Basalts of the Riphean Sequences of the Bashkirian Meganticlinorium, South Urals: New 147Sm‒143Nd and Rb‒Sr ID-TIMS Isotopic Constraints

Abstract

The first results of ¹⁴⁷Sm‒¹⁴³Nd and Rb‒Sr ID-TIMS isotopic–geochronological results of a comparative study of 12 samples of volcanic rocks of the Bashkirian Meganticlinorium, which were previously dated by zircons from these samples using the U‒Pb SHRIMP-II method showing the predominance of the Paleozoic ages among three stratigraphic levels with Riphean magmatic events in the South Urals, are presented. New ¹⁴⁷Sm‒¹⁴³Nd and Rb‒Sr ID-TIMS isotopic data showed that the volcanic rocks evolved as a result of crustal–mantle interaction. The Nd model ages (T_DM) (2302–2540 Ma) of volcanic rocks of the Taratash Anticlinorium represent the ages of the protolith characterized by ε_Nd(t) values from –17.4 to –20.5. The T_DM value (2033 Ma) of the Paleozoic volcanic rocks of the Yamantau Anticlinorium indicates a younger (Paleoproterozoic) substrate. The minimum Nd model ages (T_DM = 1160–1233 Ma) are determined for the volcanic rocks, which are spatially related to metabasalts of the Igonin magmatic event (707‒732 Ma) in the Tirlyan Syncline. The smallest ε_Nd(t) values (–3.2, –0.9, –0.7) indicating a decrease in the amount of a crustal component relative to the mantle material are determined for the Paleozoic metabasalts in the Tirlyan Syncline in the eastern wing of the Bashkirian Meganticlinorium, which is probably related to the activation of plume processes in the eastern part of the orogen. The Rb‒Sr and ¹⁴⁷Sm‒¹⁴³Nd ID-TIMS isotopic systematics of the studied volcanic rocks expands our understanding of mantle–crustal interactions within three stratigraphic levels with Riphean magmatic events of the South Urals.