https://doi.org/10.22184/2227-572X.2024.14.2.168.178

Using laser ablation with inductively coupled plasma, U-Th-­Pb isotope dating of igneous and metamorphic zircons extracted from aegirine-­bearing gneisses in the Gridino melange of the Belomorian eclogite province was carried out. Igneous cores with an age of 2.89–2.83 Ga date of the protoliths. Metamorphic grains and rims yielded an age range of 2.80–1.8 Ga with peaks at ~2.80, 2.75, 2.70 and 1.8 Ga, corresponding to the succession of tectonometamorphic events in the region. Along with typical zircons, the grains with unusual heterogeneous cores, which combine granular, vesicular and vermicular textures, were found. According to Raman spectroscopy the transformations from a crystalline to an amorphous state in them are observed. Microgranular zircons are interpreted as evidence of Mesoarchean impact event ~2.87 Ga or older.