Литосфера (Jun 2019)
Subduction, collision and plumes in the epoch of the Late Paleozoic magmatism of the Magnitogorsk zone (the Southern Urals)
Abstract
Subject. A systematization of Late-Paleozoic magmatic formations of the Magnitogorsk zone of the Southern Urals in the process of an accretion of the Magnitogorsk paleoarc to the margin of the East European continent (EEC) with formation in Famenian and Carboniferous active continent margin of South-Uralian accretionary-collisional belt was given in the work. Materials and methods. A generalization of published and manuscript materials characterizing magmatism and ore-mineralization of Magnitogorsk zone for the Devonian-Carboniferous-Permian time carried out, additional investigations of chemical composition of rocks (XRF, ISP-MS) characterizing process of accretion, subduction and plume activity, microelement distribution in them was made, the composition of rock-forming and accessory minerals (EPMA) was studied. Results. It is found that the South-Uralian accretionary-collisional belt was beginning to form in the late phase of the development of the Magnitogorsk island arc in the process its collision with EEC margin with formation in the Frasnian and Carboniferous of active continental margin. The products of Late-island-arc volcanism are represented by the porphyrite formation and in the eastern frame of the arc - by subalkaline monzonite-shoshonite-latite volcanic-intrusive association with intermediate characteristics between the subductional and interplate formations. Synchronously with them, in the backarc setting, picrite and meymechite volcanics − derivatives of a mantle plume are formed. In process of substitution of tectonic-magmatic regime from island-arc to margin-continental intraplate-type mantle series were forming. During this period, hot asthenospheric diapirs (plumes) were rising to the bottom of new-formed (accreted) margin-continental lithosphere. Along with the magmatic associations of intraplate type and rock series of intermediate geochemical type, this geodynamic situation in the Southern Urals is characterized by a presence of great volumes of mantle-crust granitoids of gabbro-tonalite-granodiorite-granite type, that were formed with a manifold manifestation of anatexis in a time interval of 365-290 Ma. Conclusion. On the whole the originality of Magnitogorsk zone geological history in the Devonian and Carboniferous, peculiarities of magmatic complexes formed here due to various geodynamic settings, are making this zone an extraordinary interesting and important object to study of processes of plume-lithosheric and mantle-crust interaction.
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