LATE PALEOZOIC REMAGNETISATION AS AN INDEPENDENT INDICATOR OF TECTONIC PROCESSES IN THE SOUTHERN URALS

Abstract

Analysis of secondary magnetization components (Late Paleozoic remagnetization) makes it possible to trace the formation of the Southern Urals folded system. The paper presents new data on the Late Paleozoic remagnetization of rocks in the Southern Urals. The results of the paleomagnetic study of rocks in various structural zones of the Southern Urals, obtained since 2009, were revised and supplemented again to identify the remagnetization component. Combined analysis of the newly obtained results and previously published data on Late Paleozoic remagnetization shows that in the western segment of the western slope of the South Urals the intermediate-temperature magnetization component (ITC) was acquired prior to or at the initial stages of deformation. In contrast, the ITC observed in the eastern segment arose after folding. In the western part of the Magnitogorsk zone in Devonian-age rocks, the average for all sites is post-folding. Deformations here occurred long before the final stage of the development of the Urals, most likely in late Devonian — early Carboniferous. In the Magnitogorsk-Bogdanovsky graben, in the early Carboniferous rocks, ITC has arisen during the process of deformation or shortly before it and at its initial stages. The Late Paleozoic remagnetisation identified in the paleomagnetic records is regional in nature and probably reflects a collisional event of the final stage of the evolution of the Ural Paleocean. Collision processes which occurred in the Southern Urals from the Late Devonian until the Late Permian time had undoubtedly left their trace in the western structures (in present-day coordinates). Within the passive margin of Baltica the collision resulted in the formation of a lateral series of fold-and-thrust structures. They started from the Main Uralian Fault westward, with possible gradual termination of this process towards the Pre-Uralian Foredeep. Paleomagnetic results of this research work support these assumptions.