Home – Home – Jornals – Russian Geology and Geophysics 2019 number 3

The chemical composition of rocks of the Murzinka-Adui metamorphic complex and the Murzinka granite pluton, a reference interformational granite pluton in the Urals, is considered. A detailed comparative analysis of ancient gneisses and related granite veins included an isotope-geochemical study of zircons from both groups of rocks. Zircons are subdivided into seven age groups (I, 1588 ± 20 Ma; II, 1060 ± 28 Ma; III, 530 ± 11 Ma; IV, 380 ± 6 Ma; V, 330 ± 9 Ma; VI, 276 ± 3 Ma; and VII, 260 ± 3 Ma). The first four groups are apparently zircons from gneisses, reworked to different extents, and the other three groups are zircons crystallized during granite genesis. The gneisses and most of the granite samples contain zircons of all the above age populations, which is evidence of trapping zircons from gneisses by granite melts, on the one hand, and the occurrence of «granite-derived» zircons in gneisses, on the other. The granitoids and gneisses of all types differ considerably in geochemical features. The behavior of trace elements and the Rb-Sr ages indicate that the formation of granites of the Murzinka massif was a discrete episode of magmatic activity. The Sr isotope ratios in the granites and gneisses indicate different degrees of the mantle-crust interaction and the participation of the material of the crystalline basement and newly formed crust in their formation.