Mineralogical and petrogeochemical features of subalkaline porphyries (Balbuk complex, Southern Urals)

The article provides a novel detailed mineralogical and petrogeochemical description of the Sharip group porphyries. They are visually divided into 4 main type by color, quantity and composition of inclusions, but in general have a similar mineral composition, being members of a single trachyandesite-trachyte association. The most important mineral determining the conditions of rock formation is amphibole, corresponding to pargasite and magnesiohastingsite (Mg# varies from 0.80 to 0.35). Amphibole crystallization began at a temperature of about 842—973 °C. Amphibole fractionation in trachyte magma caused petrogeochemical variations in the rocks, expressed in the distribution of the main petrochemical components and the level of accumulation of a number of incompatible elements. Geochemically, the Sharip porphyries are close to adakites (high Sr/Y, La/Yb ratios), and their sources could have been rocks of the lower crust of the Southern Urals (including ultramafic-mafic rocks of the Main Ural Fault and Riphean sedimentary-metamorphic formations).