Fe and Al solubilities in MgSiO₃ perovskite

Abstract

To examine the Fe and Al solubilities in MgSiO₃ perovskite, laser-heated diamond anvil cell experiments on the system (Mg,Fe)SiO₃-Al₂O₃ were performed at 30-60 GPa and 1800-2000 K.The synthesized samples were analyzed by synchrotron X-ray diffraction and analytical transmission electron microscopy (ATEM). The results show the following points. The product phases were Mg-perovskite, magneshiowustite and stishovite for 0 and 5 mol% Al₂O₃, while corundum joined the above phase assemblage for 25 and 50 mol% Al₂O₃. The chemical analyses of the perovskite phases showed that the Fe content in perovskite gradually increased with the Al content for low Al contents, but that the increasing rate became higher for higher Al contents. Under an electron microscope metal iron was recognized to coexist with perovskite for Al containing runs. These results indicate that in Mg-perovskite the substitution Mg²⁺ + Si⁴⁺ -> 2Al³⁺ is dominated for low Al contents, while the substitution Mg²⁺ + Si⁴⁺ -> Fe³⁺ + Al³⁺ increases for higher Al contents. This suggests that under the Al-rich circumstances in the lower mantle, Mg-perovskite contains the higher iron content than under the Al-poor circumstances and the part of iron is ferric.