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Alexander Slabunov, Institute of Geology, Karelian Research Centre, RAS (Russian Federation)
Victor Balagansky, Geological Institute, Kola Scientific Center, RAS (Russian Federation)
Elena Bibikova, Vernadsky Institute of Geochemistry and Analytical Chemistry, RAS (Russian Federation)
Pentti Hölttä, Geological Survey of Finland (Finland)
Petri Peltonen, Geological Survey of Finland (Finland)
Peter Sorjonen-Ward, Geological Survey of Finland (Finland)
Oleg Volodichev, Institute of Geology, Karelian Research Centre, RAS (Russian Federation)
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The eastern Baltic (Fennoscandian) Shield (BS) is mostly formed of Archean bedrock which can be divided into the Karelian (KAP), Belomorian (BP), Kola (KOP), Murmansk (MP) and Norrbotten provinces, each of which has a distinct history of crustal growth and subsequent reworking. Seismic and geological data indicate that boundaries between the provinces are mostly tectonic in nature, with the present structural architecture being a consequence of both Archean and Paleoproterozoic events. The Archean involve a granitoid associations (TTG, sanukitoids and rare subalkaline and alkaline rocks) and subordinate greenstone, paragneiss and granulitic complexes. No Eoarchean rocks have been found, but 3.6 Ga detrital zircons occur in metasediments from the KOP, while Paleoarchean Siurua granitoids from the KAP contain 3.73 Ga inherited zircons have been reported. Paleoarchean rocks are only known to outcrop in the southeastern (Vodlozero TTG suite) and western KAP (Siurua TTG suite and lower crustal xenoliths in kimberlites). Large continental masses started to grow in the Mesoarchean (3.2?3.1 Ga) forming the first microcontinents, which were progressively amalgamated during Neoarchean time; there are at least four generation of Meso- and Neoarchean greenstone complexes (3.1?2.9, 2.9?2.85, 2.85?2.75 and 2.75?2.65 Ga) and two generations of paragneiss and schist complexes (2.9?2.85 and 2.75?2.65 Ga), which reflects episodic crustal growth stages. Most of the Archean crust of the BS thus formed 2.90?2.65 Ga ago, with 2.67 Ga alkaline rocks already manifesting a mature intraplate setting for the KOP. Greenstone complexes include island-arc series and many also comprise basaltic-komatiitic (plume) associations. Fragments of Meso- (Central Belomorian complex) and Neoarchean (Iringora complex) ophiolites and Neoarchean eclogites have been found in the BP. Thus, the Meso- and Neoarchean complexes formed through geodynamic settings comparable with those operating in the Phanerozoic, including subduction (ensialic and ensimatic), collision, continental rifting and plume-lithosphere interaction. Further studies are nevertheless needed to clarify spatial and temporal relationships between tectonic units and their constituent complexes, the effects of superimposed younger processes and relationships between near-surface and deep structures. To address these issues effectively, we need to refine isotope methods for dating real geological events, especially in polymetamorphic rocks, to recognise Archean crustal fragments less affected by later processes (first of all, in the central KAP, the central KOP and the MP), and to reconstruct the original geographical position of Archean terranes using paleomagnetic methods.
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