Вестник МГТУ. 2018, том 21, № 1.

Вестник МГТУ. 2018. Т. 21, № 1. С. 61–79. DOI: 10.21443/1560-9278-2018-21-1-61-79 63 The melting degree of sedimentary rocks abruptly increases below the critical level of continental geotherm intersection with a curve of sedimentary substance melting start. That is why the differentiation of formed melts and gravity segregation shall take place at deeper depths. Heavy iron and sulphide fractions sink and ultimately settle down to the depth of convecting mantle to be gradually assimilated by its substance. Light fractions composed of separated fluids, carbonate, and silicate melts cannot rise up and are accumulated (preserved) in the lower horizons of continental plates (Fig. 3, 4), gradually forming hearths of alkaline-ultramafic, carbonatite, and lamproite-kimberlite magmas. Fig. 2. Thermodynamic conditions of the alkaline-ultramafic and kimberlite magma melting [11]: 1: juvenile mantle (basalt) melts area of existence; 2: alkaline-ultramafic and alkaline-carbonatite melts area of existence; 3: area of existence for diamond-bearing deep-seated lamproite, kimberlite, and calcareous carbonatite melt; T m : mantle temperature; T sm : mantle substance solidus temperature; T be : basalt to eclogite transition temperature; T γα : graphite to diamond transition temperature; T Lk (0): modern continental geotherm; T Lk (1.8): ancient continental geotherm at 1.8 Ga; L pl , L px , and L gr : area of stable existence for plagioclase, pyroxene, and garnet lherzolite; T ss : water-saturated sediments melting temperature Рис. 2. Термодинамические условия выплавления щелочно-ультраосновных и кимберлитовых магм [11]: 1 – область существования ювенильных мантийных (базальтовых) расплавов; 2 – область существования щелочно-ультраосновных и щелочно-карбонатитовых расплавов; 3 – область существования алмазоносных глубинных расплавов лампроитов, кимберлитов и кальциевых карбонатитов; T m – температура мантии; T sm – температура солидуса мантийного вещества; T be – температура перехода базальт – эклогит; T γα – температура перехода графит – алмаз; T Lk (0) – современная континентальная геотерма; T Lk (1,8) – древняя континентальная геотерма на момент времени 1,8 млрд лет назад; L pl , L px и L gr – области устойчивого существования плагиоклазовых, пироксеновых и гранатовых лерцолитов; T ss – температура плавления водонасыщенных осадков In the transition zone from the continental lithosphere bottom to the convecting mantle at similar chemical medium parameters, no significant jumps of temperature and density are observed. This border rather marks the phase transition of the mantle substance from hard to plastic state. It shall be expected that the