U-Pb AGE AND MINERAL INCLUSIONS IN ZIRCON FROM DIAMOND-BEARING GARNET-PYROXENE ROCKS OF THE KUMDI-KOL MICRODIAMOND DEPOSIT IN Northern Kazakhstan
A.A. Ilyin1,2, V.S. Shatsky1,2,3, A.L. Ragozin1,2
1Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
3Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
Keywords: Ultra-high pressure metamorphism, inclusions in zircon, U-Pb age, Kokchetav subduction-collision zone
Abstract
The paper presents the results of studying inclusions and determining the U-Pb age in zircon from the diamond-bearing garnet-pyroxene rock of the Kumdi-Kol metamorphogenic diamond deposit, located in the Kokchetav subduction-collision zone. The distribution of rare earth elements in garnet and clinopyroxene is used as a basis for estimating the equilibrium pressure (5.5 ± 0.3 GPa) and temperature (993 ± 24 ℃), which correspond to the diamond stability field. The composition of mineral inclusions in zircon indicates its formation at both progressive and regressive stages of metamorphism. The concordia diagram shows that zircon figurative points lie on the discordia with an upper intersection at 1953 ± 139 Ma and a lower intersection at 512 ± 4 Ma. The main peak on the graph of the probability density distribution of zircon ages corresponds to an age of 519 Ma. The presence of grossular-almandine garnet inclusions in zircon confirms the previous assumption that the basement rocks of the Kokchetav massif act as protoliths of garnet-pyroxene rocks.
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