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The large massifs of ancient granitoids of the South Yenisei Ridge are divided into three complexes that differ in the geological, geochemical, and geochronological features. The Tarak massif consists of two complexes of different ages: the S–A-type porphyritic granitoids (collisional) of the Tarak complex (1.84 Ga) and the A-type subalkaline granites (anorogenic) of the Telkun complex (1.76 Ga). The magmatic crystallization of gneiss granites of the Posolnenskii complex is interrelated with the late stage of metamorphism and falls into the age interval between the above two complexes (1789.8 ± 8.9 Ma). Metamorphic transformations of the enclosing formations are recorded by the presence of small bodies of charnockitoids with dates of 1.84 and 1.73 Ga. [ABSTRACT FROM AUTHOR]

The paper presents the results from the first 40Ar/39Ar isotope dating of eleven mafic sills recovered by deep boreholes in the eastern Siberian Platform. Most of the dates are assigned to the Devonian magmatic stage (357–379 Ma). The two previously established pulses of dike magmatism in the Yakutsk-Vilyui large igneous province also fall within this range. The ages of 397.6 ± 4.3 and 406.2 ± 5.6 Ma obtained in this study imply one more pulse of magmatism at the Emsian-Eifelian boundary. The chemical composition of the dolerites corresponds to that of the derivatives of garnet peridotite. Estimates of the depth of the melting center suggest its location both inside the mantle lithosphere and at the lithosphere-asthenosphere boundary. The Mid-Triassic age (232.6 ± 7.4 Ma) of the sill recovered by the Morkoka borehole implies the manifestation here of the second pulse of trap magmatism related to the Siberian plume. [ABSTRACT FROM AUTHOR]

Geochemical and isotope–geochronological evidence of Late Riphean intraplate magmatism within the Chernorechenskii massif at the western margin of the Siberian Craton has been obtained. These rocks crystallized from high-temperature and water-unsaturated magmas with a high content of alkalis, iron, and most noncoherent elements, which is typical of anorogenic A-type granites of intraplate settings. Their U–Pb age is 723 ± 6 Ma, coeval to the Franklin rifting event widespread in the north of Laurentia, which is associated with the break-up of Rodinia. The simultaneity of the magmatic activity and concomitant rifting, as well as a similar sequence of analogous tectonothermal events at the Arctic margin of Rodinia, confirms modern paleoreconstructions, suggesting the territorial proximity of Siberia and the cratons of the North Atlantic at that time. [ABSTRACT FROM AUTHOR]

/Ar isotopic ages of magnesioarfvedsonite (725.9 ± 6.3 myr) and phlogopite (637.6 ± 5.7 myr) from carbonatites of the Penchenga rock complex located in the South Trans Angara segment of the Yenisei Ridge have been determined. Based on this, the formation of the rock complex is associated with the start of the period of Neoproterozoic (725-700 Ma) rifting and alkaline magmatism in the region, the latter being associated with the former. The appearance of zones penetrable for magma of the 'disseminated' rifting type is associated with the development of late collision shear dislocations in a consolidated marginal continental crust. The primary melts had a plume nature, but matter from different mantle sources intermixed in the environment of the changing geodynamic regime. The younger age of the mica was apparently caused by partial remelting of carbonatites under the influence of heat and fluids generated during the formation of the adjacent large granite massif of a younger age. [ABSTRACT FROM AUTHOR]