Geodynamic of a Breakup of Western Part of the Karelian Craton: Data on 2.1 Ga Mafic Magmatism

Abstract

Mafic within-plate magmatism is the main source of information about the geodynamics of processes that lead to the breakup of continental blocks. The article discusses the problem of geodynamics of the split of the Archean supercraton Superia in the Middle Paleoproterozoic. The discussion is based on data on 2.1 Ga magmatism in the Karelian Craton, where basites of this age are represented by tholeiites of two geochemical types: depleted and enriched. Geochemically close to N-MORB, depleted tholeiites were studied in Northern Priladozhye where they form methadoleritic dike swarms at c. 2111 ± 6 Ma (U-Pb, SIMS, zircon) in the Khatunoiya locality, and pillow lavas and sills near Lake Maloye Janisjarvi. Enriched tholeiites were studied in the Lake Tulos locality where they form a large swarm of doleritic dikes at 2118 ± 5 Ma (U-Pb, ID-TIMS, baddeleyite). The results of these studies provide deeper insight into 2.1 Ga mafic magmatism. Depleted tholeiites with N-MORB geochemistry have a spatial distribution in the Karelian Craton and could be formed as a result of decompression melting of a depleted asthenospheric mantle, raising melts along the extension zones, and minimal contamination by the Archean crust. The simultaneous formation of enriched tholeiitic melts probably occurred at differentiation and crustal contamination of depleted tholeiites during melt migration through more rigid Archean crustal blocks. Data on basic magmatism with an age of 2.1 Ga in the Karelian craton, which are difficult to explain within the framework of the mantle plume rise model, are consistent with the model of lithosphere extension due to the retreat of the subduction zone in the northeastern framing of the craton, in the Lapland-Kola Ocean in the interval of 2.0–2.2 Ga years. The maximum thinning, discontinuity of the Archean continental lithosphere, and the opening of an oceanic basin at the western edge of the Karelian craton were probably controlled by the suture zone of the junction of the Neoarchean crust with the Paleoarchean blocks, a chain of which was traced in the west of the Karelian craton. An additional factor that led to breakup of the lithosphere 2.1 Ga ago could be the rise of a deep mantle plume in the Khern craton, which occupied a spatial position close to the Karelian craton in the Archean supercraton Superia.