Reaction Between Liquid Iron and Mg-perovskite

Reaction between liquid iron and Mg-perovskite was investigated at 27 GPa and up to about 3700 K to study nature of core forming process and light elements in the Earth's core. The Earth's core is supposed to contain small amount of light elements. These light elements were dissolved into liquid iron during core forming process. Deep magma ocean is supposed to have extended to the depth of the uppermost lower mantle in the core forming stage (Ohtani et al., 1997; Li and Agee, 2001). Because Mg-perovskite is the most dominant mineral in the lower mantle, reaction between the liquid iron and the Mg-perovskite occurred at base of the deep magma ocean and may have provided Si and O as the light elements into the liquid iron. And another importance of this reaction is that it may occur at core-mantle boundary to form the D" layer. Knittle and Jeanloz (1991) and Hillgren and Boehler (1999) have studied this reaction with laser-heating diamond anvil cell. But their studies had large temperature gradient in the sample room resulting in a possibility of disequilibrium. In this study, high pressure and temperature experiments were conducted with the Kawai-type multi-anvil apparatus and the sample was reached to equilibrium with uniform heating by Re cylindrical heater. Pure iron rod was packed into MgSiO₃ powder capsule, which transformed to Mg-perovskite in the experimental conditions. The sample was compressed to desired load and then heated to desired temperature and kept constant and finally quenched. Run products were analyzed with the electron microprobe. Magnesiowüsite was formed at boundary between liquid iron and Mg-perovskite in both runs at about 3700 and 3100 K. Quenched liquid iron contained oxide blobs in both runs and stishovite grew in the quenched liquid in the run made at about 3700 K. The liquid iron reacted with Mg-perovskie to form the magnesiowüstite and Si and O dissolved into the liquid iron at temperatures above 3100 K. The Si and O contents in the liquid iron were increased with increasing temperature up to 2.3 wt% O and 1.7 wt% Si in the run made at about 3700 K. Our experimental result implies that liquid iron can contain about 2 wt% Si and O at base of the deep magma ocean. The dissolution reaction of Si and O may occur also at the core-mantle boundary.