Late Devonian Calc-Alkali High-K Fractionated Granites of the "Ferroan" I-Type, Rudny Altai

The results of geological, geochemical, and isotopic-geochronological studies of Late Devonian granitoids of Rudny Altai, which formed at the Hercynian stage of tectonogenesis of the Altai-Sayan sector of the Central Asian Fold Belt, are presented. The isotopic U-Pb age of zircons ranges from 367 to 363 Ma. The geochemical characteristics indicate that leucogranites belong to high-K calc-alkaline series (SiO2 > 73 wt %, Na2O + K2O = 6.9-9.0 wt %, and Na2O/K2O = 0.7-1.2) of the calc-alkaline and alkali-calcic subtypes (MALI (modified alkali-lime index) = 6.32-8.41). Rocks are close to saturation with silica ( A/CNK = 0.9-1.2) and are characterized by a high Fe* index (0.84-0.97) and a higher F content (0.04-0.17 wt %). The variations in HSFE, LILE, and the Ga/Al ratios and a strong negative A/CNK-P2O5 correlation indicate that they belong to fractionated I-type granitoids. The Be mineralization is spatially and genetically related to leucogranites. It is suggested that the formation of granitoids was related to a synshear setting of a convergent margin as a result of oblique subduction or sliding tectonic plates of the Irtysh-Zaisan Ocean and the margin of the Siberian Continent.