Vol 525, No 1 (2025)

The article presents the results of petro-geochemical and geochronological studies of granitoid fragments collected in terrigenous sediments in the junction zone of the Gakkel Ridge with the Laptev Sea continental margin of Eurasia during the special marine geological expedition "Arctic-2022". The Carboniferous-Permian age of the granitoids and the maximum proximity of their composition to the granitoids of Northern Taimyr were established. The sources of the studied rocks in the immediate continental frame of the Gakkel Ridge and the Laptev Sea could be granitoids that participate in the structure of the fold belts of Northern Taimyr and Severnaya Zemlya.

The first isotope-geochronological studies of rocks from Matua Island (Central Kuril Islands) are presented. These rocks, found at the base of the Neopleistocene-Holocene volcanic edifice, belong to the earliest stages of magmatic activity. Based on K-Ar dating, 10 age values ranging from 3.9 to 1.02 million years were obtained for rocks from the Yurlovskaya and Dvoynaya formations. The Yurlovskaya suite was formed within the age range from the Middle Pliocene to the Gelasian (3.9±0.3–2.02±0.13 million years ago), while the Dvoynaya suite was formed during the Gelasian Age (2.09±0.14 million years ago). The formation of the extrusive dome of Mount Kruglaya and the subvolcanic body of Skala Krepost' (Ainu Bay) occurred 1.02 ± 0.13 and 1.08 ± 0.15 million years ago, respectively.

Using the high-precision (±0.02%) MC-ICP-MS method, the lead isotopic composition of galena from four Late Cretaceous (95-85 Ma) tin ore deposits of the Khingan-Bajal-Komsomolskaya metallogenic zone (KhBKZ), which is part of the Khingan-Sikhote-Alin ore province (KhSAP), was studied. In comparison with other previously studied KhSAP tin deposits, the KhSAP ore lead has lower isotopic ratios ranging as 206Pb/204Pb = 18.359-18.497, 207Pb/204Pb = 15.565-15.588, and 208Pb/204Pb = 38.369-38.404. In the 206Pb/204Pb-207Pb/204Pb diagram, the points of the KhBKZ lead isotopic compositions of the are located significantly below of orogenic evolution curve (according to the Zartman-Doe model) and the average crustal curve (µ2 = 9.74) according to the Stacey-Kramers model. According to these evolutionary characteristics, as well as the values of the Th/U parameter and the Tm model age, the KhBKZ ore lead differs from KhCAP lead, indicating a significant difference in the geochemical and geodynamic conditions of the KhBKZ deposits formation. In particular, it indicates a limited contribution of the continental crust, a significant role of mantle lead origin and the participation of a regional mantle source in the formation of tin-bearing granitoid magmas. Model calculations of the lead balance of mantle and crustal sources in the ore lead of KhCAP and KhBKZ show that for KhCAP the contribution of the mantle source was less than 50%, and, in the case of KhBKZ, it could reach 70-90%. Perhaps the main geological factor that caused the noticeable participation of mantle lead in the KhBKZ deposits was the environment of their formation: unlike the KhCAP, these deposits were formed in the environment of a transform margin, when due to the interaction of moving plates, a larger admission of mantle into the zone of granite formation and ore deposition occurred. Under these conditions, the oceanic plate could breakaway with the admission of the hot asthenosphere into the accretion prism.

The first geochronological and petrogeochemical data on the Middle Jurassic granites of the metalliferous Ariadna ultrabasic-basite intrusion of the Sikhote-Alin orogenic belt are presented. These granites with U-Pb zircon ages of 165.2 ± 1.1 and 165.48 ± 1.1 million years are highly differentiated A-type rocks formed as a result of melting of terrigenous rocks during the introduction of an ultrabasite-basite OIB melt into an accretion prism.  The results obtained confirm the hypothesis of a possible rise of asthenospheric material from under a sinking oceanic plate in an unusual geodynamic setting.

The paper presents data on the concentrations and composition of hydrocarbons (aliphatic hydrocarbons - AHC and polycyclic aromatic hydrocarbons - PAH) in ice, surface microlayer (SML, up to 1000 μm thick) and surface waters in the Barents and Kara Seas (cruise 96 of the R/V Akademik Mstislav Keldysh, July-August 2024). Due to the water content of the ice, only a slight accumulation of hydrocarbons occurs compared to surface waters and compared to the SML. As before, the influence of autochthonous processes on the composition of alkanes in ice and SML is insignificant and differs from their composition in multi-year ice. Despite the different sources of these hydrocarbon classes, a dependence in the distribution of AHC and PAH in suspension in the SML was observed for all the samples collected (r = 0.67, p = 0.05.). Key words: melting ice, surface microlayer, aliphatic and polycyclic aromatic hydrocarbons, alkanes, Barents and Kara Seas.

The article provides a characteristic of changes in the biogeochemical parameters of the Arctic Lake Imandra in a long-term series of observations. It is proven that along with a decrease in metal concentrations, the lake is becoming eutrophicated. The biogeochemical cycle of metals is considered due to the oxidation of organic matter and the development of the redox cycle, which leads to the formation of high concentrations of metals in the surface layers of bottom sediments despite a decrease in the influx of polluted wastewater. A conclusion is made about the effects of secondary pollution of the bottom layers of water and the occurrence of diagenesis processes in technogenic sludge.

In the Northern Mongolia major Early Mesozoic magmatic events are the formation of large Cu-Mo Erdenet deposits and volcanic activity in the Orkhon depression system. Even though they are spatially related, their temporal and genetic comparison have not been determined yet. This paper focuses on geochronological and geochemical studies of volcanic rocks of the Mogod Formation from three depressions (Mogod, the Khushig-Und-Er and Bugat) and data correlation with igneous rocks from Cu-Mo Erdenet deposit. The Mogod Formation mainly consists of basaltic trachyandesites and trachyandesites with subordinate trachytes. The age of volcanism was estimated using the U-Pb CA ID TIMS method on zircon from trachytes of the Bugat depression (236±1 Ma) and the ⁴⁰Ar-³⁹Ar method on amphibole from basaltic trachyandesites of the Khushig-Und-Er (230±6 Ma) and the Mogod (233±4 Ma) depressions. The obtained age interval coincides with the final stage of ore-bearing porphyry magmatism of the Erdenet deposit, located on the edge of the Bugat depression. Geochemical comparison of the Mogod Formation and the porphyry complex revealed common signatures from both basic and acid rocks, such as the depletion of HREE, Nb, Ta and Ti, as well as the significant enrichment of Ba, LREE and Sr. The obtained geological, geochronological and geochemical data allow us to conclude that the Cu-Mo magmatism responsible for ore formation and the widespread volcanism of the Mogod Formation are the result of common magmatic event.

 Lamproites are a group of ultra-alkaline rocks enriched with rare lithophilic elements and have high ratios of K₂O/Al₂O₃ and K₂O/Na₂O, the K₂Ocontentcanreach12%. The Quaternary(about56,000years old)lamproites of the Gaussberg subglacialvolcanoareauniquegeologicalobjectlocatedon the continentalmargin[Sushchevskayaetal.,2014]and,thus,provide us an opportunity to study the features of the continentalmantleunder the Antarctic continent. The rocksappear as apillowlavas,tufobreccias and as usual consistofolivine microphenocrysts,clinopyroxene,leuciteandmultipleaccessoryminerals,mainly of primaryorigin as a minororeminerals–ilmenite,titano-magnetite;amphibolesandmicas. The inclusions are up to2mm in sizeand are distributedin the bulk rock,presentedofclinopyroxene,amphibole,phlogopite,apatite,diopside.

The aim of this work was to determine the sequence and conditions of crystallization of ultrakali Gaussberg magmas based on the study of petrographic and mineralogical features of natural samples, as well as our experiments on the crystallization of the initial melt at different temperatures. During the investigation were studied 16 samples of Gaussberg lamproites, selected during the 2nd Soviet Antarctic Expedition of 1956-1958, a detailed description of which was previously presented in our works]. Previously, two groups of clinopyroxene inclusions were identified in Gaussberg lamproites, differ in the form of occurence and in the content of the main petrogenic components: more magnesian grains of diopside composition and more ferrous grains of salic composition (the so-called "green cores").To determine the geochemical features of the selected groups of clinopyroxene grains, we provide a detailed study. In addition to the previously obtained data from the rock layers, a study of the mineral in the cuts was conducted. The contents of the main petrogenic components were determined in the geochemistry of the Russian Academy of Sciences using a TESCAN MIRA 3 scanning electron microscope (ULTIM MAX 100 EMF detector). The content of impurity elements was obtained at GEOHI RAS using inductively coupled plasma mass spectrometry with laser ablation (LA-ICP-MS) on an Element-XR mass spectrometer (Thermo Finnigan) with an UP-213 laser attachment (New Wave Research).

We present the results of instrumental observations of geophysical effects that accompanied the catastrophic earthquake in Myanmar on March 28, 2025. It is shown that the seismic event was accompanied by the generation of an infrasound signal and variations in the amplitudes of the magnetic and electric fields in the surface atmosphere. It is also shown that the earthquake caused an increase in the GPS positioning error at a significant distance from the source of the event. We is demonstrate the ionospheric effect of the earthquake in the form of a variation in the critical frequency of the F2 layer of the ionosphere based on the results of processing the data from the Okinawa ionospheric sounding station.

A new methodological approach to the identification of zones of potential earthquake foci locations (FEFL), tested on the territory of the Republic of the Union of Myanmar, is proposed. It involves processing morphometric relief parameters related to seismicity in the best possible way using the method of equivalent gradations or using the fuzzy logic apparatus. The integral morphometric index (neotectonic activity index) calculated in this way is compared with the relative stress values estimated from computer modeling data. These 2 parameters form the basis of the PEFL zone identification algorithm, which may be in demand for seismic zoning, primarily of remote and poorly studied territories, since it is based on publicly available source data and is largely formalized.

This study presents the results of an investigation into the transport characteristics of Antarctic Bottom Water (AABW) through the Vema Fracture Zone in the equatorial Atlantic. The analysis is based on observational data primarily collected during expeditions conducted by the Shirshov Institute of Oceanology of the Russian Academy of Sciences and the Faculty of Geography of Moscow State University. The study incorporates direct current measurements, numerical modeling using the INMOM model, and the GLORYS12v1 reanalysis. A comparative analysis of the data from various sources was carried out to evaluate water transport through the fracture zone. The role of the Vema Fracture Zone in the spreading of AABW was examined, and the main characteristics of near-bottom flows were identified. According to direct measurements, modeling results, and reanalysis data, the transport of AABW through the Vema Fracture Zone - using the θ = 1.7°C isotherm as the upper boundary - amounts to 0.9 Sv (observations), 0.8 Sv (model), and 0.7 Sv (reanalysis). The near-bottom isotherms differ across the data sources. Nevertheless, all data types yield similar estimates of bottom water transport (with a maximum discrepancy of up to 20%), indicating good performance of the numerical modeling in the fracture zone.

Estimates of specific fluxes of methane and carbon dioxide into the atmosphere, associated with groundwater sources of continuous permafrost in central Yakutia were obtained for the first time. Average specific flux of methane from intensively emitting groundwater sources is 211±85 mgC·m^-2·h^-1, and carbon dioxide is 93±67 mgC·m^-2·h^-1, which significantly exceeds specific fluxes of these gases from many subaerial ecosystems. Dissolved methane concentration is also high and varies from 1.6 to 4.8 mg·L^-1. Research results emphasize the importance of groundwater discharge areas as methane sources in continuous permafrost and indicate the need for their further study in order to more accurately account for its contribution to the overall greenhouse gas balance and establish the origin of greenhouse gases.

In the paper discusses why the intrasecular fluctuations of  the level of the great lakes of Eurasia differ so significantly. The paper addresses both the phenomenon of the lowest position of the Caspian water level over the entire the history of observations and the problems of regulation of the Lake Baikal level that have been discussed over the past several decades. The paper substantiates the causes of an essential difference in the intrasecular fluctuations and multidirectional trends in the level of Ladoga and Onego lakes that are part of a single water system. Discussed are the specific features in the variability of the level of the great Eurasian lakes amid the global climate warming, the mechanisms of the lake level variability and the possible ways of forecasting long-term changes in lake water level.

Studies were carried out in the forest-steppe zone of the Central Chernozem region in the Belgorod and Voronezh regions.  The soil cover was mainly represented by typical and leached chernozems. The purpose of the work was to conduct an agroecological assessment of the zinc content in arable soils, fertilizers and agricultural plants. In the course of studies based on local monitoring data, it was found that the average content of acid-soluble forms of zinc in the arable layer of chernozems is in the range of 36.1-36.5 mg/kg. The results of continuous agroecological monitoring for the eighth and tenth cycles indicate that the weighted average content of mobile forms of zinc in the soils of the Belgorod region is at a consistently low level (0.5 mg/kg), and in the soils of Voronezh it has decreased from 0.45 to 0.30 mg/kg. Accumulation of this element is observed in the soils of roadside ecosystems. An important source of zinc in agroecosystems are organic fertilizers, especially manure runoff and straw-dung composts.  The average zinc content in the hay of perennial legumes ranged from 14.0-17.8, in the main production of leguminous crops - 26.5-43.5, grain crops - 17.6-28.6 mg/kg. In sunflower seeds the content of the element was 41.1, in sugar beet roots – 9.2 mg/kg. In all studied crops, with the exception of sugar beet, the zinc content in the main product was higher than in the by-product. Exceeding the maximum permissible concentrations of zinc in soils and the maximum permissible levels of content in feed products was not recorded.