Age Boundary of the Upper Precambrian Basal Rocks of the Polar Urals: Results of U–Pb (LA-ICP-MS) Dating of Zircon.

The lower age boundary of the Upper Precambrian basal sequences of the Polar Urals (Nyarovei Group) is determined on the basis of mass U–Pb (LA-ICP-MS) dating of detrital zircon. The upper boundary of the basal sequence is determined from U–Pb (LA-ICP-MS) dating of zircon from overlapping volcanic rocks of the Nemyurgan Formation. It is thus established that the Nyarovei Group formed during a narrow period in the end of the Late Riphean (~750–650 Ma). The recognition of the group as a Middle Riphean straton is erroneous. A dominant role in the formation of the Nyarovei Group was played by erosion products of adjacent blocks of crystalline rocks, the fragments of which probably include the polymetamorphic complexes in the Kharbei–Marunkeu Anticlinorium of the Polar Urals. [ABSTRACT FROM AUTHOR]