Basalts of the riphean sequence of the Bashkir meganticlinorium (southern Ural): new ¹⁴⁷Sm-¹⁴³Nd and Rb-Sr ID-TIMS isotopic constrains

The first results of ¹⁴⁷Sm-¹⁴³Nd and Rb-Sr ID-TIMS isotope-geochronological comparative study of twelve samples of volcanic rocks of the Bashkir meganticlinorium are presented, for which U-Pb SHRIMP-II dating was previously carried out using zircons extracted from these samples, which revealed the dominance of Paleozoic ages among three event-stratigraphic levels in the Riphean of the Southern Urals. New ¹⁴⁷Sm-¹⁴³Nd and Rb-Sr ID-TIMS isotope data showed that the evolution of volcanics occurred as a result of crust-mantle interaction. In the Taratash anticlinorium, Nd model ages (T_DM) of 2302–2540 Ma) of volcanics are regarded as the ages of the protolith, characterized by ε_Nd(t) values: from –17.4 to –20.5. In the Yamantau anticlinorium, the T_DM value (2033 Ma) of Paleozoic volcanics indicates a younger (Paleoproterozoic) substrate. Minimum Nd model ages (T_DM = 1160–1233 Ma) were determined for Paleozoic volcanics spatially associated with metabasalts of the Igonino magmatic event (707–732 Ma) in the Tirlyanskaya syncline. The lowest values of ε_Nd(t) (–3.2, –0.9, –0.7), indicating a decrease in the proportion of the crustal component relative to the mantle material, were obtained in Paleozoic metabasalts in the Tirlyanskaya syncline on the eastern wing of the Bashkir meganticlinorium, which may be due to activation of plume processes in the East of the folded mountain structure. Thus, Rb–Sr and ¹⁴⁷Sm-¹⁴³Nd ID-TIMS isotope systematics of the studied volcanics make it possible to expand the understanding of mantle-crustal phenomena within three event-stratigraphic levels of the Riphean of the Southern Urals.