U-Pb age of titanite from diorit of Osnytsky Block (Volyn Megablock of Ukrainian Shield)

The Osnytsky block is a constituent part of the Osnytsky-Mikashevytsky volcano-plutonic belt. The leading place in the geological structure of the Osnytsky block is occupied by the rock association, which includes a number of plutonic formations from gabbro to leucocratic granites (gabbro-diorite-granodiorite-granite association), formed in the Paleoproterozoic — 1,98—1,95 Ga. The results of lead-lead isotope dating of titanites from diorites, opened by the RPZ-5 quarry, located in the northwestern vicinity of the village Tomashhorod. Diorites were formed in the second phase, after gabroids, before the beginning of the formation of granitoids. The age of 1975 ± 9,1 Ma was obtained for them. The age calculated based on previously published data is 1973 ± 8,3 Ma, which is in good agreement with the U-Pb isotopic age of the zircons of these diorites 1974 ± 1,2 Ma. It was found that to determine the isotopic age of titanites with a high content of ordinary lead, it is enough to use only the isotopic composition of lead, calculating the age in the coordinates of the graph 207Pb/204Pb — 206Pb/204Pb, by the tangent of the angle of inclination of the regression line

On the age of white anorthosite of the Novomirgorod massif of the Korsun-Novomirgorod pluton (the Ukrainian Shield)

Xenolites of white anorthosites have been found in anorthosites of the main phase of the Novom-irgorod massif of the Korsun-Novomirgorod pluton (the Ukrainian Shield, the Ingul megablock). The age of white anorthosite has been determined by classical uranium-lead method by zircon. Isotopic study of zircon showed considerable dispersion of values that is possibly caused by heterogeneous internal structure zircon crystals and different combination of generations of different ages. The most ancient, practically concordant age has been obtained for two fractions of light rosy zircon (1796-1806 b. y). that is considerably older than the age of zircon from enclosing anorthosites (1750,2 b. y.) and in our opinion characterizes the age of anorthosite. There are several assumptions as to the origin of xenolites of white anorthosites. They can be the earlier phase of basic rocks of the pluton; a fragment of substance of the lower crust transported from the depth and changed by superposed metasomatic and hydrothermal processes, leucocrate variety of «ancient» anorthosite of AMCHG association, represented by white bronsite anorthosites in the Korosten pluton

ДО ПРОБЛЕМИ ДЖЕРЕЛА НЕОПРОТЕРОЗОЙ-ПАЛЕОЗОЙСЬКИХ МОНАЦИТІВ В ОСАДОВИХ УТВОРЕННЯХ УКРАЇНИ

Neoproterozoic-Paleozoic detrital monazites (<1500 Ma) are widely spread in the sediments of Ukraine. Age spectrum of these monazites has three maxima: 400–600, 750–850 and 900–1000 Ma. Their geochemical features are characterized on the base of discriminate diagram in coordinates Y/Th × U/Th – Sr/Y. Direct analogues of such monazites are not known in rocks of Ukrainian Shield. Possible sources of Neoproterozoic-Paleozoic detrital monazites are discussed.В осадочных образованиях Украины широко распространены детритовые монациты неопротерозой-палеозойского (<1500 млн. лет) возраста. Возрастные спектры таких монацитов имеют три максимума 400–600, 750–850 и 900–1000 млн. лет. Их геохимические особенности охарактеризованы на базе дискриминационной диаграммы в координатах Y/Th × U/Th – Sr/Y. По этим признакам прямые аналоги таких монацитов на Украинском щите неизвестны. Обсуждаются возможные источники неопротерозой-палеозойских детритовых монацитов в осадочных образованиях Украины.В осадових утвореннях України значно поширені детритові монацити неопротерозойпалеозойського (<1500 млн. ро-ків) віку. Вікові спектри цих монацитів мають три максимуми: 400–600, 750–850 та 900–1000 млн. років. Їх геохімічні особливості охарактеризовані на базі дискримінаційної діаграми в координатах Y/Th × U/Th – Sr/Y. За цими ознаками прямі аналоги такого монациту на Українському щиті невідомі. Обговорюються можливі джерела неопротерозойпалеозойських детритових монацитів в осадових утвореннях України