Shumlyanskyy L. Petrology and geochronology of rock complexes of the north-west region of the Ukrainian shield and its western slope

Results of the detailed petrological and geochronological investigations of the rock complexes of the north-west region of the Ukrainian shield and its western slope are quoted in the dissertation. The systematic investigation of the Sr and Nd isotope compositions in all rock complexes was carried for the first time by the author. Hafnium isotope composition was measured in zircons separated from a wide range of rocks. Chemical composition of all rock complexes was characterized elaborating modern high-precise methods of analysis for major and trace elements. U-Pb isotope method was elaborated to date wide range of rocks; besides this several hundred of individual zircon grains separated from various sedimentary and metasedimentary rocks were also dated. It has been shown that the "basement" in the area is composed by 2200-2040 Ma old juvenile rocks of the Tetriv-Zhytomyr orogenic belt. Osnitsk-Mikashevichi volcano-plutonic belt was formed as an active continental margin between 2000 and 1980 Ma. Formation of the Bilokorovichi depression finished by 1800 Ma; detrital material was derived from granites of the Zhytomyr complex and metamorphic rocks of the Teteriv Seriesl. At 1800-1780 Ma the studied area was affected by extensive mafic-ultramafic magmatism related to collision of Sarmatia and Fennoscandia. Simultaneously, magmatic activity at the Korosten plutonic complex was initiated. This lasted until c. 1740 Ma. Rhyolites of the Ovruch and Vilcha depressions poured our at 1761 ± 13 Ma, i.e. simultaneously with rapakivi granites of the Korosten complex. Effusive rhyolites and intrusive rapakivi possess undistinguishable composition. Maximal age of the Polissya Series sediments is defined by the youngest (1018 ± 21 Ma) zircon found in the sandstones. Finally, it has been established that Volynian flood basalt province was formed at c. 555 Ma.