New constraints on the abundances of phosphorus and sulfur in the lunar core: High-pressure and high-temperature experimental study of the Fe S P ternary system
New constraints on the abundances of phosphorus and sulfur in the lunar core: High-pressure and high-temperature experimental study of the Fe S P ternary system
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月核磷硫丰度新约束：Fe S P三元体系高压高温实验研究
DOI：
10.1016/j.gca.2022.07.024
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发表时间：
2022
影响因子：
5
通讯作者：
Shuangmeng Zhai
中科院分区：
文献类型：
--
作者：
Kuan Zhai;None YuanYin;Shuangmeng Zhai
在3- 5GPa和1173-1873 K条件下对Fe-S-P三元系进行了高压和高温实验。我们系统地研究了压力、温度和体成分对相关系、核心结晶序列以及月球核心中硫和磷的存在的影响。我们的实验结果表明，虽然高达<1重量%的磷可以溶解在固体铁中的Fe-S-P三元系在3和5 GPa，S溶解在固体铁中几乎可以忽略不计。在Fe-S-P相图的富铁侧（S+P <10wt%）观察到完全可混溶的Fe-S-P液体。结合前人的实验结果，得出了金属液中硫含量（XS液）与磷在固液间分配系数（DP）的关系式为lgDP =-1.8286-17.87 × lg 1 -XS液。Fe-S-P系统液相线和月核（S+P）含量之间的权衡很好地将液态月球外核（S+P）含量的上限限制在8.7和13.1wt%之间。利用磷系数的结果和我们的分配模型，我们进一步估算了月球液态外核和固态内核中的丰度，分别为6.08- 7.15wt%S和0.54 ± 0.01wt%P，以及0.05 ± 0.01wt%S和0.07 ± 0.01wt%P。结合观测到的月核温度和Fe-S-P液相线温度的压力依赖性，我们提出，一旦液态外核中（S+P）的丰度超过3.5wt%，随着核的演变，月核中的凝固制度将从自下而上切换到自上而下。
High-pressure and high-temperature experiments for the Fe-S-P ternary system were performed at 3–5 GPa and 1173–1873 K. We systematically investigated the effect of pressure, temperature, and bulk composition on the phase relationships, on the core crystallization sequences, and on the presence of sulfur and phosphorous in the lunar core. Our experimental results indicate that while up to <1 wt% phosphorus can be dissolved in solid iron in the Fe-S-P ternary system at 3 and 5 GPa, S dissolution in solid iron is near negligible. On the iron rich (S+P <10 wt%) side of the Fe-S-P phase diagram completely miscible Fe-S-P liquids were observed. Combined with previous experimental results, the relationship of the sulfur content in the liquid metal ( X S liquid ) and the partitioning coefficient of phosphorus ( D P ) between the solid and liquid metal follows an equation of lg D P = - 1.8286 - 17.87 × lg 1 - X S liquid . Tradeoff between the liquidus of the Fe-S-P system and the (S+P) content of the lunar core well constrain the upper limit of the (S+P) content in the liquid lunar outer core to the concentrations between 8.7 and 13.1 wt%. Using the result of the phosphorus coefficient and our partitioning model, we further assessed the abundances of 6.08–7.15 wt% S, 0.54 ± 0.01 wt% P in the lunar liquid outer core, and 0.05 ± 0.01 wt% S, 0.07 ± 0.01 wt% P in the lunar solid inner core, respectively. Integrating the observed lunar core adiabat and the pressure dependence of the Fe-S-P liquidus temperature, we propose that the solidification regime in the lunar core will switch from bottom-up to top-down once the abundance of (S+P) in the liquid outer core exceeds 3.5 wt% as the core evolves.