Geological, geochemical, Sr-Nd isotopic and U-Pb (baddeleyite, ID TIMS) age data for Jatulian mafic volcanics and sills in the Segozero syncline, Karelian Craton, provide new insights into their age and tectonic setting for coeval terrigenous and carbonate rocks. The basalts form two distinct compositional and age groups. Basalts 1 are coeval with 2223 Ma mafic intrusions while Basalts 2 are coeval to 2130 Ma mafic dykes. Basalts 1 originated through deep-seated mantle melting in plume-related intracontinental setting. Basalts 2 formed due to shallow mantle melting synchronous with intensive lithospheric thinning and extension in a syn-rift tectonic setting. These new data indicate a ca. 130-150 Myr duration for Jatulian sedimentation in the eastern part of the Karelian Craton, and a 2130 Ma maximum depositional age for the Tulomozero Formation carbonate rocks with anomalously high delta 13C values representing Lomagundi-Jatuli event.

This paper presents new data on the Tokko section of the central part of the Olekma granite-greenstone terrain (Aldan Shield, Siberian craton). The conducted studies provide grounds to propose that the Tokko section exposes a fragment of a deeply eroded greenstone belt, similar on the evolution to the Olondo greenstone belt. In that light the Tokko section may have been merged with the Olondo fragment within a single structure of the Tokko-Khani greenstone belt. Juvenile geochemical signatures of felsic magmatism in the Tokko segment support the idea of the existence of an oceanic basin in the central part of the Olekma granite-greenstone terrain, evolution of which could give rise to the formation of the subduction systems and generation of the new crust during the Mesoarchean. It has been established that the main volume of the Archean crust in the Tokko section was formed between 3.0 and 2.8 Ga, primarily contributed by juvenile granitoids, and subordinately by mafic magmatism. The following stage of the crust formation is recorded by bimodal magmatism at ca. 2.6 Ga, accompanied by the ascent of mafic asthenospheric magmas and intrusion of crustal granitoids. The rocks of this association, together with the contemporaneous granites from the eastern part of the Olekma granite-greenstone terrain, and anorthosites with granitoids of the Kalar, Altual'skii, and Dzheluiskii Complexes distributed within the junction zone of the Olekma granite-greenstone terrain and the Dzhugdzhur-Stanovoi fold region, may represent a part of the single Neoarchean anorthosite-mangerite-charnockite-granite magmatic province.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070073

Paleoproterozoic diorite–granodiorite magmatic rocks dated at 2.04–2.08 Ga are widespread at the eastern border of the Archean Kursk block of Sarmatia. The granitoids of the intrusive massifs are metaluminous calc-alkaline I-type rocks enriched in incompatible elements (LILE and LREE), with negative Ti, P, and Nb anomalies. The rocks show widely varying negative εNdT values, their zircons have broadly ranging εHfT values, and the melts were derived within a broad range of depths from heterogeneous Archean lower crustal mafic sources. The diorites were melted from the least radiogenic ancient crustal sources. The granodiorites were derived from Paleo- and Mesoarchean and more juvenile Neoarchean sources. The intense 2.06-Ga magmatism was triggered by the upwelling of the asthenospheric mantle during the break-up of subducted oceanic slab due to low-angle subduction. The break of the slab and the mafic underplating led to the crustal melting of the upper slab, which consisted of Archean and Paleoproterozoic crustal fragments of different age that had been welded as a result of earlier accretion. Diorite−granodiorite magmas were generated in chambers at different depth in the ancient Archean crust at the periphery of Kursk block, with the incorporation of Paleoproterozoic lithospheric fragments of the Eastern Sarmatian orogen into the melting sources.

We studied the composition, isotopic geochemistry and zircon U-Pb dating of Paleoproterozoic supracrustal rocks of the Uni Formation and granitoids of the Talitsky Complex of the Vyatka terrane located on the northeastern margin of the East European Craton. The obtained data were used to constrain the age, origin and tectonic setting of the Vyatka terrane, which is thought to be a part of the Paleoproterozoic Vyatka-Kama orogenic belt. Most of the gneisses and schists of the Uni Formation have greywacke protoliths, while metatuffites of andesite to dacite compositions are subordinate. All of these rocks have similar suprasubduction geochemical characteristics and highly radiogenic Nd isotopic compositions. The age of magmatic zircons from the felsic metatuffites is 2.08 Ga, and individual detrital grains from these rocks date back to ca. 2.12 Ga. Detrital zircons from the metasedimentary rocks have well-preserved crystals and multimodal U-Pb age distributions peaking at 2.08, 2.10, and 2.14 Ga. Some zircons from migmatized gneisses have 2.05-Ga-old rims, corresponding to the age of the Talitsky granitoids. The obtained data suggest that the Vyatka terrane could be considered an accretionary complex of the Vyatka-Kama orogen. The Uni Formation was formed by the accretion of sediments derived from an eroding Paleoproterozoic magmatic arcs (2.08-2.14 Ga). The completion of the accretionary tectonics was marked by the intrusion of the ca. 2.05-Ga-aged post-tectonic Talitsky granitoids. The Vyatka terrane accretionary complex contains chronologic counterparts of the West Sarmatian and Volga-Don orogens. This complements the model of a simultaneous amalgamation of Archean blocks of the Volgo-Sarmatia dating back to 2.2-2.0 Ga. Data from the Vyatka terrane confirm the model of the superposition of the East European and Siberian cratons in the Paleoproterozoic Columbia/Nuna supercontinent reconstruction. The Vyatka-Kama and Batomga belts may have been parts of a single extended Paleoproterozoic orogen that combined the Archean Volgo-Uralia and Aldan composite terranes. (c) 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Lu–Hf isotopic composition of zircons from the calc-alkaline diorite–granodiorite intrusions of the Stoilo-Nikolaevskii complex in the margin area of the Kursk block is an important indicator of petrogenesis and the tectonic environment of their formation. The morphological features of zircon, the Th/U ratio, the distribution of rare earth elements, and the high crystallization temperatures according to the Ti-in-Zrn thermometer are evidence of its magmatic nature. Isotopic Hf composition indicates inhomogeneous, primarily Paleoarchean sources with a large spread of negative εHf(T) values and model ages. The diorite–granodiorite massifs were formed in the magmatic back-arc region on the ancient continental margin.

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

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070073

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.

Aillikite dikes of carbonate–biotite composition, intersecting Paleoproterozoic banded iron formations, were discovered in the Kursk block of Sarmatia for the first time. Their age is 2.10–2.07 Ga. The aillikite dikes underwent epidote–amphibolite facies metamorphism (550°С, 2–3 kbar), and they are deformed and foliated. Primary magmatic olivine and pyroxene were not preserved. In terms of geochemistry, ultramafic lamprophyres of the Kursk block are similar to petrotypical aillikites. They are depleted in SiO2 and Al2O3 and enriched in MgO, TiO2, K2O, Cr, Ni, and Nb with highly fractionated LREE and HREE. The highly radiogenic neodymium isotopic composition is indicative of a juvenile enriched (metasomatized) mantle source of aillikites. Positive Nb and Ti anomalies suggest metasomatic alterations of the depleted lithosphere mantle by OIB melts under opening of the Tim back-arc basin. The aillikite dikes and carbonatites of the Dubravinsky complex could have been formed at different melting degrees of a single deep, lithospheric source, enriched in lithophile elements shortly before the melting episode, possibly in a suprasubduction setting about 2.1 Ga.

Metamorphosed dacitic porphyry dikes were first found in the western part of the Vorontsovka terrane, which is located in the Paleoproterozoic Volga–Don orogen at the margin of Archean Sarmatia and Volga–Ural cratons. The magmatic protolith age for the metadacites is ca. 2.07 Ga. These are ferrous, metaluminous calc-alkali I-type granitoids. The sodium specialization of the rocks and their low concentrations of Mg, Cr, Ni, and incompatible elements, with significant REE fractionation, the absence of Eu* anomalies, high Sr/Y ratio, remarkably high (Gd/Yb)n values (>10), and the radiogenic Nd isotopic composition indicate that the dacitic melts were derived from a juvenile mafic source. According to petrogenetic estimations, such conditions could be caused by the partial melting of depleted N-MORB basites in equilibrium with an eclogitic residue. The dacitic magmas were likely generated by the partial melting of mafic rocks at lower levels of the significantly thickened crust (>60 km) in relation to collision processes.

In the western part of the Aldan terrane, in the middle reaches of the Tokko river, dolerite dikes have been studied. These dolerite dikes form a swarm of submeridional trend about 1 km wide. In the thickest dike, dolerites have well-preserved primary textural and structural features and mineral composition: plagioclase + pigeonite + augite + titanomagnetite. Dolerites from the chilled margins and inner parts of the dike are homogeneous in composition, correspond to low-Mg tholeiites, have low contents of Ti and other HFSE, with weak enrichments in light REE spectra and small negative Nb anomalies. Sm-Nd isotopic studies of magmatic dolerite minerals from the central part of the dike in isochron coordinates yielded a good linear correlation corresponding to an age of 2510 ± 64 Ma, which probably records the time of crystallization of the basaltic melt. The metadolerites in the shallow dike retain plagioclase-porphyritic structures, but the pyroxenes in them are completely replaced by amphibole and chlorite. Metadolerites are contrasted by low contents of MgO, Cr and Ni and higher contents of TiO2, Fe2O3, P2O5, Nb and all REEs. The differences in the composition of the dikes may be related to the long-term (about 65%) crystallization differentiation of the initial melt and the flow of residual melt from the shallow intermediate magmatic chamber along the opening cracks. Such conditions probably existed in tectonically stable intraplate settings. The age of the studied dolerites of the dike swarm is comparable to that of the anorogenic granites of the Nelyuki Complex (~2.4–2.5 Ga), which are widespread in the western part of Aldan granulite-gneiss Terrane. The data obtained complement the characterization of the intraplate anorogenic magmatism that occurred in the western part of the Aldan Shield in the Late Archean and marked the final consolidation of a large block of Archean crust in the Chara-Olekma granite-greenstone area.

The Paleoproterozoic Tim-Yastrebovka synform of Eastern Sarmatia contains gabbroid intrusions. The largest of them is the Gnilushinskii massif of hornblende gabbros, which are calc-alkaline rocks, enriched in light rare earth and lithophile elements with a negative stable MgO–Al2O3 correlation. High-aluminous varieties represent residual melts, while magnesian ones can be complementary cumulus. The crystallization age of the massif is 2031 Ma. The massif has a post-tectonic position and a metasomatized mantle source. Post-collisional tectonics inherited the environment of the active margin, since the Archean Sm–Nd model age of gabbros indicates its position at the margin of the Kursk Archean block.

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.

According to the core data from two deep holes, the following mineral assemblages were identified in metapelitic rocks of the Uni Suite in the central part of the Vyatka Belt, sandwiched between Archean blocks in the northeastern part of the Volgo–Uralian Segment of the East European Craton: (1) Pl + Ms + Bt + Qz + Kfs + And ± Chl and (2) Pl + Bt + Qz + Kfs + Grt + Sil ± Ms ± Chl. A set of methods including classical ( Grt–Bt , GASP, Ti-in- Bt , and Ms–Bt ) and multi-equilibrium thermobarometry (winTWQ 2.34), as well as the isopleth intersection method on pseudosection diagrams (GeoPS 3.2.2.128), was applied to estimate the P–T conditions for these assemblages. The calculated P–T parameters of metamorphism are 520–650°C (or up to 690°C, according to the isopleth method) and 2–5.4 kbar. Metamorphism of paragneiss containing assemblage (2) was accompanied by anatexis in the water-saturated system. Metamorphism of rocks of the Uni Suite belongs to the relatively shallow type of the andalusite–sillimanite facies series and amphibolite facies and relates to deformations during orogenes.

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 Dubravinsky alkaline-carbonatite complex (ACC) include two relatively large plutons: the arcuate shape Dubravinka pluton and linear Chernyanka pluton intruding the Paleoarchean TTG of the Kursk block of Sarmatia and consisting of three main lithologies: alkaline pyroxenites, carbonatites (together with silicocarbonatites and phoscorites) and syenites (including alkaline granites). The carbonatites and silicocarbonatites are enriched in trace and rare earth elements, which contents vary significantly. The source for the alkaline pyroxenites and carbonatites could be enriched protoliths from the subcontinental lithospheric mantle, produced by melting and release of fluids from the subducted oceanic slab at c. 2.1 Ga. The primary igneous C and O isotope composition is preserved in the carbonatite: 813C (%o VPDB) = (-4.9) - (-6.4), 818O (%o VSMOW) = (+8.0) - (+9.8). The alkaline granites display well preserved isotope markers of a longlasting crustal prehistory indicating Paleoarchean source. The syenites have a lesser contribution of Paleoarchean crustal material. The alkaline pyroxenites and carbonatites are undoubtedly initially igneous rocks that have undergone c. 2.07 Ga-old high-temperature metamorphism. The Dubravinsky ACC is most likely 2.07-2.08 Ga-old, not much older than the metamorphic event. The Dubravinsky ACC has been formed in a suprasubduction setting from both mantle and crustal sources. It is the earliest known carbonatite complex in the World resulted from subductioncollision processes, and the first sign of transition to deep subduction of the modern style.