Ages of micas from xenoliths and xenocrysts of kimberlites of the Siberian Craton determined by 39Ar/40Ar method

Plateaus and isochronous and integral ages of ³⁹Ar/⁴⁰Ar xenocrysts and phlogopite grains from kimberlite xenoliths can be used to determine the ages of mantle processes (Hopp et al., 2008) and decipher the genesis of diamond-forming processes. Dating of deep xenoliths of kimberlites of the Siberian craton reveals a significant spread (Pokhilenko et al., 2012; Ashchepkov et al., 2015) from the Archean to the time close to the age of the host kimberlites, mainly Devonian. The most ancient ages for Udachnaya Daldyn fields for phlogopites from xenoliths of spinel harzburgites of the highest level belong to the late Archean (2.6-2.0) - early Proterozoic 1.7 -1.5 Ga. In the Alakite field, all ages are younger from 1,87 – 1,05- 0,928 - 0,87 Ga and belong to the metasomatic history of the Rodinia continent mantle. Close dates are set for xenoliths from the Obnazhennaya pipe (Kalashnikova et al. 2017).

Fig.1 PT  Udachnaya pipe. Symbols: Op: ToC(Brey, Kohler, 1990)-P(GPa)(McGregor, 1974). Cpx: 2.ToC-P(GPa)(Nimis, Taylor, 2000); 3.ToC (Nimis, Taylor, 2000 with ed. author)–P(GPa)(Ashchepkov et al., 2011); 4. eclogites ; 5. inclusions in diamond; Gar: 6.ToC (O'Neill, Wood, 1979) -P(GPa) (Ashchepkov et al., 2010Gar), 7. For eclogite garnets Chromite: 8,  inclusions in diamond; 9. chromite ToC (O'Neill, Well, 1987)-P(GPa) (Ashchepkov et al., 2010Gar), 7. For eclogite garnets Chromite: 8, inclusions in diamond; 9. chromite ToC (O'Neill, Well, 1987)-P(GPa) (Ashchepkov et al ., 2010Chr); 10 the same for inclusions in diamond; 11. Film Tom (Taylor et al., 1998)- P(GPa) (Ashchepkov et al., 2010 ilm)

Our data on micas by the ³⁹Ar/⁴⁰Ar method often reveal complex configurations of spectra. The micas of the xenocrysts of the Alakite field give several peaks, ranging from the most high-temperature and ancient, which corresponded to the upper Proterozoic - Vendian and Paleozoic, and only the lowest temperature peaks with a high Ca/K ratio corresponded to the ages of kimberlite introduction. Some peaks may be associated with the thermal effects of the Vilyusky plume (Kuzmin et al., 2012). The lowest temperature peaks, which are close in age to the time of kimberlite formation, which is confirmed by the high ³⁸Ar/³⁹Ar ratios of the gas released at the low-temperature stage, can be used very approximately for dating kimberlites, however, the release of other gases at low-temperature stages significantly increases the measurement error. All of them correspond to the interval 440 -320 Ma. The pipes Mir, Internationalnaya, Ukrainianskaya - 420, Yubileynaya -342, Botuobinskaya -352 Ma). Some definitions practically coincide with Rb/Sr ages (Griffin et al., 1999, Agashev et al., 2005, Kostrovitsky et al., 2008; Zaitsev, Smelov, 2010) and probably represent mixing lines. For many xenocrysts (Feinsteinovskaya, Ukrainskaya, Yubileynaya, Krasnopresnenskaya tr.), the interval from 600 to 500 Ma is manifested, which corresponds to the stage of the Laurasia supercontinent breakdown. The presence of relatively low-temperature plateaus with ancient ages, and high-temperature young ones implies that some stages can be correlated with the mantle history of the mineral.  RFBR grant 19-05-00788.  Supported by Ministry of Science and Higher Education.

Fig.2 PT  Sytykanskaya pipe