A Composite Structure of the Bashkir Anticlinorium: Insights from Detrital Zircons Search in Ordovician Sandstones of the Uraltau Uplift, Southern Urals

Abstract

The Bashkir anticlinorium is an extensive outcrop of Precambrian rocks within the Southern Urals, located near the south-eastern edge of the East European Platform (EEP). The Bashkir anticlinorium is subdivided by the Zyuratkul fault into two parts: the Bashkir (western part) and Uraltau (eastern part) Uplifts. The Late Precambrian strata of the Bashkir Uplift were formed at a passive margin of the Volga-Uralian part of Baltica. In contrast, the Late Precambrian strata of the Uraltau Uplift were formed far from its present-day location. Later, the Uraltau Uplift block moved along the Zyuratkul fault to its present-day position with a large-amplitude displacement. This study presents the first results of the integrated (U-Pb age, Hf-isotope and trace-elements contents) study of detrital zircons (dZr) from the Upper Ordovician sandstones of the northern part of the Uraltau Uplift. The integrated characteristics of the studied dZr provide new constraints for their primary sources. A comparison of obtained data with rock types, U-Pb and Hf model ages of the crystalline complexes of the of Volga-Uralia basement, as well as characteristics of dZr from Late Precambrian strata of the Bashkir Uplift and Kazakhstan have revealed that the Upper Ordovician sandstones of the northern part of the Uraltau Uplift contain dZr “alien” to crystalline complexes of Volga-Uralia, Kazakhstan, and Late Precambrian strata of the Bashkir Uplift. The sources of these “alien” dZr were other crustal blocks. A very high similarity of the age spectra of dZr from the Upper Ordovician sandstones, which overlain the Late Precambrian rocks units of the Uraltau and Bashkir Uplifts allows concluding that the spatial conjunction of the Bashkir and Uraltau Uplifts had occurred before the Late Ordovician time. Post-Upper Ordovician sedimentary complexes of the Bashkir and Uraltau Uplifts were sourced from identical feeding provinces in the same sedimentary basin, sealing its composite pre-Upper Ordorvician heterogeneous basement.