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U-PB AGE AND GEOCHEMISTRY OF ZIRCON FROM TUFFACEOUS SANDSTONE OF THE KOYARD RIVER (KURTUSHIBA RIDGE, WESTERN SAYAN): EVIDENCE FOR AN ORDOVICIAN SYN-COLLISIONAL VOLCANOGENIC-SEDIMENTARY FORMATION​

A. A. Mongush 1, ​F. P. Lesnov 2, N. I. Gusev 3, Ch. K. Oydup 1, Ch. M. Hertek 1, Ch. O. Kadyr-ool 1, E. K. Druzhkova 1​​

1 Tuvinian Institute for Exploration of Natural Resources SB RAS, Kyzyl, Russia; 2 Sobolev Institute of Geology and Mineralogy RAS, Novosibirsk, Russia; 3 Karpinsky Geological Research Institute, Saint Petersburg, Russia​

We present petrographic, geochemical, and Sm-Nd isotopic data on the volcanogenic-sedimentary rocks from the middle reach of the Koyard River, previously assigned to the Vendian – Lower Cambrian Chinge Formation. A tuffaceous sandstone sample was studied in detail, with additional observations from associated tuffaceous siltstone tuffite and basalts. U-Pb (LA-ICP-MS) dating of zircon from the tuffaceous sandstone defines a tight 492–507 Ma cluster and yields a concordant age of 500±3 Ma. Zircon morphology, internal textures, and trace-element signatures indicate a dominantly magmatic origin and suggest derivation from a granitoid source followed by erosion and redeposition. These results provide evidence for the evolution of an Ordovician syn-collisional volcanogenic-sedimentary unit, which can be employed to refine regional stratigraphic and paleotectonic models for the Western Sayan.

Keywords: zircon, sandstone, U-Pb dating, LA-ICP-MS, geochemistry, provenance area.

DOI 10.20403/2078-0575-2026-1-89-101

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