The deep terrestrial biosphere is the vast biome beneath the soil layer that contains the majority of the Earth's prokaryotic biomass, yet it is one of the least investigated communities. Although, estimates of deep biosphere biomass suggest biofilm cells outnumber the planktonic biomass by several orders of magnitude, most investigations target planktonic communities captured from groundwaters. This multi-year study used 16S rRNA gene sequencing to compare planktonic and biofilm communities attached to natural granitic rock, demonstrating that biofilm formation selected for taxa with distinct relative abundances and exhibited temporal development. The biofilm communities also showed a decreasing influence of introduced populations on the natural rock surfaces (macadam) present at the onset of the incubations. After two- and four-years of biofilm incubation, a community developed that was dominated by sulfur/sulfate reducing Desulfocapsaceae, Desulfobacteraceae, and BM004 along with the families UBA5619, Rhodocyclaceae, Profunditerraquicolaceae, and UBA2206. This long-term community included populations predicted to be host-associated ultra-small cells. This contrasted with previous studies of early biofilm development in deep Fennoscandian Shield groundwaters that suggested biofilm initiation was mediated by lithotrophic carbon and nitrogen fixing populations. However, metabolic predictions based upon the 16S rRNA gene-based communities also showed an autotrophic and diazotrophic community including sulfur cycling in line with the previous studies. In conclusion, this study showed long-term biofilm composition to be dissimilar to the planktonic communities with a consistent strategy for energy conservation similar to previous studies of early biofilm formation from these groundwaters.

The relationship between the Gridinsky and Kirbeysky blocks was studied using geological-structural mapping in the eastern Belomorian Province of the Fennoscandian Shield. The blocks were reworked differently during the Lapland-Kola collision. In the Gridinsky block, intrusive contacts of Early Paleoproterozoic metagabbroid dikes with an Archean host rocks structure are preserved. In the Kirbeysky Block, the Early Paleoproterozoic metagabbroids were tectonically reworked along with Archean host rocks during ductile deformations. The boundary between blocks is a thick zone of mylonitization interpreted as a thrust-nappe structure.

This paper deals with new geological, mineralogical, isotopic-geochemical (major, trace, and rare earth elements, Sm–Nd isotopic data) characteristics of the unique Kalevian (1926–1923 Ma) komatiite-tholeiitic magmatic manifestation for the first time identified in the supracrustal Kaskama Formation from the Inari terrane of the Kola-Norwegian region Fennoscandian Shield. In the massive and porphyritic komatiites, the primary (magmatic) mineral paragenesis represented by olivine 20–40%, orthopyroxene up to 5%, hornblende up to 10%, clinopyroxene 20–40% and plagioclase 20–30% was identified. Liquidus temperatures for olivine and pyroxenes calculated in the COMAGMAT3.73 software suite are in the range of ~ 1500–1200 °C. The komatiites of the Kaskama Formation belong to the Al-nondepleted type and are characterized by low REEN content (1–2 relative to C1 chondrite), a total concentration ∑REEavr = 0.15–0.36 ppm, and an unfractionated distribution of REEs, which is a consequence of the generation and evolution of their primary melts outside the field of thermodynamic conditions of garnet stability. The Zr–Y–Nb and Sm–Nd isotopic systematics of the rocks of the komatiite-tholeiitic association indicates the origin of their high-temperature primary melts from a plume source in depleted mantle (εNd(T) = +3.2 ± 0.3), which is different from the mantle sources of the Jatulian-Ludicovian picrite-komatiite association of the Central Lapland greenstone belt of Finland and the Pechenga intracratonic structure. Considering the amphibolite facies metamorphic conditions of the Kaskama Formation, it can be assumed that the komatiite-tholeiitic association is a deeply eroded (at least 10 km) section of a supracrustal volcan.

Deep groundwaters populated by diverse and active microbes are among the most energy and nutrient-limited ecosystems. Characteristics of this ecosystem (including nutrient and dispersal limitations, low cell densities, and an episodic growth strategy) interactively underpin the so far elusive eco-evolutionary dynamics of its microbiome. Here, we used genome-resolved modular metabolic analyses of disconnected deep groundwater sites in the Fennoscandian Shield to test how eco-evolutionary constraints in these deep groundwater ecosystems shape microbial genome architecture, metabolic versatility, and community assembly at different depths. The analysis revealed that lineages with larger genomes (≥ 2.6Mb) maintained higher population sizes in the deepest and most oligotrophic groundwaters, whereas lineages with known metabolic dependencies, such as and DPANN, declined in relative abundance with depth. This pattern was interpreted as consistent with limited opportunities for sustained metabolic cross-feeding in these ecosystems. Moreover, while similar ecological niches based on cross-feeding interactions and potential primary production were available across different boreholes, distinct microbial lineages appeared to occupy these niches at each site. The findings provided new insights into the role of metabolic cross-feeding in genome evolution and community assembly of deep groundwater microbiomes. By extending the streamlining theory, this study underscores the critical influence of ecological interactions, particularly metabolic exchanges, in shaping microbial life under severe nutrient limitation, offering new insights into subsurface microbial communities.

A comprehensive investigation was conducted on high-hafnium zircons from the LCT (Li-Cs-Ta) pegmatites of the Vasin-Mylk rare-metal deposit within the Fennoscandian Shield. In situ analysis of trace element composition and oxygen isotope ratios were performed using secondary ion mass spectrometry (SIMS), complemented by internal structural examination via scanning electron microscopy (SEM). The research focuses on deciphering compositional zoning within zircon crystals and characterizing their geochemical signatures to constrain crystallization conditions. The study revealed anomalously high concentrations of Hf (up to 381,000 ppm) and Li (up to 152 ppm), paired with extremely low abundances of U (~10 ppm) and total rare earth elements (~35 ppm). Marked geochemical contrasts were identified between the central and rim domains of the zircons. Central zones display well-fractionated rare earth element (REE) patterns featuring positive Ce and negative Eu anomalies, while the high-Hf rims exhibit weakly differentiated spectra with variable Ce anomalies. The identified W-type tetrad effect suggests crystallization from a melt strongly influenced by coexisting fluids. The obtained δ18O values are consistent with a mantle source and suggest crystallization within a system closed to external fluids. The zircons from the Vasin-Mylk deposit crystallized during the transitional period between the late magmatic and early hydrothermal stages of a highly differentiated pegmatite system. These results contribute to a better understanding of ore genesis in LCT pegmatite systems.

Microbial metabolism in deep terrestrial subsurface communities - amino acids as biosignatures

Geochemical whole-rock variations in the Kovdozero complex in the Lapland–Belomorian Belt (LBB) are compared with those observed in the Pados-Tundra layered complex in the Serpentinite Belt (SB) in the complementary structure in the Fennoscandian Shield. A great variety of coronitic associations exists in the entire LBB–SB system. The Kovdozero complex largely consists of more evolved products of crystallization. Our results of U–Pb dating (zircon and baddeleyite) give the dates of 2514 ± 5 and 2478 ± 6 Ma, leading to the revised age ~2.5 Ga for the Kovdozero complex. It is thus considered to be coeval with Pados-Tundra, Perchatka, and gabbro–anorthosite associations of the Belomorian province in the White Sea region. The variation trends are generally extensive, continuous and close to linear at Kovdozero, which point to crystallization of chonolithic bodies of the complex from a single portion of melt, in separate reservoirs that likely communicated to develop as a whole in the connected system. The extreme degree of differentiation of derivatives of the initial komatiitic magma occurred in the large-scale plume. It led to the development of shallowly emplaced complexes grading from dunitic rocks and associated chromitites with Ru–Os–Ir mineralization at Pados-Tundra (the center) to leucocratic gabbroic rocks at Kovdozero, and likely to gabbro–anorthosite rocks of the Belomorian province (the periphery); these are considered the final products in the megastructure. The εNd(T) values are slightly negative at Kovdozero: −0.43 and −0.60. They imply some degree of crustal contamination of the initial magma. The generalized date of 2.5 Ga likely represents the age of the coronitic complexes of ultrabasic–basic rocks that crystallized from portions of komatiite-derived melts in hypabyssal settings of the LBB–SB megastructure in the eastern Fennoscandian Shield.

In 2021, seismic monitoring of the Russian territory of the East European Platform was carried out by 41 stationary seismic stations. Two new stations were opened: “Umba” (UMBA) on the Baltic Shield and “Inta” (IN0) in the Komi Republic. 225 seismic events of tectonic and man-made-tectonic nature were recorded. Weak natural and natural-man-made seismicity was recorded on the Kola Peninsula. The most significant earthquakes in magnitude with M~3 occurred in the Dnieper-Donets aulacogen. For the first time, earthquakes of the Caspian on salt-dome region of the Caspian Basin were included in the EEP earthquake catalog. Monitoring seismicity in this zone is necessary, since peaceful nuclear explosions were previously carried out here. The total volume of seismic energy released in 2021 is ΣE=15.62·109 J, which is approximately close to the energy released in 2017 and 2019.

Using lithological, geochronological, paleontological, geomorphological data, as well as modeling reconstructions according to the isolated basin method, the Late Neopleistocene-Holocene events were identified, which consistently manifested themselves in the White Sea coastal areas within the Fennoscandian (Baltic) Shield. These events are: the Mikulinian Boreal marine transgression, characterized by at least two phases; a short-term expansion of the Early Valdaian glacier to the coastal Kola Peninsula; the Middle Valdaian marine transgression and regression; short-lived marine environments and a huge glacier expansion in the Late Valdaian; the formation of proglacial freshwater reservoirs salinized during a glacio-eustatic marine influx in the Alleröd during the Late Glacial marine transgression; a marine regression started in the early Holocene because of the dome-shaped glacio-isostatic rebound and uneven tectonic uplift, which was interrupted by the early-middle Holocene marine transgression. Currently, the coastal line is regressing as a result of glacio-isostatic and neotectonic uplift of the earth’s crust on the Kola Peninsula, but over the past 4000 years, only neotectonic uplift has been manifested within the Karelsky Coast. Powerful earthquakes occurred in the studied areas, induced by the relaxation of the earth’s crust after the glacial load and more attracted to the Kandalaksha Bay area, which is the most tectonically active area in the eastern Baltic Shield.

The results of U–Pb (ID-TIMS, single grain) of monazite from aluminous gneisses (Chupa belt, Belomorian province) define the age of two metamorphic events associated with the formation of the Belomorian and Lapland–Kola orogens (the age of monazite is 2736 ± 30 and 1857 ± 4 Ma, respectively). These monazite ages are consistent with results of local U–Th–Pb (LA-ICP-MS) geochronological studies of zircon with Paleoproterozoic age of rims and 2809 age of cores 2809 ± 17 Ma.

We constrain lithospheric thickness across northeastern Eurasia using a new thermo-compositional model that jointly interprets seismic tomography and gravity data, including gravity gradients from the GOCE mission. This integrative approach provides a self-consistent threedimensional thermal structure of the lithosphere that incorporates compositional variations within lithospheric keels, yielding robust thickness estimates. The results demonstrate a strong link between lithospheric thickness and tectonic evolution. Archean and Proterozoic terranes such as the Siberian Craton and the eastern Fennoscandian Shield preserve thick keels (>200 km), reflecting early stabilization through melt depletion (and the interactions with mantle plumes and rifting episodes for the Siberian Craton), while the Timan–Pechora block also retains anomalously thick lithosphere, consistent with Paleozoic orogenic reworking and stabilization. The northeastern Barents Sea displays intermediate lithosphere (160 km to 180 km), likely representing a Proterozoic–Paleozoic fragment within the Arctic basement mosaic. In contrast, the Ural Orogen forms a sharp lithospheric boundary between the East European Craton and the thermally modified West Siberian Plate, which was profoundly affected by Mesozoic rifting and plume activity. East of the Verkhoyansk Range, lithospheric thickness decreases to less than 100 km in Phanerozoic terranes such as Chukotka, the Anadyr–Koryak Fold Belt, and Kamchatka, where subduction, terrane accretion, and arc magmatism maintain a hot, dynamic lithosphere. Overall, the lithospheric structure of northern Eurasia reflects the interplay of four fundamental processes: Archean craton stabilization, Paleozoic orogenesis, Mesozoic plume–rift modification, and ongoing Pacific subduction. These processes collectively shape the strong lateral contrasts that define the geodynamic framework of Eurasia

The Scandinavian Mountains span c. 1500 km and broadly follow the trace of the Scandinavian Caledonides, formed during the collision between Baltica and Laurentia. While the formation of this orogen is well established, the origin and timing of the present-day topography remain debated. This study investigates the structure and evolution of the deep-seated masses supporting the present-day topography. A comprehensive review of geological and geophysical data facilitates new integrated gravity–isostatic and thermal modelling, enabling a quantitative understanding of the interplay between the crust–Moho system (CMS) and the lithosphere–asthenosphere system (LAS). Crustal thickening from the Norwegian coast toward the Baltic Shield initially raises topography, while farther inland a thicker lithosphere subdues topography despite a thick crust. Offshore, crustal thinning persisted from the Late Mesozoic through the Paleogene. However, inland areas show no evidence of significant post-Permian crustal thinning or magmatism. These observations indicate that the underlying isostatic structure was established primarily during and in the aftermath of the Caledonian orogeny, with the modern topography representing a long-lived remnant sculpted by slow erosion and passive isostatic rebound.

Abstract. The Ertelien and Langedalen magmatic Ni–Cu sulfide deposits are hosted within mafic intrusions of the Kongsberg Lithotectonic Unit in the southwestern Fennoscandian Shield, formed in a convergent-margin tectonic setting. The Ertelien deposit occurs within a gabbronorite intrusion of approximately 600×500 m, with the main sulfide mineralization being located at the contact with the surrounding gneiss. In contrast, the Langedalen deposit consists of 1–2 m massive sulfide lenses hosted in 10–50 m gabbronorite lenses that are extensively deformed within shear zones. Sulfide mineralization in Ertelien ranges from disseminated to net-textured and massive ores, whereas Langedalen ranges primarily comprise massive sulfide lenses. A distinctive feature of Langedalen ranges is the local presence of an Au-rich quartz vein adjacent to the sulfide lenses. In both deposits, pyrrhotite is the dominant sulfide mineral, followed by pentlandite and minor chalcopyrite. Secondary pyrite is present, particularly in altered zones. This study provides a comprehensive characterization of the Ertelien and Langedalen deposits and constrains their genesis within a convergent-margin context. We analysed S, platinum group elements (PGEs), TABS+ (Te, As, Bi, Sb, Se), and other chalcophile elements in whole rocks and sulfide minerals across different ore textures, as well as U–Pb and Hf isotopes in zircon. Whole-rock geochemistry reveals a positive correlation between S and Ni, Cu, and Co, with sulfide tenors of ca. 2.2 wt % Ni, 1.5 wt % Cu, and 1200 ppm Co. Sulfides from both deposits are notably depleted in PGEs, consistently with derivation from a PGE-depleted parental magma compositionally similar to cogenetic dykes. This depletion may result from an event of prior sulfide segregation. However, we suggest that an alternative explanation is that the parental magmas were derived from a hydrous metasomatised pyroxenitic mantle source. In addition, a zircon U–Pb crystallization age of 1559±7 Ma and εHf(i) values of +3 to +5 for the Ertelien intrusion support formation during a prolonged subduction-related magmatic episode involving oceanic crust recycling. Despite post-magmatic alteration and secondary pyrite formation, sulfide minerals largely preserve their primary magmatic signatures, comparably to other Ni–Cu magmatic systems globally. However, parts of the Langedalen sulfides exhibit hydrothermal overprint, reflected in elevated concentrations of mobile elements (Te, As, Bi, Sb), likely linked to the formation of the Au-rich quartz vein.

In the northwestern part of the Onega structure, at the southeastern margin of the Baltic Shield, dislocations previously attributed to slump folds were identified in the sand unit and described in detail. It was established that these formations form a paragenesis of deformation structures in soft sediments. Possible hypotheses for their formation are discussed and a seismogenic model is presented.

The paper discusses the distribution of basites aged 2.4 Ga within the Fennoscandian Shield. In the Kola Province, olivine-bearing dolerite dykes and differentiated sills of picritic dolerite have been recognized. Meanwhile, in both the Murmansk and Karelia Cratons there occur doleritic dykes. Additionally, volcanics from the Vetreny Belt show similar ages (2407 Ma). Within the Belomorian Province, olivine gabbro-norite dykes and differentiated intrusive bodies also formed at ~ 2.4 Ga. Hence, basites of 2.4 Ga age are widely distributed across the Fennoscandian Shield. Potential temperature conditions and composition analyses of 2.4 Ga dykes and sills within the Kola Province indicate their formation occurred under T > 1500 °C and P > 2.3 GPa, implying a possible mantleplume origin.

The Gimoly Greenstone Belt (GGB) is located in the central Karelian Craton on the Fennoscandian Shield. The volcanogenic and sedimentary rocks of the Gimoly Group are interpreted as a stratotype of an Upper Lopian (Neoarchean) volcano sedimentary rock sequence in Central Karelia. The GGB’s granite-greenstone complex is overlain with angular unconformity by Paleoproterozoic (Sumian, Jatulian) rocks. We propose a new model for the stratification of the GGB’s greenstone complex based on original geological and geochronological data. New stratigraphic units are given the older names that are already in use. The authors assume that the Gimoly Greenstone Belt consists of three stratotectonic associations (SТА): Gimolozero, Mezhozero, and Sukkozero. Isotopic dating of zircons (LA-ICP-MS) from felsic volcanics shows that the age of 1) andesites from the Mezhozero STA is 2824 ± 3 Ma, and 2) that of andesite-basalts interbedded with polymictic conglomerates is 2752 ± 2.4 Ma. Neoarchean felsic volcanics have been known as part of the GGB previously, but their Mesoarchean counterparts have been found for the first time. GGB’s western flank consists of Gimolozero STA’s basalts. These metabasalts are similar in chemical and isotopic composition to the mafic rocks occurring in the komatiitic-basaltic sequence of the Kontokki Group of the Kostomuksha Greenstone Belt. Thus, the new geochronological and geological data can now be used for differentiating three STAs in the GGB 1) the Gimolozero basaltic (most probably Mesoarchean) STA, 2) The Mezhozero STA made up of andesites and interrbedded with BIF and carbonaceous schists dated as Mesoarchean (2.82–2.81 Ga), and 3) the Sukkozero STA composed of andesite basalt-andesites with conglomerate lenses of Neoarchean (2.76–2.74 Ga) age.

As a result of petro-paleomagnetic studies, banded iron formations (BIF) have been typified by their magnetic properties. The main magnetization carrier minerals in BIF 2 and BIF-4 samples are single-domain magnetite and monoclinic pyrrhotite. The latter is identified by a characteristic rise in the cooling curves at 350 °C. It is shown that magnetite in the rocks is single-domain and ‘encapsulated’ in quartz grains. Investigation of the Anisotropy of magnetic susceptibility (AMS) permitted differentiating between highly and weakly magnetic samples: highly magnetic samples are dominated by a high degree of anisotropy associated with the transformation of the magnetic fraction and remagnetization of the rocks. The high AMS in the BIF-2 samples and Neoarchean conglomerates (2710 Ma) is associated with the predominance of layered-structure monoclinic pyrrhotite in the rocks. Weakly magnetic samples are predominantly anisotropic. Definitive stepwise demagnetization allowed us to distinguish at least two magnetization components in the studied samples. The average direction of the low-temperature component identified in all sites is near-aligned with the Svecofennian remagnetization for the Karelian Craton. The average direction of the high-temperature component in BIF-2 samples is close to that in Neoarchean conglomerates and coincides with the direction of the Lapland-Kola remagnetization (ca. 1.96 Ga). The identified metachronous magnetization components testify to uneven remagnetization of rocks within the same stratum. The Mesoarchean (2.8 Ga) rhyolite and Paleoproterozoic (2.42 Ga) gabbro samples may contain primary magnetization components dated to 2.72 and 2.42 Ga, respectively. Selective remagnetization of rocks differing in composition is observed.

Metallogenic and ore-forming systems of the Ladoga structure of the Fennoscandian Shield

We present the main results of the lithological, geochemical, and paleontological study of Paleoproterozoic carbonate rocks of the eastern part of the Fennoscandian Shield. The maximum carbonate accumulation in the east of the Fennoscandian Shield during the Paleoproterozoic occurred in the range of 2.1–2.0 billion years ago. The vast majority of carbonate rocks are confined to the Onegian (Jatulian superhorizon) and low part of the Zaonezhsky (Ludikovian superhorizon) horizons of the regional stratigraphic scale. A case study of two large paleobasins on the Karelian Craton, the Onegian in the southeast and the Pana-Kuolajarvian in the northwest, reveals that the results of the multidisciplinary geological approach do not contradict, but complement each other. The characteristic features of the Jatulian sedimentary carbonates are their redness, preserved sulfates and chlorides, as well as various pseudomorphoses after them, an abundance of various microbialites and enrichment with the heavy carbon isotope 13C. The Ludikovian carbonate rocks have gray color, contain no evaporite minerals, few microbialites, and slightly deviate in the carbon isotopic composition from the sea-average values. The distribution spectra of rare earth elements in carbonate rocks of Jatulian age from the Onegian paleobasin clearly show a negative Ce anomaly of varying intensity, indicating an oxidizing environment with variable oxygen content. The oxygen content in the Pana-Kuolajarvian paleobasin was stable, but lower. At the same time, in both the Onegian and Pana-Kuolajarvian paleobasins, the oxygen content remained transitional from dysoxic to oxic conditions. The positive Eu anomaly in rocks of both basins indicates hydrothermal material input to the sedimentation area, and entry of basic pyroclastic material is possible. Based on the whole dataset, including isotopic and geochemical data, we draw conclusions regarding the carbonate deposition environments that occurred in this area in the time range of 2.1–2.0 billion years ago. Carbonate accumulation in intracratonic basins evolved from evaporitic shallow-water conditions in the Jatulian time to a relatively deep, open marine environment with increased volcanic activity in the Ludikovian.

Historical data, new findings and latest research results are combined to produce an updated assessment of the mineral resources of metals in the Republic of Karelia. The factual background for the study is the results of the assessments of strategically and economically important deposits and large manifestations of metals in the Republic of Karelia done by specialists of the IG KarRC RAS, PGO Sevzapgeologiya, VSEGEI, IGGD RAS, VIMS, St. Petersburg State University, PO Nevskgeologiya, and JSC Polymetal. General information is provided on the history of subsoil use in the republic in the past. It is emphasized that the geological structure and formation history of useful minerals reflects various successive stages of the development of the Precambrian Earth’s crust in the region. Specifically, attention is given to the relationship between tectonic movements, deep-seated processes and geological events which determined the specific features of the geodynamic processes in the eastern part of the Fennoscandian Shield. Karelia’s main metal ore objects are named, such as the Kostomuksha ore district, which includes the Kostomuksha and Korpanga iron ore fields with a series of deposits and occurrences of iron ores and is part of the Severostal business ecosystem. Much emphasis is placed on the oxide low-sulfide titanomagnetite ores of the Pudozhgorskoye deposit of liquation-magmatic genesis within Burakovskiy lopolith boundaries, Aganozerskoye deposit of chromium and nickel ores, and Shalozerskoye occurrence of chromium ores with the associated precious metal mineralization. The vanadium-uranium ore type with carbonate-mica metasomatites and micas of the Onega ore region is characterized through the case of the Srednyaya Padma deposit. It is mentioned that the Lobash molybdenum-rhenium deposit is one of the world’s largest molybdenum-porphyry deposits of Archean age with favorable conditions for its open-pit mining. Economically important mineral resources include the Lobash-1 copper-gold deposit, the Maiskoye gold-quartz deposit, the Elmus gold ore cluster, and the Taloveis gold occurrence. The large Kitelskoye tin deposit in European Russia is located in the western tin-polymetallic subzone of the Salmi-Uksinsko-Kitelskaya ore zone. The first industrially promising platinum metal site, Viksha, was discovered in Karelia, and the Lukkulaisvaara platinum-palladium occurrence was found in layered intrusions in the Kuusamo-Paanajarvi- Tsipringa rift structure. In the Ladoga region, the Karku deposit of an “unconformity”- type uranium formation was studied in Riphean albite-carbonate-mica metasomatites.