Middle Paleozoic Rhyolite of the Gorny and Rudny Altai: Geochronology and Composition

摘要

The paper reports the results of geological, geochemical, and isotope-geochronological studies of subvolcanic rhyolites of NW Gorny Altai and Rudny Altai, which belong to the large Hercynian volcanic systems: Altai-Minusa and Altai-Salair, respectively. U-Pb zircon dating revealed two age groups: similar to 410-405 and 390-381 Ma. The isotope-geochemical characteristics of the rhyolites demonstrate high epsilon(Nd)(T) from +2.6 to 6.0 with relatively young model ages T(DM) = 851-966 Ma in Rudny Altai and older model ages, up to 1266 Ma, in NW Gorny Altai. The rhyolites show transitional geochemical signatures between within-plate and island-arc felsic magmas. The results obtained are consistent with two-stage evolution of volcanism and its migration from the continent to the ocean.