Abstract
Biotite-garnet-sillimanite-cordierite gneisses from the Leshchev zone of the Middle Volga megablock in the Volga-Ural segment of the East European craton have been studied. The obtained Sm-Nd model age of the rocks is 2.8 Ga. U–Pb isotope-geochronological study of zircon cores from these rocks was carried out. The CL images revealed several generations of the zircon cores. The obtained age of the main sources of detrital zircon is 2.58 Ga. Single zircon grains have ages of cores of 2.4, 2.7, and 3.1 Ga. The calculated ɛNd(2500) = = –0.6 indicates the crustal or mixed mantle-crustal nature of the protolith of these gneisses. High-alumina metaterrigenous rocks of the Bolshecheremshanskaya Group, the Leshchevskaya zone, and the South Volga supracrustal complex are considered as elements of time and spatial secuence of sediments of Neoarchean and Paleoproterozoic basins with a protoplatform base and a passive continental margin, successively replacing each other.
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