Volume 526, Nº 2 (2026)

This paper presents the results of a study of zircons recovered from ancient and modern diamond placers of the Lena–Anabar subprovince of the Siberian Diamond Province. The study includes U–Pb dating and the determination of trace and rare earth element concentrations using a SHRIMP-IIе ion microprobe. The research covered all major economic diamond placers of the Anabar, Kuonam, and Prilensky districts, along with placer occurrences in the Lower and Middle Olenek, Muno–Tyung, and Primorsky diamond-bearing regions.

Zircons associated with diamonds yielded Jurassic, Triassic, Late Devonian–Early Carboniferous, and Silurian–Early Devonian ages. These dates correspond well with the known ages of primary kimberlite sources. Analysis of both balance-grade and mined-out placers indicates that approximately 75% of the placer diamond deposits were sourced from Triassic primary kimberlite bodies.

A study was conducted on the shales and gneisses of the Pikamskaya Suite, which are part of the Tersk Terrane of the Lapland-Kola Orogen, Eastern Fennoscandia. These metamorphosed under amphibolite facies conditions rocks had a sedimentary protolith corresponding in composition to graywackes and lithites. Their accumulation occurred in an active tectonic setting during the erosion of predominantly felsic complexes with suprasubduction geochemical characteristics and Paleoproterozoic model ages t_Nd(DM) from 2.2 to 2.5 Ga. U-Th-Pb isotopic studies on detrital zircon revealed a multimodal age distribution with peaks ranging from 3.6 to 1.97 Ga. The predominant zircon grains are magmatic in origin with ages ranging from 1.97 to 2.2 Ga. Such zircons contain cores with older ages from 2.4 to 3.6 Ga. All the obtained data indicate that the sedimentary rocks of the Pikamskaya Suite formed through the erosion of Paleoproterozoic magmatic complexes, which contained an Archean crustal component, and were likely formed in a continental arc setting. Igneous rocks, which could have been the source for the predominant zircon age group of 2.02–2.20 Ga, are not known either within the Lapland-Kola Orogen or beyond its borders. The complete disappearance of igneous rocks of this age may be related to subduction and/or tectonic erosion. All the obtained data indicate that subduction processes in the Lapland-Kola ocean began at least 2.2 Ga ago, which sets a constraint on models of the early stages of the tectonic evolution of the Lapland-Kola Orogen.

Geochemical and geochronological (U-Pb zircon, ID-TIMS) studies of igneous rocks of the Olekma-Stanovoy dike complex in the eastern segment of the Stanovoy volcano-plutonic belt of the Central Asian orogenic belt have been performed. The emplacement age of rhyolite dikes from this complex has been established at 110±1 Ma, corresponding to the completion of the formation of the Stanovoy volcano-plutonic belt in its eastern segment within the Dzhugdzhur-Stanovoy superterrane. This terminal magmatic pulse of the Stanovoy belt (110 Ma) is represented exclusively by felsic rocks, including rhyolite dikes of the Olekma-Stanovoy complex, rhyolites of the Ugan volcanic field, and granites of the Irakan complex. All of them are classified as high-silica and high-alumina rocks of increased alkalinity with a predominance of potassium, and belong to the transitional geochemical type between A- and S-type granites. Unlike earlier granitoids from the batholithic stage of the Stanovoy volcano-plutonic belt's formation, they are enriched in rare elements, are significantly more differentiated, and lack the geochemical features of adakite-type magmatism characteristic of earlier igneous rocks in the eastern segment of this belt. These rocks likely formed under conditions of lithospheric extension, which is fully consistent with the concept of the formation of the Stanovoy volcano-plutonic belt during the post-collisional stage of geological evolution in the northeastern sector of the Central Asian orogenic belt.

In order to identify the sequence and conditions of crystallization of sulfides in a carbonatite melt, the isotopic composition of sulfur in pyrrhotite, pyrite, chalcopyrite, jerfisherite, sphalerite, alabandine and valleriite from rocks of the carbonatite series of the Guli alkaline ultramafic massif (Maimecha-Kotui province) was firstly studied using local femtosecond laser ablation and mass spectrometry. Alabandine, manganese-rich wurtzite, and iron-rich sphalerite are successively crystallized in polyphase sulfide assemblages of phoscorite and carbonatite. It was established that wurtzite crystallization began at a temperature of 660 °C and ended at 450 °C. The sulfur isotope composition (δ³⁴S) in sulfide minerals from phoscorite varies from -3.0 to -5.8‰ (n=24), with the exception of two analyses of Ni-bearing pyrite, characterized by a higher δ³⁴S value of -1.6±0.14‰. For sulfides from carbonatite, a steady shift towards lower δ³⁴S values was revealed (δ³⁴S from -3.9 to -6.9 ‰, n=22), which is typical for hydrothermal (carbothermal) environments. The δ³⁴S values for the most common sulfides – pyrrhotite, djerfisherite, pyrite – show variation and decrease from early to late generations, which is explained by an increase in the degree of oxidation and a decrease in the temperature of the carbonatite melt during the successive crystallization of phoscorite and carbonatite. The sulfur isotope composition of sulfides from carbonatite series rocks is indicative of a magmatic fluid source. No values characterizing the transition of sulfur from the sulfide to the sulfate state have been established.

Microorganisms (streptomycetes) have been identified for the first time that concentrate niobium. Based on its biochemical properties, this element has no known biological function and likely inhibits bacterial viability. Fossilized fragments of streptomycetes in the form of ball-shaped, tangled thin hyphae (200-300 nm thick) with a high niobium content (up to 29-32 wt% Nb) were discovered using scanning electron microscopy in the uniquely REE-Nb-rich ores of the upper horizon of borehole 6529 of the Yuzhny site of the Tomtor deposit.

New results of zircons study (U-Pb method, SHRIMP II) from metavolcanites of the upper structural-material unit of the Maksyutovsky complex, the Sakmara River, the Novotroitsky settlement area are presented. It is established that zircons from metavolcanites form three age clusters. Magmatic, oceanic populations of zircons of the Cambrian (517±7 million years) age fix the crystallization of basalt. Ancient continental-type zircons of Proterozoic (2060±22 Ma) age are xenogenic. Metamorphogenic zircons of Devonian (411±5 Ma) age reflect metamorphic processes corresponding to the conditions of the wynchite-green schist facies.

As a result of a comprehensive mineralogical and geochemical study of the Vladimirskoye gold deposit (Eastern Sayan), the authors for the first time established gold-bismuth-sulfosolic mineralization, unique to the southeastern part of the Eastern Sayan. The existence of various Bi, Pb, and Ag sulfosalts in ores, native bismuth and silver, which form specific geochemical associations and mineral accretions, indicates the complex genesis of ores and the involvement of polymetallic melts in the concentration and redistribution of gold and silver. The formation of ores is associated with the interaction of embedded collisional granitoids with rocks of the Sialic Archaean-Early Proterozoic basement of the Gargan block. The process of granitoid intrusion was accompanied by remobilization of matter and the appearance of a series of shear deformations at the accretion-collision stage (490-420 Ma) of the restructuring of the active continental margin. The concomitant high-temperature metamorphism of the amphibolite facies affected the redistribution and concentration of ore components.

Two isolated upper molars M1 of the ancient sun bear Helarctos malayanus praemalayanus (von Koenigswald, 1935) are described from the Middle Pleistocene deposits of the Tham Hai cave locality in northeastern Vietnam (Lang Son Province). Their structure shows morphological features typical for M1 of Middle Pleistocene representatives of the species. This is the first description of remains of H. m. praemalayanus from the Middle Pleistocene of Vietnam that expands understanding of the dental morphology and distribution of sun bears during the Pleistocene. Judging by dental measurements of H. malayanus from various localities of Southeast Asia, sun bears in the Middle Pleistocene were distinctly larger than modern ones. Apparently, at the end of the Late Pleistocene, sun bears became smaller and predominantly arboreal.

This paper examines for the first time the palynological characteristics from Elgygytgyn Lake sediments that were deposited during marine oxygen isotope stage 23 (MIS23). This stage, spanning the Piacenzian stage of the Pliocene and the Quaternary, previously had been a missing link in the lake's palynological record. The reconstruction of MIS23 phytocenoses closes the missing interval. This section of the Elgygytgyn Lake core represents the continuous record of the response of plant communities in Polar Chukotka to climate change during the Late Pliocene and Quaternary.

Keywords: oxygen isotope stage, lake sediments, Elgygytgyn Lake, Polar Chukotka, pollen zone, forest-tundra

This paper presents the results of studying a megathrust earthquake (Mw = 8.8) that occurred on July 30, 2025 in the Pacific near the east coast of the Kamchatka Peninsula. Ground motions with Community Internet Intensity (CII) ranging from 4.8 to 8.5 were felt in the Kamchatka Region and on Paramushir Island of the Sakhalin Region. Several buildings were damaged. The triggered tsunami caused inundation and damage to a number of facilities in Severo-Kurilsk (Paramushir Island) and on Shumshu Island. We have reconstructed the high-frequency source-related acceleration spectrum (A₀ = 1.26·10²⁰ N·m/s²) based on seismic recordings and macroseismic data and determined the role of high slip areas (asperities) on a fault plane in generating strong ground motion. The obtained results provide an explanation for the contrast between the high magnitude of the event and a moderate level of seismic impacts and a relatively low degree of destruction. The mean recurrence interval between megathrust earthquakes (Mw ≥ 8.5) in the Kamchatka segment of the subduction zone is 57.6 ± 21.6 years.

The seismic structure of three contourite drifts (sedimentary bodies formed by bottom currents), first identified in the Romanche Fracture Zone, is described. One of these drifts is the deepest known in the World Ocean. The drifts were formed by the flow of the Antarctic Bottom Water and are considered potential natural archives of the history of bottom water circulation in the Central Atlantic. Each of the identified drifts is separated from the fracture zone wall by an erosional contourite moat. The contourite moats were excavated by the current simultaneously with the formation of the drifts.

Boussinesq approximation generalized to account for compressibility of the liquid core was used in direct numerical 3-D modeling of turbulent thermal convection in a spherical shell. The modeling employed Archimedes, Rosby, Reynolds and Peclet dimensionless numbers corresponding to Ar=10¹⁰, Ro=10^-7, Re=Pe=10⁶. Introducing in the model Reynolds and Peclet numbers, which were assumed 1 in the previous works allowed computations equivalent to significantly greater Rayleigh number up to Ra=10²². Modeling results indicate that ring-like structures orthogonal to the rotation axis are formed in the liquid core. In the rotating spherical shell these structures correspond to toroidal flow patterns which move in opposite directions. Averaged rotation velocity of the liquid core is characterized by oscillations similar to the observed oscillations of length of day (LOD).

First detailed reconstruction of the natural environment of the North-Minusinsk Depression based on the study of a continuous, 280-centimeter long sedimentary core from the meromictic Lake Shira is presented. The age model is based on ten AMS¹⁴C dates. The main part of the section is represented by annually laminated series or varves, which allows the reconstruction with an average temporal resolution of 20 years. Limnogenesis at the lake's geometric center began ca. 5700 calibrated years ago. Vegetation changes in the North-Minusinsk Depression and around Lake Shira suggest a continental semiarid climate with decadal-centennial fluctuations in plant-available moisture. The local vegetation around Lake Shira was predominantly steppe and forest-steppe. The maximum expansion of steppe and the lowest lake level during the studied period are reconstructed at ca. 5700-4600 BP and 880-510 BP. The latter correlates with the Little Ice Age, the main glacial stage of the Holocene in the Russian Altai Mountains. Botryococcus abundance minima correlate well with the formation of whitish carbonate silts in Lake Shira sediments and can indicate both a lake level decline and disruption of its water column stratification.