Metal-related mineral assemblages as probes into protoplanetary gas-solid interactions

目前，水、氮化合物和其他挥发性物质如何在太阳原行星盘中相互作用，并最终对陆地海洋和大气做出贡献，在很大程度上是未知的。在这个项目中，我们关注的是在太阳系的头一千万年里，富含铁的金属颗粒与挥发性物质的反应。由于它们的高反应性，金属是研究所涉及的原行星过程的理想矿物学探测器。在球粒陨石中观察到的典型反应产物是富铁的硫化物和氧化物，如磁黄铁矿、镍黄铁矿和磁铁矿。我们的目标是得出决定性的标准，以区分气-固相互作用和液体-水蚀变作为这些金属相关矿物组合的成因机制，我们的目标是阐明涉及的挥发性储层。特别是，我们将解决尚未解决的和突出的问题，蒸发的多组分(彗星状)冰是否在原行星气-固相互作用中发挥了重要作用。我们将通过双重方法检验形成假说：(I)通过对球粒陨石中与金属相关的矿物组合的矿物学和显微结构分析重建物理化学形成条件，(Ii)通过使用氢、硫化氢、水、氨和氮的混合物在低压气体混合炉中进行气体-金属相互作用的新的实验研究。透射式电子显微镜将是主要的分析工具，二次离子质谱仪将补充氧、硫和氮的同位素分析。结果有望极大地增强我们对原行星相互作用和挥发性物质储藏库的了解。如果能够证明涉及蒸发的多组分冰，那么这一过程及其物理化学条件将对太阳星云的局部氧化还原状态和原始有机物种的演化产生重要影响，这些原始有机物种可能包含在这些冰中，并可能与其他挥发物一起输送到早期地球。如果这种机制最终被证明是不可行的，那么流星母体内的流体介导的改变很可能比目前认为的要复杂得多，需要修改。

At present, it is largely unknown how water, nitrogen compounds, and other volatile species interacted in the solar protoplanetary disk and, eventually, contributed to the terrestrial oceans and atmosphere. In this project we focus on the reactions of iron-rich metal grains with volatile species during the first ten million years of the Solar System. Due to their high reactivity, metals constitute ideal mineralogical probes into the protoplanetary processes involved. Typical reaction products observed in chondritic meteorites are iron-rich sulfides and oxides, such as pyrrhotite, pentlandite, and magnetite. We aim at deriving decisive criteria in order to differentiate between gas-solid interactions and liquid-water alteration as mechanisms for the origin of such metal-related mineral assemblages, and we aim at elucidating the involved volatile reservoirs. In particular, we will address the unresolved and eminent question whether evaporated multi-component (comet-like) ices played significant roles in protoplanetary gas-solid interactions. This is suggested by novel, nitride-bearing sulfide assemblages, pointing to the former presence of gaseous ammonia.We will test formation hypotheses by a dual approach: (i) By the reconstruction of physicochemical formation conditions from mineralogical and microstructural analysis of metal-related mineral assemblages in chondritic meteorites, (ii) by novel experimental investigation of gas-metal interactions in a low-pressure gas mixing furnace using mixtures of hydrogen, hydrogen sulfide, water, ammonia, and nitrogen. Transmission electron microscopy (TEM) will be a central analytical tool and will be supplemented by secondary ion mass spectrometry (SIMS) for isotopic analysis of oxygen, sulfur, and nitrogen.The results are expected to largely enhance our understanding of the protoplanetary interactions and reservoirs of volatile species. If it can be shown that evaporated multi-component ices were involved, the process and its physicochemical conditions will have important implications for the local redox state of the solar nebula and the evolution of primordial organic species, which were probably contained in such ices and could have been delivered to the early Earth along with other volatiles. If such a mechanism turns out to be unfeasible, the fluid-mediated alteration within meteoritic parent bodies was likely much more complex than currently thought and will require revision.