Nyartin metamorphic complex in the Subpolar Urals: the primary nature of metamorphic rocks and paleogeographic conditions of formation of the protoliths

The article presents the results of petrogeochemical studies of rocks of the Lower Proterozoic gneiss-migmatite Nyartin complex in the Subpolar Urals, the material composition of which is still relatively poorly investigated. The considered complex is composed of polymetamorphic formations; this makes the using of traditional petrographic and lithologic methods for identification of their primary nature very difficult or impossible. In this case, the decisive importance for establishing the primary substrate of metamorphites is their chemistry. Reconstruction of the original composition of metamorphites was carried out, and the paleogeographic conditions of protolith formation were performed for the first time on the basis of interpretation of previously published papers on the chemical and mineralogical composition of rocks, and new petro- and geochemical data. It was found that the igneous rocks of andesite-basaltic set of tholeiite and calc-alkaline series were initial formations for orthometamorfites. Polymicticaleurolites, greywacke and quartz-feldspathic sandstones were substrate for metaterrigenous rocks. In turn, the igneous rocks of basic and acid composition as well as recycled sediments with different degrees of petrochemical maturity were original material for aleurolites and sandstones. The formation of volcanic-sedimentary substrate of the Nyartin metamorphites took place in the dry cold climate at quite strongly rugged topography.