Structural evolution of the southern part of the Suvanyak metamorphic complex and its framing (Southern Urals)

Abstract

The mesostructural parageneses of the Suvanyak metamorphic complex that composes the western part of the Uraltau zone (antiform), as well as the complexes that compose the western side of the Zilair synclinorium and the Sakmara zone (allochthon), adjacent to the Uraltau zone, are studied. The sequence of their formation and the structural evolution of the studied region have been established. It is shown that in the deformational history of the studied region, associated with the Late Paleozoic intercontinental collision, which assured the geodynamic evolution of the Ural paleo ocean, three stages of deformation are distinguished. The first stage of the D1 deformation, expressed in the formation of the F1 folds and associated thrusts of western and southwestern vergence, is associated with the movement of the Sakmara allochthon in an eastern direction. The second stage of the D2 deformation is marked by the formation of the F2 folds and folded thrusts of eastern and northeastern, less often southeastern vergence, due to back thrusting processes. Back thrusting occurred under conditions of sublatitudinal compression directed from east to west, while the entire package of allochthonous plates did not shift to the west. The reason for this could be the presence of a significant obstacle that did not allow allochthon to carry out further advance in the western direction. With continued pressure from the east, from the volcanogenic formations of the former Magnitogorsk island arc and the impossibility of moving to the west, the more eastern complexes moved under the more western ones, and the latter, respectively, moved eastward. The third stage of deformation D3, marked by the formation of asymmetric S folds with steeply dipping hinges, corresponds to the post-collision strike-slip movements widespread throughout the Ural folded region, which finally shaped the structural appearance of the region.