On the specification of the chronostratigraphic scheme of the Buzko-Rosynskyi block of the Ukrainian Shield

Abstract

In the current correlation chronostratigraphic scheme of early Precambrian of the Ukrainian Shield, among Neoarchean supra crystalline formations of the Buzko-Rosynskyi block, it is identified the Rosynsko-Tikytska series, which consist of the Myzynivska and Lysianska strata and the independent Volodarsko-Bilotserkivska strata, which are located on the same stratigraphic level in the scheme.
 According to the results of the mapping of metamorphic formations within this block during the geological survey of scale 1:200 000 (articles “Bila Tserkva”, “Uman”, “Lyubashivka”, “Kotovsk”, “Haisyn”, “Skvyra”) it is established these stratas are located in the section in a following order: the lower one is the Myzynivska, the middle one is the Volodarsko-Bilotserkivska and the upper one is the Lysianska and they form a single Rosynsko-Tikytska series. Also, these works did not confirm the presence in the region of the Bilotserkivska group of magnetic anomalies of two-pyroxene schale among the rocks of the Volodarsko-Bilotserkivska strata. This is a sign of their higher metamorphism degree. The hypersthene is present in the area of the Volodarka then only in high-iron rocks. Its presence is associated with a local temperature increase during metamorphism due to the high oxidative ability of iron. This indicates the possibility of its crystallization under conditions of amphibolite facies. A powerful argument in favor of this is the occurrence of a relatively thin carbonate-ferruginous-siliceous strata among thick amphibolite-gneiss and crystalline-schist-amphibolite strata which metamorphosed under amphibolite facies conditions. It indicates the low probability that the metamorphism of the iron ore could occur locally in other conditions.
 The obtained new data on the composition of the Rosynsko-Tikytska series and the actual stratigraphic sequence of stratas in it, indicates the necessity of making appropriate changes in the current correlation chronostratigraphic scheme of early Precambrian formations of the Ukrainian Shield.