L.M. Stepanyuk
https://orcid.org/0000-0001-5591-5169
O.B. Vysotsky
https://orcid.org/0000-0002-3542-4685
A.M. Baran
https://orcid.org/0000-0002-5326-8014
O.V. Kovtun
https://orcid.org/0000-0003-0475-8778
T.I. Dovbush
https://orcid.org/0000-0002-3512-3313
N.O. Kovalenko
https://orcid.org/0000-0002-3203-7145
I.M. Kotvitska
https://orcid.org/0000-0002-2593-3953
M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine 34, Acad. Palladin Ave., Kyiv, Ukraine, 03142
https://doi.org/10.15407/gof.2024.45.044
The article presents the results of the study of uneven-grained granite (sample 14/23), pegmatoid granite (sample 15/23) and pyroxene plagiogneiss (sample 16/23), exposed in the abandoned quarry of Lozuvatka, and also determined the isotopic age of these rocks based on monazite. For uneven-grained granite (sample 14/23), almost concordant age values were obtained, the discordance is in the range from –1.6 to –3.8, while the age, according to the 207Pb/206Pb ratio, ranges from 2022.8 Ma to 2014, 6 Ma. The smallest age was obtained for the smallest fractions. Taking into account the slight discordance, the weighted average value of the age according to the 207Pb/206Pb isotopic ratio was calculated — 2018.4 ± 6.9 Ma, which corresponds to the time of formation of the youngest granites of the Kropyvnytskyi complex. For the pegmatoid granite (sample 15/23), an age of 2037.5 ± 2.2 Ma was obtained by the upper intersection of the concordia by the regression line calculated from the obtained data, which is in good agreement with the time of intrusion of the granites of the Kropyvnytskyi complex. Accordingly, granitoid magmatism in the crystalline rocks of the Lozuvat area lasted about 20 million years in the age interval of 2.02—2.04 Ga ago. In order to find out the source of the parent granite melts, the anatomy of zircon crystals from the mentioned granite samples, as well as from pyroxene plagiogneiss (sample 16/23), for which the isotopic composition of strontium in apatite was also determined, was studied. Pyroxene plagiogneisses were formed due to crustal matter (87Sr/86Sr = 0.70703 ± 0.00004), sedimentary (volcanogenic-sedimentary) nature, at the same time they were not a substrate for granites.
Key words: isotopic age, monazite, plagiogneiss, pegmatoid granite, Kropyvnytskyi complex.
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