PETROGENESIS OF THE UTLYKTASH SYNCOLLISIONAL GABBRO COMPLEX IN THE SOUTHERN URALS: FEATURES OF MAGMA FORMATION DURING MANTLE-CRUST INTERACTION
E.L. Kunakkuzin1, I.R. Rakhimov2, T.B. Bayanova1
1Geological Institute of Kola Science Centre, Russian Academy of Sciences, Apatity, Russia
2Institute of Geology of the Ufa Federal Research Centre, Russian Academy of Sciences, Ufa, Russia
Keywords: Southern Urals, collisional basic magmatism, petrology, geochemistry, Nd-Sr isotopic composition, U-Pb zircon age
Abstract
We have conducted petrological, geochemical, and geochronological research on gabbro intrusions of the Utlyktash complex in the northern part of the West Magnitogorsk zone in the Southern Urals. The studied intrusions are confined to the wings of the Imangulovo syncline formed due to the syncollisional setting and to its surroundings. According to new LA-ICP-MS data, the age of the Uraz gabbro massif is 333 ± 3 Ma. The geochemical features and Nd-Sr isotopic composition of the Utlyktash complex indicate that a weakly depleted PM-type mantle is a source for gabbroids with subsequent significant magma fractionation and minor crustal assimilation (up to 6%). Thermodynamic modeling supports the fractionation model of a single parental melt from which all the studied gabbro bodies crystallized. The ID-TIMS and LA-ICP-MS U-Pb zircon dating (ranging from 0.44 to 2.73 Ga) has revealed the involvement of ancient continental crust and ophiolitic material from the Main Ural fault zone, along which the Magnitogorsk island-arc terrane was thrust onto the Laurussia paleomargin. The geological position of the Utlyktash complex and its geochemical correlation with basalts from the central part of the Magnitogorsk megazone suggest its formation during syncollisional rifting in the early Carboniferous, preceding the assembly of the Laurasia supercontinent.
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