URALIAN MAGMATISM - AN OVERVIEW

This paper is an attempt to summarize current knowledge of Uralian mag matism, focusing on those aspects relevant for understanding its geody namic evolution. The Urals consist of three tectonomagmatic domains: a Suture Sector, in the west, and two N-S imbricated Island-Are Contine ntal 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 ma ntle of the Russian plate to the suboceanic lithospheric mantle of the subducted Uralian palaeo-ocean. The two Island-Are Continental Sector s represent the transition from oceanic to continental environments in the middle and south Urals. Collisional magmatism started in the Silu rian 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 indic ates that the subducted slab was dipping eastward during that period. The Northern and Southern Island-Are Continental Sectors show many sim ilarities regarding the nature and spatial-temporal distribution of ma gmatism, but there are also some important differences which probably indicate somewhat different geodynamic regimes. In the Northern Sector , Carboniferous tonalite-granodiorite batholiths have features compati ble with an origin by melting of the oceanic crust in the subducted sl ab. In the Southern Sector, however, Carboniferous tonalite-granodiori te batholiths have features more consistent with a melting event withi n the lower continental crust above the subduction zone than with melt ing within the subducted slab. Upper Carboniferous-Permian granites ha ve high Sr-87/Sr-86(initial) in the north (e.g., 0.7120 in the Murzink a batholith) but very low Sr-87/Sr-86(initial) in the south (e.g., 0.7 045 in the Dzhabyk batholith) in spite of rocks from both batholiths b eing equally peraluminous and showing evidence of derivation by anatex is of metasediments. The low Sr-87/Sr-86(initial) at Dzhabyk might ind icate that in the Southern Sector the accretionary prism grew very rap idly, thus allowing involvement in upper Palaeozoic melting events.