Heat delivered from accretionary impacts is thought to have led to extensive melting of early Earth’s silicate mantle, resulting in a deep magma ocean covering the surface. The mantle’s oxygen fugacity is thought to have increased over accretion and core formation due to increasingly oxidated impactors and lower mantle self-oxidation, but the influence of this on the solidus of deep primitive mantle materials has not been well constrained. Here we assess the effect of oxygen fugacity on conditions at the bottom of a magma ocean by experimentally determining the solidus of mantle pyrolite at pressures of 16–26 GPa at high oxygen fugacities. We find that over this pressure range, the solidus in experiments conducted under oxidizing conditions is at least 230–450 °C lower than in experiments conducted under more reducing conditions. Assuming constant magma ocean temperature, this would imply a magma ocean floor that deepens by about 60 km for each log unit increase in mantle oxygen fugacity. The strong influence of oxygen fugacity on mantle melting suggests that models of early Earth thermal evolution and geochemical models of core formation should be reassessed.

人们认为，增生撞击产生的热量导致了早期地球硅酸盐地幔的广泛融化，形成了覆盖地表的深层岩浆海洋。人们认为，由于日益氧化的撞击体和较低的地幔自氧化，地幔的氧逸度在吸积和核心形成过程中有所增加，但这对深部原始地幔物质固相线的影响尚未得到很好的限制。在这里，我们通过实验确定高氧逸度、16-26 GPa 压力下地幔叶绿岩的固相线，评估氧逸度对岩浆海洋底部条件的影响。我们发现，在此压力范围内，在氧化条件下进行的实验中的固相线比在还原性条件下进行的实验中至少低 230–450 °C。假设岩浆海洋温度恒定，这意味着地幔氧逸度每增加一个对数单位，岩浆海底就会加深约 60 公里。氧逸度对地幔熔化的强烈影响表明，应该重新评估早期地球热演化模型和地核形成的地球化学模型。