Tectonic evolution, volcanic features and geochemistry of the Paleoproterozoic Salla belt, northern Fennoscandia: From 2.52 to 2.40 Ga LIP stages to ca. 1.92–1.90 Ga collision

Abstract

This study adapts the LIP and mantle plume model for magmatic events in the northern Fennoscandian Shield at 2.51–2.49 Ga and 2.45–2.44 Ga, corresponding globally to the Mistassini LIP and Matachewan LIP systems in the Superior craton. We propose a new model for the Salla belt, where the 2.45–2.44 Ga represents the plume arrival, and both radiating swarm and the circumferential stages. Associated 2.45–2.43 Ga layered intrusions and granites form intrusions ringing the plume centre close to the present NNW part of Fennoscandia.In the Salla belt, the subaerial magmatism of the Sumi system (Salla group) initiated at ca. 2.45–2.44 Ga and followed by volcanism of the subaqueous to subaerial Sariola system (Kuusamo group) at ca. 2.43 to 2.40 Ga. A more primitive magmatic stage at 2.43–2.40 indicates a final gravitational collapse of the LIP mantle plume. Calc-alkaline to tholeiitic affinities indicate that volcanism resulted from the content of the core-related fluids in the plume heads. Enriched in LILE elements with negative Nb and Ta anomalies compared to primitive mantle, suggest continental crustal contamination in a within-plate plume-driven rift setting. Volcanic structures indicate lava cooling, gas expansion and escape processes, and vapor differentiation processes and devolatilization of lava, which are suggestive of continental flood basalts and/or pahoehoe-type lava flows.Based on our structural-tectonomagmatic model, shield-wide systems suggest a correlation of the Seidorechka formation in the Imandra–Varzuga Belt and the upper part of the Sumi sequence within the Lekhta and Shombozero Belts with the 2.45–2.44 Ga Salla group Sumi volcanics in the Salla belt. In addition, the volcanics of the Sariola system (Kuusamo group) are correlated with the Vetreny Belt, the Kairala–Noukajärvi–Aapajärvi formations in Kuolajärvi, and the Polisarka formation in the Imandra–Varzuga Belt. The most peripheral part of the Lapland foreland fold and thrust belt (1.92–1.90 Ga) includes the Salla belt, where E–W contraction first led to E-vergent thrusting followed by a thick-skinned tectonic style with reverse faults and long-wavelength folds.