URANIUM-LEAD ZIRCON AGE OF CRYSTALLINE ROCKS OF THE INHUL DOMAIN

• Date: 2026
• Main Authors: Степанюк, Л.М., Висоцький, О.Б., Шумлянський, Л.В., Баран, А.М.
• Format: Article
• Language: Ukrainian
• Published: Institute of Geological Sciences, NAS of Ukraine 2026
• Subjects: granite; gneiss; zircon; uranium-lead isotope method; Ingul domain
• Online Access: http://geojournal.igs-nas.org.ua/article/view/344760
• Journal Title: Geological journal

Supracrustal formations of the Inhul-Inhulets Group, which form the protolith for granitoids of the Kropyvnytsky (formerly Kirovohrad) and Novoukrainka complexes, are the most widespread in the geological structure of the Inhul Domain within the Ukrainian Shield. In the eastern part of the domain, Archean rocks of the Auly and Konka Groups occur, forming the protolith for plagiogranitoids of the Mesoarchean Inhul Complex. The morphology of zircon crystals from plagiomigmatite of the Inhul complex, plagiogneiss of the Spasove Formation of the Inhul-Inhulets Group, and porphyry-like granites of the Kropyvnytsky complex was studied using optical microscopy; their age determination was performed employing U-Pb LA-ICP-MS and SIMS methods. The isotopic composition of Hf in zircon from both plagiomigmatite and porphyry-like granite was also analysed. Zircon crystals from plagiomigmatite, based on the 207Pb/206Pb ratio, have ages ranging from 3251 ± 16 Ma to 2564 ± 53 Ma. The plagiogneiss of the Spasove Formation predominantly contains zircon of Archean age, with 13 out of 15 analysed crystals being older than 2.5 Ga. Most crystals lie on a discordia that intersects the concordia at 2939 ± 90 Ma and 2103 ± 210 Ma. Porphyry-like granites formed during the Paleoproterozoic (2060–2040 Ma) through melting of ancient crust, as indicated by numerous inherited zircon cores and the Hf isotopic composition (εHf ranging from -5.7 to -10.9, with a model age of approximately 3000 Ma according to the felsic crust model).