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

Plateau, isochron and integral ages of 40Ar/39Ar 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. Datings of deep xenoliths of kimberlites of the Siberian Craton reveal a significant spread (Pokhilenko et al., 2012; Solovieva et al., 2017b; Ashchepkov et al., 2015) from the Archean to a time close to the age of the host kimberlites, mainly Devonian. The oldest ages for the Udachnaya tr of the Daldyn field for phlogopites from xenoliths of spinel harzburgites of the uppermost level belong to the late Archean-early Proterozoic 2.1-1.5 Ga. In the Alakit field, all ages are younger than 1.6–1.05 and 0.928–0.87 Ga and belong to the metasomatic history of the Rodini mantle. Similar dates have been established for xenoliths from the Obnazhennaya trench (Kalashnikova et al., 2017).

Our 39Ar/40Ar data on micas often reveal complex spectral configurations. Micas from the Alakit field xenocrysts yield a series of peaks, beginning with the highest-temperature and oldest, which correspond to the Upper Proterozoic, Vendian, and Paleozoic, and only the lowest-temperature peaks with high Ca/K ratios correspond to kimberlite emplacement ages. Some peaks are possibly related to the thermal influence of the Vilyui plume (Kuzmin et al., 2012). The lowest temperature peaks are close in age to the time of kimberlite formation, which is confirmed by high 38Ar/39Ar ratios of gas released at the low-temperature stage, and can be used for dating kimberlites very approximately; however, the release of other gases at the low-temperature stages significantly increases the measurement error. All of them correspond to the interval 440-320 Mir, Internatsionalnaya, Ukrainskaya - 420, Yubileynaya - 342, and Botuobinskaya - 352); some determinations practically coincide with Rb/Sr ages (Griffin et al., 1999, Agashev et al., 2005, Kostrovitsky et al., 2008) and probably represent mixing lines. For many xenocrysts (Fainshteynovskaya, Ukrainskaya, Yubileynaya, and Krasnopresnenskaya pipes), the interval from 600 to 500 million years is manifested, which corresponds to the stage of breakup of Laurasia. 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 minerals.