Preservation of radiogenic argon in mantle micas in situ: Dating of deep seated inclusions from the Shavaryn-Tsaram Paleovolcano, Mongolia |
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| Authors: | S V Vysotskii S Yu Budnitskii S V Rasskazov A V Ignat’ev T A Velivetskaya and A A Karabtsov |
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| Abstract: | This article presents new data on isotopic (K/Ar) dating of a series of volcanic units of the Shavaryn-Tsaram Volcano based
on rocks and minerals and the chemical composition of deep seated micas. Four age intervals have been identified, one of which
is pertinent to the Middle Miocene (15.5–12.2 Ma) and the other three, to the Quaternary (1.87–1.82, 1.44–1.33, and 0.54–0.44
Ma). The age intervals correlate with the known volcanic events. The xenolites examined are most similar to fragments of a
deep seated alkalineultramafic rock complex whose formation proceeded during the last 15.5 myr and was accompanied by sporadic
effusion of alkali-basaltoid lavas onto the surface. The micas from the inclusions of the Shavaryn-Tsaram Volcano had a high
activation energy of migration of radiogenic argon, which ensured argon accumulation during the radioactive transformation
of 40K and preservation in situ. The high equilibrium temperature of garnet lherzolite (1050–1150°C) and the calculated pressure
(20–22 kbar) played the role of mutually compensating factors in argon diffusion; high temperatures enhanced diffusion, while
pressure suppressed it. |
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