NOVOUKRAINSKYI MASSIF: SOURCE OF ORIGINAL MAGMAS AND TIME OF FORMATION

Abstract

The Ingul Megablock of the Ukrainian Shield is an area of mostly Paleoproterozoic continental crust located between the Dniester-Buh and Middle Dnieper Archean cratons. Its central part is occupied by the Korsun-Novomyrhorod anorthosite-rapakivigranite massif, which is 1757—1740 Ma, and the Novoukrainskyi massif, which is 2037—2034 Ma. A wide range of granitoids (biotite, garnet-biotite, hypersthene-garnet-biotite porphyry, trachytoid granites, granosyenites, and quartz syenites) participates in the geological structure of the Novoukrainskyi massif; medium and basic rocks of the monzonite series (quartz monzonites, monzonites, monzodiorites) play a significantly smaller role, gabbromonzonites) and gabroids (norites and gabbronorites). The article presents the results of the optical-microscopic study of the internal structure of zircon crystals and uranium-lead isotopic dating of monazite from trachytoid granite (sample Bo-1) and from the xenolith of giant-grained biotite-hypersthene granite (sample Во-2a) of the Novoukrainskyi massif, exposed by the Voynivskyi block stone. For trachytoid granite, sample Bo-1, an age of 2035.3 ± 2 Ma was obtained, for the age of monazite from a xenolith of coarse-grained granite, sample Bo-2a, we take the weighted average age value according to the 207Pb/206Pb isotopic ratio —2035.2 ± 1.8 Ma. Isotopic age values for monazites from trachytoid granite and coarse-grained granite xenolith expanded in the Voynivskyi block stone quarry completely coincide with the results of determining the age of gabroids (according to zircon) and granitoids according to monazite: 2037.4 ± 0.6 million years and 2034.8 ± 0.6 million years, respectively. Thus, the time of formation of the crystalline rocks of the Novoukrainskyi massif (2037—2034 Ma) completely coincides with the time of formation of granitoids of the Kirovohrad complex (2040—2020 Ma), which, taking into account the anatectic nature of the granitoids of both the Novoukrainskyi and Kirovohrad complexes, gives grounds for uniting the granitoids both complexes into one, for example, the Kropyvnytskyi complex, leaving only habroids as part of the Novoukrainskyi complex.