Uralian magmatism: an overview

This paper is an attempt to summarize current knowledge of Uralian magmatism, focusing on those aspects relevant for understanding its geodynamic evolution. The Urals consist of three tectonomagmatic domains: a Suture Sector, in the west, and two N-S imbricated Island-Are Continental Sectors in the east. The Suture Sector comprises lower Palaeozoic mafic-ultramafic complexes which show eastward impoverishment in LILE, thus reflecting the transition of the subcontinental lithospheric mantle of the Russian plate to the suboceanic lithospheric mantle of the subducted Uralian palaeo-ocean. The two Island-Are Continental Sectors represent the transition from oceanic to continental environments in the middle and south Urals. Collisional magmatism started in the Silurian and persisted till the Permian, migrating progressively eastward and increasing in abundance of LILE and Sr-87/Sr-86(initial). Magmatic polarity is very similar to that of modern subduction zones and indicates that the subducted slab was dipping eastward during that period. The Northern and Southern Island-Are Continental Sectors show many similarities regarding the nature and spatial-temporal distribution of magmatism, but there are also some important differences which probably indicate somewhat different geodynamic regimes. In the Northern Sector, Carboniferous tonalite-granodiorite batholiths have features compatible with an origin by melting of the oceanic crust in the subducted slab. In the Southern Sector, however, Carboniferous tonalite-granodiorite batholiths have features more consistent with a melting event within the lower continental crust above the subduction zone than with melting within the subducted slab. Upper Carboniferous-Permian granites have high Sr-87/Sr-86(initial) in the north (e.g., 0.7120 in the Murzinka batholith) but very low Sr-87/Sr-86(initial) in the south (e.g., 0.7045 in the Dzhabyk batholith) in spite of rocks from both batholiths being equally peraluminous and showing evidence of derivation by anatexis of metasediments. The low Sr-87/Sr-86(initial) at Dzhabyk might indicate that in the Southern Sector the accretionary prism grew very rapidly, thus allowing involvement in upper Palaeozoic melting events.