Vol 516, No 2 (2024)

The paper, based on geological and geophysical data obtained during 55-th expedition of the research vessel “Akademik Nikolaj Strakhov”, examines the structure of the King’s Trough and its immediate surroundings (King’s mesostructural cluster), located on the eastern flank of the Mid-Atlantic Ridge in the North Atlantic. Six provinces were identified within the southeastern part of the King’s Trough, based on the results of bathymetric mapping, each of which has its own morphostructural appearance, which was formed as a result of multistage tectonic and volcanic processes, alternating and conjugate with each other in time. According to seismoacoustic profiling data, three main types of seismic faces have been identified: a) pelagic complexes; b) deposits of turbidite flows; c) chaotic facies of gravitational genesis. It is shown that the anomalous magnetic field of the study area is a superposition of linear and isometric anomalies. The first were formed during the generation of oceanic crust in the axial spreading zone. The second are associated with volcanic massifs formed in intraplate conditions. The obtained data confirm the assumption that the formation of the King’s Trough was preceded by the formation of an extended arched uplift, which became the scene of intense intraplate volcanism, the intensity of which increased from the southeast to the northwest. This stage was followed by subsidence of the axial part of the uplift with the formation of the King’s Trough and the Peak and Freen Troughs.

The work is devoted to solving the problem of correctly determining capillary pressure functions during mathematical modeling of oil displacement processes during flooding of productive formations. It is shown that the use of these functions, determined in laboratory conditions using traditional methods using capillarimeters and high-speed centrifuges, when modeling processes of oil displacement from low-permeability productive reservoirs can lead to significant errors. The work notes that when conducting laboratory studies in rock samples, there is no formation of residual oil in a stationary form, while in real conditions of displacement of oil by water from productive formations, residual oil is formed in the rock, and in low-permeability formations the residual oil saturation can reach 50% or more of the pore volume. To obtain capillary pressure curves that more reliably reflect the real processes in productive formations during their flooding, it is proposed that when preparing rock samples for laboratory research, it is proposed to provide for the process of preliminary formation of residual oil saturation in these samples. This will make it possible to more reliably simulate the processes of oil displacement during waterflooding of productive formations in real conditions, especially when developing low-permeability oil and gas reservoirs.

The paper presents new isotopic U–Pb data (LA-ICP-MS) method of zircon from the main types of intrusive rocks at the Kuru-Tegerek gold-copper-molybdenum skarn deposit situated in the Chatkal segment of the Middle Tien Shan. This and other gold, copper, tungsten and molybdenum deposits are parts of the extended Late Paleozoic metallogenic belt of Tien Shan. The concordant isotopic U–Pb values obtained for zircon autocrysts from the rocks of sequential intrusive phases span over the interval from approximately 323 to 311 Ma. This interval comprises the crystallization of gabbro-diorite (from 323.5±2.5 Ma to 323.2±6.8 Ma) and tonalite (from 321.4±3.8 Ma to 311±3.8 Ma). The age dates obtained for these zircon autocrysts correspond to the emplacement of these moderate-potassic intrusions in the Late Carboniferous and are almost coincident with the isotopic dates previously known for the high-potassic intrusions of the porphyry Cu–Au–Mo deposits of the Almalyk mineralized cluster (Kurama segment of the Middle Tien Shan), which were also emplaced in the Late Carboniferous (about 330–310 Ma). This corresponds to the subduction tectonic regime occurred in this region in relation to the steep-dipping (in the Kurama segment) or flat (in the Chatkal segment) subduction of a tectonic plate toward the north, under the structures of the Kazakhstan-Northern Tien Shan continental massif and accreted segments of the Middle Tien Shan. The intrusive rocks studied at the Kuru-Tegerek deposit contain also zircon xenocrysts (including these in the core of complex crystals) with the isotopic U–Pb age of some 1.9–2.1 Gb. These dates are in agreement with the age of metamorphic rocks in the Tarim craton basement and indicate the presence of the ancient continental crust in this segment of the Middle Tien Shan.

Field studies of hydromineral deposits of the Southern Urals, as well as the results of studying the ion-salt and gas composition of groundwater show that liquid runoff from pyrite deposits in the region can become serious deposits of secondary mineral raw materials in the future. Dump waters are mineral resources in which, according the concentration level, the content of the main elements is commensurate with the average content in ores.

New evidence of the Early Silurian sublithospheric magmatic activity in the eastern part of the Altai-Sayan orogen has been obtained, which occurred between large-scale mantle magmatic episodes of the Middle–Late Ordovician and Devonian. These are the dikes of high-Mg (MgO 15–22 wt %) picritic dolerite of the Naryn complex in the western part of the Tuva-Mongolian superterrane. The dike complex consists of simple picritic dolerite dikes and combined dikes which compose a central picritic dolerite and granitoids along contacts with mingling zone between them. The picritic dolerite geochemical signature is similar to the enriched basalt of mid-ocean ridges or within-plate regions and indicates sublithospheric mantle source of therm. The origin of initial picritic dolerite melts occurred at depth about 120–140 km, temperature of 1600–1640°C and melting degree up to 20% of a dry peridotite. These values are consistent with the origin conditions of the hot spot magmas. The granitoids from combined dikes had crustal geochemical signature and were formed due to anatexis of the Tuva-Mongolian superterrane host rocks initiated by the picritic dolerite intrusion. The U–Pb zircon age (SHRIMP-II) of leucogranite from the combined dyke is 439±3 Ma witch interpreted as age of the Naryn dyke complex. Early Silurian mantle magmatic activity of the Southeastern Tuva most likely caused the migration of the Siberian paleocontinent over the African mantle hot field.

The Archean-Proterozoic transition in Earth's history is marked by significant changes in mantle dynamics and temperature regimes. A notable consequence is the disappearance of Al-depleted komatiites in the late Archean and the nearly complete absence of true komatiites since the Proterozoic. In this study, we present the investigation of the 2.41 Ga komatiitic basalts of the Vetreny Belt, dating back to the Archean-Proterozoic boundary. These rocks provide unique data on the composition of olivine and chromite, as well as on the crystallization temperatures based on Al-in-olivine geothermometry for Vetreny Belt komatiitic basalts. The temperatures of the earliest stages of crystallization were approximately 1240±25°C, indicating the presence of water in the melt and aligning with measured water contents of 0.4±0.2 wt. % H2O in the melt inclusions. However, during crystallization, the komatiitic basalt melt underwent degassing, resulting in mass crystallization and a temperature rise of approximately 20°C due to latent heat release. The degassing of water from the melt suggests crystallization in the surface conditions.

The sources of terrigenous material involved in the structure of Neogene rare metal-titanium placers on the northeastern side of the Dnieper-Donetsk Basin (DDB) were determined using lithological and mineralogical methods was used, including U-Pb geochronological and chemical study of detrital zircon. Characteristics of the accessory mineral association of the placer, the morphology of individual mineral grains, and the depletion of U, Th, Y, Yb in most of the zircon population indicate that the source was chemical residue probably formed on Proterozoic (70%) and Neoarchean (15%) metamorphic rocks. The presence of zircon crystals with Paleozoic U-Pb age and high contents of U, Th, Y and Yb indicates the proximal source destruction of igneous rocks of Neoproterozoic-Early Paleozoic trap formations, Devonian igneous and volcanic-sedimentary rocks of the DDB. Perhaps the development of salt tectonics, which is widespread in the DDB, facilitated the involvement of debris from the above rocks in sedimentary recycling.

For the first time (by methods Scanning Electron microscopy, X-ray spectral microanalysis and cathodoluminescence method) REE mineralization studies have been conducted in alkaline rhyolites of the Pechalninsky ore field (North-East of Russia), a potentially larger-volume source of HREE. It is shown that in the direction of fluidity, thin interlayers composed of crystalline aggregates of pyroxenes and/or amphiboles impregnated with a silicate substance alternate in the rock, and ribbon-like thin strips and lace separations of Fe, Ti, and Mn hydroxides that have replaced titanomagnetite (relict secretions of which are partially preserved). Microcrystalline aggregates of pyroxenes and/or amphiboles contain the finest inclusions of REE secretions (5–7 microns), the determination of mineral species of the latter is difficult due to the small particle sizes. Scanning electron microscopy (EMF) has determined that these secretions are REE phosphates. Concentrically zonal and radially radiant REE secretions have been revealed in the relics of titanomagnetite crystals. The first ones are represented by silicates enriched with Yt and REE. In them, the content of REE varies unevenly from the center to the edge. Radially radiant aggregates are represented by oxides and/or carbonates containing REE (La, Ce and Nd predominate). The results obtained can be used in the development of enrichment technology.

Origin of volcanism along the Kuril-Kamchatka island arc (KKIA) was analyzed. Geophysical observations show variations in slabʼs properties. Different widths of the volcanic belt in the north and south of the KKIA are caused by changes in the slab's angle. The Bussol Strait rift system may be generated by significant changes in the slab's velocity. We proposed that the back-arc basin plays a dominant role in formation various slabʼs parameters and volcanism manifestations along the KKIA.

The geochronological, geochemical and Sr-Nd isotopic features of Late Mesozoic volcanic rocks associated with the development of the Nerchinsk depression in Eastern Transbaikalia are presented. Its structure involves the sequences of high-potassium subalkaline volcanic rocks containing of 55 to 73 wt.% SiO₂.⁴⁰Ar/³⁹Ar isotope dating of bulk rock samples was performed. ⁴⁰Ar/³⁹Ar dating results from high-K basaltic andesite gives value of 150.8±1.8 Ma and from latite is 131.0±1.6 Ma. Volcanic rocks are characterized by depletion of hydrophobic Ti, Nb and Ta, slightly negative εNd(T) values, but increased in εSr(T), that probably indicates contamination processes of primary melts by crust component. In terms of their geological and geochemical characteristics, the volcanic rocks of the Nerchinsk depression belong to the shoshonite-latite series of the rear part of the Greater Khingan volcanic region, which formed in the subduction setting of a continental active margin.

Dissociation of pore methane hydrate in ice- and gas-bearing sediments at external pressure below the equilibrium has been simulated in mathematical and physical (laboratory) models. The mathematical model, along with the experiment, provides constraints on dissociation kinetics. The suggested theoretical model confirms the trend of decreasing hydrate saturation of frozen soil S_h~Aτ^(-n). observed previously in experiments. The physical model makes basis for calculating the coefficients A and n, while the mathematical modeling shows how the coefficients depend on the problem parameters. The theoretical estimates agree with the experimental results, both qualitatively and quantitatively. The results of mathematical and physical modeling have implications for key factors that control self-preservation of pore methane hydrates in frozen sediments.

When processing satellite data of total electron content on the route between GLONASS, GPS satellites and ground receiving stations located in the Primorsky Territory of Russia, disturbances of the electronic layer with periods ranging from 5 minutes to 45 minutes caused by natural fluctuations in the atmospheric region were identified. The isolated vibrations affecting the sea surface cause fluctuations in the aquatic environment with periods ranging from 5 minutes to 40 minutes.

Prognostic estimates of changes in the climatological boundary of the permafrost zone as a function of the average annual air temperature on the territory of the Bolshezemelskaya tundra under various scenarios of the development of the world economy until the middle of the XXI century have been obtained. It is shown that the shift of the climatological boundary of permafrost, determined by the threshold value of the average annual air temperature, in the north-eastern direction observed in the period from 1950 to 2010, according to the adjusted scenario forecasts, obtained using a climate model, will continue in the coming decades under any scenario of the development of the world economy and is an inevitable consequence of anthropogenic influence on the climate. The results of the study are important for assessing the prospects and development of a network of long-term observations, which is being created to monitor the state of permafrost and greenhouse gas fluxes in the Russian Federation.

Several places were discovered in the mountains of the Kodar ridge in Transbaikalia, that are regularly visited by bighorn sheep (Ovis Nivicola) for the purpose of consuming coal (Chepinskaya Formation, Jurassic). According to observations an adult ram eats from tens to hundreds of grams of coal gruss and dust at once. A comprehensive study of “eatable” coals was carried out, including their geochemistry with determination of the content and balance of mobile forms of microelements, including rare earth elements (REE). It has been established that the sum of REE in coal varies from 0.19 to 0.27 kg/t, which is 3.5–4 times higher than the clarke value. The REE composition is dominated by elements of the light subgroup (LREE). The presence of monazite, xenotime and rhabdophane in the consumed coals was established by analytical scanning electron microscopy. An acid (HCl, pH-1) extract from minerals showed, that among the elements released from coal, only some microelements, including LREEs, are most likely to be of greatest importance for animals. The data obtained, considering our previously conducted landscape-geochemical studies of mass geophagy areas in the Sikhote-Alin, the Gorny Altai and on the island. Olkhon (Baikal), suggest that the reason for the regular consumption of coals by bighorn sheep on the Kodar Ridge is due to the animals intention to restore the disturbed balance of REE in the body.

The possibility of short-term and long-term forecasting of water levels, including those associated with dangerous hydrological phenomena on the Marmarik River, using various probabilistic approaches, including regression dependencies, an integrated moving average autoregression model, and multilayer perceptron models, is considered. To evaluate the effectiveness of prognostic methods, the statistical parameters of a random process are calculated, while recommendations are given using the classical criteria for the effectiveness of issued forecasts. For long-term forecasting, the expediency of using the integrated moving average autoregression model was assessed, while it is noted that these models in the classical representation are not applicable due to time gaps, and therefore it is recommended to focus on the mathematical expectation of a random process. For short-term forecasting one or two steps ahead, the method of training artificial neural networks was used. The analysis carried out in the work revealed that in the case of short-term forecasting of water levels for one period in advance (12 hours), it is most expedient to focus on the value of the water level attributable to the date of issue of the forecast, the standard error of such a forecast is 5 cm. For a 24-hour water level forecast forward, it is expedient to develop neural network forecasting models, taking into account the development of the situation on Gomraget―Meghradzor. A further increase in the quality of the outputs is possible when using data for a longer observation period and a whole year. At the same time, as an alternative to neural network forecasting models, physical and mathematical (hydraulic) models of the formation of water levels can be used.