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Russian Geology and Geophysics

2010 year, number 5

THE OLKHON METAMORPHIC TERRANE IN THE BAIKAL REGION: AN EARLY PALEOZOIC COLLAGE OF NEOPROTEROZOIC ACTIVE MARGIN FRAGMENTS

D.P. Gladkochuba, T.V. Donskayaa, V.S. Fedorovskyb, A.M. Mazukabzova, A.N. Larionovc and S.A. Sergeevc
a Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
bGeological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017, Russia
cA.P. Karpinsky Russian Geological Research Institute (VSEGEI), Federal Agency of Mineral Resources, Srednii prosp. 74, St. Petersburg, 199106, Russia
Keywords: Terrane, collision, granulite, zircon, SHRIMP-II, island arc, backarc basin, Neoproterozoic, Early Paleozoic, Siberian craton, Baikal region, Paleoasian ocean
Pages: 447-460

Abstract

We report data from the Khadarta, Khoboi, and Orso metamorphic complexes of the Olkhon terrane in the western Baikal region. High-grade rocks in the three complexes might have been derived from active continental margin rocks (island arc-backarc basin system). The backarc basin history possibly began at 840-800 Ma, according to SHRIMP-II U-Pb zircon ages of the Orso gneiss. Many tectonic units in the Olkhon terrane belonged to the active margin of the Barguzin microcontinent, which rifted off the Aldan province of the Siberian craton in the Early Neoproterozoic. The accretion of the microcontinent to the craton was accompanied by high-grade metamorphism recorded in the Khadarta and Khoboi granulites. The 507±8 Ma and 498±7 Ma SHRIMP-II U-Pb zircon ages of the latter complexes, respectively, may refer to the earliest evolution stage of the Olkhon metamorphic terrane. New data for the Olkhon terrane agree with the ages of other high-grade complexes along the southern Siberian craton (Slyudyanka, Kitoikin, Derba) and correspond to the initiation of the Central Asian orogen. With these data, the Olkhon metamorphic terrane has been interpreted as an Early Paleozoic collisional collage of fragments of the microcontinent's Neoproterozoic active margin.