ABSTRACT
As was shown in the previous chapters, among the problems related to geologic structure and formation conditions of mafic-ultramafic massifs, spatiotemporal relationship between the ultramafic and gabbroid bodies composing such massifs and their dating remain a hotly discussed subject. For quite a long time, these issues have been dealt with mainly on the basis of structure-geological and petrographical research methods. As geochemical and especially isotope techniques were applied far more rarely, it has not always been possible to establish with certainty age relations in ultramafic and gabbroid bodies composing such massifs. In recent years, greater possibilities for solving such problems have been provided with the development of isotope methods for dating rocks and minerals, specifically, the U-Pb method for analysis of individual zircon grains with the use of SHRIMP II multicollector secondary-ion mass-spectrometers. Afterward, along with the age determinations made on zircons from granitoids [Rudnev et al., 2012], alkaline igneous rocks [Vrublevskii et al., 2014], and metamorphic rocks [Kaulina, 2010; Turkina et al., 2014], the zircons from gabbroids [Krasnobaev et al., 2007; Bortnikov et al., 2008; Tsukanov and Skolotnev, 2010; Skolotnev et al., 2010; Ledneva et al., 2012; etc.], ultramafic rocks [Knauf, 2008; Fershtater et al., 2009; Malitch et al., 2009; Lesnov et al., 2010a; Badanina and Malich, 2012; Oh et al., 2012; Ronkin et al., 2013; etc.] and chromitites [Savelieva et al., 2006, 2007] began to be more widely used for such estimates.
