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.”
