Compression of MgSiO3 and (Mg,Fe)SiO3 perovskites based on the pressure generation technique using sintered diamond anvils in a Kawai-type apparatus

(Mg,Fe)SiO3 perovskite and ferro-periclase are abundant minerals in the Earth’s lower mantle and hence their pressure-volume-temperature (P-V-T) relations are very useful in interpreting the seismological observations. Previous researches suggested the significant change of compressibility (P-V relation) of ferro-periclase due to the spin transition in iron at pressure of 30-70 GPa (Fei et al., 2008; Ito et al, 2010), whereas compressibility change caused by spin transition in (Mg,Fe)SiO3 perovskite is not reported yet. Iron content in silicate perovskite is much lower than that in ferro-periclase and pressures for spin transition in perovskite is expected to be higher than 70 GPa. Therefore, precise determination of volume at wide pressure range is required to access the change of P-V relation associated with spin transition in perovskite. Although pressure range in Kawai-type multianvil high pressure apparatus (KMA) is insufficient to cover whole mantle conditions, KMA enables us to have a large sample and uniform heating for high temperature experiment. In this study, we developed the experimental technique to expand the pressure range in KMA and applied this technique to measure the volumes of MgSiO3 and (Mg,Fe)SiO3 perovskites to observe the change in P-V curve related to spin transition. We conducted high pressure experiments at synchrotron facility, SPring-8, Japan, using a KMA equipped with sintered diamond anvils with 1.0 mm truncated edge length, and we succeeded to expand the pressure limit to ~ 95 GPa (at press of 6.5 MN) at 700 K based on Au pressure standard (Tsuchiya, 2003). In the experiment, we measured the volumes of MgSiO3 and (Mg,Fe)SiO3 perovskites simultaneously as a function of temperature and pressure. In this pressure range, little change in the volume ratio between MgSiO and (Mg,Fe)SiO3 perovskites is expected by preliminary volume analyses. We re-calculate the volumes and expand pressure range more and more in future.