Visn. Nac. Akad. Nauk Ukr. 2017. (2) 54-59
https://doi.org/10.15407/visn2017.02.054

L.M. Stepanyuk, V.L. Prykhod’ko, S.I. Kurylo, T.I. Dovbush, I.M. Kotvits’ka
Semenenko Institute of geochemistry, mineralogy and ore formation of the National Academy of sciences of Ukraine, Kyiv

"BASEMENT" OF KYIV

Kyiv is located within the Eastern slope of the Ukrainian Shield. The crystalline basement is represented by metamorphic rocks of Rosinskiy-Tikytskyy series and granitoids. The basement is closed off by Phanerozoic healts, the thickness of which increases from West to East and varies from tens to hundreds of meters. Rocks of the crystalline basement of Kyiv were raised for the study to the surface through a few boreholes, one of which is Novobelitska 1 with a depth of 1927 m. According to drilling materials the crystalline basement lies at 290 m. Basement rocks are represented mainly by shadow migmatite of granodiorite composition with small lenticular inclusions of amphibole-biotite gneiss. The main goal of the research is to determine the time and origin of granodiorite melts. Zircons was dated by uranium-lead method, isotope composition of strontium was studied in apatite and Sm-Nd isotope systems in the granodiorite. The sample from the borehole was tested at the interval of 488-504 meters.  The age of the granodiorite in 2059±12 million years was determined based on the results of uranium-lead isotopic dating of the zircon crystals with no visible relict cores. The Sm-Nd isotopic studies of bulk sample of the granodiorite and the isotopic composition of strontium apatite accesorio found that the granodiorites formed by Paleoproterozoic crustal substrate (εNd = of-2.1; 87Sr/86Sr = 0,70501±6), the substance of which was separated from depletive mantle no earlier than 2.42 million years ago in Paleoproterozoic. The granodiorites were formed by Paleoproterozoic crustal substrate (εNd = of-2.1; 87Sr/86Sr = 0,70501±6). It was found by Sm-Nd isotopic studies of bulk sample of the granodiorite and isotopic composition of strontium in accessories apatite. The meter of granodiorite seceded from depletation mantle no earlier than 2,42 million years ago, in Paleoproterozoic.

Keywords: Rosinskо-Tikyckyi megablok, granodiorite, zircon, uranium-lead isotope method.

 Language of article: ukrainian

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