CH₄ + N₂ composition and salinity up to 9.7 wt. % in equiv. NaCl. The composition of native gold (fineness varies from 960 to 550‰) and minerals of productive mineral associations has been determined. Ore-forming fluids of gold-sulfide-quartz ore occurrences of the accretionary Schrenk-Fadeevskaya zone (Yasnenskoye and Malinovskoye in North-East Taimyr) are more oxidized and less saline compared to the gold-quartz occurrences of the orogenic type of the Mininsko-Bolshevitskaya myogeoclinal zone (Nizhnelitkenskoye, Vidimoe, Nerpichye).

The oxygen isotopic composition of minerals (Qtz, Zrn, Kfs) and bulk samples of Late Cretaceous porphyritic leucogranites of the Omsukchan trough, which are associated with the formation of tin and Sn-polymetallic mineralization, was studied. The δ¹⁸O values of bulk samples of leucogranites decrease from +9.7‰ (outside the Dukat ore field) to 10.6‰ (within the ore field), and the light isotope characteristics are mainly an attribute of feldspars and correspond to isotope exchange with meteoric fluid (δ¹⁸О = –15‰), over a wide range of T at limited fluid-to-rock ratios (W/R from 0.9–1.6 to 0.3–0.1). Unlike feldspars, the δ¹⁸O values of quartz and zircon are partially changed, in the former, probably, by the diffusion mechanism, and in the later, by the dissolution-precipitation one.

A microtomographic study of the internal structure of sulfide minerals from ore varieties of rocks of two industrial deposits of the Arctic zone of the Russian Federation – disseminated ore of the Pilgujarvi Cu–Ni deposit of Pechenga and ore gabbronorites of the platinum-bearing Fedorovo-Pansky complex (Kola Peninsula) was carried out. It is shown that all studied sulfide samples have a homogeneous structure without obvious defects or silicate inclusions larger than 1 µm. The absence of silicate microinclusions larger than one micron in sulfides suggests an isomorphic form of REE occurrence in sulfides and, to some extent, eliminates the debatable problem of the influence of microinclusions on the results of Sm–Nd isotope-geochronological studies of sulfides. The presence of smaller (10–500 nm) silicate microinclusions is highly likely to be unable to control the total REE budget in a sulfide mineral. The conclusion about the absence of a significant effect of microinclusions on the obtained ages is confirmed by the results of Sm–Nd dating using sulfides from the same mineral samples: the Sm–Nd ages of the ores of the Pilgujarvi Cu–Ni deposit were 1965 ± 87 Ma; ore gabbronorites of the Fedorovo-Pansky complex – 2482 ± 61 Ma, which is in good agreement with the dates obtained earlier using other isotopic systems (U–Pb, Re–Os).

The results of a geochronological study (U–Pb SHRIMP-II) of zircon from granodiorites and plagiogranites of the main phase of the Tallain pluton of the Baikal-Vitim belt are presented. The obtained estimates of the age of the magmatic cores of zircon from granodiorite and plagiogranite coincide with each other within errors and are interpreted as the age of crystallization of rocks of the main phase of the Tallain pluton 661 ± ± 6 million years. The weighted average age of the metamorphic zircon shells of these rocks is 637 ± 5 million years. High positive values of ɛNd (660) +7.2 and +7.3 in the rocks of the main phase indicate a juvenile source of the parent melts. Based on new and previously published geochronological data, a conclusion is made about the formation of similar late Neoproterozoic juvenile gabbro-granite associations of the Baikal-Vitim belt at the turn of 660 million years (Tallain complex) and 603–615 million years (Padorinsky complex).

The study of natural archives, such as bottom sediments of lakes and seas, becomes promising for paleoreconstructions due to the conditions of rapid changes of the environment, anthropogenic impact, and insufficient data of instrumental measurements. Based on a radioisotope dating using the non-equilibrium ²¹⁰Pb, the modern sedimentation rates for the last 150 years in the southern part of the Tatar Strait have been established. According to the two models (CIC and CRS), the sedimentation rate was 0.20–0.22 сm/year.

A narrow-crowned sauropod tooth from the Udurchukan Formation (Maastrichtian) at Blagoveshchensk locality (Amur oblast, Russia) is morphologically identical with the teeth of Nemegtosaurus from the Nemegt Formation (Maatsrichtian) Mongolia and can be referred to the titanosaurs of the family Opisthocelicaudiidae. This tooth is the only sauropod find from the Late Cretaceous of Russia.

One of the possible mechanisms causing significant emissions of methane into the atmosphere within the Arctic shelf may be the decomposition of gas hydrates. Their accumulations within the Arctic shelf formed almost simultaneously with the formation of permafrost, which contributed to the emergence of a zone of stable existence of gas hydrates. The subsequent flooding of the Arctic shelf led to the degradation of the permafrost and the violation of the conditions for the existence of hydrates. To assess the state of the stability zone, methods of mathematical numerical modeling are used. Standard seismic methods are widely used to localize gas hydrates, but monitoring their physical state requires the development of fundamentally new approaches based on solving multiparameter inverse seismic problems. In particular, the degree of attenuation of seismic energy is one of the objective parameters for assessing the consolidation of gas hydrates: the closer they are to the beginning of decomposition, the higher the attenuation, and hence the lower the quality factor. Thus, the methods of seismic monitoring of the state of gas hydrates in order to predict the possibility of developing dangerous scenarios should be based on solving a multi-parameter inverse seismic problem. This publication is devoted to the presentation of this approach.

The paper investigates the question of the influence of viscosity on the rate of development of instability in heavy viscoelastic geosystems with an anomalous density distribution over depth. Geomaterials are considered as incompressible, and the Maxwell model of viscoelasticity (that makes it possible to adequately describe the dynamics of geosystems even in the case of huge viscosity of geomaterials) is adopted for them. Along with viscoelastic systems, the elastic comparison systems are considered, which are characterized by the same anomalous stratification and the same values of shear stiffnesses as the viscoelastic systems studied. Bilateral estimates for the increment of growth of the fastest mode of loss of stability (the “main increment of growth”) are obtained, which are valid for any viscosity. It has been found that the main growth increment always exceeds the main growth increment for the unstable elastic comparison system, which is determined by the inertial properties of the latter together with the degree of supercriticality of the parameters characterizing its unstable equilibrium state. As viscosity increases, the main growth increment for the viscoelastic system tends from above to the corresponding increment for the unstable elastic comparison system. In the case of stability of elastic comparison systems, the corresponding viscoelastic systems are unstable, but the rate of development of their instability is very low due to the great viscosity of geomaterials. Precisely and only in the case of stability of comparison systems, the viscosity slows down this rate, and for geosystems with extremely great viscosity, the manifestation of their instability during real observation times is very small. The analysis carried out confirms the fact that the study of stability and instability of elastic comparison systems can serve as a methodological basis for studying stability and instability of viscoelastic geosystems.

When mesoscale vortices interact with the flow, there are three variants of their behavior: rotation, nutational oscillations, and unlimited elongating. This paper describes the physical conditions of vortex transforming into filaments. We estimate the proportion of vortices that are stretching out into filaments in the World Ocean and some regions. Due to the elongation, the vortices redistribute the energy from mesoscale to submesoscale.

The durability in waters of matrices for rare-earth – actinide fraction HLW has been studied at 25 (1 atm.), 200 or 240°C (pressure of saturated vapor). The samples composed of Nd₂ZrTiO₇ (cubic pyrochlore-type structure) or Nd₄(Ti,Zr)₉O₂₄ (orthorhombic symmetry, no natural analogue), phases were obtained by induction melting in a “cold” crucible. Leaching rate of Nd (imitator of REE-MA fraction) on the 28th day of experiment was lower than 5 × 10^–8 g/(cm² day). These results confirmed a very high durability of the ceramic waste forms in hot underground waters.

A mathematical model of oleic spot propagation based on the laws of conservation of mass and total energy of the system is constructed. Compact solutions of this model are presented both for machine oil stains of limited area and for unlimited spills of crude oil. Experiments have been carried out to study the dynamics of spreading of a compact spot of reference engine oil and crude oil under various physical conditions. Comparison of experimental and theoretical results showed their good agreement for all dynamic modes of the process under study.