Parautochthonic paleooceanic and island-arc complexes of the Southern Urals

Abstract

Research objects. Paleozoic (Ordovician–Middle Devonian) volcanic-sedimentary complexes of the contiguous Sakmara and Mugodzharskaya structural zones of the Southern Urals, which have a paleo-oceanic and island-arc nature. Мaterials and methods.The work was carried out on the basis of many years of personal research of the author with the involvement of literature data on other folded zones of the Southern Urals. Main results. In the early Devonian, the first intense clustering of different facies complexes of rocks took place, which determined the tectonic face of the modern western part of the fold belt. The uniformity and set of Paleozoic formations in all structures of the Urals are maintained along its entire strike and are not repeated in neighboring zones.The drilling data showed the primary character of bedding of the rocks of the Upper Devonian Zilair Formation on the dislocated volcanogenic-sedimentary deposits of the Lower-Middle Paleozoic. Thrust contacts are observed only in the marginal parts of the zone. The almost textbook views on the cover bedding of the Kraka and Kempirsai hyperbasite massifs are in contradiction with the data on the presence of “roots” up to 4–8 km deep in them. By the beginning of the Devonian, the Kempirsai massif was located within the Sakmara zone and was “cross-linked” with the surrounding effusive rocks of the Middle Ordovician by gabbro-diabase dykes. According to the results of seismometric studies, features of similarity of the deep structure of the base of the Sakmara zone with the structure of the Magnitogorsk-Mugodzharskaya zone, which also revealed a melanocratic basement, have been established. Conclusions. The formed structural zones of the Southern Urals are distinguished by a set of rocks of the same age, their stratigraphic range, and the autonomy of feeding areas. These differences have survived to this day. All subsequent tectonic episodes, including the sharpening epochs, only complicated the appearance and structure of the Southern Urals, without changing the relative position of structures that arose in the Early Devonian. There was no transfer, swarming of rocks from one zone through another in any of the subsequent stages of compression. The Early Devonian stage was the first, but at the same time the most intense, which determined the tectonic face of the modern western part of the Urals.