Characterizing and modeling melting relations in the system MgO-SiO₂ at lower mantle pressures rely on the location of the eutectic points for MgO-MgSiO₃ and MgSiO₃-SiO₂. While at an uppermost lower mantle pressure there is general consensus on the eutectic composition in the former, large discrepancies exist for MgSiO₃-SiO₂ from experiments in the diamond anvil cell, ab-initio simulations and models built on them. In order to address this discrepancy, we have performed multi-anvil press experiments at GPa for Mg₄Si₆O₁₆ and Mg₃Si₇O₁₇ at temperatures of K and K. In the experiments at K, we observe the presence of partial melt. The recovered Mg₄Si₆O₁₆ sample shows SiO₂ stishovite as the liquidus phase, and electron microprobe analysis of the quenched melt determines as the eutectic composition. We fit a thermodynamic model to describe the melting relations in the MgO-SiO₂ system, and extrapolate to core-mantle boundary pressure. At 136 GPa, we predict that the eutectic points have moved further away from enstatite composition, and solidus temperatures remain similar for MgO-MgSiO₃ and MgSiO₃-SiO₂.

中文翻译：

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下地幔熔化：MgO-SiO2 系统中的实验和热力学建模

在较低地幔压力下表征和模拟 MgO-SiO ₂系统中的熔化关系依赖于 MgO-MgSiO ₃和 MgSiO ₃ -SiO ₂共晶点的位置。虽然在最高的下地幔压力下，对于前者的共晶成分存在普遍共识，但金刚石砧座中的实验、从头算模拟和建立在其上的模型中的MgSiO ₃ -SiO ₂存在很大差异。为了解决这种差异，我们在GPa 条件下对 Mg ₄ Si ₆ O ₁₆和 Mg ₃ Si ₇ O进行了多砧压机实验₁₇在K 和K 的温度下。在K的实验中，我们观察到部分熔化的存在。回收的Mg ₄ Si ₆ O ₁₆样品显示SiO ₂ stishovite为液相，电子显微探针分析淬火熔体确定为共晶成分。我们拟合了一个热力学模型来描述 MgO-SiO ₂系统中的熔化关系，并外推到核-幔边界压力。在 136 GPa 时，我们预测共晶点已远离顽火石组成，并且 MgO-MgSiO ₃和 MgSiO ₃ -SiO _{2 的}固相线温度保持相似.