Scientific publications

We have obtained the first data on the age, elemental and isotopic geochemistry for C-adakites of Sarmatia within the Tim and Vorontsovka terranes with the Archean continental and Paleoproterozoic oceanic crust types, respectively. In the Tim back-arc basin, subvolcanic bodies of rhyolites with adakitic geochemical characteristics have an age of ~2.05 Ga. They are metaluminous and ferruginous, with an elevated amount of alkalis and a predominance of K2O over Na2O. In the Vorontsovka terrane, dacite and rhyolite porphyries have an age of about 2.07 Ga. They are ferruginous, metaluminous rocks of the calcic-alkaline series. The Na specialization, low concentrations of Mg, Cr, Ni, and
incompatible elements with high REE fractionation and absence of Eu* anomalies, high Sr/Y and especially (Gd/Yb)n ratios, and radiogenic Nd isotope composition suggest a juvenile basite source of the felsic melts. Paleoproterozoic Sarmatian crustal adakites were derived by the breakup of a collisional orogen from melting centers in the lower crust (> 60 km) in equilibrium with garnet-bearing restite. K-rhyolites with adakitic characteristics in the Tim terrane were derived in the same way as Na-rhyolites and dacites in the Vorontsovka terrane, through the breakup of a single collisional orogen from melting centers in the lower crust under high pressure in equilibrium with garnet. However, they differ sharply in geochemistry and Nd isotope composition depending on the source – the Archean continental crust of the TTG-predominated Tim terrane and the Paleoproterozoic basite oceanic crust in the Vorontsovka terrane.