AGE OF THE HANNIVKA GRANITE (MIDDLE-DNIEPER MEGABLOCK OF THE UKRAINIAN SHIELD)

Abstract

The Middle-Dnieper megablock, which is a fragment of the craton, differs from other cratons found on Earth. This is because of the large variety of granitoids (Tokiv, Mokro-Moskowka, and Demuryne complexes) in the former that were formed after the Mesoarchean TTG. Thus, the Middle-Dnieper megablock is important for studying the genesis and geodynamic formation conditions of Late Archaean granitoids. The granitoids in the Middle-Dnieper megablock are not well understood. They include the Hannivka granites of the East Hannivka monocline of the Kryvyi Rih-Kremenchuk structure, whose age and stratigraphic position has been a matter of a long-standing debate. The purpose of the work is to study the geochemistry, genesis and U-Pb age of the Hannivka granites. Based on our results, the Hannivka granites possibly formed in the crust resulting from the melting of older rocks. They differ from other Late Archean granitoids of the Middle-Dnieper megablock by their high U (56.4 ppm) content and the presence of Mo (4.3 ppm). The Hannivka granites underwent tectonic reworking during a collisional event about 2.0 billion years ago, which is probably associated with the kalishpatization of these rocks. The U-Pb age of the cores of zircons sampled from the Hannivka granites, determined by LA-ICP-MS method, are about 2827±16 million years in age. Younger rims probably formed during kalishpatization. The Hannivka granites are the same age as the granitoids of the Mokro-Moskowka and Tokiv complexes. Late Archean granitoids were formed between 2.99-2.7 Ga in the Middle-Dnieper granite-greenstone block and in the geologically similar granite-greenstone block KMA are 2.6 Ga in age. In the Pilbara craton, which is a Paleoarchean granite-greenstone complex, the age of biotite and feldspar granites is similar to the age of the rocks on the Middle-Dnieper megablock (2.94-2.93 Ga). The difference in magmatism ages may be due to the drift of the different cratons above mantle plumes of different ages.