The Khmilnyk structural and tectonic unit and its geological and geophysical essence

• Дата: 2025
• Автори: Yentin, Volodymyr, Gintov, Oleg, Guskov, Sergii, Mychak, Sergii, Pavliuk, Oleksandra, Zalizniak, Dina
• Формат: Стаття
• Мова: Ukrainian
• Опубліковано: S. Subbotin Institute of Geophysics of the NAS of Ukraine 2025
• Теми: Ukrainian shield; Khmilnyk gravity minimum; leucogranite intrusion; three-dimensional density model; radon sources; uranium occurrences; alkaline gabbro-diabases; diamonds
• Онлайн доступ: https://journals.uran.ua/geofizicheskiy/article/view/329385
• Назва журналу: Geofizicheskiy Zhurnal

The Khmilnyk structural and tectonic node is an extraordinary case for the Ukrainian Shield. It is located in its southwestern part (Berdychiv Uplift), at the intersection of three deep faults, and is a clearly manifested deep-penetrating section of the crystalline basement (thermoblast). Its conditional length from west to east is about 40 km, and the epicenter falls on the Khmilnyk gravity minimum with dimensions of 25×25 km and relative intensity of −16 mGal, which coincides with the area of reduced magnetic field intensity. According to a comprehensive geological and geophysical interpretation of these data, the nature of the minimum is due to the manifestation of a local center of Proterozoic acid magmatism among the granitoids of the Berdychiv complex, represented by a mushroom-shaped massif of garnet leucogranites of a biotite composition, traced to a depth of 15 km, i.e., to the zone of existence of a possible granite melt. The mushroom shape of the granitoids, whose density is 0.1 g/cm3 less than that of Berdychiv granites, is explained by subhorizontal penetration of the melt in the near-surface part of the crust in the form of sills. Magmatic activity within the massif and in the area of its endo-exocontacts is accompanied by deep degassing in the form of radon emanations and manifestations of uranium mineralization. The area of the entire Khmilnyk structural and tectonic unit is characterized by numerous manifestations of dike gabbro-diabase Proterozoic magmatism, contrasting halos of indicator minerals of kimberlites and diamond fragments in the sedimentary cover. Detailed petrologic and geochemical characteristics of garnets in general and pyropes in particular are presented. It is shown that the garnets of the study area are of crustal-mantle origin. Some are identical in chemical composition and colorimetric parameters to the garnets of diamond-bearing bimineraleclogites from kimberlites of diamond-bearing provinces of the world. The pyrope is dominated by orange garnets, which indicates a high content of eclogite association varieties. More than a dozen pyrope halos have been identified, lesson smaller than the pyrope halo of the world-famous Snap-Lake deposit (Canadian Shield).