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UDC 550.42:551.14+550.93(51)

https://doi.org/10.26516/2541-9641.2026.2.116

EDN: BOYMBW

U–Th Dating of Middle to Late Pleistocene Volcanic Rocks from Sayans, Siberia and Hangay, Central Mongolia

E.P. Chebykin¹, S.V. Rasskazov^1,2, I.S. Chuvashova^1,2, D.I. Parfenov^1,2

¹Institute of the Earth's Crust SB RAS, Irkutsk, Russia

²Irkutsk State University, Irkutsk, Russia

Abstract. Isochron ages from non-equilibrium ²³⁸U series have been obtained for Middle-Late Pleistocene volcanic rocks of the Sayan Mountains (Russia) and Hangay Mountains (Mongolia). Some of these are consistent with K–Ar ages. The data obtained indicate that volcanic activities occurred in both areas during the time interval 400–350 Ka, only in the Sayan Mountains during the period 230–60 Ka, and again in both areas during the last 50 Ka. High initial thorium isotope ratio (²³⁰Th₀/²³²Th) (up to 6.0) was determined in rocks from the first time interval, while a consistent decrease in this parameter was observed in rocks from later eruptions. The exception was the volcanic episode 120–112 Ka, for the rocks of which in the Sayan Mountains a wide range (²³⁰Th₀/²³²Th) was obtained – from 1.17 to 1.34.

Keywords: Central Asia, Quaternary period, ²³⁸U-series, volcanism

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Chebykin Eugenyi Pavlovich,

Candidate of Chemistry,

664003 Irkutsk, Lermontov st., 128,

Institute of Earth’s crust, SB RAS,

Leading specialist,

tel.: (3952) 51–16–59,

email: cheb@lin.irk.ru

Rasskazov Sergei Vasilevich,

Doctor of Geology and Mineralogy, Professor,

664033, Irkutsk, Lermontov, 128,

Institute of Earth’s crust of SB RAS,

Head of the Laboratory for isotopic and geochronological studies,

664025, Irkutsk, Lenina st., 3,

Irkutsk State University, Geological Faculty,

Head of the Dynamic Geology Chair,

tel.: (3952) 51–16–59,

email: rassk@crust.irk.ru

Chuvashova Irina Sergeevna,

Candidate of Geology and Mineralogy,

664033, Irkutsk, Lermontov st., 128,

Institute of Earth’s crust, SB RAS,

Senior Researcher,

664025, Irkutsk, Lenina st., 3,

Irkutsk State University, Geological Faculty,

assistant professor,

tel.: +79149052401,

email: chuvashova@crust.irk.ru

Parfenov Daniil Igorevich,

664033, Irkutsk, Lermontov st., 128,

Institute of Earth’s crust, SB RAS,

Lab Assistant,

664025, Irkutsk, Lenin st., 3

Irkutsk State University, Geological Faculty,

student of the 3-d course.

 

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