Zircon from banded iron formation as a sensitive indicator of its polychronous background: a case study on the Kostomuksha greenstone belt, Karelian Craton, Fennoscandian Shield

ABSTRACT

Zircon is not a common accessory mineral of banded iron formation (BIF), but it occurs in all BIF samples from the Kostomuksha Greenstone Belt (KGB) in the Karelian Craton of the Fennoscandian Shield. The Kostomuksha BIF is of Algoma type and is part of three variably old rock associations: BIF-1 is part of a sedimentary sequence in Mesoarchean (2.87–2.84 Ga) basaltic komatiites with dacites, BIF-2 is located in Meso-Neoarchean (2.8–2.79 Ga) felsic volcanics, and BIF-3 is part of a Neoarchean (2.76–2.74 Ga) greywacke unit with felsic volcanics. Analysis of zircon has revealed grains with cores and several generations of rims. The U-Th-Pb systems of zircon indicate that its isotopic age varies considerably from 2.98 to 1.89 Ga, forming up to 4 age clusters in each sample. Most samples contain single inherited grains. The bulk of zircon in BIF is younger than the host rocks and is interpreted as metamorphic. Most of metamorphic zircons display an oscillatory zoning, and their Th/U ratio varies from 0.01 to 4.7, i.e. their origin is hard to interpret reliably, based on the above characteristics. Paleoproterozoic (1.89–1.85 Ga) zircons from BIF-1 and 3, occurring as rims and individual grains, are related to local tectono-thermal processes simultaneous with the formation of the Svecofennian orogen and were described for the central Karelian Craton for the first time. Thus, both inherited and metamorphic zircons have been revealed in Meso-Neoarchean BIF metamorphosed repeatedly in the Neoarchean-Paleoproterozoic under up to amphibolite-facies conditions. All metamorphic generations of zircons from BIF are correlated with the tectono-thermal events in the Karelian Craton, including the effect of the Svecofennian orogeny.

KEYWORDS:

• Banded iron formation
• zircons
• isotopic age
• Archean
• Paleoproterozoic
• Kostomuksha greenstone belt
• Karelian craton

Acknowledgments

The authors are grateful to K.G. Erofeyeva, V.S. Sheshukov and A.S. Dubenskiy of GIN RAS (Moscow) for zircon analyses and discussion of the data. The authors also wish to thank Dr. Robert J. Stern, Dr. Chris Yakymchuk and two anonymous reviewers for comments that have helped improve the manuscript, as well as G. Sokolov who translated the manuscript.

Prof. Anthony Robert Prave from the University of Saint Andrews is gratefully acknowledged for editing the authors’ English translation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2023.2248501

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by the Russian Science Foundation under Grant number 22-17-00026, https://rscf.ru/project/22-17-00026/.