Том 517, № 1 (2024)

The first U-Pb dating of detrital zircon from chromite sandstones of the Middle Permian Sabantuy paleoplacer, localized in the Southern Pre-Urals, has been obtained. The distribution of U-Pb dates is unimodal with a peak at 420–400 Ma. Two-thirds of all ages are Devonian, and more than half of them correspond to the Early Devonian, during which supra-subduction ophiolitic and accompanying high-pressure metamorphic complexes were formed in the Southern Urals, and ultramafic-mafic magmatism was occurred. These spatially combined geological bodies exposed in the melange zone of the Main Uralian Fault or tectonically moved to the west of it as a ophiolite allochthons, are the main sources of detrital chromite and zircon in the Sabantuy paleoplacer.

The paper presents the results of U-Th-Pb (LA-ICP-MS) geochronological studies of detrital zircon from Quaternary sands of the Tokko basin on the eastern flank of the Baikal rift zone. The study shows, that their main sources were Mesoarchean tonalite-trondhjemite orthogneisses and metavolcanics, as well as Meso- and Neoarchean syn- and post-collision granitoids of the Charа-Olekma geoblock of the Aldan shield, which are located near the Tokko basin. Moreover, the supply of sedimentary material into it could have occurred during the melting of glaciers that covered the Udokan Uplift in the south and the Kodar Uplift in the north in the Middle-Late Quaternary.

U–Pb (LA-ICP-MS) geochronological studies of detrital zircon from rocks of the Early Proterozoic Khargituy Formation of the Sarma Group, distributed in the central part of the Baikal uplift of the basement of the Siberian craton and included in the structure of the Sarma zone of the Akitkan orogenic belt, were carried out. It was established that the Khargituy Formation included rocks formed at different time intervals: <2.7, 2.15–1.95 and <1.7 Ga. It is shown that Meso- and Neoarchean age peaks (2.7–3.1 Ga) are characteristic of zircon from leucocratic gneisses, which indicates the formation of gneiss protoliths after 2.7 Ga due to the destruction of Archean granitoids of the Sarma zone of the Akitkan orogenic belt and igneous rocks of the Anabar superterrane basement of the Siberian craton. The time interval of 2.15–1.95 Ga corresponds to the accumulation of protoliths of mica-quartz schists, which is justified by the age of the youngest zircon grains – 2150 Ma and the age of metamorphism of these rocks – 1.95 Ga. The presence of an age peak at 1833 Ma and younger zircon grains with ages in the range of 1675–1785 Ma in a sample of mica-quartz schist taken from another area of rock outcrops attributed to the Khargituy Formation indicates that the accumulation of protoliths of these rocks occurred after the formation of the Akitkan orogenic belt and the South Siberian postcollisional magmatic belt. The results obtained indicate that the rocks attributed to the Khargituy Formation of the Sarma Group of the Western Baikal region cannot be considered as a single stratounit, since their formation occurred at different stages of the evolution of the Akitkan orogenic belt. Thus, as a result of the research, it was shown that, based on new data, the deposits of the Khargituy Formation should be divided into complexes of different ages (stratounits), each of which corresponds to a certain stage of the geological evolution of the territory.

The paper presents the isotopic U-Pb study data (LA-ICP-MS method) of zircon from intrusive rocks of the Sonkul and Kokturpak plutons situated along the deep-seated fault system of the “Nikolaev Line” in the eastern Kyrgyzstan. These plutons of high-potassic rocks are spatially and genetically associated with the Kumbel and Kashkasu W-Mo-Cu-Au deposits, respectively, as well as other occurrences of W and W-Au mineralization. Together with other Au, W and Cu deposits, they are parts of the extended metallogenic belt of Tien Shan. The concordant isotopic U-Pb ages of zircon autocrysts for the consecutive intrusive phases span over the interval of approximately 303 to 283 Ma. This interval included the crystallization of olivine gabbro (299±2 Ma) in the Sonkul pluton, monzonite (300±3 Ma) in the Kokturpak pluton, granodiorite of the main intrusive phase (299±3 Ma in the Sonkul pluton and 297±4 Ma in the Kokturpak pluton), and monzogranite (289±4 Ma in the Sonkul pluton and 285±2 Ma in the Kokturpak pluton). Zircon antecrysts dated at 306–311 (to 323?) Ma have also been distinguished. The age data obtained correspond to the pluton emplacement in the Late Carboniferous-Early Permian initially in subduction-related and then post-collisional tectonic settings. Besides, in the Middle Tien Shan, this age interval corresponds to one of the regional pulses of high-potassic calc-alkaline and shoshonitic magmatism. A distinct metallogenic evolution corresponds to these pulses that is expressed in the change from porphyry Cu-Au-Mo deposits related to the early pulse to essentially tungsten (W-Mo-Cu-Au) and then essentially gold deposits related to younger pulses. The rocks also contain zircon xenocrysts with ancient age (in the order of 1.5–2.5 Ga) that probably represent the age of the Tarim craton basement.

We obtained the data on the vertical distribution of thiosulfate and sulfite by derivatization with monobromobimane in the water column of the Black Sea for the first time. Thiosulfate and sulfite appeared in detectable quantities below the redox interface along with the appearance of hydrogen sulfide. On the continental slope, the concentration of sulfite reaches 1.12 µM, and thiosulfate 0.53 µM in sea water with a potential density of 16.40–16.80 kg/m3. In the deep part of the sea at a depth of 400 m (potential density 16.96 kg/m3), the concentrations of sulfite and thiosulfate reach their maximum of 1.74 µM and 0.98 µM, respectively. A comparison of data on thiosulfate obtained after filtration and without filtration showed that in the upper part of the anoxic layer, up to 100% of thiosulfate is associated with bacterioplankton. Microbial bound thiosulfate in the cell gradually decreases to a depth of 600 m. These data and the correlation with sulfite and particulate organic carbon suggest that in the upper part of the anoxic zone, thiosulfate and sulfite are predominantly a result of the activity of chemoautotrophic bacteria.

Large (up to 4 cm) crystals of euhedral olivine and its intergrowths with clinopyroxene were discovered in the alkali-basaltoid dikes of the Western Sangilen, South-Eastern Tuva. The composition of olivine (Mg# 81–83, NiO 0.2–0.3 wt. %) differs sharply from the composition of olivines from mantle and gabbroid parageneses. It is shown that olivine is a liquidus phase that crystallized from an alkali basaltic melt at pressures of 10–13 kbar in intermediate magma chambers located at depths of 34–43 km, which corresponds to the level of the crust-lithospheric mantle boundary for the Western Sangilen.

Clay minerals formed as a result of hydrothermal activity within kimberlite pipes were redeposited into the horizons of the Lower Jurassic diamondiferous deposits of the near-facies facies. The mineral composition of the Lower Jurassic Dyakhtar sequence, composed of paleodeluvium and paleokarst deposits, has been studied in the immediate vicinity and at a distance from kimberlite pipes. Mixed-layer minerals with structural heterogeneities, in which an increased concentration (up to 0.1 wt %) of lithium is noted, were found in sections of erosion plumes of weathered varieties of kimberlite rocks. The thickness of sediments with such minerals decreases sharply at distances of more than 2 km from the desired kimberlite body. The identified features in the mineral composition of the deposits overlying kimberlite pipes can be used as new prospecting signs of diamond potential during geological exploration of primary sources of diamonds.

Modern features of the geodynamic regime, defined from neotectonic deformations of the sedimentary cover and seismicity, show that the southern trough of the Charlie Gibbs twin transform fault develops in the transtension mode, and the northern one in the transpression mode. Features of activity in the structure of the sedimentary section upper part were noted in the eastern passive parts of the fault at a distance of at least 150 km from the active rift zone of MAR. Dislocations of normal fault kinematics, signs of increased sedimentation rate and mass transport deposits of landslide processes near the slopes of the trough are manifested in the sedimentary section of the southern trough. Median ridge with folded structures overlain by sediments with angular unconformity is established in the axial part of the northern trough. Faults south of the ridge are interpreted as thrusts. At the present stage, the Northern trough is accompanied by the formation of a piercement structures chain of the median ridge during the compression of deep matter and concomitant deformations of the sedimentary cover.

The research objective is an investigation of extreme storm waves in the coastal zone from Volna Village (Kerch Strait area) to Adler on the north-eastern Shelf of the Black Sea over a climatic time span. The primary research method is numerical modelling using the MIKE 21 SW spectral wave model. As a result of calculations, hourly fields of spatial distributions of key wave parameters were obtained for the Black Sea area from January 1979 to December 2023, i.e., for the past 45 years. The analysis was conducted considering the separation of the wave field into two components: wind waves and swell. The research revealed that over the last 45 years, the north-eastern coast of the Black Sea experienced the impact of 41 storms with significant wave heights exceeding 5 meters. Two November storms in 2007 and 2023 were truly extreme, with significant sea wave heights reaching 9 meters and power exceeding 500 kW/m. Average heights of storm waves along the coast varied between 4-6 meters, and average power was around 150 kW/m. The highest waves developed in the areas of Anapa, Utrish, and Idokopas. Average values of heights and powers of wind waves showed a general tendency to decrease when moving from the northwest coast to the southeast, while swell, on the contrary, increased. Several relatively homogeneous sections in terms of the development of wind waves and swell were identified in the coastal zone. In the structure of average storm waves between Volna and Anapa, wind waves absolutely dominate. Between Cape Myskhako and Idokopas, the contribution of wind waves to the total wave energy exceeds swell by 2–2.5 times. Between Arkhipo-Osipovka and Tuapse, the energy of wind waves slightly surpasses the energy of swell. Further, south of Tuapse, the contribution of swell becomes predominant. In terms of the ratio of the contribution of wind waves and swell along the coast, two distinct regions stand out: near Anapa, the overall wave climate is determined by wind waves, while in Adler, it is determined by swell.

The dynamic characteristics of the stratospheric polar vortices at levels from 100 to 1 hPa (minimum vortex area, minimum mean wind speed along the vortex edge, and minimum wind speed at which there is a dynamic barrier), obtained using the vortex delineation method with geopotential based on ERA5 reanalysis data, presented for the first time. Seasonal changes and average winter vertical profiles of the vortex area, mean wind speed along the vortex edge, and mean temperature inside the vortex for the Antarctic and Arctic polar vortices were obtained. The average daily probability of weakening of the dynamic barrier along the vortex edge in winter was determined based on data for 1979–2021 over the Arctic and Antarctic. It is shown that the lowest probability of weakening of the dynamic barrier (and possible breakdown of the polar vortex) in winter can be traced at levels from 30 to 3 hPa and reaches less than 50% in the Arctic and less than 1% in the Antarctic. At the 50 hPa level, the probability of weakening of the dynamic barrier is 53.7% in the Arctic and 1.4% in the Antarctic.

A cave formed during the process of sulfuric acid speleogenesis (SAS) was explored on the territory Uzbekistan. Evidence of sulfate speleogenesis includes the characteristic morphology of the cave, the upward flow of warm groundwater of a chloride-sulfate sodium-calcium composition with the release of hydrogen sulfide, the widespread development of ascending passage, the presence of biomats in water, and characteristic secondary minerals. Based on the chemical composition of the water and the values of stable isotopes of oxygen and deuterium, it was concluded that the underground water of the cave are formed by mixing infiltration waters and buried sedimentogenic waters of marine sediments. The cave is an example of active sulfuric acid speleogenesis in Uzbekistan.

It was previously established that soil drying changes their properties and, in particular, the characteristics of a specific soil organic substance – humic substances (HS). HS is the basis of soil organomineral gels that cover and bind soil particles. When water is removed from the soil, hydrophobization and compression of gels occur, as a result of which the properties of soil samples may change. The restoration of soil gels of air-dry samples should reduce the discrepancy between the data obtained when studying the soil properties of dried and non-dried soil samples. The purpose of the work is to find ways to restore the structure of soil gels. Samples of 6 types of soils were studied. Methods of vibration viscometry, laser diffractometry, scanning electron microscopy (SEM), photocolorimetry and conductometry were used in the work. It has been found that drying of soil samples increases the size of supramolecular formations (SMFs) from the soil and reduces the viscosity of soil pastes, a parameter characterizing the structure and ability of gels to swell. To restore the structure of soil gels, it is proposed to reduce the size of the SMFs from the HS to the initial ones. SMFs separation of air-dry samples was carried out by moistening the soils and subsequent treatment with various influences: temperature, ultrasound and freezing. Using SEM, it is shown that heating and ultrasound treatment do not reduce, but increase the size of the SMFs. Humidification of air-dry soils, exposure to moisture for 2 weeks and subsequent freezing bring the viscosity of pastes of a number of studied soils closer to the condition of samples that have not been dried. This process occurs due to the return of the SMFs size to the values of the initial soils, as evidenced by the data on the distribution of the size of suspended particles on a laser diffractometer. Thus, a method for restoring gel structures in dried soils to the state of the original soils is proposed.

Using Sentinel-1 satellite radio interferometry data, the geodynamics in the area of the epicenter of the destructive Mw = 6.8 earthquake that occurred in Morocco on September 8, 2023, were studied using the Stacking-InSAR method applied to 801 interferograms. Over the period from January 2019 to September 2023, local surface subsidence with an average speed of 1.5 cm/year was discovered, and the maximum speed was identified in 2023 and amounted to 24 cm/year, for areas with a developed melioration system located above aquifers. Based on an integrated analysis of changes in the water equivalent thickness, measured from satellite gravimetric data for 2000–2023, and the amount of precipitation, it was found that the surface subsidence was due to a huge irrigation draft. Assuming the similarity of shapes of isoseists of earthquakes with close epicenters, a comparison of the isoseists of earthquakes that occurred in 2014 and 2023 was carried out, which made it possible to identify the expansion of the contours of the isoseists towards the descending surface areas for the earthquake from 2023. This process, along with the tectonic movements of the Eurasian and Nubian plates, is believed to increase the stress-strain state between two aquifers, what caused the Mw = 6.8 earthquake in Morocco on September 8, 2023.