Main Stages of the Kostomuksha Greenstone Belt Banded Iron Formation Genesis, Karelian Craton: U–Th–Pb Dating of Zircon

We studied zircon from a banded iron formation (BIF) in the Kostomuksha greenstone belt, Karelian Craton, for the first time. Here, the BIF is associated with Mesoarchean basalt–komatiites (BIF-1) and felsic volcanics (BIF-2), as well as Neoarchean graywackes and felsic volcanics (BIF-3). All of the BIFs contain accessory zircon. Analysis of its isotopic age shows the existence of one to four age clusters in each sample. There are single grains of detrital zircon in most of studied BIF. The age of this grains are commensurable or older, than the containing BIF rocks. The ages of detrital zircons in each BIF associations are different: 2.84 Ga in BIF-1 and 2.98–2.75 Ga in BIF-3, with there being no detrital zircons in BIF-2. The majority of zircons in the BIF are of metamorphic origin. All BIF groups contain 2.75- to 2.72-Ga zircon, while BIF-3 groups carry 2.65- to 2.64-Ga zircon associated with felsic magmatism. For the first time, 1.89- to 1.85-Ga rims and grains of zircon from BIF-3, indicative of local tectonothermal processes simultaneous with the formation of the Svecofennian orogen, are described.