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，并最终形成陆地海洋和大气层，这在很大程度上是未知的。在这个项目中，我们专注于富铁金属颗粒与挥发性物质在太阳系最初一千万年的反应。由于它们的高反应性，金属构成了理想的矿物学探针，以了解所涉及的原行星过程。在铁陨石中观察到的典型反应产物是富含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-水蚀变的机制，这种金属相关的矿物组合的起源，我们的目的是阐明所涉及的挥发性油藏。特别是，我们将解决未解决的和突出的问题是否蒸发的多组分（彗星状）冰在原行星气固相互作用中发挥了重要作用。新的含氮化物硫化物组合表明了这一点，指出以前存在气态氨。我们将通过双重方法检验形成假说：（i）通过对南极陨石中与金属有关的矿物组合进行矿物学和显微结构分析，重建物理化学形成条件，（ii）通过在低压气体混合炉中使用氢气、硫化氢、水、氨和氮气的混合物的气体-金属相互作用的新颖实验研究。透射电子显微镜（TEM）将是一个中心的分析工具，并将辅之以二次离子质谱（西姆斯）的氧，硫，氮的同位素分析，其结果预计将大大提高我们的理解原行星的相互作用和水库的挥发性物种。如果能够证明蒸发的多组分冰参与其中，则该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具有重要意义，这些物种可能包含在此类冰中，并可能与其他挥发物一起沿着传递到早期地球。如果这种机制被证明是不可行的，那么陨石母体内的液体介导的变化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.