THE AGE OF ZIRCON FROM METASEDIMENTARY ROCKS OF THE TERNUVATE STRATA (WEST AZOV BLOCK OF THE UKRAINIAN SHIELD)

Abstract

In the West Azov the Ternuvate strata comprises metamorphic rocks that builds up the Haichur arcuate structure, which is about 72 km long. Its western part lies within the Andriivka fault zone, which separates the Vovcha and Huliaipole blocks, while the eastern part is located within the Ternuvate fault zone, which is traced on the Remivka block. The rocks composing the Haichur structure have irregular and laterally variable composition and changeable thickness, and show dynamometamorphic structures of boudinage and schistosity. The upper part of the Ternuvate strata is composed mainly of metasedimentary rocks — gneisses and biotite schists, garnet-biotite, magnetite-amphibole and feldspar quartzites. The lower part comprises volcanogenic rocks — amphibolites, metaultrabasites and biotite-amphibole gneisses. Using the LA-ICP-MS method, 38 zircon crystals from muscovite-biotite gneisses of the upper part of the Ternuvate strata were analyzed. According to geochemical data, they are metamorphosed greywacke. Zircon belongs to several age populations (3.65—3.45 and 3.3—2.95 Ga), corresponding to the major stages of the formation of the Archean crust in the West Azov domain, i.e., formation of the oldest basement and granite-greenstone complexes of the Paleoarchean and Mesoarchean ages. Identical populations of the detrital zircon were established in the early Precambrian metaterrigenous rocks of the Krutobalka Formation of the Sorokyne greenstone structure. The similarity of the Paleoarchean crust (3.45—3.65 Ga) of the West Azov block (Ukrainian Shield) and the Kursk-Besedine granulite-gneiss area of the Kursk Magnetic Anomaly (KMA) block is obvious, whereas the Paleoarchean and Mesoarchean complexes (3.3—2.95 Ga) correspond to the rocks of Mykhailiv and Orel-Tim granite-greenstone area of the KMA block. The Archean complexes of the Sarmatia are of the same age as similar formations of the Kaapvaal craton in South Africa, Bastar craton in India, North China Craton, Slave craton in Canada and others, which were formed since the Eoarchaean.