An Archaean Tonalite–Trondhjemite–Granodiorite Association of the Kursk Block (Voronezh Massif): Composition, Age, and Correlation with the Ukrainian Shield

Аннотация

Framing of the Archaean greenstone belts of the Kursk Block (KB) of the East Sarmatia preserves rocks of the TTG association: those do not form massifs with distinct boundaries, but occur as fields gradually transiting into gneisses and migmatites. According to Sm–Nd isotope–geochemical data, the TTG are characterized by positive values of ε_Nd(2960) = +0.3…+1.6 and protolith model ages of Т_Nd(DM) = 3100–3200 Ma. Magmatic protoliths of the Kursk Block TTG were formed about 2960 Ma by melting from a juvenile basite source. These age estimates are significantly younger than heterochronous (3.19, 3.13 and 3.07 Ga) TTGs of the Middle Dnieper granite–greenstone terrane. On the other hand, the similarity of εNd(T) implies a single source of their protoliths. Consequently, the KB TTGs, apparently, are a result of transformation of an older sial crust preserved within the Middle Dnieper Block.