First Determination of the Isotope Age of the Andesite–Dacite Complex of the Eastern Zone of the Middle Urals

Resumo

This paper reports on the first U–Pb dating of zircons from dacites of the volcanic paleo-edifice of the andesite–dacite complex of the Eastern Zone of the Middle Urals orogen. The Eastern Zone involves the retroshariage and sheet-folded structural subzones. The volcanic complex, which includes vent and peri-vent facies, lies in the sheet-folded subzone among flyshoid and carbonate deposits with Middle Devonian fauna. This subzone forms the easternmost border of the orogen. The age of zircon grains is 389 ± 5.6 Ma, which is also in accordance with the Middle Devonian. Therefore, the sedimentary and volcanic complexes were formed around the same time, but based on their composition and structure, in different facial conditions. The sedimentary deposits were accumulated in shallow basins; the volcanic deposits were likely formed in the subaerial conditions surrounded by a shallow sea basin. We suppose that the manifestation of andesite–dacite volcanism in association with the sediments of shallow basins most likely points to the spatial and age-related displacement of the geodynamic and facial conditions of volcanism to the eastern periphery of the orogen.