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Russian Geology and Geophysics

2006 year, number 6


V.N. Smirnov, G.N. Borozdina, L.I. Desyatnichenko*, K.S. Ivanov, T.Yu. Medvedeva**, and I.F. Fadeicheva*
Institute of Geology and Geochemistry, Uralian Branch of the RAS,
7 Pochtovy per., Ekaterinburg, 620151, Russia
* Uralian Geological Experimental and Methodological Expedition,
55 ul. Vainera, Ekaterinburg, 620144, Russia
** Department of National Control of Environment of Uralian Federal District,
55 ul. Vainera, Ekaterinburg, 620144, Russia
Keywords: Paleo-ocean, continental rift volcanism, island-arc volcanism, conodonts, age, Ordovician, Urals
Pages: 752-759


In the course of regional geological surveys of the Central Urals guide conodonts were found. On the basis of these findings, we dated the volcanosedimentary deposits of the western slope formed under the conditions of continental rifting (leading ultimately to the rupture of the continental plate and to the birth of an ocean) and the volcanic complexes developed on the eastern slope of the Urals at the base of an island arc, whose origin suggests the existence of a mature oceanic structure. Thus, a sufficiently narrow age interval has been established to time the ocean opening. According to the data obtained, the rift-related tholeiitic volcanic rocks of the western slope were formed immediately before the continental crust had broken and the continental rift had transformed into oceanic, as late as the Middle Ordovician. The island-arc volcanic complexes of the eastern slope began to form in the Late Ordovician. This implies that the paleo-ocean in the Central Urals opened about the time of Middle-Late Ordovician transition.