CONTINENTAL CRUST IN GORNY ALTAI: NATURE AND COMPOSITION OF PROTOLITHS
N.N. Kruka, A.G. Vladimirova, G.A. Babinb, S.P. Shokalskyc, N.V. Sennikovd, S.N. Rudneva, N.I. Volkovaa, V.P. Kovache and P.A. Serovf
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, prosp. Akad. Koptyuga 3, Novosibirsk, 630090, Russia
bSiberian Research Institute of Geology, Geophysics, and Mineral Resources, Krasnyi prosp. 67, Novosibirsk, 630091, Russia
cA.P. Karpinsky Russian Geological Research Institute, Srednii prosp. 74, St. Petersburg, 199106, Russia
dA.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, prosp. Akad. Koptyuga 3, Novosibirsk, 630090, Russia
eInstitute of Precambrian Geology and Geochronology, nab. Makarova 2, St. Petersburg, 199034, Russia
fGeological Institute, Kola Scientific Center, ul. Fersmana 14, Apatity, 184200, Russia
Keywords: Crust-forming processes, protoliths, juvenile crust, Gorny Altai
Pages: 431-446
Abstract
The history of the Vendian-Early Paleozoic formation of protoliths of continental crust in the Gorny Altai segment of the Central Asian fold belt is considered, and their composition, isotopic characteristics, and formation mechanisms are estimated. We have established two stages of crust-forming processes in Gorny Altai: Early and Late Caledonian, with the different structures of formed geoblocks and nature and compositions of crustal protoliths.
At the Early Caledonian stage, fragments of oceanic lithosphere of basic composition (MORB, OIT, OIB) (TNd (DM - 2st) = 0.65-1.1 Ga) formed, as well as island arcs with andesite-basaltic and andesitic protoliths with low contents of incompatible elements (TNd (DM - 2st) = 0.7-0.9 Ga). At the Late Caledonian stage, the redistribution of the substance of these blocks and the external supply of material led to the formation of the heterogeneous crust of turbidite basins with an oceanic basement and andesite-dacitic upper-crustal protoliths (TNd (DM - 2st) varies from 0.8-0.9 Ga in the framing of the volcanic arc of Altaids to 1.4-1.6 Ga at the boundary of the Altai-Mongolian microcontinent).
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