Paleoproterozoic A- and S-granites in the eastern Voronezh Crystalline Massif: Geochronology, petrogenesis, and tectonic setting of origin

Abstract

The eastern part of the Voronezh Crystalline Massif hosts coeval S- and A-granitoids. The biotite-muscovite S-granites contain elevated concentrations of Si, Al, and alkalis (with K predominance) and relatively low concentrations of Ca, Mg, Ti, Sr, and Ba, show pronounced negative Eu anomalies, and have low concentrations of Y and HREE. The biotite A-granitoids are enriched in Fe, Ti, P, HFSE, REE and have strongly fractionated REE patterns with deep Eu minima. According to their Rb/Nb and Y/Nb ratios, these rocks are classified with group A2 of postcollisional granites. The SIMS zircon crystallization age of the granitoids lies within the range of 2050–2070 Ma. Both the A- and the S-granitoids have positive ɛNd(T) values, which suggests that they should have had brief crustal prehistories and were derived from juvenile Paleoproterozoic sources. The simultaneous derivation of the A- and S-granites was caused by the melting of the lower crust in response to the emplacement of large volumes of mafic magma in an environment of postcollisional collapse and lithospheric delamination with the simultaneous metamorphism of the host rocks at high temperatures and low pressures. The S-granites are thought to be derived via the melting of acid crustal material in the middle and lower crust. The A2 granites can possibly be differentiation products of mafic magmas that were emplaced into the lower crust and were intensely contaminated with crustal material.