Kostenko O. Geochemistry and radiogeochronology of granitoids of Volyn megablock.

Geochemical and petrographic features and age determinations of the granitoids located within the folded basement of Volyn megablock of Ukrainian shield (Sheremetiv, Zhytomyr, Buky, Kyshyn complexes) are presented in this study. The plagiogranitoids of Volyn megablock according to the age and mineral composition are allocated for the first time in a diorite- tonalite- plagiogranite association which is well correlated with the same rock association in Rosyn-Tikych megablock. The isotopic dating of the Zhytomyr complex two-feldspathic granites is done for a number of allochthonous massifs (Zhytomyr, Berezivka, Hulyanka, Gorodske, Serby, Kurchytsya). The formation of the Proterozoic ultrametamorphic plagioclase and K-feldspar rock association of Volyn megablock took place in two stages of the geological evolution: over 2,09 Ga, and between 2,08 - 2,04 Ga. According to the isotopic data the porphyritic granites of Novograd - Volyn massif (2,043 Ga) belong to Zhytomyr complex. New geochronological data show the age of the Kyshyn complex granites between 1,975 and 1,94 Ga. The rubidium-strontium isotope system of apatites from the granitoids is investigated as well. The geochemical specialization of granitoids formations and the molybdenum positive specialization of the Kyshyn complex granites are defined.