Paleoproterozoic Rock Metamorphism of the Nyartin Complex, the Subpolar Urals

Abstract

In the Urals, Archean and Paleoproterozoic formations are revealed as a part of some polymetamorphic complexes which crop out onto the day surface in relatively small tectonic blocks (up to the first thousand square kilometres in area). Belonging of rocks composing polymetamorphic complexes within the Western tectonic zone of the Urals, which located west of the Main Ural Fault, to the Archean-Paleoproterozoic section is most reliable. These complexes are interpreted as fragments of the heterogeneous crystalline basement of the Ural part of the East European craton. Nevertheless, belonging of only two South Ural complexes: the Taratash and Aleksandrov to the Archean-Paleoproterozoic section causes no special disputes due to the relatively weak geochronological study of the polymetamorphic formations. They are framed by the weakly metamorphosed Lower Riphean deposits; reliable geochronological data are obtained on them, which unambiguously indicate the early Precambrian age of rock metamorphism. The existing Early Precambrian dates (with the prevalence of Late Precambrian and Paleozoic ages) for other Ural polymetamorphic complexes are interpreted in different ways. Therefore, their attachment to the Lower Precambrian section is disputed by many researchers. Taking into account the already available data and the first results of mass U-Pb dating of metamorphogenic zircons from gneisses of the Nyartin polymetamorphic complex in the Subpolar Urals, the Paleoproterozoic age of the earliest stage of rock metamorphism is substantiated in the paper. This gives grounds for the conclusion that this geological object belongs, as well as the Taratash and Alexandrov complexes in the Southern Urals, to the Lower Precambrian formations involved into the Uralides’ structure.