Age restrictions and possible Provenance basal deposits of the Riphean Subpolar Urals

Abstract

Introduction: The isotope-geochronological data obtained in recent years for the Precambrian formations of the Lyapinsky meganticlinorium of the Subpolar Urals, where the most complete section of the Precambrian of the Timan-Northern Ural region is revealed, indicate the need for a significant adjustment of the existing schemes of the Precambrian stratigraphy of this region. The question of the lower age boundary of the basal deposits of the Upper Precambrian part of the section remains the most problematic. The article presents new results of U-Pb (LA-SF-ICP-MS) dating of detrital zircons from the rocks of the Puiva Formation in order to further substantiate the age of the basal deposits of the Riphean of the Subpolar Urals and clarify possible provenance of terrigenous material during their formation. Methodology: The research methods consisted in establishing the morphological features and internal structure of detrital zircons using a BioOptik SR-400 polarizing microscope and TESCAN VEGA3 LMH scanning electron microscopes with an X-MAX50 mm Oxford instruments energy-dispersive attachment and JSM-6400 with a Link energy spectrometer. Isotopic dating of zircons was performed by the U-Pb (LASF-ICP-MS) method based on an Element XR single-collector magnetic sector mass spectrometer with inductively coupled plasma and an UP-213 laser ablation device. Results and Discussion: As a result of the studies, the Late Riphean age of the basal deposits of the Upper Precambrian of the area under consideration (Puiva Formation) was confirmed and it was shown that at the initial stages of formation of the Upper Precambrian section, the role of crystalline basement rocks as provenance of terrigenous material was not great or was completely absent. The provenance of clastics to the subpolar Urals sedimentation basin occurred mainly from the Fennoscandian part of the Baltic. Starting from the late Puivin time, the role of local provenance gradually increased, while the role of Scandinavian crystalline complexes, on the contrary, decreased, which, in turn, could be associated with the regression of the sedimentation basin. Conclusions: In the Late Precambrian, the northeastern periphery of the East European Platform, including the Subpolar Urals, Northern and Middle Timan, belonged to the same continental margin. The time of its inception (about 900 Ma ago) is determined by the age of the Puiva Formation – the basal straton of the typical Upper Precambrian section of the Timan-Northern Uralt region.