In situ measurements of the majorite‐akimotoite‐perovskite phase transition boundaries in MgSiO3

Here we report the phase boundaries between majorite, akimotoite (ilmenite), and perovskite in MgSiO3 determined by in situ measurements in a multi‐anvil apparatus. We used both gold and platinum as internal pressure standards at high pressure and temperature. Our results obtained at 1400‐2000°C, together with previous results obtained at 1000‐1200°C by Ono et al. [2001], precisely locate the akimotoite‐perovskite transition boundary at P (GPa) = 25.09 ‐ 0.0027 × T (°C), based on the P‐V‐T equation of state of gold [Anderson et al., 1989]. Our new experimental data show the position of triple point to be 20.0 GPa and 1920°C. The present measurements reconfirm our earlier study [Hirose et al., 2001] that Anderson's gold pressure scale gives slightly higher pressures than the platinum pressure scale proposed either by Jamieson et al. [1982] or Holmes et al. [1989].