Lower proterozoic metapelites in the northern Yenisei Range: Nature and age of the protolith and the behavior of material during collisional metamorphism |
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Authors: | I I Likhanov V V Reverdatto |
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Institution: | 1.Institute of Geology and Mineralogy, Siberian Branch,Russian Academy of Sciences,Novosibirsk,Russia |
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Abstract: | The variable P-T metamorphic conditions studied in the Fe-Al metapelites of the Karpinskii Range Formation are regarded as typical of collision-related
metamorphism in the trans-Angara part of the Yenisei Range. Recently obtained geochronologic (SHRIMP-II U-Pb zircon dating)
and geochemical data on the distribution of major and trace elements are used to reproduce the composition of the protolith,
the facies conditions under which it was formed, the tectonic setting, and the age of the eroded rocks. The metapelites are
determined to be redeposited and metamorphosed material of Precambrian kaolinite-type weathering crusts of predominantly kaolinite-illite-montmorillonite-quartz
composition. The protolith of the rocks was formed via the erosion of Lower Proterozoic granite-gneiss complexes of the Siberian
craton (dated mainly within the range of 1962–2043 Ma) and the subsequent accumulation of this material in a continent-marginal
shallow-water basin in a humid climate and tectonically calm environment. These results are consistent with data of lithologic-facies
analysis and geodynamic reconstructions of the Precambrian evolution of geological complexes in the Yenisei Range. Mass-transfer
analysis with the use of the evaluated rock compositions and calculated chemical reactions indicates that the differences
in the REE patterns of metapelites from distinct zones can be explained mostly by the chemical heterogeneity of the protolithic
material and, to a lesser extent, by metamorphic reactions at a pressure increase. |
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