Structural Evolution and Deformation Stages of the Middle-Late Paleozoic Collisional Complexes of the Paleooceanic Sector of the Southern Urals

The structural studies of the structural-formational zones of the paleoceanic sector of the Southern Urals were conducted in detail. The formation sequence of mesostructural parageneses was established, allowing us to reconstruct the structural evolution of the region and develop a new model based on the metamorphic features of the East Ural megazone, in which the megazone is part of the Magnitogorsk island-arc system. The Magnitogorsk island-arc is partially ensialic and partially ensimatic. In the structural evolution of the paleooceanic sector of the Southern Urals during Middle-Late Paleozoic collisional events, D1 and D2 deformation stages were identified. The first stage of deformation, D1, was expressed in the formation of west-vergent isoclinal folds in the west of the Magnitogorsk megazone and east-vergent folds in its east. In the East Ural megazone, southeast- and west–southwest-vergent folds formed during the stage D1. The stage D1 marked the oblique sinistral collision of the Magnitogorsk island arc with the margin of the Baltica paleocontinent at the end of the Devonian. As a result of deformations occurring under sinistral transpression, a bivergent “palm tree” structure formed in the Southern Urals during the stage D1, with the formation of west-vergent F₁ folds (in the Aktau-Tanalyk zone) and east-vergent folds (in the eastern West Magnitogorsk and East Magnitogorsk zones), as well as southeast- and west–southwest-vergent folds (within the East Ural megazone). The second stage of deformation, D2, was associated with the late Paleozoic Ural intercontinental collision at the end of the Middle Carboniferous–Permian. The stage D2 marked the completion of the Main Ural Fault zone and the formation of north–west-vergent F₂ folds in the Aktau-Tanalyk zone. The  stage D2 includes the formation of west- and northwest-vergent folds in the East Mugodzhar megazone and all structures of the Trans-Ural megazone. The formation of late, predominantly sinistral strike-slip folds with steeply dipping hinges corresponded to the stage of post-collisional strike-slip movements that completed the structural and geodynamic evolution of the Ural Paleoocean.