Uranium-Lead by Monacite Geochronology of Granites Distributed in the Middle Current of ihe River Ros (Ros-Tikich Megablock Ukrainian Shield)

Abstract

Granitoids play a leading role in the geological structure of the Ros-Tikich megablock. The rocks of the Ros-Tikich series, which form the supercrystalline base here, have survived among the granitoids only in the form of some remnants of different sizes. In the coastal outcrops of the middle course of the river Ros (east of Bila Tserkva) and in the quarries located near the river, the most common are two-feldspar granitoids, isolated as part of two complexes – Uman and Stavyshche. Plagiogranitoids and supercrustal rocks have survived among them in the form of separate fragments. Of the accessory uranium-containing minerals, zircon and titanite are present in two-field spar granites, and monazite was found in single samples of granites in which titanite was absent. The age of obscure porphyry-like granite discovered by the Ostrivsk quarry – 2063.5 ± 1.2 million years and uniformgrained granite, distributed in the quarry of the village of Bovkun – 2042.5 ± 8.6 million years. The obtained values of the isotopic age of these granites are in good agreement with the results of uranium-lead isotopic dating of zircons from twofeldspar granites of the Ros-Tikich megablock (1990-2080 million years). This allows us to propose to combine the granites of the Stavyshche and Uman complexes into one Paleoproterozoic complex.