アルミニウムを含む下部マントル物質の鉱物化学

抄録

Recent high-pressure and high-temperature experiments strongly imply the possibility of non-stoichiometry for Al, Fe³⁺ containing MgSiO₃ perovskite and the related Al-phases. Therefore, the non-stoichiometric behavior of perovskites in the MgSiO₃-MgAlO_2.5 system and also in the multi-component system which are similar to natural mantle minerals and rocks was discussed by considering the trivalent cation substitution mechanism: 2^VI Si⁴⁺ ⇔ 2^VI (Al³⁺, Fe³⁺) + V_O^••. Since the behavior of Al coupled with iron in the MgSiO₃ perovskite is much more complicated because of the issue of fO₂ conditions, it is still under discussion. For dealing with the chemical behavior of Fe³⁺ in the perovskite, the electron energy-loss spectroscopy (EELS) in transmission electron microscopy (TEM) is becoming a powerful tool by which we can determine the Fe³⁺ / ΣFe ratio of coexisting phases separately on a nanometer order of resolution. It is expected that the EELS method combined with TEM techniques will be very useful to characterize synthetic high-pressure mantle minerals.