Geochronology of Crystalline Rocks of the Shumyliv Section of the South Bug River Valley (Haisyn Block)

Abstract

The Haisyn complex rocks (sobites (Shcherbakov, 2005)), consisting of diorite-like rocks and amphibolites, which biotite granites develop, is outcroping near the village of Shumyliv along the South Bug river and in an abandoned open pit mine (on South of Shumyliv). The rocks are characterized by high magnetization according to magnetic survey results. A linear magnetic anomaly extends in the north-east direction (NE 69º) with a distance of more than 35 km. Entin et al. (2019) proposed that this magnetic anomaly is caused by a dyke with a felsic or intermediate composition. The internal structure of accessory zircon crystals from quartz diorite and granite were studied. In both types of rocks, zircon crystals are complex and consist of three different generations. The first generation consists of fractured nuclei of light pink color, which apparently grew in rims of zircon of the 2nd and/or 3rd generation. Zircon of the second generation is light pink in color. It forms rims around the first generation of zircon, but also occasionally occurs the interior core areas of crystals. Third generation zircon forms rims around the first two generation zircons, or growth episodes. As usually, the heads of crystals have a light brown to brown color. The age of formation of monazite in the granite and titanite in the quartz diorite was determined by the uranium-lead isotope method. The two endogenous geological processes have ages of 2049 ± 6 million years and 2005±2 million years, respectively.