Vol 508, No 1 (2023)

In the southern part of the Ulutau terrane (Central Kazakhstan), a complex of volcanogenic rocks of basalt-rhyolite composition of the Zhiide series has been studied. Based on the U–Pb (SIMS) geochronological study of accessory zircons, an estimate of the age of rhyolites was obtained for the first time – 1338 ± 5 million years, which corresponds to the first half of the Ectasia period of the Mesoproterozoic. The features of the composition of the basic and acidic effusions indicate their formation in the context of continental rifting caused by the activity of the mantle plume.

The results of the study of the chemical composition and isotopic characteristics of the sulfur of disseminated pyrite and arsenopyrite from metasomatites of the Malo-Taryn, Badran, Khangalas, V’yun and Shumniy orogenic gold deposits of the Yana-Kolyma metallogenic belt are presented. Pyrites and arsenopyrites have a non-stoichiometric composition. Arsenopyrites are characterized by sulfur enrichment (As/S from 0.77 to 0.99), minor of Sb, Co, Ni and Cu with a total concentration of up to 0.15 wt %. Pyrites contain the same elements (total concentration up to 3.71%), less often Pb, depleted with S and enriched with As (up to 3.16 wt %). The ratio of Ni/Co in pyrite is 10.0 > Ni/Co > 0.1, it is characteristic of hydrothermal negatively charged pyrite with high conductivity (p-тип). It is assumed that the “invisible” Au⁺ is found in disseminated pyrite and arsenopyrite mainly in an isomorphic structurally related form. A range of values δ³⁴S from –6.4 to +5.6‰ in sulfides, is characteristic of juvenile/magmatic sources of sulfur of the studied deposits.

Within the East Sayan rift zone of the Late Paleozoic Barguzin salic large igneous province (SLIP), along with alkaline-peralkaline granitoids with ore mineralization, mafic subvolcanic bodies (gabbroids, mafic dykes) are common. One of the typomorphic mafic – peralkaline granitoid association is the Snezhnoye beryllium deposit. Using the U–Pb LA–ICP–MS method, mafic dykes of the Snezhnoye beryllium deposit were dated. The age of zircons from the diabase (dolerite) dyke was 301 ± 6 Ma, and from the microgabbro one, 297 ± 2 Ma. The obtained dates are close to the age of fluorite-beryl mineralization (306 Ma) and peralkaline granites with Ta-Nb mineralization attributed to the Ognite complex (311–295 Ma). The geochemical features of mafic dykes suggest the generation of mafic magmas from an asthenospheric mantle source, which, taking into account the intracontinental setting, testifies in favor of the plume-mantle nature of mafic – alkaline-peralkaline granitoid magmatism of the East Sayan rift (rare-metal) zone.

For the first time, rare earth (REE)-fluorocarbonates were found in the ore-bearing rocks of the Safyanovsky copper-zinc-pyrite deposit (Middle Urals): synchysite, bastnasite, in association with fluorite, calcite, dolomite, barite, pyrite, sphalerite. Samples with REE-fluorocarbonate mineralization were found at a depth of 262 m in an altered near-ore zone of pyrite-carbonate-kaolinite-sericite-quartz composition in contact with massive pyrite-chalcopyrite and pyrite-sphalerite ores. It is assumed that REE-fluorocarbonates were formed from a hydrothermal solution together with fluorite and calcite. This event may be associated with a period of hydrothermal activity manifested at the post-collision stage of the development of the Ural folded system.

We consider the evolution of the A-type granite magmatism in the Cryogenian period during the tectonic transformation of the Yenisei Ridge from a postcollisional setting to the early development stage of an active continental margin. We report geochronological and geochemical data for A-type granites of two intrusions – the Strelka pluton belonging to the Glushikha postcollisional complex (752–718 Ma) and the Yagodka pluton of the Tatarka active continental margin complex (711–629 Ma). The new U-Pb and Ar/Ar geochronological data for the postcollisional Glushikha plutons indicates that the age intervals for these complexes can be combined, showing the uninterrupted evolution of A-type magmatism during the change in tectonic setting of the region.

For accessory zircon from ash tuffs of the Basu and Zigan Fms of the Asha Vendian (Ediacaran) Group of the Southern Urals obtained isotopic U–Pb age (SIMS (SHRIMP II) и La–ICP–MS). The compositions of rare-metal enriched tuffs correspond to rhyolites, comendites, trachytes, trachyandesites. The concordant value of the U–Pb age of zircon from the tuffs of the Basu Formation is 578 ± 7, 577 ± 7 and 568 ± 5 Ma (SHRIMP II). The age of the zircon from the other two points of the Basu Formation is 573 ± 4 and 574 ± 3 Ma (La–ICP–MS). The age of zircons from the tuffs of the Zigan Formation is 566 ± 5 Ma (SHRIMP II). Tuffs accumulated in the hinterland of the marginal continental volcanic belt.

The distribution of rare earth elements (REEs) has been studied for the first time in different morphotypes of ferromanganese formations (FMFs) from the East Siberian Sea, namely, ferruginous and ferromanganese crusts, discoid nodules, and biomorphoses. The FMFs were formed at different distances from the land and, accordingly, from the main sources of sedimentary material during (sub)oxic diagenesis. Seaward, with an increase in the oxidation of sediments, primarily because of reducing sedimentation rates, FMFs, against a rising manganese content in them (Mn from 0.09% to 12.34%, Mn/Fe from 0.01 to 1.15), show a decrease in the total REE content (ΣREE from 166.90 ppm to 96.86 ppm), depletion in cerium (Cean from 0.90 to 0.71), and enrichment with middle REEs. Due to the rapid growth of FMFs, which should be faster than sedimentation rates, reactive REE species do not have time to accumulate; therefore, REE total content in FMFs is everywhere lower than in sediments.

The isolated upper premolar P⁴ of a multituberculate mammal is described from the new Early Cretaceous locality of Shavar-Ovoo in Mongolia (Övörkhangai aimag, Guchin-Us sum). It demonstrates the morpho-logy and measurements typical for Arginbaatar dmitrievae Trofimov, 1980 (Arginbaataridae). This is the first record of Arginbaatar (and the Early Cretaceous multituberculates of Mongolia in general) outside of the Höövör valley.

The study of the dynamics of periodic variations with periods from 1 to 27 days using the wavelet transform and scaling analysis by the method of maxima of the modules of the wavelet transform coefficients is carried out using the results of instrumental observations of the geomagnetic field performed at the Belsk Central Geophysical Observatory in 2008 and 2018 (low solar activity) and in 2014 (high solar activity). A change in the intensity of periodic variations is established. Close to monofractal nature of diurnal geomagnetic variations is shown. The 27-day variation and its harmonics have a higher degree of multifractality during solar activity maximum compared to solar activity minimum.

The spectral and dynamic parameters of the sources of regional seismic events have been studied for the territory of the Northwestern Caucasus using stations from the network of the Geophysical Survey, Russian Academy of Sciences and Crimean network. This is the first study for the region using such a large dataset. Moment magnitudes-Local magnitude calibration have been established for earthquakes of small and medium magnitude in the study area and linear dependence M_w = M_L + 0.16 is recommended for use. An interdependence between the values of energy classes and local magnitudes was also obtained, which can help to further improve the procedures for processing seismological monitoring data at Caucasian stations and the formation of regional catalogs.

Primary production (PP) and chlorophyll “a” concentration (chl “a”) estimates in the Eurasian Arctic are discussed, where the continued climatic warming with increased “Atlantification” advance the sea ice losses. The maximum integrated PP and the total chl “a” content observed in the marginal ice zone (MIZ) of the Barents Sea with weakened stratification of the water column and reached 1109 mgC m^–2 day^–1 and 118 mg m^–2. Nearby the ice edge in the Nansen Basin, the main part of PP formed in the upper mixed layer and did not exceed 469 mgC m^–2 day^–1, the chl “a” content of 56 mg m^–2. In the early and late phytoplankton bloom in MIZ, the typical leading role of picophytoplankton in carbon fixation revealed. Large centric diatoms, microphytoplankton, dominated at the peak bloom stage in 2020 with the dense marine ice cover of the Nansen Basin. A similar phenomenon was previously observed only in the Arctic shelf seas and was not recorded in the high-latitude basins of the Arctic Ocean. With the sparse ice cover of the Nansen Basin in 2021, the main primary producers at the peak bloom were pico- and nanophytoplankton. The low variability of assimilation numbers at all bloom stages (1.7 ± 0.3 mgC mg chl “a”^–1 h^–1) indicates the acclimatization of phytoplankton to changing environment. The ecological flexibility of the primary production are link of the MLZ ecosystems in the studied seas of the European Arctic during the period of climate change is confirmed.

A comparison of the new results on diatom micropaleontology with the available paleooceanological data on core PS1243-2 and global/regional paleoclimate archives made it possible to assume that neoglaciation in the central Norwegian-Greenland Basin near the Arctic front began no later than 4500 years ago. From this level, the Arctic front gradually approached the study area. There was a decrease in the influence of the mixed Arctic-Norwegian water, and the conditions on the surface became more contrasting, with an increase in signs of Arctic or North Atlantic (from the Norwegian Current) water. The moments of the greatest contrast are noted during short-term warmings of the Late Holocene.

The analysis of winter atmospheric blockings in the Northern Hemisphere (NH) under climate changes in 1980–2018 was carried out. The results of the analysis indicate a significant increase in the total duration of winter atmospheric blockings τ in the NH in recent decades. The noted trend was revealed against the background of a rapid increase in the NH surface air temperature T in winter seasons. The parameter of sensitivity of the atmospheric blockings duration to changes in the NH surface air temperature in winter seasons for the period 1980–2018 was estimated. The statistically significant estimate obtained means an increase in τ by more than one and a half times with an increase in the mean winter surface air temperature of the NH by 1K. A more significant relationship with T was obtained for values of τ above the average value of τ_c for the period 1980–2018, while at τ < τ_c, the relationship was found to be statistically insignificant. The noted features are associated with differences in different phases of the key modes of climatic variability. In particular, the mean value of the surface air temperature of the NH in winter in the positive phase of the Atlantic Multidecadal Oscillation (AMO) within the analyzed period of 1980–2018 significantly exceeded the corresponding mean value of T in the negative phase of AMO. At the same time, it was found that the mean value of the winter blockings duration in the NH in the positive AMO phase is one and a half times longer than in the negative AMO phase. For winter seasons, the estimates of the relationship between τ and the intensity of the Arctic anticyclonic center of action depending on the AMO phase were obtained.

The influence of contact with water of soil aggregates of chernozem, sod-podzolic and gray forest soils on their water stability has been studied. It is established that an increase in the contact time of soil aggregates with water leads to a gradual decrease in their water stability. The conducted verification of the effect of salt solutions on the water stability of soil aggregates showed that the loss of water stability of aggregates in contact with water is not directly proportional to the disjoining pressure. It was found that when soil aggregates come into contact with water, fractal clusters of humus particles (F-clusters) are isolated from them. It is suggested that F-clusters, which are the basis of soil gels, determine the physical basis of soil waterproofness.

Methods of mathematical modeling were used for estimating an influence of tectonic faults activation of safety of a facility for final isolation of high-level radioactive waste at the site Yeniseiskiy (Krasnoyarsk region) by methods of mathematical modeling. A 3–D model of radionuclides transport by groundwater was considered taking into account a heterogeneity of rock permeability. Faults of different orientation were considered. We showed that a formation of new near-meridional faults or an activation of ancient ones did not exert a substantial influence on velocity of radioactive pollution propagation in underground medium. Near-latitudinal faults can affect the radionuclides to a more extent. We considered a possibility to confine this influence due to a technogeneous decrease of rock permeability within a relatively short interval of the fault zone.