A small Archaean belt — diverse age ensemble: A U–Pb study of the Tipasjärvi greenstone belt, Karelia Province, central Fennoscandian Shield, Finland

Abstract

The Archaean Tipasjärvi greenstone belt is a small area (ca. 5×25km) located within the Karelia Province in Central Fennoscandian Shield, Finland. The belt forms the southernmost part of the larger Archaean Suomussalmi–Kuhmo–Tipasjärvi greenstone complex. The present study results for this site are based on zircon grains of 12 metavolcanic and metasedimentary rock samples that were studied with the single-grain secondary ion mass spectrometry (SIMS) U–Pb method. Our data indicate that the volcanism in the belt took place over three separate episodes: ca. 2.84Ga, 2.82Ga and 2.80Ga. The oldest volcanic rocks are older than the oldest dated tonalitic pluton adjacent to the belt. The main geochemical characteristics of the samples reveal that the felsic volcanic rocks of the different age groups resembled each other. However, contrasting trace element geochemical characteristics between the different age groups are also distinguishable. The detrital zircon record agrees with previous observations indicating that the sediments accumulated at least 50Myr after the formation of the youngest volcanic rocks. During sediment deposition, older crustal material (>3.0Ga) was exposed within the source area. The geochronological results in this study enable us to update the chronostratigraphic interpretation of the Tipasjärvi greenstone belt and to compare these results to those from other parts of the Archaean Suomussalmi–Kuhmo–Tipasjärvi greenstone complex and adjacent tonalitic plutons.