Stages of Deformation and Formation of the Middle-Late Paleozoic Collision Structures of the Paleocontinental Sector of the Southern Urals

The article presents the results of structural studies in the areas of distribution of fold structural complexes that formed the main structural-formational zones of the paleocontinental sector of the Southern Urals. The sequence of formation of mesostructural parageneses of these complexes is considered, and the Middle-Late Paleozoic structural evolution of the study region is determined. Structural evidence of the previously assumed existence of the united Sakmara‒Kraka allochthon is obtained. The three stages of deformation, which are distinguished in the Hercynian deformation history of the Southern Urals region, are established. At the first stage of deformation (D1), the formation of F1 folds of southeastern and (rarely, northwestern) vergence occurred. Stage D1 is associated with the oblique left-lateral collision of the Magnitogorsk island arc with the margin of the Baltica paleocontinent. The second stage of deformation (D2) is marked by the formation of F2 folds and associated thrusts of western and southwestern vergence. Stage D2 is associated with the movement of the Sakmara‒Kraka allochthon in the western direction. At the third stage of deformation (D3), the formation of F3 folds and cofold thrusts of eastern and northeastern vergence occurred. Stage D3 is due to the processes of back thrusting, which occurred under conditions of sublatitudinal compression directed from east to west, when the package of allochthonous plates did not shift to the west. At the final stage of deformation, left-lateral folds with steeply dipping hinges were formed, which corresponds to postcollisional strike-slip movements. That stage completed the main phase of structural evolution of the Southern Urals region.