The schists and gneisses of the Pikamka Formation, comprising the Tersk Terrane of the Lapland-Kola Orogen, Eastern Fennoscandia, have been studied. These rocks, metamorphosed under amphibolite facies, had a sedimentary protolith corresponded in composition to graywackes and lithits. They were accumulated in an active tectonic setting during the erosion of predominantly felsic complexes with suprasubduction geochemical characteristics and Paleoproterozoic TNd(DM) values from 2.2 to 2.5 Ga. U–Th–Pb isotopic studies on detrital zircon revealed the multimodal distribution of ages with peaks ranging from 3.6 to 1.97 Ga. Zircon with ages from 2.4 to 3.6 Ga is represented only in cores in the predominant population of younger (1.97–2.2 Ga) magmatic zircon crystals. This indicates the origin of sedimentary rocks of the Pikamka Formation via the destruction of the Paleoproterozoic magmatic complexes. These complexes contained the Archean crustal component and were probably formed in continental arc tectonic setting of a continental arc. Igneous rocks, that served as a source for the predominant zircon age group of 2.02–2.20 Ga, are not known either in the Lapland–Kola Orogen or beyond. The complete disappearance of igneous rocks of this age could be caused by subduction and/or tectonic erosion. All obtained data suggest that subduction in the Lapland–Kola Ocean began at least 2.2 Ga ago, that give constraints for the model of early stages of the tectonic evolution of the Lapland–Kola Orogen.
Zhitnikova et al. (2026) studied this question.