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AGE AND PALEOTECTONIC SETTING OF THE DEVONIAN VOLCANISM OF THE KOLYVAN-TOMSK FOLDED ZONE, INSIGHTS FROM DETRITAL ZIRCON GEOCHRONOLOGY OF THE MITROFANOVSKAYA FORMATION

F. I. Zhimulev 1, J. Gillespie 2, S. Glorie 2, A. V. Kotlyarov 1, E. V. Vetrov 1, 3, J. De Grave 4

1 V. S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia; 2 Tectonics, Resources and Exploration (TraX), Department of Earth Sciences, University of Adelaide, Adelaide, Australia; 3 Siberian Research Institute of Geology, Geophysics and Mineral Resources, Novosibirsk, Russia; 4 Laboratory for Mineralogy and Petrology, Department of Geology, Ghent University, Ghent, Belgium

The Middle Devonian volcanic formations of the Bugotak complex compose the lower tectonic nappe of the Kolyvan-Tomsk folded zone and are exposed within the most elevated blocks of the zone, namely Ordynsk, Bugotak and Mitrofanovo ones. As a result of uranium-lead dating of detrital zircon from volcanicclastic rocks in the top of the Mitrofanovskaya Formation, it was established that the volcanogenic rocks of the Mitrofanovo uplift of the Kolyvan-Tomsk folded zone were formed in the range of 395–380 Ma. The Middle Devonian outbreak of volcanism occurred after a long interruption in the magmatic activity and sedimentation of the region. The neodymium isotope composition of the studied rocks (εNd (T) = 6.9 for the age of 380 Ma) indicates that a depleted mantle was a source of the Middle Devonian volcanism of this zone. The volcanic belt, fragments of which are formations of the Bugotak complex, was established on the Salair continental block formed by the Early Paleozoic juvenile crust developed under suprasubduction conditions. The Middle Devonian volcanism was accompanied by a split of the continental crust and the opening of the sea basin, the carbonate-terrigenous deposits of which compose the Upper Devonian-Early Carboniferous sedimentary sequence of the Kolyvan-Tomsk folded zone. In the basement of the Kuznetsk basin there are no any blocks of the Precambrian continental crust.

Keywords: geochronology, zircon, volcanism, West Siberia, Devonian.

DOI 10.20403/2078-0575-2018-3-13-24