Middle Ordovician effusive rocks of the Khamsara terrane (Tyva) as an indicator complex

Abstract

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 A2-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.