The age of unusual xenogenic zircons from Yakutian kimberlites |
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| Authors: | N V Vladykin E A Lepekhina |
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| Institution: | (1) Astronomical Observatory, University of Valencia, Paterna, Valencia, Spain |
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| Abstract: | Several spindle-shaped grains of zircon, which have a small size (<0.25 mm) and a distinct purplish pink coloration were found
in the crushed samples of kimberlites from the Aykhal, Komsomolskaya-Magnitnaya, Botuobinskaya (Siberian platform), and Nyurbinskaya
(Yakutia) pipes and olivine lamproites of the Khani massif (West Aldan). U-Pb SHRIMP II zircon dating performed at the VSEGEI
Center for Isotopic Research yielded the ages of 1870–1890 Ma for the pipes of the Western province (Aykhal and Komsomolskaya)
and 2200–2750 Ma for the pipes of the eastern province (Nyurbinskaya and Botuobinskaya), which allowed us to consider these
zircons to be xenogenic to kimberlites. Although these zircons resemble in their age and color those from the granulite xenoliths
in the Udachnaya pipe 2], no other granulite minerals are found there. Thus, major geological events in the mantle and lower
crust, which led to the formation of zircon-bearing rocks, happened at 1800–1900 Ma in the northern part of the kimberlite
province, whereas in the Eastern part of the province (Nakyn field) these events were much older (2220–2700 Ma). It is known
that the period of 1800–1900 Ma in the Earth’s history was accompanied by intense tectonic movements and widespread alkaline-carbonatite
magmatism. This magmatism was related to plume activity responsible for overheating the large portions of the mantle to the
temperatures at which some diamonds in mantle rocks would burn (northern part of the kimberlite province). In the Nakyn area,
the mantle underwent few or no geological processes at that time, and perhaps for this reason this area hosts more diamondiferous
kimberlites. The age of olivine lamproites from the Khani massif is 2672–2732 Ma. Thus, these are some of the world’s oldest
known K-alkaline rocks. |
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