New data on the period of existence of the continental margin subduction zone in the Middle Urals

Abstract

U–Pb (SIMS) dating of zircons from granite of the Petrokamensk gabbro–granitoid complex, marking termination of the Devonian island–arc magmatism in the Verkhisetsk–Tura Zone of the Middle Urals, gave an age of 386 ± 3 Ma. Zircons from the West Verkhisetsk granitoids, the formation of which corresponds to the beginning stage of magmatism of the continental margin in the region, yielded ages of 386.6 ± 4.1 and 381.8 ± 6.0 Ma. This suggests that the change in the regime of the island–arc geodynamic mode to an active continental margin took place at the boundary of the Middle and Late Devonian. The upper boundary of existence of the continental margin subduction zone is determined by the closure of the Ural paleo-ocean and the beginning of continental collision processes, which resulted in accumulation of flysch in the Ural foreland trough from the second half of the Bashkirian Stage.