Pre-collisional (> 0.5 Ga) complexes of the Olkhon terrane (southern Siberia) as an echo of events in the Central Asian Orogenic Belt |
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| Institution: | 1. Institute of the Earth''s Crust, Siberian Branch of the Russian Academy of Sciences, 128 Lermontov Str., Irkutsk 664033, Russia;2. Geological Institute, Russian Academy of Sciences, 7 Pyzhevskii per., Moscow 119017, Russia;3. Far East Federal University, 8 Sukhanova Str., Vladivostok 690091, Russia;4. School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Republic of Korea;5. Centre of Isotopic Research, A.P. Karpinsky Russian Geological Research Institute (VSEGEI), 74 Sredny prosp., St. Petersburg 199106, Russia;6. Institute of Earth Sciences, St. Petersburg State University, 7/9 Universitetskaya emb., St. Petersburg 199034, Russia;7. Department of Earth and Environmental Sciences, Chungbuk National University, Cheongju 28644, Republic of Korea;8. Division of Earth and Environmental Sciences, Korea Basic Science Institute, Ochang 28119, Republic of Korea;1. Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Wroc?aw, ul. Podwale 75, Wroc?aw, Poland;2. Institute of Civil Engineering, Poznań University of Technology, ul. Piotrowo 5, 60-965 Poznań, Poland;3. Polish Geological Institute - National Research Institute, ul. Rakowiecka 4, 00-975 Warszawa, Poland;4. CIRES and Department of Geological Sciences, University of Colorado, Boulder, USA;5. Centre of Isotopic Research, All-Russian Geological Research Institute, Sredny prospect 74, 199 106 St. Petersburg, Russia;6. Faculty of Geology, Geophysics and Environmental Protection, AGH – University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków, Poland;7. Department of Earth Sciences, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden;8. St. Petersburg State University, Institute of Earth Sciences, Universitetskaya emb.7/9, 199034 St. Petersburg, Russia;9. Department of Geological Sciences, Indiana University, 1005 East 10th Street, Bloomington, IN 47405, USA;10. Laboratory for Isotope Geology, Swedish Museum of Natural History, P.O. Box 50 007, 10405 Stockholm, Sweden;1. A.A. Trofimuk Institute of Petroleum Geology and Geophysics, 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. M.V. Lomonosov Moscow State University, Leninskiye Gory, Moscow, 119991, Russia;4. Geological Survey of Western Australia, 100 Plain Str., East Perth, WA 6004, Australia;5. A.P. Karpinsky Russian Geological Research Institute, Srednii pr. 74, Saint Petersburg, 199106, Russia;1. Federal State Institution of Science Geological Institute of Russian Academy of Sciences, Pyzhevsky lane 7, Moscow 119017, Russian Federation;2. Federal State Unitary Enterprise “A.P.Karpinsky Russian Geological Research Institute”, 74, Sredny prospect, 199106 Saint-Petersburg, Russian Federation;3. GeoSep Service, 1521 Pine Cone Road, ID 83843, USA;4. Rosneft Oil Company, Dubininskaya str., 31A, 115054 Moscow, Russian Federation;5. Institute of Earth Sciences, St.-Petersburg State University, Universitetskaya emb., 7/9, St-Petersburg, Russian Federation |
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| Abstract: | The Olkhon terrane is a part of the Early Palaeozoic accretionary-collisional system in the northern Central Asian Orogenic Belt (CAOB). The terrane was produced by an Ordovician collision as a collage of numerous chaotically mixed tectonic units composed of rock complexes of different ages originated in different tectonic settings. The pre-collisional history of the terrane is deciphered using new data on zircon ages and chemistry of rocks from several complexes. The oldest Olkhon rocks are the 1.87–1.83 Ga granulite and gneissic granites of the Kaltygey complex, which is an exotic Palaeoproterozoic tectonic slice. The next age group consists of the Ust-Zunduk orthogneisses (807 ± 9 Ma) and the Orso amphibolites and gneisses (792 ± 10 and 844 ± 6 Ma). Samples of both complexes have negative εNd(t) values. The Ust-Zunduk and Orso complexes can have formed in active margins of continents or in crustal blocks other than southern Siberia. The Ediacaran subduction-related rocks of the Olkhon complex may have formed in an island arc setting within the Palаeo-Asian Ocean (PAO). The protolith of schists after volcanic rocks has an age of 637 ± 4 Ma and shows positive ?Nd(t) values. The Ediacaran/Cambrian Tonta mafic granulites (ca.545 Ma), with OIB affinity and slightly positive ?Nd(t), were derived from an enriched mantle source and may represent a fragment of an oceanic island. The Cambrian Shebarta gneisses after continental-arc greywackes with negative ?Nd(t) values were deposited in a back-arc basin of a microcontinent within the PAO, between 530 and 500 Ма. The Cambrian Birkhin metamorphics after PAO mature island-arc rocks have U-Pb ages of ca. 500–490 Ma and positive ?Nd(t) values. All pre-collisional complexes in the Olkhon terrane have their analogues among the rocks formed during main events in the northern CAOB history. Thus the reconstructed milestones in the Olkhon terrane history appear to be an echo of events in the CAOB northern segment. |
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