Uranium-Lead Age of Granites of Kirovohrad Massif of the Inhul Megablock of the Ukrainian Shield

Stepanyuk, L.M.; Konoval, N.; Dovbush, T.І.; Kovtun, Oksana V.; Vysotsky, O.B.; SNISAR, V.P.

doi:10.15407/mineraljournal.43.04.056

Mìneral. ž.

2021

DOI: 10.15407/mineraljournal.43.04.056

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Uranium-Lead Age of Granites of Kirovohrad Massif of the Inhul Megablock of the Ukrainian Shield

L.M. Stepanyuk¹,

N. Konoval²,

T.І. Dovbush³

et al.

Abstract: The porphyry-like biotite-garnet granites (sample KВ-5-1) of the Sokolivkа quarry were studied. The quarry is located in the Kirovohrad granite massif on the southwest of Kropyvnytsky city. The aim of our geochronology investigation is to determine the age of granites of the Kirovohrad massif by the U-Pb isotope method using monazite. The age of granites from Kirovohrad massif by the U-Pb method using monazite has not been determined yet. According to our data, the porphyry granites of the Kirovohrad massif (S… Show more

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Cited by 4 publications

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The Specific Uranium-Lead Isotopic System of Monazite From the Leucocrate Gneiss of Priazovia

Stepanyuk,

Dovbush,

Vysotsky

et al. 2023

Geohim. rudoutvorennâ

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The uranium-lead isotopic system of monazites from leucocratic gneiss (Pryazovsky megablock) was studied and the age of their formation was determined. Monazites from leucocratic gneiss are characterized by significant discordance, which is obviously due to the radiogenic component of impurity lead. In our case, the reverse discordance is to a large extent obviously due to the addition of radiogenic lead, which was captured by monazite during crystallization and is a component of impurity (abnormal composition) of lead. Calculating the age of monazite using a concordia diagram (Arens-Wetherill method) gave the following results: at the upper intersection of the regression line, the age was 2029 ± 145 and 1106 ± 337 Ma, at the lower one MSWD = 35. Taking into account the rather large contents of ordinary lead in the monazite samples studied and the significant dependence of the isotopic age determination results on the adequately introduced correction for ordinary (impurity lead), the isotopic composition of which may not correspond to the isotopic composition of ordinary lead according to Stacey and Kramers, calculated the relationship between numerical age values obtained from the 207Pb/206Pb isotopic ratio and the 206Pb/204Pb ratio, which sufficiently characterizes the content of ordinary lead. Therefore, the numerical values of the age, calculated using different models, according to the obtained analytical data, are quite different: 2027 Ma, 2037 ± 18, 2029 ± 145, and 2099 Ma. In our opinion, the isotopic date, 2037 ± 18 Ma, calculated by the isotopic composition of lead, taking into account the errors in the determination of lead isotopic ratios, corresponds to the time of monazite crystallization to a greater extent. Within the margin of error, it coincides with the date of 2029 ± 145 Ma, obtained from the upper intersection of the discordia with the concordia in the coordinates of the Ahrens-Weatherill method.

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The Specific Uranium-Lead Isotopic System of Monazite From the Leucocrate Gneiss of Priazovia

Stepanyuk,

Dovbush,

Vysotsky

et al. 2023

Geohim. rudoutvorennâ

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Geochemistry of Xenoliths in Rapakivi Granites of the Korsun-Novomyrhorod Pluton (Ukrainian Shield)

Shniukova¹,

Tomurko²,

Konoval³

2023

Mìneral. ž.

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Rapakivi of the Korsun-Novomyrhorod pluton (KNP), being the latest Precambrian granites of the central part of the Ukrainian shield, contain older acidic and intermediate rocks as xenoliths, the geochemical features of which reflect the Early Proterozoic geodynamic situation. Rapakivi granites, their differentiates and three types of xenoliths in them, represented by plagiogneiss, pink granite and charnockitoid (mangerite), were selected in the northwestern part of the KNP for geochemical studies. Analysis findings were compared with the geochemical characteristics of similar rocks of igneous and metamorphic Precambrian complexes that surround the KNP and could serve as a source of xenoliths. Based on distribution patterns of rare earth elements, lithophile elements content and their ratios relations in the rocks, taking into account their petrographic composition, it was established that plagiogneiss belongs to the upper part of the Inhul-Inhulets series, pink granite belongs to the Kirovohrad complex, and charnokitoid belongs to the intermediate rocks of the Tashlyk complex. In the latter, acid charnockitoids (enderbites) are probably younger than intermediate ones and were formed in another geodynamic setting. Pink granite, like the granites of the Kirovohrad complex, shows collisional geochemical features, in contrast to the rapakivi granites containing these xenoliths, which have predominantly within-plate geochemical characteristics. Thus, in the form of xenoliths in rapakivi those rocks were preserved that had been generated before and during the collision that occurred about 2 billion years ago and constructed a crust thickening at the site of the Inhul megablock, under subsequent extension of which about 1.75 billion years ago the KNP was intruded. Acid charnockitoids of the Tashlyk complex and rocks of the Novoukrainian complex, which are absent in xenoliths, probably were formed after the collision.

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Novoukrainskyi Massif: Source of Original Magmas and Time of Formation

Stepanyuk,

Kovtun,

Vysotsky

et al. 2023

Mìneral. ž.

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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.

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Uranium-Lead Age of Granites of Kirovohrad Massif of the Inhul Megablock of the Ukrainian Shield

Cited by 4 publications

References 10 publications

The Specific Uranium-Lead Isotopic System of Monazite From the Leucocrate Gneiss of Priazovia

The Specific Uranium-Lead Isotopic System of Monazite From the Leucocrate Gneiss of Priazovia

Geochemistry of Xenoliths in Rapakivi Granites of the Korsun-Novomyrhorod Pluton (Ukrainian Shield)

Novoukrainskyi Massif: Source of Original Magmas and Time of Formation

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