Vol 522, No 2 (2025)

The results of U-Pb (SHRIMP) geochronological study enable to substantiate the ages of the key magmatic complexes in the Burkhan anticlinorium (BA) of the North Tianshan (NTS). Metarhyolites of the Tegerekkol Member, which represents the middle of three levels of felsic volcanic rocks in the Mesoproterozoic section of the BA, yield an age of 1138 ± 7 Ma. The timing of volcanism corresponds to the episode of emplacement of the oldest ca 1160–1120 Ma Mesoproterozoic granites in the Kochkorka and Makbal anticlinoria in the north and northwest of the NTS. Similar geochemical characteristics of the volcanic rocks in the BA and the granites in the Makbal area suggest that they represent products of similar parental melts. The time of epidote-amphibolite metamorphism in the Tegerekkol Member can be estimated in the range of ca 1140–1080 Ma based on the age of metarhyolite and the Pb-Pb age of weakly metamorphosed limestones that lie unconformably above. The post-kinematic granodiorites of the Djamanechke intrusion, previously considered Mesoproterozoic, yielded an age of 478 ± 5 Ma. Older ages obtained by previous multigrain zircon analyses may reflect the presence of ca 1140 Ma inherited old cores and zircon xenocrysts, which were likely derived from volcanic rocks of the Tegerekkol Member surrounding the intrusion. Considering the age of the youngest granite-gneisses that experienced ductile deformation and the established age of undeformed granite, the timing of the latest metamorphic episode in the BA is estimated in the range of ~494–478 Ma. This corresponds to the age a major structural and metamorphic event, broadly expressed in the NTS at the beginning of the Early Ordovician.

According to the results of paleomagnetic study, which are part of intergrated bio-, chemo- and magnetostratigraphic studies of the Upper Cretaceous of the North Caucasus, analogs of magnetic chrons C34n and C33r were identified in the Podkumsky quarry section near the city of Essentuki. Due to this, the Santonian-Campanian boundary was drawn in the section, by analogy with the limitotype of the Campanian Stage of Bottaccione (Italy), and the early Campanian age of the deposits was substantiated, by analogy with the reference section of the Campanian Stage in Kudrino village (Crimea). The high paleomagnetic quality makes the Podkumsky quarry a unique section of the Upper Cretaceous in magnetostratigraphic terms and a promising object for determining paleomagnetic poles and studying the fine structure of the Late Cretaceous geomagnetic field.

The paper presents first isotopic U-Pb zircon data (LA-ICP-MS method) on the intrusive rocks from the Yakhton stock, which is spatially and probably genetically related to the Yakhton tungsten skarn (tungsten-polymetallic-gold) deposit. This deposit, together with the other W and Au deposits, is part of the largest Au-W metallogenic belt of Tien Shan. The deposit is represented by zones of hydrothermally-altered skarn with scheelite and sulfides (pyrrhotite, chalcopyrite), and later (overprinting) near- and within-intrusive stockworks of veins and veinlets of late metasomatites (propylitic and phyllic alteration) with scheelite-gold and Ag-polymetallic mineralization. The concordant isotopic zircon U-Pb data obtained (305 ± 2 Ma for the early monzonite-quartz monzonite, 304 ± 2 Ma for the granodiorite of the main phase, and 285.4 ± 1.8 Ma for granite) indicate the intrusion emplacement in the Late Carboniferous-Early Permian. This is similar to the dates of the intrusions at the large Jialu Au-W deposit, which is situated in the same metallogenic zone and comprises, together with the early scheelite skarn, also late metasomatites with intense Au-W mineralization corresponding to a large Au deposit. Such age, geological and metallogenic proximity to the Jilau deposit highlights a potential of discovery of significantly greater, than it is currently known, Au-W mineralization at the Yakhton deposit.

The article presents the results of the study of the late Precambrian volcanogenic-sedimentary iron ore Bozdak series of the Sarysu-Teniz watershed in the west of Central Kazakhstan. The first U–Th–Pb (SIMS) age estimates (718±5 Ma) of accessory zircons from trachyrhyolites indicate that they formed at the very beginning of the Cryogenian period of the Neoproterozoic. Geochemical features of the effusive rocks indicate that the accumulation of ferruginous quartzites was accompanied by contrasting basalt-trachyrhyolite volcanism in a rift setting.

The paper presents the results of experimental modeling of the crystallization conditions of subcalcic Cr-rich garnets in the serpentine – chromite – carbonatite system at a pressure of 5 GPa and a temperature of 1300 °C. In the experiments, a mineral association of highly magnesian olivine and orthopyroxene, garnet and chrome-spinel was formed. It has been established that subcalcic Cr-pyrope can crystallize in the form of metacrystals during metasomatism as a result of infiltration of the fluid phase. In the presence of graphite, the fluid phase has a complex composition with predominance of hydrocarbons and oxygen-, nitrogen-, and sulfur-containing organic compounds with minor amount of inorganic gases, including CO2 and H2O.

The U-Pb (ID-TIMS) age of Ti-rich andradites (319±1 Ma) from calcite-silicate vein rocks uncovered by the Akhmatovskaya and Perovskitovaya mines in the contact zone of Precambrian gabbroids of the Kusa-Kopan intrusive complex and carbonate rocks of the Satka Formation in the Southern Urals has been determined for the first time. The mineral association of vein calcite-silicate rocks corresponds to rodingites. The U-Pb age of garnets from the veins coincides with the stage of the most intense folding and thrust deformations in the area of the Main Ural Rift and Magnitogorsk zone – 335-285 Ma. New geochronological data indicate a complex multistage history of mineralization of silicate-carbonate rocks in the contact zone of Kusa-Kopan gabbroids and Riphean carbonates.

The first ikaite find in bottom sediments of the East Siberian Sea is described. The ikaite was crystallized under low temperatures (probably around 7 °C) with the participation of carbon from oxidized organic matter (diagenesis).

New ⁴⁰Ar/³⁹Ar age data obtained from phlogopite and amphibole in alkaline-ultramafic lamprophyres of the Zhlobin and Severo-Uvarovichi fields within the Pripyat segment of the Pripyat-Dnieper-Donets rift system indicate that the emplacement of the lamprophyric pipes occurred within the interval of 372–381 ± 2 Ma, i.e., at the Givetian and Frasnian boundary. The early rifting/initial magmatic phase, during which the kimberlites and related alkaline ultramafic rocks were formed, occurred sub-synchronously in different parts of the developing rift system. This suggests the existence of a weakened metasomatized region of the lithospheric mantle beneath the future rift.

The results of sediments study in Lake Pertozero in the south-western coastal part of the Onega Peninsula, complemented by previously published results of the studies of the coastal sections of marine terraces, enabled reconstructing the relative sea-level changes in the southern part of the Onega Bay in the Late Glacial and the Holocene. In the Late Glacial, the depression of Lake Pertozero was inundated by the waters of a freshwater proglacial lake, which level could reach 30 m a.s.l. The regression of the proglacial lake below the elevation of Lake Pertozero (11.6 m a.s.l.) took place around 11.1 ka cal. BP. After ~11 ka cal. BP and at least until ~10.1–9.5 ka cal. BP the relative sea level in the southern part of the Onega Bay exceeded ~4 m a.s.l. However, it did not reach the elevation of Lake Pertozero where freshwater benthic diatoms characteristic of recently isolated lakes flourished that time. The subsequent regression terminated prior to ~7.6 ka cal. BP. The relative sea level during the subsequent transgressive phase exceeded 7-7.5 m above sea level, however, remained below 11 m, as evidenced by the presence of exclusively of freshwater species in the diatom assemblages of Lake Pertozero. The reconstructed dynamics of the relative sea-level changes in the southern part of the Onega Bay generally correspond to those in the western part of the White Sea, the north-western and eastern coasts of the Onega Peninsula, however, the time frames and amplitudes of the transgressive and regressive stages differ markedly.

Based on the analysis of the results of instrumental observations, it is shown that the 4.2 magnitude earthquake that occurred on January 12, 2025 in the Black Sea was accompanied by well-recorded acoustic effects and variations in electric and magnetic fields recorded at a considerable distance from the seismic event. The ionospheric effect of the earthquake under consideration has been established in the form of variations in the critical frequency F2 of the ionospheric layer f₀F2, according to the data of the Nicosia ground-based sounding station located at a distance of 1113 km from the epicenter of the earthquake.

In developing the theoretical foundations of surface-wave seismoacoustic methods for non-destructive testing of layered geophysical media, the field of applicability of the previously proposed analytical approach based on conservation of energy flow [9] for estimating the amplitudes of surface waves in layered inhomogeneous media with a smooth horizontal change in elastic parameters within the layers has been investigated. The results of comparing analytical and numerical solutions for model media of various structures are presented, the dependence of the discrepancy on the geometric parameters of the model and the contrasts of elastic parameters are investigated, and the conditions of applicability of the analytical approach to practically significant problems solved by means of a family of surface-wave seismic exploration methods are evaluated.

The paper presents the results of calculating the near-surface mean annual temperatures (MAT) and the mean annual precipitation (“simple” and “more rational” variants) for source areas using the major oxide composition of mud rocks of the Riphean stratotype. It was found that during most of the time interval 1750–600 Ma, the climate was comparable to, according to the classification [20], temperate (9 ≤ MAT < 23°C) and, less often, tropical (MAT > 23°C) or dry cold (MAT < 18°C). Considerations are put forward about the relationship of the Riphean paleoclimate both with the sublatitudinal drift of crustal blocks and with various subglobal and local events.

The article presents the results of the analysis of spatiotemporal patterns of long-term river runoff dynamics in the Ural River basin. The absence of statistically significant and unidirectional trends is noted, which is due to the transformations of the intra-annual runoff distribution within the studied basin. Climate-induced changes in river water content are confirmed by the synchronicity of runoff fluctuations in most rivers of the Ural River basin. Five phases of runoff change in the studied basin for 1938-2022 are distinguished, characterized by different duration and intensity.

Assigning to the calendar time scale of the first in Russia and the longest in the world 377-year "charcoal" tree-ring chronology (TRC), numerous radiocarbon dating of charcoal fragments from slags and the unique find of tree bark argue for operating of box-shaped iron-smelting furnaces of the Kosh-Agach type in the Chuya-Kurai paleo metallurgical province (Russian Altai) in the 7^th-8^th centuries AD, i.e. in ancient Turkic times. This result closes the recently announced “paradox of ancient Turkic metallurgy” – the inexplicable sudden disappearance of iron production in Southern Siberia in the 7^th century AD. The constructed “charcoal” TRC indicates that the “old wood” effect in the high mountainous Chuya-Kurai region is at least 290-370 years. The enrichment of slags with ancient parts of wood of long-lived trees does not allow the time of smelting events to be directly established even with numerous ¹⁴C dating. The only way to solve the "old wood" problem is to date the bark, which is a unique find. Cross-dating of charcoal fragments from three distant paleometallurgical sites shows the presence of a common climatic signal: about 1.5-1.3 ky ago, the now forestless eastern periphery of the Chuya Basin was occupied by tree vegetation, which completely disappeared under conditions of progressive aridization and intensive cutting for economic needs by nomads.