Compositional Variability of Deep Spinel Peridotite Xenoliths from Late Cenozoic Basalts from the Shiliin-Bogd and Achagiin-Dush Volcanoes of Southeastern Mongolia: Reconstruction of Processes in the Continental Lithospheric Mantle

From major oxides and trace elements in deep-seated xenoliths of garnet-free peridotites from a basalt pedestal and cinder-basalt edifice of the Shiliin-Bogd volcano, rocks are subdivided into groups according to the degree of depletion–enrichment and the effect of garnet on their compositions. Processes of depletion of peridotites with the restite formation, metasomatism with enrichment of rocks in light rare earth elements (REE), and mixing of various components of peridotites with the fluid one of protomantle are established. Limited compositions of peridotite xenoliths from the volcanic edifice associated with anorthoclase and clinopyroxene megacrysts is determined. The data obtained are compared with those on deep-seated peridotite xenoliths from cinder of the Achagiin-Dush volcano located 6 km from the Shiliin-Bogd one. It is inferred that compositions of deep-seated rocks under the volcanoes show different variability. A sequence of generation of the continental lithospheric mantle is reconstructed.