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AGE AND PETROGENESIS OF ACID VOLCANITES OF THE ALGANSKY MOUNTAINS OF THE KORYAK HIGHLANDS (NORTHEASTERN OF RUSSIA)

The isotopic dating of U-Pb by the zircon method of volcanic acid zircons of the Konachan complex (Algansky mountains, northwestern part of the Koryak highlands) confirmed their Late Eocene age (34.6 ± 0.5-38.8 ± 0.4 Ma, Priabon). It has been shown that silicic rocks are represented by moderately potassium, peraluminous (ASI = 1.23–1.30), moderately and high magnesian differences, often with a high content of Cr and Ni. The contents of Sr, Y and Yb are adakite. High ratios of 143Nd/144Nd and low 87Sr/86Sr in the rocks of the complex, the distribution pattern of rare and rare-earth elements suggest that the source of salite melt, to some extent contaminated by sedimentary material, was metabasites. The formation of the Konachan complex is caused by magmatism during accretion of terranes of the Olyutor-East Kamchatka island-arc system [27]; compression processes led to the blocking of the upwelling front of the continental asthenosphere, initiating intense crustal anatexis and silicate magmatism.