| Реферат: | eng: The paper reports data on metapelites (gneisses and crystalline schists) from various Early Precambrian lithostratigraphic units of the Yenisei Range (Kan and Yenisei complexes, Garevka Unit, and Teya Group). A representative selection of 57 samples from the examined vertical section were analyzed for major oxides, LILE, transition elements, HFSE, REE, radioactive elements, and other trace and minor elements. The most important distinctive geochemical feature of metapelites composing most of the vertical section is their elevated concentrations of Al, which are higher than in the Post-Archean Australian Shale (PAAS), K, Rb, Ba, Ga, Sc, Pb, Th, Nb, Y, and REE. These data and the systematics of elements in certain discriminant diagrams testify that the metasedimentary complexes in the sedimentation basin and the rocks associations composing the erosion area (crystalline massifs of the ancient basement of the Siberian craton) were strongly geochemically differentiated and mature. The composition of the eroded crustal material was close to the average composition of the post-Archean continental crust and PAAS. The metapelites of the Kuzeeva Unit in the Kan Complex and Penchenginskaya Formation in the Teya Group were the only ones that could have basic rocks as an additional source of material, as also follows from the elevated Cr concentrations of the rocks and their REE systematics. The three types of REE patterns of the metapelites largely correspond to the composition of the rocks that composed the ancient drainage areas and the degrees of the differentiation and averaging of their terrigenous material. The first predominant type corresponds to PAAS and the averaged composition of the upper continental crust. The second and third types of the REE patterns with high and low La N/Yb N ratios, respectively, and with or without negative Eu anomalies provide evidence of the contribution of tonalite-trondhjemite-granodiorite (TTG) or basite sources typical of granite-greenstone provinces. In certain diagrams, the compositional fields of Early Precambrian metapelites in the Yenisei Range almost exactly coincide with the compositional fields of regional fine-grained Riphean terrigenous rocks. This suggests that the Late Precambrian sedimentary rock sequences inherited their geochemical features from more ancient rocks. The reproduced ancient geodynamic environments in which the Early Precambrian metaterrigenous complexes of the Yenisei Range were accumulated correspond to ensialic continental marginal basins. The rocks of the Kan and Yenisei complexes and the Garevka Unit were formed mostly on active continental margins and, less frequently, on passive margins. The protoliths of metasedimentary rocks of the Teya Group were accumulated in a subplatform environment at a passive margin. © 2012 Pleiades Publishing, Ltd.
|