Figure 1

Phase boundaries of the post-spinel transition in Mg₂SiO₄. Data points were calculated based on the Tange 3BM MgO scale¹¹. Open and solid circles with error bars identify the stable phases as ringwoodite and bridgmanite + periclase, respectively. The black solid line is the expected condition of the 660-km discontinuity^{7,8,16,17,18,19,20,21}. The red (T-3BM) and blue (T-Vinet) solid lines are phase boundaries evaluated using the fixed points obtained in this study and the Clapeyron slopes of ref.⁴ after re-calculation with the Tange 3BM and Vinet MgO scales, respectively. The purple dashed line [F04 (S-3BM)] is the original phase boundary determined by ref.⁴ using the MgO scale proposed by ref.¹². The aforementioned red [F04 (T-3BM)] and blue [F04 (T-Vinet)] dashed lines are therefore the phase boundaries recalculated from the original data of ref.⁴ using the specified scales. Brg: bridgmanite; Pc: periclase; Rw: ringwoodite.