Age and Stratigraphic Position of a Supracrustal Complex (Kaskama Block, Inari Terrane, Northeastern Kola–Norwegian Region of the Fennoscandian Shield)

Abstract

The U–Th–Pb age (SIMS) of magmatic (T = 730–744°C) zircon from intermediate and felsic metavolcanics (1923–1926 Ma) of the supracrustal complex in the Kaskama block of the Inari terrane (northwestern part of the Kola–Norwegian region of the Fennoscandian Shield) were obtained for the first time. This makes it possible to attribute these metavolcanics to the Paleoproterozoic Kalevian suprahorizon. The source of primary metarhyodacite and metabasalt in the Kaskama block was the Paleoproterozoic continental lithosphere not younger than 2390–2384 Ma with an essential contribution of juvenile material (εNd(Т) = +1.2…+2.8). The ages of the spatially related tonalites of the Kuroaivi massif (1936 ± 7 Ma, εNd (T) = +0.1) and of the granitoid massifs of the Southern Pechenga zone (1950–1940 Ma) are older, within the errors of the U–Th–Pb age determinations, than the volcanosedimentary deposits of the Kaskama unit and the Vepsian of the South Pechenga zone. This stage of granite formation separates two geodynamic stages in the Kola–Norwegian region of the Fennoscandian Shield: the early continental rifting in the Yatulian–Ludikovian time and a stage similar to the suprasubductional formation setting of the continental lithosphere of the Inari terrane (1926–1850 Ma).