The study of the volcano–sedimentary sequence in the lower part of the Zaonega formation in the Paleoproterozoic Onega structure (Karelian craton, Fennoscandian Shield) has shown that tuffaceous and high-silica rocks predominate in its composition. High-silica rocks (SiO2 up to 94 wt

Columnar jointing occurs commonly in igneous rocks and rarely in sedimentary rocks. We report the results of combined field and petrological studies, Raman spectroscopy and column geometry analysis of columnar jointing in Paleoproterozoic carbon-bearing rocks, Eastern Fennoscandian Shield, NW Russia. The columnar rocks occur near the contact with the saucer-shaped dolerite sill emplaced in the unconsolidated organic rich sediments. Columnar jointing aureole (1 to 7 m) and column architecture strongly depends on the contact morphology. Columnar jointing is caused by the contraction of organic-rich sediments due to generation and further release of gas and oil rich fluid. The results of integrated studies indicate that fluidization driving the jointing is associated with not only the dehydration, but also with the mobilization of gas and oil rich fluid due to the thermal maturation of organic matter. Columnar jointing is associated with intensive fluid circulation and devolatilization evidenced by the numerous veins, globules, and vugs filled with migrated carbonaceous matter and secondary minerals in the columnar rocks as well as high vesicularity of dolerites near the contact. The redistribution of the mobile elements (K, Rb, LREE) along with the significant enrichment of S near the contact also indicates the intensive fluid circulation. The study contributes to understanding of mechanism of columnar jointing in sedimentary rocks and formation the fracture networks in organic-rich sediments.

New U–Pb data for zircon from the Konchezero sill reliably determine the age of the Suisari Formation of the Ludicovian and the limit of the maximum age of the volcanogenic–sedimentary Zaonega Formation with isotope-light carbon and the Shunga isotope event.

We present new results of geochronological, rock magnetic, paleomagnetic and paleointensity studies of the olivine gabbro dyke located at the northern part of the Murmansk craton, NE Fennoscandia (the Kola Peninsula). According to its geochemistry, petrographic and geochronology features, the dyke belongs to the 2.68 Ga dyke swarm, as confirmed by Sm-Nd mineral isochron. We find a significant difference in the rock magnetic and paleomagnetic characteristics of the central and marginal parts of the dyke, which is independently supported by petrography and geochemistry. It is shown that the rocks of the central part of the dyke retained not only their primary mineral composition, but also the primary component of the natural remanent magnetization. We use its direction to determine the 2.68 Ga virtual geomagnetic pole for the Murmansk craton: Slat = 68.64292° N, Slong = 37.7945° E, N = 41 specimens, Plat = –73.5°, Plong = 138.9°, dp/dm = 3.2°/3.4°, paleolat = –65.9°. We also obtain reliable estimates (17 samples) of the Earth’s magnetic field intensity at ca. 2.68 Ga: VDM value is found to be 1.85 × 1022 A m2 corresponding to the geomagnetic field several times weaker than the present-day field.

The name Mallomonas silvicola (Chrysophyceae) is validated by means of indicating its type. A new description and microphotographs are presented.

Mafic intraplate magmatism is the main source of information about the geodynamics of processes that lead to the breakup of continental blocks. The article discusses geodynamics of the breakup of the Archean supercraton Superia in the Middle Paleoproterozoic. The discussion is based on data on 2.1 Ga magmatism in the Karelian Craton, where mafic igneous rocks of this age are represented by tholeiites of two geochemical types: depleted and enriched. Geochemically close to N-MORB, depleted tholeiites were studied in the Northern Ladoga Region where they form dike swarms at ca. 2111 ± 6 Ma (U-Pb, SIMS, zircon) in the Hatunoiya locality, and pillow lavas and sills in the Lake Maloe Jänisjärvi locality. Enriched tholeiites were studied in the Lake Tulos locality where they form a large swarm of doleritic dikes of age 2118 ± 5 Ma (U-Pb, ID-TIMS, baddeleyite). The results of these studies provide deeper insight into 2.1 Ga mafic magmatism. Depleted tholeiites with N-MORB geochemistry have a wide spatial distribution in the Karelian Craton and could be formed via decompression melting of a depleted asthenospheric mantle, raising melts along the extension zones, and minimal contamination by the Archean crust. According to modelling results, enriched tholeiitic melts probably occurred due to differentiation and crustal contamination of rising depleted tholeiitic melts through more rigid Archean crustal blocks. Data on ca. 2.1 Ga mafic magmatism in the Karelian craton are difficult to explain within the mantle plume rise model, but are consistent with the model of lithosphere extension due to a retreat of a subduction zone in the northeastern margin of the craton, in the Lapland-Kola Ocean at 2.0–2.2 Ga. The intensive thinning and rupture of the Archean continental lithosphere and opening of an oceanic basin at the western margin of the Karelian craton were probably controlled by the suture zone of the junction of Neoarchean and Paleoarchean crustal blocks, traced in the western part of the Karelian craton. An additional factor that led to the ca. 2.1 Ga lithospheric breakup could be a rise of a deep-seated mantle plume in the Hearne craton, neighboring to the Karelian craton in the Archean Superia supercraton.

ABSTR A C T Several published Mesoproterozoic paleogeographic reconstructions suggest proximity of northern Laurentia and southern Siberia. However, the apparent absence of the traces of the ca. 1.27 Ga giant Mackenzie magmatic event in southern Siberia was somewhat contradictory to this hypothesis. Here we present geochronological, miner-alogical, geochemical, Nd isotopic, and paleomagnetic data from the Srednecheremshansk dyke-shaped intru-sion, which was recently found in the Sharyzhalgay uplift of the southern part of the Siberian craton and which can be related to the Mackenzie event. The plagioclase-bearing peridotite of this intrusion yielded U-Pb (ID-TIMS) baddeleyite concordia age of 1260 +/- 3 Ma, which is interpreted as the time of their emplacement. This age is close to the previously published baddeleyite age of gabbro from the same intrusion (1258 +/- 5 Ma). The Srednecheremshansk intrusion is composed of ultramafic and mafic rocks. The main rock-forming minerals of the intrusion are olivine, orthopyroxene, clinopyroxene, phlogopite, and plagioclase in various proportions. Sulfide mineralization of the intrusion is represented by pentlandite nodules. The chemical composition of Sredne-cheremshansk ultramafic and mafic rocks correspond to subalkaline peridotite gabbro and gabbro. These rocks are characterized by negative epsilon Nd(t) values range from-6.3 to-6.9. Ultramafic and mafic rocks have similar geochemical and isotopic characteristics, indicating their generation from a single subcontinental lithospheric mantle source. The chemical composition of the Srednecheremshansk intrusion is similar to those of the ca. 1.27 Ga Muskox mafic-ultramafic intrusion of the Mackenzie Large Igneous Province in northern Laurentia. Paleo-magnetic data permit a variety of possible Laurentia-Siberia reconstructions in Mesoproterozoic. The combina-tion of geochronological, geochemical, and paleomagnetic data allows the relation of the Srednecheremshansk intrusion with the Mackenzie magmatic event.

The amorphous carbonaceous material (CM) in mafic igneous rocks is important for deciphering the relationships between igneous and hydrocarbon systems in Earth interior. Deciphering of CM in Precambrian rocks it is a challenge because of reworking by later superimposed events but could give insights into evolution of these systems in time. We report the results of combined field and petrological studies, Raman spectroscopy and carbon isotope analysis of well-preserved ca. 2.0 Ga pillow lavas in the Onega Basin, Karelian craton, Eastern Fennoscandian Shield. In these rocks CM is present in both pillow and inter-pillow areas as poorly ordered carbon. In the MORB-like basalts of the Zaonega Formation, CM occurs in post-magmatic veinlets formed via migration of hydrothermal fluids. In the OIB-type basalts of the Suissary Formation, CM is found in amygdales, inclusions in feldspar, and in devitrified volcanic glass indicating a CM deposition via a rapid cooling of C-rich magma. Despite morphological diversity carbon isotopic composition indicates a biogenic origin of CM in both the MORB- and OIB-like basalts. The most likely source was the Paleoproterozoic oilfield in the Zaonega Formation, commonly referred to as the Shunga event.

The results of U–Pb (ID-TIMS) and U–Th–Pb (LA-ICP-MS) geochronological studies of baddeleyite from dolerite dikes of the Sulumat Complex and detrital zircon from red arkose sandstones of the Kebekta Group of the Ugui graben, Aldan Shield, are presented. It has been established that the Kebekta Group has an age of 2.01–1.87 Ga. The provenance areas of the Kebekta Group deposits were the Archean (2.92–2.52 Ga) igneous and metamorphic complexes of the Chara–Olekma Geoblock and the zone of its junction with the Western Aldan Megablock of the Aldan Shield, as well as the Paleoproterozoic (approximately 2.01 Ga) complexes unidentified on the present erosion level. The obtained geochronological data do not contradict the correlation of terrigenous rocks of the Kebekta Group of the Ugui graben and the Kemen Group of the Kodar–Udokan trough. The deposition of arkose sandstones of the Kebekta Group correlates in age with the glaciations in Australia and Sweden (approximately 1.9–1.8 Ga) associated with the formation of the Columbia/Nuna supercontinent. It cannot be excluded either that the deposition of the rocks in the Ugui graben was related to the inflow of glacial material into the intracontinental extensional basin from the southern and/or western (in modern coordinates) framing of the Chara–Olekma Geoblock at the stage of collapse of the Paleoproterozoic orogen.

Giant mafic dykes are the key markers of the Earth’s evolution in the Precambrian and have been the subject of extensive research. This article presents the results of the paleomagnetic, rock-magnetic, and paleointensity Banc studies of the Great Dyke of the Kola Peninsula (2.68 Ga). The mean paleomagnetic direction of the characteristic magnetization component and the paleomagnetic pole of the Murmansk craton were calculated using the data from 5 sites (n = 41 samples): D = 117.6°, I = 77.1°, K = 40.9, α95 = 12.1°, slat = 69.265°, slong = 34.35447°, plat = 51.5°, plong = 70.7°, dp/dm = 21.1°/22.6°, and paleolat = 65°. The rocks under study were thoroughly examined for their thermomagnetic properties, revealing that the main carriers of remanent magnetization are single-domain or small pseudo–single-domain (group A) or multidomain (group B) magnetite. The paleointensity values Banc = (6.16 ± 0.92) μT were obtained for 12 samples from group A by the Thellier–Coe method. The corresponding mean virtual dipole moment VDM2.68Ga = (0.85 ± 0.13)×1022 Am2 was determined. These new findings align with previous results on the Archean and Proterozoic objects, indicating that the Earth’s magnetic field was remarkably weak in the Late Archean.

The Yalguba Ridge volcanic rocks form part of the Middle Paleoproterozoic (ca. 1.97 Ga) volcano-sedimentary sequence within the Karelian Craton in the Fennoscandian Shield. Yalguba variolitic textures are known worldwide and have been previously considered to originate from liquid immiscibility. The present study reveals two new variolite types recognized in the Yalguba sequence: (1) Variolites with unzoned varioles have distinct chemical and mineralogical compositions of varioles and matrix that support an origin by liquid immiscibility. They were recognized in quenched zones of pillows, so it might be assumed that melt separation caused by liquid immiscibility occurred before magma emplacement. The difference from the previously described variolites lies in the variole microtexture and might be caused by the various cooling conditions. (2) Spherulitic variolites have varioles composed of andesine–oligoclase spherulites embedded in the cryptocrystalline matrix with oligoclase–anorthoclase composition, thus the variole and matrix have similar chemical and mineralogical composition. The mineralogical and textural features of these variolites suggest that the spherulites have a primary magmatic origin due to the rapid cooling of superheated magma. The variety of variolitic textures in the Yalguba section might be caused by the different H2O saturation of parental magma and cooling conditions.

First records for Russia of naviculoid diatom from the Yaroslavl Region, and micromycetes from the Republic of North Ossetia — Alania, green alga for the Leningrad Region and Yamal-Nenets Autonomous Area, fragilarioid diatom for the Kaliningrad Region, red alga for the Nizhny Novgorod Region, cyanoprokaryota for the Leningrad Region and Chukotka Autonomous Okrug, and crustaceous red alga for the Autonomous Republic of Adjara of Georgia, macromycetes for the Leningrad Region, Khanty-Mansi Autonomous Area — Yugra, Republic of Tuva, Trans-Baikal Territory, myxomycetes for the Trans-Baikal Territory, lichens and allied fungi for the Murmansk and Tver regions, republics of Karelia and Tuva, Yamal-Nenets Autonomous Area, Altai and Khabarovsk territories, cyanolichen for the Urals and the Orenburg Region, mosses for the Lipetsk Region, republics of Ingushetia and Buryatia, Krasnoyarsk and Trans-Baikal territories are presented. The data on their localities, habitats, distribution are provided. The specimens are kept in the herbaria ALTB, GSU, IBIW, IRK, KPABG, LE, MHA, MW, NNSU, NSK, PZV, TBI, UUH, VU, YSU, and the Diatom collection of the Laboratory for Algology of IBIW RAS. Sequences of 16S, and 16S–23S ITS cyanobacterial RNA regions, ITS1-5.8S-ITS2 fungal and ITS1-2 moss nrDNA regions of some specimens have been deposited in the GenBank.

The results of geochronological and petrological studies of the largest mafic dyke in the northern part of the Fennoscandian Shield, called the Great Dyke of the Kola Peninsula (GDK), are presented. According to U-Pb D-TIMS baddeleyite dating, the GDK crystallization age is 2680 ± 6 Ma. The age of host granites is 2.75–2.72 Ga (U-Pb, zircon, SHRIMP-II). The dyke has a simple internal structure with no signs of multistage melt injection. It comprises equigranular and plagioclase-porphyritic dolerites and gabbro that are amphibolitized to varying degrees. All rocks are low-Mg (Mg# less than 0.37) with low concentrations of Cr and Ni, and were derived through differentiation of more primitive melts. The analysis of geochemical and Sr-Nd isotopic data suggests that GDK melts could be formed by mixing of two types of mantle melts: depleted asthenospheric melt and enriched melt formed via melting of a lithospheric mantle. The weakly fractionated HREE patterns indicate that primary GDK melts originated at shallow (<60 km) depths outside the garnet stability field. The generation and injection of melts of the Neoarchean GDK occurred immediately after large-scale granitic magmatism and main crustal growth event in the Murmansk Craton and marked the cratonization of the continental lithosphere in the northeastern part of the Fennoscandian Shield.

Analysis of the evolution of the Belomorian Mobile Belt (BMB) suggests that the metamorphism of gabbroic rocks was accompanied by their remagnetization and that lateral variations in magnetization constituents carry evidence for the time sequence of the extension of the western foreland of the Lapland-Kola orogen (LKO) to upper crustal levels. The latter formed while the Nuna/Columbia Supercontinent was being made up. The combined study of metamorphosed Paleoproterozoic igneous complexes has revealed a remagnetization trend in BMB rocks. The study has shown that the remagnetization front spread here from the north-west to the south-east and that it seems to be due to the collision pattern upon LKO formation. In addition, remagnetization in the southern BMB and in the southeastern Karelian Craton, dated at 1.65-1.60 Ga, was revealed. It seems to be due to the final episodes of formation of the Svecofennian orogen.

A tectonic map is a cartographic image of models showing the structure (architecture) of the earth crust/lithosphere and the geodynamic settings of formation of its constituent mineralogical complexes. A new tectonic map of Karelia has been compiled 1) to delineate areas differing in formation of Earth crust and 2) to analyze the Archean to Paleozoic evolution of geodynamic settings upon the formation of the region's earth crust.

Abstract Geological, geochemical, isotopic and geochronological data for Paleoproterozoic mafic intrusions and dykes indicate that distinct magmatic events dated at c. 2.50, 2.45, 2.40, 2.30, 2.23 and 2.12 Ga can be distinguished in the Belomorian Province, Eastern Fennoscandian Shield. The similarity of Paleoproterozoic magmatic barcodes for the Belomorian Province and the Karelian Craton in the c. 2.5–2.1 Ga interval suggests a neighbouring position of these crustal segments in an Archean continent. Intensive tectonic and metamorphic reworking of mafic intrusions and dykes in the Belomorian Province during the c. 2.0–1.8 Ga Lapland–Kola Orogeny produced differences in mineral assemblages and tectonic position in comparison with the Karelian Craton.

The estimation of crystallization and metamorphic reworking ages of mafic rocks in the polycyclic Precambrian areas is a difficult problem. Magmatic baddeleyite can be partially or completely replaced by polycrystalline zircon within a wide range of temperature and pressures, from greenschist to granulite facies. Evaluation of the age of each phase of the zircon–baddeleyite aggregates can provide information on both the age of the magmatic crystallization and metamorphism. U-Th-Pb (SHRIMP-II) and U-Pb (ID-TIMS) geochronological studies were carried out for single baddeleyite grains and zircon–baddeleyite aggregates from gabbronorites (“drusites”) of the Ambarnsky massif (Belomorian Province, Fennoscandian Shield). The petrological studies indicate the simultaneous growth of coronas at the olivine–plagioclase boundary and zircon rims around baddeleyite. U-Pb (ID-TIMS) dating of single baddeleyite grains yielded 2411 ± 6 Ma crystallization age of gabbronorites of the Ambarnsky massif. U-Pb (ID-TIMS) dating coupled with the discrete chemical abrasion give an age of 1911 ± 35 Ma for metamorphic zircon rims. The obtained results indicate that coronitic textures in the gabbronorites were formed 500 million years later than the magmatic crystallization of rocks as a result of the granulite-facies metamorphism that was probably related to the Lapland-Kola orogeny.

Available data suggest that the breakup of the Neoarchean Kenorland supercontinent at 2.5-2.4 Ga was likely triggered by a large mantle plume upwelling that caused significant magmatism. Here, we present 2D high-resolution magmatic-thermomechanical numerical models of extension of the continental crust underplated by a hot mantle plume material. Using this model, it is demonstrated that mantle plume underplating generates a large amount of mafic melt by decompression melting. This melt penetrates into the extending continental crust along normal faults thereby forming multiple generations of mafic dyke-like intrusions along normal faults. In case of extension velocity of 0.2-1 cm/yr, lower crustal heating and hot mafic melt emplacement may cause partial melting of the continental crust that can generate significant volume of felsic melts. This in turn triggers emplacement of felsic intrusions that temporarily and spatially associate with the mafic dyke-like intrusions. The modeling results agree well with geological data from the Karelian Craton and provide possible explanation for the observed association of Paleoproterozoic mafic dykes and felsic intrusions which formed in a relatively short time interval (up to 20 Myrs) in the early stages of the supercontinent breakup.

Table S1. Data on chemical composition of Paleoproterozoic mafic dykes and 20 intrusions in the Belomorian Province

Tectonic and fluid reworking of deep-seated mafic intrusions in the orogenic belts often erase primary magmatic characteristics, and crystallization parameters of mafic melts enriched in volatiles remain an issue. This study presents new U-Pb geochronological data for zircons, mineral composition, whole-rock geochemistry and Sr-Nd isotopic data for Pechnoy ca. 2.2 Ga mafic layered sill in the central Belomorian province, Eastern Fennoscandian Shield. The Pechnoy intrusion comprises low-alumina, silica-undersaturated, Cl enriched mafic rocks depleted in HREE and HFSE with epsilon Nd values of -0.1-+1.5 and (87Sr/86Sr)2200 = 0.7024-0.7039. Field and petrological studies indicate that studied rocks preserved relicts of primary magmatic characteristics because it was encapsulated in host gabbronorite intrusion and avoided intensive fluid reworking during 1.8-2.0 Ga Lapland-Kola orogeny. Variations of mineral composition, major, and trace elements within intrusion originated via in situ fractional crystallization with dominated settling of clinopyroxene and plagioclase. Chlorine distribution within intrusion and in the host rocks inferred a magmatic origin Cl enrichment. High-Na scapolite is the main concentrator of the Cl in the rocks. The inclusions of scapolite in the relict magmatic plagioclase and higher Ca content relative to adjacent Na-rich plagioclase likely indicate early crystallization of high-Na scapolite. Trace element and isotopic characteristics of rocks indicate OIB and subduction modified SCLM signatures of their primary melts. A comparison of the available data for Pechnoy sill and coeval mafic sills in the Karelian Craton reveals a common mantle source for ca. 2.2. Ga igneous rocks in the Fennoscandian Shield although intrusions in the Belomorian province represent deeper levels of 2.2 Ga large igneous province plumbing system.