Beginning ca. 2.76 Ga, evolution of the Kola-Karelia crust was related to the intracontinental high-temperature metamorphic (up to granulite facies) and magmatic events in combination with formation of the basins related to rifting and infilling with intracontinental volcanic and sedimentary sequences initiated by plume-type processes in the mantle. The geological events corresponding to intracontinental evolution were expressed not only in the formation of new rock associations, juvenile to a significant extent, but also in reworking of previously formed rocks. The age, content, and mode of geological activity are somewhat different in the Kola and the Karelian-Belomorian regions. The Karelian-Belomorian region is oval in plan view. The long axis of this oval extends for 600–700 km in the meridional direction; its maximum width is 400–450 km. The southern part of this oval structure is cut off along the NW-trending boundary with the Paleoproterozoic Svecofennian accretionary orogen. The main constituents of the Karelian-Belomorian region are: epicontinental sequences of greenstone belts (Kostomuksha, Khedozero-Bolsheozero, Gimoly-Sukkozero, Jalonvaara) and paragneiss belts (Hattu, Nurmes); granulite-gneiss complexes and intrusive enderbite-charnockite series; sanukitoid-type granitoid intrusions and lamprophyre dikes, along with migmatization and emplacement of within-plate young granites; and local manifestations of granulite-facies metamorphism superposed on older rocks. Concentric spatial distribution of related geological units is characteristic of the Karelian-Belomorian region. The geometric pattern of the region can be satisfactorily explained assuming initial activity of a mantle plume ca. 2.76 Ga in the central part of the region. A peak of activity was related to the events that occurred ca. 2.74–2.70 Ga. The geochronological data show that a region of high-temperature processes expanded from its center (2.76–2.73 Ga) to the periphery (2.74–2.70 Ga). The concentric character of the tectonic structure was eventually formed as a result of these processes. Widespread high-temperature magmatism and metamorphism in combination with formation of synformal and linear sedimentary basins indicate the setting of anorogenic extension and vigorous influx of extracrustal heat, i.e., a large event related to a mantle plume. In contrast to the Karelian-Belomorian hot region, the coeval Kola region of intracontinental manifestations of high-temperature metamorphism and magmatism is characterized by oval-block geometry. This area, confined to the central part of the Kola Peninsula, extends for 600 km in the northwestern direction, having a width of ~200 km. It is possible that this area extends further to the southeast beneath the platform cover. The main tectonic units are the intracontinental greenstone belts (Sør-Varanger, Titovka, Uraguba, Olenegorsk, Voche-Lambina, Kachalovka, Runijoki–Khikhnajarvi, and Strelna system) in the Inari-Kola microcontinent, the granulite-gneiss Central Kola complex, and the Keivy volcanotectonic paleodepression. Sanukitoid intrusions play a modest role. The Keivy volcanotectonic paleodepression is situated in the eastern Kola Peninsula. Rocks of this tectonic unit are peculiar, and many of them have no obvious analogs in the Fennoscandian Shield or elsewhere. The major Neoarchean amphibolite-gneiss association consists of calc-alkaline to subalkaline garnet-biotite and subalkaline-peralkaline aegirine-arfvedsonite gneisses, as well as biotite-amphibole and amphibole gneisses, amphibolites, and rheomorphic alkali granites. In the western part of the paleodepression, gneisses (metavolcanic rocks) are cut through by small Sakharjok and Kuljok nepheline syenite intrusions. Geochronological estimates characterize two outbursts of magmatic activity separated by a long gap. The early outburst corresponds to magmatic crystallization of calc-alkaline metavolcanic rocks at 2.90–2.87 Ga. The second vigorous outburst documented at 2.68–2.63 Ga corresponds to eruption of subalkaline and subalkaline-peralkaline volcanic rocks, emplacement of alkali and nepheline syenites, and crystallization of gabbro-anorthosite of the Tsaga-Acherjok complex. The duration of the main magmatic phase is ~50 m.y., whereas the preceding gap lasted for ~200 m.y. A model of a volcanotectonic depression largely filled with pyroclastic flows seems plausible to explain pre-metamorphic events. Such manifestations of volcanic activity are inherent to intracontinental domains and related to activity of mantle plumes; similar processes can also develop in the back extensional zone of active continental margins. The synchronism of felsic volcanism and emplacement of the typically intracontinental gabbro-anorthosites form a sound argument in favor of an intracontinental setting for the Keivy paleodepression. The geometry of the Kola region can be satisfactorily explained in terms of mantle-plume activity noted ca. 2.76 Ga in the marginal part of this region; a peak of activity in its central part is related to the events that happened ca. 2.68–2.63 Ga.

Abstract The Early-Mid-Palaeozoic successions of the Pechora Basin along continent Baltica's northeastern margin unconformably overlie Neoproterozoic complexes of the Timanide orogen; further west, Palaeozoic platform strata cover the East European Craton basement. The latter is exposed in the northern parts of the Fennoscandian (Baltic) Shield and is also present beneath the Neoproterozoic (perhaps also Mesoproterozoic) and younger successions of the Mezen Basin. Geophysical data help define the crustal and upper mantle structures of this part of northwestern Russia, from the Kola Peninsula to the Uralide orogen. Within the Shield, seismic refraction and near-vertical reflection profiling allow the terranes of Archaean and Palaeoproterozoic age, defined at the surface (the Murmansk, Kola Liinakhamary, Central Kola, Keivy and Belomorian terranes, and the Pechenga-Imandra-Varzuga and Lapland-Kolvitsa Granulite Belts constituting the Lapland-Kola orogen, and the West Karelian, Central Karelian and Vodlozer terranes forming the Karelian province), to be traced into the deeper crust, promoting interpretation of various early Precambrian compressional and extensional regimes. Thrusting, transcurrent and extensional faulting have been identified in a crust that has been partly thickened during late Archaean and Palaeoproterozoic collision and locally extended both in back-arc basin settings and during syn-post-collisional collapse. The main Fennoscandian terranes can be traced southeastwards beneath the Mezen Basin based on gravity and magnetic data. Seismic profiling shows that the Phanerozoic successions of this basin overlie intracratonic rifts of Neoproterozoic and possibly Mesoproterozoic age. The rifts are composed of a number of half-graben, the details of which are well defined by vibroseis reflection profiling. During the development of Mezen Basin rifts, a Neoproterozoic passive margin was established in the vicinity of what is now the Timan Range. Late Neoproterozoic (Vendian) orogeny emplaced slope-rise turbidite-dominated successions southwestwards onto the platform. Towards the hinterland of the Timanides (also referred to as Baikalides), beneath the Phanerozoic Pechora Basin, a combination of potential field and seismic surveys, both shallow reflection and deep refraction profiling, have allowed analysis of the crust and uppermost mantle. Neoproterozoic magmatic arcs, Grenville-age(?) microcontinents and possible oceanic domains are inferred to exist beneath the early Palaeozoic unconformity. A vast region of Neoproterozoic accretion reaches from the western Urals, northwards beneath the Pechora Basin and the eastern Barents Shelf.