New data on the trace element composition and Lu-Hf isotopic system of zircons from the Early Cambrian granites of the Ufaley block (Middle Urals): a step to the correction of geodynamic concepts

Research subject . Composition and isotopic parameters of zircons and their host granites of the Bitim complex, localised in the eastern part of the Ufaley block (Middle Urals). Materials and methods . The determination of trace element composition and Lu-Hf isotope system in zircons was carried out by LA-ICP-MS (the “Geoanalitik” shared research facilities of the IGG UB RAS, Ekaterinburg). Results and conclusions . The images and geochemical features of the main zircon population from granites confirm their magmatic genesis and minimal alteration, which proves previously defined Vendian- Cambrian (520 ± 9 Ma) age for the granites. Younger zircons (401–459 Ma) differing in composition from the older ones, were formed during subsequent tectonic-thermal activity, possibly under the fluid action. The mixed mantle-crustal nature of substrate for the granite melting is indicated by specific isotopic parameters (87Sr/86Sr = 0.703389, εHf(t)aver = +6.3) and a number of characteristic ratios for zircons and granites. The geodynamic concepts of the granite formation settings of the Bitim complex are corrected: in the Vendian–Early Cambrian, a transform-type margin has developed in this sector, the divergent movements on which have been accompanied by a break in the continuity of the crust and the intrusion of a deep mantle diapir; the participation of the slab substance in the magma generation might also be assumed. Conclusions . The results obtained can be used for the geological mapping and correction of a general geodynamic scheme for the junction zone between the Ural Mobile Belt and the East European platform.