Main stages of the Kostomuksha greenstone belt Banded Iron Formation genesis, Karelian Craton: based on U-Th-Pb dating of zircon

Abstract

We studied zircon from banded iron formations (BIFs) in the Kostomuksha greenstone belt (KGSB), Karelian Craton, for the first time. Here, BIFs are associated with Mesoarchean basalt-komatiites – BIF-1 and felsic volcanics – BIF-2, as well as with Neoarchean graywackes and felsic volcanics – BIF-3. All the BIFs contain accessory zircon. Analysis of its isotopic age shows the presence of 1-4 age clusters in each sample. There are single grains of detrital zircon in most of the studied BIFs. The grains are of commensurable or older age than the BIF enclosing rocks. The ages of detrital zircons differ among BIF association: 2.84 Ga in BIF-1, no detrital zincon in BIF-2, and 2.98–2.75 Ga in BIF-3. Most of the zircon in the BIFs is of metamorphic origin. All BIF groups contain 2.75–2.72 Ga zircon, while BIF-3 also has 2.65–2.64 Ga zircon associated with felsic magmatism. Rims and grains of 1.89–1.85 Ga zircon from BIF-1 and BIF-3, indicative of local tectono-thermal processes simultaneous with the formation of the Svecofennian Orogen, are reported here for the first time.