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.

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.