Crystallization of high-Ti ferrospinel under P-T conditions of the upper mantle

Results of an experimental study of spinel crystallization in silicate systems with various Fe and Ti concentrations (mixtures of picrite-basalt, alkali basalt, peridotite, serpentinitized and carbonatized kimberlites with picroilmenite, metal iron, and pyrite in various proportions) at pressures of 15 to 50 kbar and temperatures up to 1600degrees C are presented. High-Ti ferrospinel forms in all of the systems studied (the concentration of ulvospinel in the solid solution attains 86%). Its crystallization is most pronounced in systems with ultrabasic rocks (peridotites and kimberlites) and at a pressure of 50 kbar at which the ferrospinel associates with olivine. Two trends of the relationship between Fe and Ti oxides are established: negative, in solid solutions of ulvospinel and magnetite, and positive, in Ti-rich ferrospinel forming at pressures higher than 25 kbar.