Granitoid Intrusions at the Periphery of the Kursk Block as Part of a Paleoproterozoic Silicic Large Igneous Province in Eastern Sarmatia

Paleoproterozoic diorite–granodiorite magmatic rocks dated at 2.04–2.08 Ga are widespread at the eastern border of the Archean Kursk block of Sarmatia. The granitoids of the intrusive massifs are metaluminous calc-alkaline I-type rocks enriched in incompatible elements (LILE and LREE), with negative Ti, P, and Nb anomalies. The rocks show widely varying negative εNdT values, their zircons have broadly ranging εHfT values, and the melts were derived within a broad range of depths from heterogeneous Archean lower crustal mafic sources. The diorites were melted from the least radiogenic ancient crustal sources. The granodiorites were derived from Paleo- and Mesoarchean and more juvenile Neoarchean sources. The intense 2.06-Ga magmatism was triggered by the upwelling of the asthenospheric mantle during the break-up of subducted oceanic slab due to low-angle subduction. The break of the slab and the mafic underplating led to the crustal melting of the upper slab, which consisted of Archean and Paleoproterozoic crustal fragments of different age that had been welded as a result of earlier accretion. Diorite−granodiorite magmas were generated in chambers at different depth in the ancient Archean crust at the periphery of Kursk block, with the incorporation of Paleoproterozoic lithospheric fragments of the Eastern Sarmatian orogen into the melting sources.