Geodynamic and paleogeographic features of the formation of metaterrigenous deposits at the base of the Paleozoic section of the ridge Maldynyrd (Subpolar Urals)

Abstract

Introduction: The article presents the results of the geochemical study of metaterrigenous deposits at the base of the Paleozoic section of the Maldynyrd range (Subpolar Urals). We studied the distribution features of petrogenic, rare earth, and rare elements in various lithological types of rocks in the foundation/cover zone of contact in order to trace changes in the material composition of Lower Paleozoic deposits from bottom to top along the section and to clarify the geodynamic and climatic conditions of sedimentation and nutrition sources. Interest in these studies is explained, among other things, by the fact that gold ore occurrences discovered at the end of the 20th century were associated with the contact of Riphean-Vendian and Paleozoic deposits in the examined area.

Methods: The content of rock-forming oxides in the rocks was determined by the gravimetric chemical method, while the content of rare and rare earth elements was identified using an Agilent 7700x inductively coupled plasma mass spectrometer. The phase composition of the rocks was determined on a Haoyuan DX-2700BH X-ray diffractometer.

Results and discussion: Geochemical characteristics of deposits of various genetic types in the foundation/cover zone of contact from the central part of the Maldynyrd range (Subpolar Urals) showed that the maximum content of rare earth elements was found in diaspore-bearing pyrophyllite-muscovite shales and minimal content was found in metagravels of the Obeiz formation. CIA, CIW, and ICV values indicated the connection between pyrophyllite-muscovite shales and the weathering crust. The position of the figurative points on the ICV–CIA diagram demonstrated the presence of moderately weathered magmatic formations of acidic and mafic compositions in the Obeiz metagravels. The figurative composition points of all metaterrigenous formations were located in the fields of the passive continental margin in the reconstruction diagrams of paleogeodynamic conditions.

Conclusions: The conducted studies showed that the substrate for the formation of the pyrophyllite-muscovite shales at the base of the Paleozoic section was the weathering crust of the acidic volcanics of the upper subformation of the Sablegorskaya formation. Diaspore-bearing muscovite-pyrophyllite shales preserved and concentrated the geochemical features of the underlying acidic volcanics. Alkesvozhskaya rocks often contain redeposited mica material from the underlying metamorphosed weathering crust and fragments of acidic volcanic rocks themselves altered to varying degrees. The destruction products in the sediments of the Obeiz formation contain magmatic rocks of acidic and basic composition.