Литосфера (Apr 2017)
Riphean magmatism and ore formation, preceding the disclosure of the Uralian Paleoocean (western slope of the Southern Urals)
Abstract
The analysis of the evolution of composition and mineral occurences of the Low and Middle Riphean magma-tic rocks from the riftogenic structures of the Bashkirian anticlinorium involving of some neighboring structures from the western slope of the Southern Urals was produced. In time the evolution is following: from rocks having the geochemical features as OIB (trachybasalts of the Sibirka deposit) and rocks as E-MORB (volcanic rocks of the Mashak formation, basic and acid rocks of the Kusa-Kopan’ complex, dyke swarms etc.) to rocks with N-MORB pecularities (Nazyam metabasites). This evolution agrees with the change of isotopic and geochemical parameters. Initial ratios of Nd isotopes of magmatic rocks and their ore-metasomatic haloes vary from the negative values noting to the formations from mature continental crust (gabbro and Ti-Mt-Ilm ores of Kusa-Kopan’ complex deposits) to positive values (εNd +4…+5 and more of Nazyam amphibolites), it reflects the increase of the depletion degree of the Riphean-Vendian lithospheric mantle and the evolution of magmatic and fluid sources in time. Described regularity for the age interval 1750-1200 Ma as well as data on Nd and Sr isotopes for magmatic rocks of continental crust formation of Uralian epioceanic orogen indicate the possible disclosure of the oceanic basin to the east of the East European platform during the Middle Riphean.
