北京高压科学研究中心Lin Yanhao等人在研究受氧逸度控制的陆地岩浆海底的熔融中取得新进展。相关论文于2024年7月16日发表在《自然—地球科学》杂志上。

据介绍，由增生撞击产生的热量导致了早期地球硅酸盐地幔的大范围熔融，形成了覆盖地表的深层岩浆海洋。地幔的氧逸度被认为在吸积和地核形成过程中增加，这是由于越来越多的氧化撞击物和下地幔的自氧化作用，但这对深部原始地幔物质固体逸度的影响尚未得到很好的限制。

本研究通过在高氧逸度下16-26GPa压力下实验测定地幔岩固相线，评估氧逸度对岩浆海洋底部条件的影响。研究发现，在这个压力范围内，在氧化条件下进行的实验中的固相线至少是230-450℃，比在更多还原条件下进行的实验低。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，岩浆海底将加深约60km。氧逸度对地幔熔融的强烈影响表明，早期地球热演化模式和地核形成的地球化学模式应该被重新评估。

附：英文原文

Title: Melting at the base of a terrestrial magma ocean controlled by oxygen fugacity

Author: Lin, Yanhao, Ishii, Takayuki, van Westrenen, Wim, Katsura, Tomoo, Mao, Ho-Kwang

Issue&Volume: 2024-07-16

Abstract: 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 16–26GPa 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 60km 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.

DOI: 10.1038/s41561-024-01495-1

Source: https://www.nature.com/articles/s41561-024-01495-1