Vol 514, No 2 (2024)

The age of potassium-bearing minerals from high-K nepheline syenites, libeneritized and carbonatized nepheline syenites, as well as pseudoleucite syenites of the Bogdo alkaline massif (Arctic Siberia) was determined by the ⁴⁰Ar/³⁹Ar method. As a result of generalization and analysis of the ⁴⁰Ar/³⁹Ar dating data, on the summary thermochronological diagram for minerals from the rocks of the Tomtor massif, the Udachnaya-Vostochnaya kimberlite pipe, and alkaline rocks of the Bogdo massif, the polychronicity of the formation of alkaline complexes of the Tomtor type at the Paleozoic stage was revealed. Based on isotopic data, a complex, three-stage history of the formation of the rocks of the Bogdo massif is reconstructed, with the manifestation of the Late Devonian-Early Carboniferous stage – the most productive for rare-metal-rare-earth mineralization. The Devonian period of the formation of the Tomtor and Bogdo massifs is associated with the impact of the Vilyui plume on the eastern edge of the Siberian craton. A close age interval is fixed during the formation of the rocks of the Kola alkaline province.

According to the Anabar massif western slope geological survey in the Kotuy River middle reaches, the Kotuy intrusive complex was identified. It represented by dolerite-gabbrodolerite sills and dikes of Vendian age (556 ± 28 Ma). A number of sills are characterized by 30–80 m thickness, and dikes often have a length of the top tens km. The complex distribution area is the first hundreds of km². At the same time, the geodynamic reasons for the formation extensive intrusive bodies in the north of Siberia in the Vendian are not clear. We present new geochronological, geochemical and paleomagnetic data indicating that at least part of the Kotuy magmatic complex intrusions in the middle reaches of the Kotuy River should be attributed to the ~1500 Ma Kengede magmatic complex (Kuonamka large magmatic province). In this light, the question arises about the correctness of the allocation of the stage of intrusive magmatism of the Vendian age on the western slope of the Anabar massif.

The ⁴⁰Ar/³⁹Ar isotope dating of newly formed micas and chlorites from thrust zones made it possible to establish that they were formed in the Tithonian (150 Ma). The thrusts involved sedimentary rocks of a wide age range from Devonian to Triassic. In the Silurian rocks of the Drem-Hed Mountains of Wrangel Island, an older stage of deformations of 257 Ma was established for Wrangel Island, which corresponds to the Late Permian stratigraphic interval, and indicates the existence of deformations after the manifestation of the Ellesmere orogeny in the Early Carboniferous.

Unusual zircon-titanomagnetite ores were discovered the ore field of the Tretyakovskoe gold-fluorite deposit, which is part of the Gilberinsky gold-silver-fluorite-rare-metal ore cluster. Quartz-fluorite vein-like bodies (vein zones) forming the deposit are areas of metasomatic argillization, fluoritization and silicification, with a thickness of about 0.3–1 m, rarely up to 2.3 m. A feature of quartz-fluorite ores of the Tretyakovskoe deposit is their increased gold content. According to exploration data, gold grades in ores vary from 0.3 to 19.5 ppm, with an average value of 3 ppm, silver – 1.9–18.6 ppm, with an average value of 7 ppm. Unusual zircon-titanomagnetite ores are composed of an aggregate of Fe-Ti minerals with rare thin veinlets of quartz-chlorite composition, containing numerous segregations of idiomorphic zircon crystals and rare dissemination relative to apatite, quartz and monazite. In situ U-Pb isotopic dating of zircon using LA-ICP-MS showed a value of – 277±1.5 Ma, corresponding to the age of rift magmatism in Western Transbaikalia. The discovery of such unusual zircon-titanomagnetite ores in association with gold-fluorite mineralization determines the possibility of finding a new type of complex ores similar to the precious metal ores of South Australia in the territory of Transbaikalia.

Within the Altai-Sayan fold region, covering the territory of the East Tuva Highlands and Eastern Sayan, one of the richest rare metal provinces of Russia is concentrated. Deposits of rare metals, elements and lands formed within its limits have different ages and arose in different geotectonic environments and in different metallogenic eras. They are associated with the introduction of alkaline rock masses that are common along the fault system between the caledonids of the Altai-Sayan fold region and the Tuvino-Mongolian Precambrian superterrane. Their distribution range is also defined as the East Sayan rare metal metallogenic zone (VSMZ), which arose due to the impact of mantle plumes on the southwestern framing of the Siberian platform. Geochemical and geochronological studies were carried out at the Ilei fluorite-phenakite ore show. Ore development resulted from the introduction of Ognite complex granitoids into the limestones of the Mongoshin formation, which became a geochemical barrier to the igneous fluid enriched with fluorine and Be. Geochronological Rb-Sr and Ar-Ar studies have shown that subalkaline granites, as well as acidic volcanites of the Ilean sequence, are of Middle Devonian age ~ 390 million years, which is consistent with age estimates for the rocks of the Ognite complex. Thus, the same age of magmatism and ore formation at the Ilei ore phenomenon indicates the contribution of Devonian magmatism to the formation of rare metal mineralization within the VSMZ.

The paper considers the results of a study of particles of carbonaceous substance and sulfur isotopes of associated sulfides in metapelites of the Neoarchean banded iron formation (BIF) of the Kostomuksha greenstone belt of Karelia (Karelian Craton of the Fennoscandian Shield). According to the petrographic observations, the carbonaceous matter occurs within and between silicate minerals’ grains, inside sulfides or at the grain boundaries, separating sulfide crystals from biotite or amphibole. Scanning electron (SEM) and atomic force (AFM) microscopy revealed the several types of the carbonaceous material varying in structure and carbon content. Raman spectra approved both well-structured graphite and weakly structured graphite (kerogen) components of the carbonaceous substance. The isotopic composition of total organic carbon is typical for biogenic processes. The obtained δ¹³C_org value within the range of –27,9– –30,6‰ is consistent with carbon fixation by photo- or chemoautotrophs. The sulfur isotopy of the associated sulfides is marked by positive Δ³³S anomaly (up to +0.94‰) and negative δ³⁴S values (–2.06‰ ─ –4.1‰). Positive Δ³³S values indicate sulfur genetic association with photochemical elemental sulfur (S₈) from the atmosphere, while negative δ³⁴S values reflect isotope fractionation in bacterial-mediated processes. Based on these observations, we believe that the initial carbonaceous substance has mainly organic origin.

We present new data on the U–Th–Pb geochronology, mineralogy, geochemistry, and Sm-Nd and Rb-Sr isotopes for granitoids and associating subalkaline rocks of the Tarbagannakh pluton of the Allakh-Yun tectonic zone in the Verkhoyan fold-thrust belt. These rocks, including trachyandesibasalt dikes, combined into the Uemlyakh complex, were formed ca. 120 Ma from a continental crust source probably with input from and enriched mantle component. Rapakivi granites are reported for the first time in these intrusions – their origin is an important reference for understanding the geodynamic formation setting for this complex. We propose a tectonic model for the formation of these rocks due to slab break-off during the development of the active continental margin in the Aptian age. We discuss that this magmatism was conducive for the widespread development of metasomatic processes until the end of the Aptian age and was at the same time a source of gold mineralization of the overlapping Okhotsk-Koryak metallogenic belt.

A geodynamic model of the modern Earth is constructed based on the SMEAN2 global seismic tomography model with an emphasis on the Arctic region. For a spherical Earth model, a solution to the Stokes equation for a viscous fluid was obtained based on seismic tomography data using the finite element method using the CitcomS code. The resulting distributions of temperature anomalies and velocity fields of mantle flows explain the main features of the modern geodynamics of the Arctic region. The temperature difference in the subcrustal mantle between the relatively “cold” western Arctic shelf (Barents and Kara seas) and the “warmer” eastern Arctic shelf (from the Laptev Sea to the Bering Strait) reaches 100 degrees, which correlates with the observed intense methane emission from the shallow shelf of the Eastern Arctic caused by permafrost degradation and destruction of gas hydrates against the background of elevated environmental temperatures. The greenhouse effect of methane in the atmosphere, in turn, contributes to climate warming in the Arctic. The region of Iceland and eastern part of Greenland, under the influence of the mantle upwelling, is characterized by a hot subcrustal mantle and increased heat flow at the surface, causing instability and melting of the Greenland ice sheet from below.

The fossils of the genus Yochelcionella Runnegar et Pojeta, 1974 from the Salanygol and Khairkhan formations of the Zavkhan structural-facies zone were re-studied as a part of the general revision of malacofauna from the Vendian–Lower Cambrian deposits of Western Mongolia. It was found out that studied strata, in addition to the earlier reported species Y. parva Zhegallo, 1996 and Y. crassa Zhegallo, 1996, contain two other forms identified as Y. chinensis Pei, 1985 and Yochelcionella sp. Y. chinensis has the widest distribution among species of the genus Yochelcionella and can be successfully used to correlate sediments of remote paleobasins. The diagnosis and composition of the genus Yochelcionella are revised, the species Y. chinensis is described.

For the first time we showed that the often-used approximation of the Andrade rheology with only one parameter is oversimplified and might lead to incorrect conclusions when studying the internal structure of the planets of the Solar System. Instead, we used an Andrade rheology with two empirical parameters: α and ζ. Earth’s viscoelastic Love numbers for the principal lunar semidiurnal tide M₂ were computed for two viscosity profiles and for 16100 different combinations of α and ζ values. The comparison of the computed Love numbers with its measured values allowed us to constrain the set of values of both parameters that successfully describe the rheological properties of Earth’s mantle.

An analytical solution is obtained for seismic wave fields in a spherically symmetric Earth. Asymptotics is used for stable calculation of wave fields. It is shown that the classical asymptotics in the case of a ball of large (in wavelengths) dimensions gives an error in the solution. The original asymptotics is used for efficient calculation of a solution without errors with high detail. A program has been created that makes it possible to carry out calculations for high-frequency (1 hertz and higher) teleseismic wave fields in a discrete (layered) sphere of planetary dimensions. Calculations can be carried out on personal computers with OpenMP parallelization. In the works of V. Yu. Burmina (2010, 2019) proposed a spherically symmetric model of the Earth. It is characterized by the fact that in it the outer core has a viscosity and, therefore, an effective shear modulus other than zero. For this model of the Earth, a highly detailed calculation was carried out with a carrier frequency of 1 hertz. As a result of the analytical calculation, it was found that high-frequency oscillations of small amplitude, the so-called “precursors,” appear ahead of the PKP waves. An analytical calculation showed that the theoretical seismograms for this model of the Earth are in many respects similar to the experimental data. This confirms the correctness of the ideas underlying its construction.

The data of gas geochemical studies of bottom sediments of the Laptev-Siberian transition zone are presented. The established isotope-geochemical indicators determine the dominance of epigenetic hydrocarbon gases of various gas sources in the sediments. Methane concentrations up to 8.3047 cm³/ kg and the sum of its homologues up to 0.0260 cm³/kg indicate the formation of hydrocarbon anomalies exceeding the anomaly criteria for Arctic shelf sediments by 166 and 26 times. The main geological factors for the formation and distribution of anomalies in the bottom sediments of the Laptev-Siberian transition zone are the high gas content of the underlying sediments and gas sources, fold and fault tectonics, geostructural position, seismic activity and depth of occurrence of hydrocarbon sources.

The dynamic barrier is one of the physical characteristics of the polar vortices; it prevents subpolar air masses from penetrating into the vortex and contributes to a temperature decrease inside the vortex in the lower stratosphere. In the presence of a dynamic barrier in winter, chlorine compounds involved in the ozone destruction cycle accumulate on particles of polar stratospheric clouds (PSCs) and heterogeneous reactions occur with the formation of molecular chlorine, and with the appearance of solar radiation over the polar region, photochemical reactions begin, leading to large-scale ozone depletion. When the dynamic barrier is weakened in winter, the temperature inside the vortex rises, PSC melts and, thus, the accumulation of chlorine cycle reagents on PSC is interrupted. We proposed dividing the Arctic polar vortex dynamics into 3 types according to the consequences: (1) the strong vortex, whose activity results in ozone depletion, (2) the weak vortex with breakdown in winter, marked by a sudden stratospheric warming, and (3) the stable vortex with an episode (episodes) weakening of the dynamic barrier in winter without ozone depletion in the period from late winter to spring. We have for the first time proposed a characteristic of the dynamic barrier of the polar vortex at all pressure levels from 100 to 1 hPa and described the consequences of its weakening. Using the vortex delineation method based on the data of the ERA5 and MERRA-2 reanalyses, we showed that in all cases when the polar ozone depletion was not recorded from late winter to spring under the conditions of the stable polar vortex, the dynamic barrier weakening and PSС melting was observed in midwinter.

Using scanning micro-X-ray fluorescence analysis using synchrotron radiation, profiles of changes in the depth of the section in the elemental composition of the banded clays of Lake Peyungda (Krasnoyarsk Territory, Evenkia), located 30 km southwest of the epicenter of the Tunguska event (1908), were obtained. The age model is confirmed by the presence of a dated layer of anomalous thickness associated with the fall and explosion of the Tunguska cosmic body (TCB). Changes in element contents in dated core layers are compared with instrumental meteorological observation data over the last century, and a relationship is found between the average annual temperature of the region and the elemental composition of coeval layers of bottom sediments (transfer function). Approximation of the transfer function to the sampling depth of the sedimentary section made it possible to reconstruct the air temperature in the studied region over the past 1000 years. Comparison of the resulting reconstruction of average annual temperatures in the study area with global temperature reconstructions for the Arctic region for the same period shows the presence of general trends and extremes.

Summary of the results of the analysis of the spatiotemporal variability of sub-mesoscale eddy structures on the surface for Lake Ladoga from May to October 2019–2022 is conducted. The original data consists of over 1000 high-resolution Sentinel-1A/B images. It has been found that eddy structures are widely distributed during the warm period of the year in the lake’s basin. A total of 496 surface manifestations of eddies were recorded. The average diameter of the observed structures was 2 km. More than 90% of the recorded eddies belong to the sub-mesoscale variability range. Cyclonic rotation was observed in 84% of the structures. The seasonal maximum of eddy activity is observed during the development of stable stratification over most of Lake Ladoga. Eddies are most frequently encountered to the north and northeast of Valaam Island in areas with depths of around 100 meters, but in close proximity to the unevenness of the seabed. Eddy formations are often observed on the cold side of the frontal boundary during the existence of the spring thermocline, indicating their important contribution to water exchange and mixing processes.

Anomalously intensive gas seeps on the sea surface due to damage to Nord Stream 1 and Nord Stream 2 underwater gas pipelines in the Baltic Sea have been analyzed using optical (Kanopus-B and Sentinel-2B) and radar (Sentinel-1A) satellite images. Positive contrasts of NRCS (up to 7.5 dB) registered by Sentinel-1A radar and of spectral reflectance (up to 0.73 units) registered by Kanopus-B and Sentinel-2B optical sensors have been detected in the area of such gas seeps. Those seeps’ features were revealed on the sea surface, namely dome-shaped swells, fountains, vortices, foam, wave breaking, surface wave structure disturbance, and wind shadow. Taking into account the volume and density of gas located in the damaged pipelines, it is shown that the total volume of methane release was no more than ~ 0.51 Tg, i. e., less than 0.1% of the annual global methane emissions into the atmosphere.