Аннотация:In the subduction zones, the mantle depths are enriched by crustal matter. Basalt, in comparison with pyrolite, contains higher concentrations of SiO2, Al2O3, CaO, FeO, Na2O, K2O. It is assumed that the so-called postspinel phases (Akaogi et al., 1999) with structures of calcium ferrite, calcium titanate and marokite are concentrators of crustal elements in the transition zone and the lower mantle. In this work, an in situ study of the Mg-Al-Cr-O system was carried out. The phases of Mg2(Al,Cr)2O5 and Mg(Cr,Al)2O4 composition were synthesized. The Mg2(Al,Cr)2O5 phase has a modified ludwigite (Pbam) structure, and the Mg(Cr,Al)2O4 phase has a calcium titanate structure and crystallizes in the Cmcm space group. It was studied up to 30 GPa in a diamond anvil cells. As a result, it was found that at 12-16 GPa the color of the crystal changes from green to red, which persists with a further increase in pressure. This change is not stable, as the pressure decreases, the crystal turns green again. The phases described above are undoubtedly stable in mantle conditions and can be considered as host-phases for crustal elements in the Earth's mantle.
