The nature of xenoliths in the Novaya Melovatka intrusion, Voronezh Crystalline Massif

The paper presents petrographic and petrochemical data on metaterrigenous (comparable with rocks of the Vorontsovka Group) and metamamatic ultramafic–mafic xenoliths in the Paleoproterozoic Novaya Melovatka intrusion in the Voronezh Crystalline Massif (VCM). The intrusion was drilled through by Voronezh Stratigraphic Borehole at Site 3210 of Geotraverse 1-EV. The concordant U-Pb zircon age of a gabbrodiorite xenolith is 2138 ± 25 Ma, and a rock of this age has no analogues among any other magmatic complexes in the geological legend currently adopted for VCM. The younger zircon age value of 2052 ± 22 Ma is thought to be explained by the thermal effect of the Novaya Melovatka intrusion, which was emplaced at 2049 ± 10 to 2057 ± 12 Ma. Xenoliths from this intrusion and from norite of the Elan’ Complex are petrochemically similar to one another and comparable with oceanic-type rocks (cumulus and differentiated mafic–ultramafic series). According to circumstantial evidence, the former were emplaced at relatively shallow depths of 20–30 km in the middle and lower Paleoproterozoic crust, whereas the latter were intruded into the mantle at a depth of 40–50 km, which suggests that the Voronezh block of VCM contains no Archean continental crustal component. The paper reports dada on differences between the Ni-bearing and metallogenically barren mafic–ultramafic massifs.