Evolution of volcanism and geodynamic settings in the Sakmara zone of the Southern Urals in the early Paleozoic

Research subject. Northern part of the Sakmara zone of the Southern Urals, represented by the Krakinsko-Mednogorsk paleovolcanic belt, including the Mednogorsk ore district and the Blavinsko-Komsomolskoye ore field. Aim. To reconstruct the paleogeodynamic settings during the Cambrian–Early Devonian in the Sakmara zone. Methods. An analysis of geological, petrogeochemical, structural-tectonical, and paleovolcanological data obtained by the authors and those reported in literature using conventional and new petrogeochemical diagrams. Results. The following stages of tectono-magmatic evolution in the Sakmara zone were distinguished: (1) Cambrian–Early Ordovician, continental rifting; (2) Early–Middle Ordovician, oceanic spreading; (3) Early Silurian, suboceanic rifting, serpentinite protrusions, edaphogenic breccias, siliceous rocks (starting a subduction zone); (4) Late Silurian–Early Devonian, island-arc basalt-rhyolite volcanism and sulfide deposits, volcanism of the shoshonitic and alkaline series, formation of the rear island arc. The Sakmara zone features no analogues of boninite volcanism (D1e2) typical of the West Magnitogorsk zone, which indicates the absence of signs of the volcanogenic strata of the Voznesensk–Prisakmar zone being pushed into the Sakmara structural zone. Conclusions. (1) In the Cambrian–Early Devonian, volcanogenic and volcanogenic-sedimentary formations and strata of the Sakmara zone formed a megacycle, starting with the processes of continental and oceanic rifting, which led to the subduction process and generation of the frontal and rear island arcs. (2) The volcanism in the Sakmara and Voznesensk–Prisakmar zones developed autonomously, without tectonic transfers from east to west. (3) The partial coincidence of the formation age of the Chanchar (D1lh–e1) complex of the Sakmara zone and the Turin complex (S2p–D1lh) of the Tagil zone suggests the presence of a reduced continuation of the western wing of the Tagil zone in the Sakmara zone.