MIDDLE ORDOVICIAN EFFUSIVE ROCKS OF THE KHAMSARA TERRANE (Tyva) AS AN INDICATOR COMPLEX
S.I. Shkol’nik1, A.V. Ivanov1, L.Z. Reznitsky1, E.F. Letnikova2, Hyaiyu He3, Zhiqlang Y3, Youjueen Li3, I.A. Vishnevskaya2, I.G. Barash1
1Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
2V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
3Institute of Geology and Geophysics, Chinese Academy of Sciences, 19, Beitucheng West Road, Beijing, 100029, China
Keywords: Volcanic rocks, U-Pb age, accretion, Khamsara terrane
Abstract
Felsic rocks of the Khamsara terrane in Tyva (southern Siberia) have been studied in terms of major- and trace-element compositions and U-Pb isotope geochronology. The Khamsara Formation rocks have compositions of A 2-subtype within-plate anorogenic volcanics derived from molten continental crust and SIMS U-Pb zircon ages of 463.9 ± 2.8 and 461.7 ± 3.1 Ma of two rhyolite porphyry samples. The Khamsara volcanics are compared with subvolcanic granitoids of the Ognit complex in the Biryusa terrane (Sharyzhalgai basement inlier of the Siberian craton) adjacent to the Khamsara terrane. The volcanics and the granites are coeval and share compositional similarity. The Khamsara Formation is interpreted as a cap complex that marks the upper age bound of the accretionary-collisional events when amalgamated terranes in this part of the Central Asian orogen accreted to the Siberian craton.
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