PROVENANCE OF THE BOEVAYA GORA SECTION (SOUTHERN CIS-URALS) AT THE PERMIAN-TRIASSIC BOUNDARY AS A CONSEQUENCE OF THE PALEO-URALS EVOLUTION

On one hand, heavy minerals of terrigenous rocks make it possible to obtain unique information on configuration of the direction of clastic sediment transport into the basin and on the other to reconstruct the time for erosion of petrocomplexes of the provenances. In order to reconstruct the paleogeographic setting of the Southern Cis-Urals and the orogenic evolution of the Paleo-Urals at the Permian-Triassic boundary, the authors evaluated the composition and stability of the provenances for the Permian-Triassic terrigenous rocks of the Boevaya Gora section (Orenburg region) based on the analysis of the heavy minerals – zircon and garnet. Heavy mineral samples were taken from sandstones of three stratigraphic levels: Upper Permian, Lower Triassic, and paleontologically barren interval in the immediate vicinity of the Permian-Triassic boundary. The results of U-Pb LA-ICP-MS dating of detrital zircon and analysis of garnet end-members proportions have shown that the provenances covered the petrocomplexes of the tectonic zones of the Ural foldbelt – Uraltau, Main Uralian fault and Magnitogorsk, which allows reconstructing the Paleo-Urals orogen main-watershed axis position at the Permian-Triassic boundary east of that of the present day. It is shown that the source areas near the Boevaya Gora section remained stable during the whole time of accumulation of the studied part of the section. This conclusion is confirmed by the results of measuring the anisotropy of magnetic susceptibility in the studied rocks, which also suggest the strengthening of hydrodynamic regime in the terminal Permian and predominantly meridional direction of the clastic sediment transport.