U–Pb AGE OF DETRITAL ZIRCON IN THE CEMENT OF EARLY PRECAMBRIAN POLYMICTIC CONGLOMERATES OF CENTRAL KARELIAN DOMEN, KARELIAN PROVINCE, FENNOSCANDIAN SHIELD

U–Th–Pb LA-ICP-MS was used for dating detrital zircons extracted from the cement of the Neoarchean and Palaeoproterozoic polymictic conglomerates of the Karelian province, Fennoscandian shield. For the first time obtained a chemical composition of terrigenic and volcanogenic rocks of the gimolskaya formation. Obtained data showed that the detrital zircons from the cement of conglomerates of different ages yield similar results of about 2750 Ma. In the Neoarchean conglomerates of the Sukkosero area dominate clasts of the gneissic tonalite and plagioporphyry. They are identical in chemical composition with the Neoarchean (2.78–2.73 Ga) TTG, granodiorite, and metadacite of the Central-Karelian domain. The feature of these rocks is increased content of Ba (900–1200 ppm), Sr (600–700 ppm), and ratios Sr/Y = 34–90, (La/Yb)n = = 17–30. The chemical composition of the cement (the values of CIA < 55 and the negative values of the function DF(x)) is similar to the composition of clasts, which means cement is composed of finer clasts of the same rocks. The Paleoproterozoic conglomerates of the Vottomuks area contain zircon from felsic rocks of the Neoarchean basement/ The chemical composition of the cement of the Paleoproterozoic conglomerates and the predominance of basaltic andesites of sumii is evidence of the post-sumii (<2.45 Ga) age of these rocks. The absence of the Paleoproterozoic zircon in cement can be the result of the absence of it in the Paleoproterozoic source rocks. The age of Neoarchean conglomerates from the gimolskaya formation is less than 2.75 Ga.