Malyi Zadoi Peridotite−Gabbronorite Massif: Computational Modeling of Crystallization and Evaluation of Indicator Geochemical Parameters of the Parental Melt

Model calculations were used to estimate the compositions of melts during fractional crystallization corresponding to the formation of the Malyi Zadoi massif, which is located in the Irkut block of the Sharyzhalgai uplift in the southwest of the Siberian craton. It is shown that the gabbronorites of the massif are comagmatic to the plagioperidotites and olivine gabbronorites. The estimates obtained for the composition of the model melts are used to characterize the composition of the mantle source of the parental melt. The geochemical characteristics led us to suggest that the parental melt of the Malyi Zadoi massif was formed by melting an enriched source, a conclusion consistent with isotope data that indicate that the mantle Sm/Nd ratio decreased in the Archean. The probable source of the parental melt could consist of depleted lithospheric mantle material metasomatized by felsic melts coming from rocks of a subducting oceanic plate.