Abstract This paper considers the lithospheric structure and evolution of the wider Barents–Kara Sea region based on the compilation and integration of geophysical and geological data. Regional transects are constructed at both crustal and lithospheric scales based on the available data and a regional three-dimensional model. The transects, which extend onshore and into the deep oceanic basins, are used to link deep and shallow structures and processes, as well as to link offshore and onshore areas. The study area has been affected by numerous orogenic events in the Precambrian–Cambrian (Timanian), Silurian–Devonian (Caledonian), latest Devonian–earliest Carboniferous (Ellesmerian–svalbardian), Carboniferous–Permian (Uralian), Late Triassic (Taimyr, Pai Khoi and Novaya Zemlya) and Palaeogene (Spitsbergen–Eurekan). It has also been affected by at least three episodes of regional-scale magmatism, the so-called large igneous provinces: the Siberian Traps (Permian–Triassic transition), the High Arctic Large Igneous Province (Early Cretaceous) and the North Atlantic (Paleocene–Eocene transition). Additional magmatic events occurred in parts of the study area in Devonian and Late Cretaceous times. Within this geological framework, we integrate basin development with regional tectonic events and summarize the stages in basin evolution. We further discuss the timing, causes and implications of basin evolution. Fault activity is related to regional stress regimes and the reactivation of pre-existing basement structures. Regional uplift/subsidence events are discussed in a source-to-sink context and are related to their regional tectonic and palaeogeographical settings.

The basement of the East European Platform corresponding to northeastern Sarmatia is known as the Voronezh Crystalline Massif (VCM). The Kursk microcontinent, which lies in northeastern Sarmatia, occupies the bulk of the Voronezh Crystalline Massif. The predominant portion of the Kursk microcontinent is a combination of sedimentary–volcanic complexes making up greenstone belts and granite-gneiss (granite-migmatite) associations of the granite-greenstone domain bearing the same name. The smaller Kursk–Besedino granulite-gneiss terrane is situated in the central part of the microcontinent. The following sequence of events may be proposed as a preliminary model of crustal evolution: (1) Paleo- to Mesoarchean: formation of granite-greenstone continental crust (3.7–3.1 Ga); (2) events related to the activity of a mantle plume 2.85–2.82 Ga ago: underplating by mantle-derived magmas; formation of an intracontinental depression; its rapid filling with sediments, including Fe-rich varieties; and metamorphism of granite-greenstone basement and the sedimentary fill of the depression; and (3) Neoarchean and/or Paleoproterozoic: collisional compression and transformation of the depression into a synformal tectonic nappe.

The major tectonic units of the Neoarchean Volgo-Uralia continent, which is ~600,000 km 2 in area, are contrastingly expressed in regional gravity and magnetic maps. Interpretations of seismic images of the crust along the TATSEIS geotraverse in combination with 3D density and magnetic crust models provide insights into the volumetric representation of tectonic structures of various ranks. Granulite-gneiss crust of Volgo-Uralia is characterized by elevated thickness (~60 km and locally up to 65–70 km). The deep structure of Volgo-Uralia assumes that the entire crustal section, including the lower crust, is composed of high-density granulite metamorphic facies rocks. Specific structural units called ovoids play the main role in the structure of this continent. The ovoids are bowl-shaped crustal blocks, round or oval in plan view, 300–600 km across, and with the base reaching a level of crust-mantle interface at ~60 km. Ovoids are bounded by conic surfaces of reverse (thrust)-faults, along which their outer parts are thrust over the framework. The Tokmov, Buzuluk, Verkhnekamsk, Krasnoufimsk, and Orenburg ovoids, which generally are not in contact with one another, are dominated by mafic granulites, gabbroic rocks, gabbroanorthosites, and ultramafic rocks. A significant contribution of deep-seated intrusive rocks suggests that metamorphism developed in the lower and middle crust at high PT parameters that exceed the maximum estimates (940–950 °C, 9.5 kbar) recorded in samples of borehole cores. The interovoidal space is occupied by elongated oval synforms up to 200–400 km long. This space is considered to be an interovoidal domain, which includes three relatively narrow, compressed synforms (Yelabuga-Bondyug, Kilmez, Chusovaya) and four oval synforms (Srednevyatka, Verkhnevyatka, North-Tatar, Almetevsk). The Tokmov ovoid is framed in the southeast by the Tuma and Penza belts. Synforms are filled with metasedimentary granulites and mafic metaigneous rocks. The protoliths were formed over the time interval from 3.4–3.2 to 3.1–3.0 Ga. The internal zoning of the Volgo-Uralia crust is related to numerous local centers within ovoids and interovoidal region. At least two high-temperature metamorphic events were followed by periods of retrogression: 2.74–2.70 and 2.62–2.59 Ga. The areal and especially high-temperature character of tectonothermal processes during formation of the Neoarchean crust of the Volgo-Uralia Craton, and distinct geometrization of space with recognition of several concentric domains, finds a universal explanation in ascent of multiple plumes.

The Bryansk-Kursk-Voronezh intracontinental collisional orogen was formed by the juvenile Middle Paleoproterozoic assemblages in combination with Early Paleoproterozoic complexes and areas of reworked Archean crust. The crucial events fall in the time interval 2.1–2.0 Ga. The orogen includes a sequence of second-order, near-meridional orogens, which, in turn, consist of tectonic belts. From the west eastward, these are the Krivoi Rog–Bryansk orogen, the orogen of the Kursk magnetic anomaly (KMA), and the East Voronezh orogen. The latter may be regarded as an axial (central) structural element, which marks a transient rupture of the continental crust. The north to south extent of the orogen along the strike of the second-order orogens reaches 900 km long and ca. 900 km in width. The Krivoi Rog–Bryansk orogen consists of two groups of tectonic belts. Its western region is composed of tectonic nappes pertaining to the Kulazhino gneiss and the Bryansk granulite-gneiss belts. The eastern region, including the Krupetsk-Znamensk belt and the Meshchevsk system of tectonic sheets, with significant role of intensely deformed banded iron formations (BIF) of the Kursk and Oskol groups, is also the western imbricated margin of the Archean Kursk craton. The volcanic-sedimentary BIF belts play the main role in the structure of the KMA orogen. The second important component is composed of subvolcanic and plutonic mafic-ultramafic, felsic, and alkaline rock complexes. Granite-gneiss domes are related to the final stage of the orogen evolution. The East Voronezh orogen consists of the Lipetsk-Losevka volcanic-plutonic belt and the Vorontsovka imbricated thrust belt, separated by the Losevka-Mamon suture. The evolution of the Bryansk-Kursk-Voronezh orogen as a whole includes: onset of rifting within the Archean Kursk craton (2.59–2.53 Ga); terrigenous and chemical sedimentation including BIF and volcanic activity (2.5–2.10 Ga), periodically accompanied by emplacement of intrusions (2.6–2.5 Ga and 2.1–2.05 Ga); metamorphism under granulite-facies conditions in the Kulazhino and Bryansk belts at 2.13 Ga and in the Vorontsovka belt at 2.10 Ga; intrusive magmatism in the Vorontsovka belt generally synchronous with high-temperature metamorphism; suprasubduction magmatism and formation of the Lipetsk-Losevka volcanic-plutonic belt 2.10–2.05 Ga ago; the collision-related reverse and thrust faulting and folding in the BIF belts accompanied by westward and south-westward overturning; rheomorphism and formation of granite-gneiss and granite-migmatite domes deforming the fold-nappe assemblages in the BIF belts of KMA; and the tectonothermal activity of postcollisional and anorogenic stages (2.07–1.9 Ga) expressed by emplacement of alkaline ultramafic and gabbro-syenite intrusions in the Lipetsk-Losevka belt and its hinterland. The most active phase of tectonic evolution spanned the time interval 2.1–2.0 Ga, which was no less than 100 Ma long and coincided with the active stage of extension, sedimentation, and high-temperature metamorphism in the northern part of the East European craton.

The Late Paleoproterozoic Lapland–Mid-Russia–South Baltia orogen surrounds the Karelian craton as a wide arc, separating it from Volgo-Uralia and Sarmatia. The orogen extends for more than 3000 km; its width in the northern and central segments is 400–700 km and increases to 1000 km in the southwest. The Lapland sector of the orogen is characterized by specific spatial distribution of tectonic belts composed of low-grade metavolcanic-metasedimentary rocks and granulite-gneiss complexes. The former are localized along the orogen boundaries; in turn, the axial zone is mainly formed by alternation of low-angle tectonic sheets varying in thickness from a few to 20–25 km. The sheets are composed of Paleoproterozoic granulite-gneiss complexes and Archean granite-greenstone and amphibolite-gneiss assemblages. The geological history of the orogen is subdivided into four stages. (1) The Early Paleoproterozoic magmatism (2.53–2.41 Ga, locally up to 2.32 Ga) corresponds to the initial stage in evolution of the superplume, which induced rifting of the Archean continent. This stage includes: the early volcanism (ca. 2.5 Ga), the layered peridotite-gabbronorite intrusions (2.53–2.42 Ga), bimodal volcanism (2.45–2.42 Ga), emplacement of the minor mafic intrusions that were later transformed into drusites (2.46–2.43 Ga), formation of the Pyrshin-Kolvitsa gabbro-anorthosite complex (2.51–2.42 Ga), and intrusions of charnockites and K-rich granites (2.50–2.43 Ga) and granitoids (2.50–2.41, up to 2.37–2.36 Ga). The Pyrshin-Kolvitsa gabbro-anorthosites underwent granulite-facies metamorphism along with mafic protolith of the Lapland and Kolvitsa-Umba granulite complexes. The domain of initial magmatism in the Kola-Karelia region is a NW-trending band, 1000–1100 km in extent and 300–450 km in width. The area of manifestation of various modes of Early Paleoproterozoic magmatic activity can be regarded as a large igneous province. (2) The initial magmatism was followed by a long-term (2.3–2.1 Ga) stage of quiescent tectonics. Sedimentation in the Karelian Province initially occurred in the vast lacustrine-alluvial plain, then in the nearshore marine and continental evaporite basin, and by the end of this stage in a shallow-water marine basin characterized by deposition of evaporite carbonate and sulfate sediments and growth of numerous stromatolite reefs. The accumulation of salt has been documented by deep drilling in the Onega depression. The basement and sedimentary sequence were cut through by a NW-trending dike swarm almost synchronously with sedimentation. In the southwestern part of the basin within Karelia, separate lava fields were formed, whereas in Kola Peninsula, volcanic activity was much more intense, and sedimentation had been suppressed. (3) The resumption of tectonic activity by the onset of the Late Paleoproterozoic is recorded in a vigorous pulse of magmatic activity (2.11–1.92, locally up to 1.88 Ga), which was somewhat similar to the Early Paleoproterozoic initial magmatism. It developed within the same NW-trending band as the Early Paleoproterozoic initial magmatism. As in the previous case, the area of the Late Paleoproterozoic magmatism corresponds to the definition of a large igneous province. It involves: (i) mafic volcanic rocks inherent to continental and oceanic rifts (including the Jormua ophiolite complex) in combination with a bimodal rhyolite-picrite association close in geochemistry to ocean-island basalt and subvolcanic minor gabbro and wehrlite intrusive bodies (2.11–1.92 Ga); (ii) volcanic-sedimentary and mafic-ultramafic subvolcanic complexes of the Onega depression (ca. 1.98 Ga); (iii) Kimozero kimberlites (ca. 2.0–1.8 Ga); (iv) Jaurijok complex of gabbro-anorthosite intrusions (from 2.0–1.95 to 1.88 Ga); and (v) alkali intrusions (from 1.97–1.95 to 1.88 Ga) and granitoid plutons (ca. 1.95 Ga). All gabbro-anorthosite bodies of the Jaurijok complex are localized at the base of nappe-thrust ensemble of the Lapland granulite belt, i.e., in exactly the same position as the Early Paleoproterozoic Pyrshin-Kolvitsa complex. Appearance of the suprasubduction magmatism in volcanic-sedimentary belts almost at the same time (1.93–1.86 Ga) marked a change from the extensional regime to compression in the Paleoproterozoic history of the East European craton for the first time in Paleoproterozoic history. (4) The subsequent stage, with predominance of collisional and postcollisional processes (1.87–1.70 Ga), resulted in eventual formation of the intracontinental collisional orogen. In the history of the Lapland and Kolvitsa-Umba granulite-gneiss belts, an emplacement of the Pyrshin-Kolvitsa gabbro-anorthosite and granulite-facies metamorphism M0 were broadly coeval with Early Paleoproterozoic plume-influenced rifting of the Archean supercontinent ca. 2.51–2.44 Ga. This period was followed by deposition of volcaniclastic protoliths of the lower part of the Lapland granulite complex, which probably occurred within the intracratonic extensional basin. The next episode of plume-related extension, which induced emplacement of the Jaurijok gabbro-anorthosite bodies, lasted from 1.97 to 1.89 Ga. High-grade metamorphism M1 (ca. 1.95 Ga) and then pervasive granulite-facies metamorphic events M2 (1.95–1.91 Ga) and M3 (1.91–1.89 Ga) followed at the end of this episode. At the same time, in the area of low-grade volcanic-sedimentary belts, opening and subsequent closure of local intracontinental oceans occurred due to rapid subduction and/or obduction of the oceanic lithosphere. The Mid-Russia sector (basement of the East European platform—territory of the Moscow syneclise) is the central part of the southern branch of the Lapland– Mid-Russia–South Baltia orogen surrounding the Karelian craton in the south. The Totma belt extends along the northern boundary, separating the Paleoproterozoic orogen from the Karelian craton, while the southern boundary, which separates the Paleoproterozoic orogen from the Volgo-Uralia continent and Sarmatia, is marked by the Aprelevka and Kazhim belts. The Kashino, Zubtsovsk-Diakonovo, Dmitrov-Galich, Moscow, Lezhsk-Grivino, and Oparino granulite-gneiss thrust-nappe belts are crucial in the upper-crustal structure of the Mid-Russia sector. They are combined with Archean or Paleoproterozoic gneiss-amphibolite-migmatite complexes in the Bologoevo, Tver, Bukalovo, and Ivanovo-Sharya belts. As a whole, the Mid-Russia sector of the Paleoproterozoic collisional orogen is a giant synform, 300–350 km wide and 1400 km long. The synform is composed of tectonic sheets, 6–8 km thick, alternating in vertical and lateral directions and formed by the Paleoproterozoic and Archean granulite-gneiss and migmatite-amphibole-gneiss complexes. It is bordered by tectonic sheets of volcanic-sedimentary belts conformably plunging southeast. The South Baltia sector of the orogen (basement of the East European platform—Southern Baltic region and Belarus) is composed of a series of arcuate (crescentic) belts consisting of metamorphic rocks ranging in grade from greenschist to epidote-amphibolite or from high amphibolite to granulite facies. The sector, which extends for 1200 km toward the northeast, is up to 800 km wide. The arcuate outlines of belts in the South Baltia sector are convex to the east. The internal structural elements of belts and their boundaries are generally characterized by westward centroclinal plunges. In the west, the South Baltia sector is cut off by the Transeuropean suture (Teisseyre-Tornquist Line), which separates it from the Hercynides of East Europe. The eastern part of the South Baltia Sector contains the Staraya Russa–South Finland granulite-gneiss belt, Ilmenozero migmatite-amphibolite-gneiss belt, and Vitebsk and Toropets granulite-gneiss allochthons. The northern segment of the South Baltia sector dominates the area and is composed of alternating arcuate (crescentic) belts: the Belarus-Baltic granulite-gneiss belt, Latvia–East Lithuania migmatite-amphibolite-gneiss belt, and West Lithuania granulite-gneiss belt at the western boundary of the East European craton. In the southern segment of the South Baltia sector, the sequence of the belt from west to east includes the Central Belarus migmatite-amphibolite-gneiss belt and the southern part of the Vitebsk granulite-gneiss allochthon. The South Baltia sector is, to a greater extent, similar in composition and structure to the other sectors of the Lapland–Mid-Russia–South Baltia intracontinental orogen. This implies that granulite-gneiss belts of the South Baltia sector most likely are underlain by Archean or Early Paleoproterozoic crust.

In this chapter, the available seismic and geological data are integrated and applied to the East European craton as a whole. The deep structure and seismic characteristics of the granite-greenstone crust in the Archean microcontinents vary significantly. The unevenly distributed and vaguely oriented short reflections are occasionally gathered into packets. The intensely reflecting bodies with high acoustic impedance correspond to greenstone belts reaching many tens of kilometers in extent. The oval acoustically transparent domains in the middle-crustal level are composed of moderately dense rocks that correspond to granitoid plutons. The total thickness of the crust in granite-greenstone domains can vary from 40 km in the Kola-Karelia continent to 50 km in the Kursk microcontinent. The Archean granulite-gneiss complexes form the delineated belts localized in the upper crust. These are synformal tectonic nappes, the vertical thickness of which reaches 15 km. A special case is the Volgo-Uralia continent, the crust of which is completely composed of granulite-gneiss rocks partly replaced by retrograde metamorphic assemblages. The granulite-gneiss crust is distinguished by significant thickness (~60 km; maximum 65–70 km). The lower-crustal “layer,” ~35 km thick, consists of inclined tectonic sheets plunging in a northwestern direction and penetrating the upper mantle. The interface between upper and lower crust is replaced by acoustically transparent granitoid crust 10–20 km in thickness. The Middle Paleoproterozoic East Voronezh intracontinental collisional orogen between the Archean Kursk and the Khopior microcontinents is represented by a “crocodile-jaw” structure. The structural pattern in the seismic image of the crust clearly indicates a Paleoproterozoic age of lower-crustal layer and shows the absence of the Paleoproterozoic lower-crustal complex at the base of the Kursk craton proper. The Late Paleoproterozoic intracontinental Lapland–Mid-Russia–South Baltia orogen surrounds in a wide arc the Karelian craton in the northeast, east, south, and southwest. The upper crust in the inner zone of the orogen in the Mid-Russia sector is composed of alternating granulite-gneiss and gneiss-migmatite-amphibolite tectonic sheets 5–10 km thick, deformed in gentle synformal folds. The marginal zones consist of south-plunging tectonic sheets of the Totma belt in the north and the Aprelevka belt in the south. The Totma sheet, reaching 10 km in thickness and dipping at a mean angle of 5°–10°, is traced by reflectors from the basement surface (interval 1700–1800 km) to the crust-mantle interface (interval 2000–2200 km). These parameters, along with composition of the rocks, allow interpretation of the Totma belt as a suture zone, separating the synformal structural assemblage from the lower crust. In the Paleoproterozoic Svecofennian accretionary orogen, interpretation of the FIRE-1 profile shows that the Central Finland granitoid massif is a nearly horizontal, sheetlike intrusive body that conceals an accretionary complex—a succession of tectonic sheets, 10–20 km thick, which plunges northeast at angles of 10°–12° down to the crust-mantle interface at a depth of 65 km and can be traced beneath the margin of the Karelian craton for more than 150 km. The lower-crustal layer, often called a reflectivity zone, is always present at the base of the Lapland–Mid-Russia–South Baltia orogen and the Archean cratons surrounded by this arcuate orogen. This layer was formed in the Early Paleoproterozoic as a result of under- and interplating of mantle melts accompanied by granulite-facies metamorphism. The increase in thickness of the lower-crustal layer is related to hummocking (mutual over- and underthrusting and wedging) of tectonic sheets at the base of the crust. The lower-crustal layer of the Kola-Karelia continent was formed before the main collisional events, which took place in the Late Paleoproterozoic. The structure of the crust depicted by seismic reflectors indicates in some cases that the crust-mantle interface has remained unchanged since the time of crust formation, whereas in other situations, this boundary is younger than the bulk crust. The crust-mantle interface beneath the East European craton reveals manifold deviations from its persistent near-horizontal outline due to bending, plunging, and apparent dissolution of lower-crustal sheets in the mantle. The underlying upper mantle reveals a number of indistinct reflectors imaged as dashed lines, which trace lower-crustal structural elements incorporated into the mantle. These domains are regarded as crust-mantle mixtures. The crust images along the seismic lines exhibit widely varying structural features and degrees of contrast (sharpness) of the crust-mantle interface. The following structural and morphological types of the crust-mantle interface are distinguished beneath the East European craton: (1) a smooth, generally flat or horizontal or slightly sloping boundary with an abrupt decrease in number of reflectors at the lower edge of intensely reflecting layered lower crust; (2) a boundary similar to the previous type but periodically interrupted at sites where the sheetlike fragments of the lower crust sharply bend and sink into the mantle and acoustically as if they dissolve therein; (3) a serrated boundary in the regions of consecutive plunging lower-crustal tectonic sheets into the mantle; these domains are commonly conjugated: reverse-thrust assemblages in the upper crust rise in the same direction as the lower-crustal sheets plunge; (4) a serrated boundary confining from below the ensemble of inclined tectonic sheets that form the crust completely or partly; (5) a diffuse crust-mantle interface that is observed where a distinct lower-crustal reflectivity zone is absent; and (6) a phantom (disappearing) crust-mantle interface that separates acoustically transparent crustal and mantle domains that can be detected by seismic-refraction exploration. Integration of the entire body of information allowed us to simulate the 3D deep structure of the Early Precambrian crust of the East European craton as a whole using sections along the 1-EU geotraverse, cross-traverse 4B, TATSEIS regional profile, and FIRE-1 and FIRE-4 profiles. The 3D deep structure of the East European craton is represented by the tectonically delaminated Early Precambrian crust with a predominance of gently dipping boundaries between the main tectonic subdivisions and a complexly built crust-mantle interface. The integral model includes Archean granite-greenstone domains and granulite-gneiss areas and Paleoproterozoic accretionary and intracontinental collisional orogens.

The earliest events in the geological history of the Early Precambrian crust of the East European craton (3.5–2.93 Ga) resulted in the emergence of spatially separate and genetically independent areas of continental crust (continental embryos), the dimensions of which rarely exceeded a few hundred kilometers across. The period between 3.05 Ga and ca. 2.75 Ga was a time of mainly plate-tectonic development: origin, evolution, and accretion of ancient island-arc systems, and collision of microcontinents. The Vedlozero-Segozero and Sumozero-Kenozero systems of greenstone belts, Tipasjärvi-Kuhmo-Suomussalmi and Central Belomorian greenstone belts in Karelia, and the Kolmozero-Voronya greenstone belt in the Kola Peninsula are interpreted as accretionary systems transformed in collisional orogens. The Belomorian eclogite province is structurally linked with the Central Belomorian greenstone (suture) belt. The Kovdozero granite-greenstone terrane is formed by granitoids and gneisses hosting metasediments and metavolcanics of several greenstone belts, which belonged to the Parandovo-Tiksheozero island arc. The amalgamation of the continental domains that made up the bulk of the Archean crust in the growing East European composite craton took from 2.82 to 2.66 Ga, but the main events had terminated by 2.75 Ga. During the period from 2.79–2.55 Ga, specific areas of intracontinental thermal and tectonic activity (hot regions) developed in the inner portions of the recently formed continent: Karelian-Belomorian and Kola areas in the eastern Fennoscandian Shield and extensive Volgo-Uralia granulite-gneiss area in the eastern part of the East European craton. These processes marked a principally new evolutionary episode in the Early Precambrian history of the East European craton. Widespread high-temperature magmatic and metamorphic processes and the development of synformal structures and linear sedimentary basins testify to an anorogenic extensional environment and a significant influx of heat to the crust, i.e., a significant event of mantle-plume type. During the Paleoproterozoic (2.53–1.87 Ga), a number of intracontinental collisional orogens were produced within the East European craton. The largest of them are the Lapland–Mid-Russia–South Baltia intracontinental orogen and the Svecofennian accretionary orogen. The Lapland–Mid-Russia–South Baltia orogen surrounds the Karelian craton as a wide arc, separating it from Volgo-Uralia and Sarmatia. The orogen extends for more than 3000 km; its width in the northern and central segments is 400–700 km and increases to 1000 km in the southwest. The Lapland sector of the orogen is characterized by spatial distribution of tectonic belts composed of low-grade metavolcanic-metasedimentary rocks and belts of high-grade metamorphic rocks, including granulite-gneiss complexes. The former are localized along the orogen boundaries; in turn, the axial zone of the orogen is mainly formed by alternation of low-angle tectonic sheets varying in thickness from a few to 20–25 km: sheets composed of Paleoproterozoic granulite-gneiss complexes with a predominance of metamorphosed juvenile intrusive and volcanic bodies and sedimentary rocks alternate with the sheets of Archean granite-greenstone and amphibolite-gneiss complexes. The Paleoproterozoic evolution of the Kola-Karelia continent and, accordingly, the Lapland–Mid-Russia–South Baltia orogen, is subdivided into four episodes: (1) ca. 2.53–2.3 Ga: failed rifting of the Archean continent; (2) 2.3–2.1 Ga: quiescent within-plate activity and diffuse rifting that can be regarded as “failed attempts” to break the supercontinent; (3) 2.1–1.95 Ga: rifting of the Kola-Karelia continent; and (4) 1.95–1.87 Ga: origin of the intercontinental collisional orogens. The Paleoproterozoic pulse of tectonic activity, which transformed the Neoarchean Kola-Karelia continent, continued for more than 600 m.y. Globally speaking, Early Paleoproterozoic magmatic and thermal activities were largely constrained within the ancient continent that then included North America and most of the eastern European continent, including the Fennoscandian Shield (Lauroscandia). Analysis of the extensive data leads us to distinguish a new type of tectonic structure: the intracontinental oval orogen formed in the inner portions of continents under the effect of large mantle plumes. It is an oval-shaped tectonic ensemble of regional rank with diameters from 600–1000 to 2500–3000 km, of which at least a part is characterized by concentric structure and metamorphic zonation or which contains bowl-shaped crustal structures. Intracontinental orogens contain granulite-gneiss complexes, derivatives of juvenile (though crust-contaminated) mafic magmas (gabbro-anorthosites and layered mafic-ultramafics), intrusions of “dry” high- temperature, within-plate–type granites, enderbites, and charnockites, and low-grade sedimentary-volcanic belts. The oval or oval-concentric structure excludes the possibility that intracontinental orogens originated as a result of processes at convergent plate boundaries. Their size and morphology and the evidence of a vast influx of mantle heat make intracontinental orogens comparable to oceanic plateaus and large igneous provinces on the continents. The fundamental changes in Earth's geological evolution that occurred at the Mesoarchean-Neoarchean boundary (ca. 2.75 Ga) can be related to the transition from Archean “microplate tectonics” to Paleoproterozoic “supercontinent tectonics” (or “microocean tectonics,” with regard to the limited size of the Red Sea–type oceans that were formed within the partly fractured supercontinent). The origin of Earth's first supercontinent, a landmass covering much of Earth's surface, by 2.80–2.76 Ga, should have played an extremely important role in restyling the system of convection cells in the underlying mantle. The style of tectonic processes and the geodynamic environment of plate tectonics in the Neoarchean–Paleoproterozoic differ from those in both the Archean and the Phanerozoic: the Archean tectonics of multiple “miniplates” was much more similar to Phanerozoic plate tectonics than to the Neoarchean–Paleoproterozoic “tectonics of supercontinents.”

The first broad Russian experiment aimed at the study of the deep structure of Earth's crust and upper mantle by the common midpoint (CMP) method along the 1-EU geotraverse and cross-traverse 4B was realized in 1995–2008 in the territory of the East European Platform under the Russian Federal Program on Development of the State Geotraverse Network and Deep and Superdeep Boreholes. At the same time, the EGGI profile, geotraverses TATSEIS, ESRU 2003–2005, and DOBRE in Ukraine, as well as the system of profiles under the FIRE project in the adjacent territory of Finland were acquired. Integration of the existing geological maps and available geological (in the widest sense: structural, geochemical, geochronological, and so forth) data with results of geological interpretation of seismic images of the crust and upper mantle have led to a three-dimensional (3D) model of the deep crustal structure of the East European craton and a significant revision of previous ideas on the deep structure and Early Precambrian evolution of the region. In the geological interpretation of seismic data, we attached particular significance to the direct tracing of geological boundaries and fault zones recognized on the seismic-reflection pattern and the section of effective acoustic impedance toward the present-day surface and to their correlation with mapped geological and tectonic units. Comparison of the seismic image geometry with the geology of the eastern Fennoscandian Shield at the present-day erosion level shows that the reflection pattern matches the general trends of compositional layering, gneissic banding, and schistosity. The roughly homogeneous structural domains of the crust correspond to relatively large tectonic sheets, 3–5 km thick. Their inner structure commonly is not discernible in reflection patterns. The 3D model of deep structure in the Kola-Lapland region is based on correlation of tectonostratigraphic complexes depicted in the geological-tectonic map with structural subdivisions recognized as a result of interpretation of seismic crust images and their tracing to depth. In addition to the geological section along the 1-EU geotraverse, the model includes the section along the FIRE-4–4a profile that crosses the western part of the region studied in Finland. The 3D model shows the Paleoproterozoic tectonic structures (Lapland granulite-gneiss belt and its structural and evolutionary relationships with lower-crustal granulites, the structure and tectonic position of the Tana belt) and Archean tectonic structural units (the Central Kola granulite-gneiss belt, the Inari-Kola granite-greenstone domain, and the boundary zone between the Kola craton and the Belomorian orogen). The detailed 3D model of the crust and uppermost mantle in the Karelian-Belomorian region is also based on correlation between the exposed geological structure and geological interpretation of seismic images along the 1-EU geotraverse and cross-traverse 4B. The geological interpretation of the seismic crust image along the FIRE-1 profile serves as the additional basis for the Svecofennian accretionary orogen and its boundary with the Kola-Karelia continent. The model of the crust in the Karelian-Belomorian region contains the Paleoproterozoic tectonic structures (East Karelian imbricate thrust belt, Svecofennian accretionary orogen, and Onega Depression) and also Archean tectonic structures (Kuhmo-Segozero and Kovdozero microcontinents, and Chupa granulite-gneiss belt). The deep structure of the platform basement beneath the Moscow syneclise is an immediate extension of the Fennoscandian Shield. The basement structure in this area was controlled by Paleoproterozoic processes resulting in formation of the Lapland–Mid-Russia–South Baltia intracontinental orogen. The 3D model shows the marginal Totma and Aprelevka volcanic-sedimentary belts, and a synformal structure for the upper crust in the central domain of the orogen. The rock complexes of the Zubtsov-Diakonovo granulite-gneiss belt in the northwest and the Dmitrov-Galich belt in the southeast make up a distinctly outlined stage in the synform section. These complexes are underlain by gneiss-migmatite-amphibolite associations of the Bologoevo and Ivanovo-Sharya belts and are overlain by similar rocks of the Tver and Bukalovo belts. Lastly, the Kashin synformal granulite-gneiss belt is localized in the upper part of the section. The alternation of rocks of differing metamorphic grade clearly indicates the tectonic or tectonized stratigraphic character of the section in the Nelidovo synform. The crust sandwiched between the southward-plunging Totma and Aprelevka belts is characterized by rough layering. The reflections and boundaries of crustal sheets outlined in agreement with this pattern plunge southward beneath the Archean Sarmatia and Volgo-Uralia continental blocks. The deep crustal structure of the Voronezh Crystalline Massif is determined by a succession of geodynamic settings and Archean and Paleoproterozoic tectonic events that resulted in the formation of the Archean crust in the Kursk granite-greenstone domain and probably in the Khopior microcontinent, the Middle Paleoproterozoic East Voronezh orogen, and the Late Paleoproterozoic North Voronezh orogen. The 3D model applies particularly well to the Middle Paleoproterozoic East Voronezh orogen. The orogen is localized in the area of collision of the Kursk and Khopior microcontinents, which differ markedly in crustal structure and composition. The crocodile-type tectonic structure of the East Voronezh orogen is clear evidence for collisional compression. The countermotion of microcontinents resulted in the wedge-shaped structure of the Kursk microcontinent extending for 150 km, delamination of crust in the Khopior microcontinent, and counterdisplacement of tectonic sheets coherently thrust over and under the Kursk microcontinent. The tectonic structure of the central and western Volgo-Uralia continent to a depth of 15–20 km is characterized by sections of 3D models of effective density and magnetization. The second block of information on the Volgo-Uralia continent deep structure comes from results of seismic profiling along the TATSEIS, ESRU 2003–2005, and URSEIS geotraverses. The TATSEIS geotraverse crosses a significant part of the Volgo-Uralia continent from southeast to northwest. The seismic crust images along this geotraverse not only create the basis for interpretation of regional deep structure, but also robustly link the crustal models of the western and southeastern parts of the Volgo-Uralia continent. The data along the ESRU 2003–2005 geotraverse played an important role in ascertaining the deep structure of the Krasnoufimsk ovoid, which is overlapped by sedimentary fill of the Ural foredeep. Additional evidence was provided by the URSEIS geotraverse. The Archean crust, slightly modified in the Paleoproterozoic, which forms the East European Platform basement in the Volgo-Uralia continent, is made up of mafic granulites, khondalite, mafic-ultramafic intrusions, and granitoid plutons. The 3D model of the crust based on the TATSEIS geotraverse demonstrates the deep structure of the Vetluga synform in the Tokmov ovoid and of the interovoid domain. Ovoids play a crucial role in the Volgo-Uralia continent structure and occupy no less than 60% of the crust. In 3D representation, they are bowl-shaped blocks, round or oval in outline, and 300–600 km in diameter at the basement surface, and with a base at the level of the crust-mantle interface, i.e., at a depth of 60 km. The thickness of crust of the interovoid domain does not commonly exceed 50 km. Two types of elongated oval synforms are distinguished: the interovoid ovals (Verkhnevyatka, North Tatar, Almetevsk), up to 200–300 m long, with aspect ratio of 2:1–3:1, and the interovoid belts (Usovo, Vyatka, Kilmez, Elabuga-Bondyuga, Tuma-Penza, as well as Zhiguli-Pugachev homocline), 300–400 km in extent, with aspect ratio of 4:1–5:1. The bottom of the largest interovoid oval crossed by the TATSEIS profile reaches 25 km in depth. In crustal section, the structural elements of the interovoid domain are underlain or partly crosscut by acoustically transparent layers composed of the Bakaly-type granitoids. The lower crust of the interovoid domain is ~35 km in thickness and is composed of tectonic sheets plunging toward the northwestern end of the geotraverse and penetrating into the mantle.

In Chapter 2, we showed that the eclogite-facies metamorphism within the Mesoarchean–Neoarchean Belomorian eclogite province can be correlated with “hot” subduction. However, was such a thermal regime specific to the Archean? Comparison of pressure-temperature-time paths and data for peak metamorphic parameters demonstrates the general similarity of the Archean and Paleoproterozoic eclogites worldwide and their association with anomalously “hot” environments. In contrast, Phanerozoic high- and ultrahigh-pressure eclogite complexes formed in connection with “warm” subduction zones. The high-temperature character of the eclogite-facies metamorphism in the Proterozoic is impossible to explain through a distinctively anomalous thermal regime, as is often suggested for the Archean mantle. The occurrence of high-temperature conditions during eclogite-facies metamorphism can be attributed to either subduction of a mid-ocean ridge (Archean, Belomorian eclogite province) or to interaction with mantle plumes (Proterozoic).

The Boltysh meteorite impact crater formed in the Ukrainian Shield on the margin of the Tethys Ocean a few thousand years before the Cretaceous-Paleogene boundary and was rapidly filled by a freshwater lake. Sediments filling the lake vary from early lacustrine turbidites and silts to ~300 m of fine silts, organic carbon–rich muds, oil shales, and lamenites that record early Danian terrestrial climate signals at high temporal resolution. Combined carbon isotope and palynological data show that the fine-grained organic carbon–rich lacustrine sediments preserve a uniquely complete and detailed negative carbon isotope excursion in an expanded section of several hundred meters. The position of the carbon isotope excursion in the early Danian stage of the Paleogene period, around 200 k.y. above the Cretaceous-Paleogene boundary, leads us to correlate it to the Dan-C2 carbon isotope excursion recorded in marine sediments of the same age. The more complete Boltysh carbon isotope excursion record indicates a δ 13 C shift of around -3‰, but also a more extended recovery period, strikingly similar in pattern to the highest fidelity carbon isotope excursion records available for the Toarcian and Paleocene-Eocene hyperthermal events. Changes in floral communities through the carbon isotope excursion recorded at Boltysh reflect changing biomes caused by rapidly warming climate, followed by recovery, indicating that this early Danian hyperthermal event had a similar duration to the Toarcian and Paleocene-Eocene events.