Early Devonian volcanics of southeastern Gorny Altai: Geochemistry,isotope (Sr,Nd, and O) composition,and petrogenesis (Aksai complex) |
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| Institution: | 1. Gorno-Altaiskaya Ekspeditsiya, ul. Sovetskaya 15, Maloeniseiskoe, 659370, Altai Territory, Russia;2. National Research Tomsk State University, pr. Lenina 36, Tomsk, 634050, Russia;3. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;4. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;1. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;2. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;4. Institute of Archeology and Ethnography, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Lavrent’eva 17, Novosibirsk, 630090, Russia;1. Kazan Federal University, ul. Kremlevskaya 18, Kazan, 420008, Russia;2. Borok Geophysical Observatory of the Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Borok Village 142, Yaroslavl, Region, 152742, Russia;3. S.I. Subbotin Institute of Geophysics, National Academy of Sciences of Ukraine, pr. Palladina 32, Kyiv, 03680, Ukraine;1. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;2. Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia;3. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;1. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;2. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;3. A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia |
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| Abstract: | Geological, geochemical, and isotope (Sr, Nd, and O) parameters of Early Devonian (405 Ma) volcanics of southeastern Gorny Altai (Aksai and Kalguty volcanotectonic structures) are discussed. The studied igneous rock association comprises magnesian andesitoids, Nb-enriched andesite basalts, and A-type peraluminous silicic rocks (dacites, rhyolites, granites, and leucogranites). Magnesian andesitoids (mg# > 50) are characterized by a predominance of Na among alkalies (K2O/Na2O ≈ 0.1-0.7), medium contents of TiO2 (~ 0.8-1.3 wt.%) and Al2O3 (~ 12-15 wt.%), enrichment in Cr (up to 216 ppm), and low Sr/Y ratios (4-15). The Nb-enriched (Nb = 10-17 ppm) andesite basalts have high contents of TiO2 (1.7-2.7 wt.%) and P2O5 (0.4-1.4 wt.%). The A-type granitoids are characterized by high contents of K(K2O/Na2O ≤ 60) and alumina (ASI ≤ 2.9) and depletion in Ba, Sr, P, and Ti. The magnesian andesitoids and Nb-enriched andesite basalts are products of melts generated in the metasomatized lithospheric mantle; silicic magmas were formed through the melting of Cambrian-Ordovician metaturbidites of the Gorny Altai Group and, partly, Early-Middle Cambrian island-arc metabasites. The above rock association might have resulted from a plume impact on the lithospheric substrates of the continental paleomargin during the evolution of the Altai-Sayan rift system. |
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