实验研究压力对硅酸盐熔体中Fe3+/ΣFe比值的影响

In natural and synthetic silicate melt, the structural properties of Fe2+ and Fe3+ and the Fe3+/ΣFe ratio have been received broad attention for at least 30 years, because the Fe3+/ΣFe ratio not only reflects, but also in many cases can establish the oxygen fugacity (fO2). Due to the different pressure effects on the coordination structure and volume properties of Fe2+ and Fe3+ in silicate melts, pressure will also affect the Fe3+/ΣFe ratios in silicate melts, further, the oxygen fugacity(fO2). The effect of pressure on the Fe3+/ΣFe ratio in silicate melts is necessary to understand the redox environment of the early terrestrial planet magma ocean. So far, the highest pressure of experimental studies is only 7GPa, but for Mars and Earth, the core formation pressure is ~14 GPa and >25 GPa, respectively. Therefore, this project is going to determine the Fe3+/ΣFe ratio in silicate melts under 25-80 GPa with experimental apparatus combining micro measurements. The results will help people further understand the structure properties of Fe2+ and Fe3+ in silicate melts at high pressure, and provide important constraints for early magma ocean redox gradients and evolution.

硅酸盐熔体中Fe2+和Fe3+的结构性质以及Fe3+/ΣFe比值在至少30年以来受到广泛关注。这是因为Fe3+/ΣFe不仅可以反映，而且在许多情况下可以建立硅酸盐熔体的氧逸度（fO2）。由于压力对硅酸盐熔体中Fe2+和Fe3+的配位结构以及体积性质方面的影响会存在差异，因此压力也会影响硅酸盐熔体中的Fe3+/ΣFe，并进一步影响氧逸度。对早期类地行星岩浆洋的氧化还原环境的研究需要人们了解压力对硅酸盐熔体中Fe3+/ΣFe，以及氧逸度的影响。目前前人的实验研究最高只到7GPa，而对于火星和地球而言，早期核幔分异的压力分别为~14GPa和>25GPa。因此本项目拟结合实验岩石学，微区测量手段和热力学模拟，测定25-80GPa下硅酸盐熔体中Fe3+/ΣFe比值。研究结果将进一步理解高压下硅酸盐熔体中Fe2+和Fe3+的结构性质，并为早期岩浆洋氧化还原梯度以及延缓提供重要制约。

硅酸盐熔体中Fe2+和Fe3+的结构性质以及Fe3+/ΣFe比值在至少30年以来受到广泛关注。这是因为Fe3+/ΣFe不仅可以反映，而且在许多情况下可以建立硅酸盐熔体的氧逸度 (fO2)。由于压力对硅酸盐熔体中Fe2+和Fe3+的配位结构以及体积性质方面的影响会存在差异，因此压力也会影响硅酸盐熔体中的Fe3+/ΣFe，并进一步影响氧逸度。早期类地行星岩浆洋的氧化还原环境是研究类地行星氧化还原状态演化的起点，而氧化还原状态剖面需要人们了解压力对硅酸盐熔体中Fe3+/ΣFe，以及氧逸度的影响。前人的实验研究最高到23GPa，而对于火星和地球而言，早期核幔分异的压力分别为~14GPa和>25GPa。而前人实验在>8GPa条件下得到的淬火产物均为结晶矿物，其所测得的Fe3+/Σfe很有可鞥已不能代表熔体时期的Fe3+/ΣFe。本项目结合实验岩石学，同步辐射微区测量手段，测定35-70GPa下硅酸盐熔体中Fe3+/ΣFe比值。初步发现随着压力的升高，Fe3+/ΣFe持续降低。对已获得数据的进一步解析将获得熔体内Fe3+和Fe2+的结构变化，基于此结论的热力学建模可以为为早期岩浆洋提供氧化还原状态剖面。