Condensation of cometary silicate dust using an induction thermal plasma system
Condensation of cometary silicate dust using an induction thermal plasma system
复制标题
使用感应热等离子体系统凝结彗星硅酸盐尘埃
DOI：
10.1051/0004-6361/202142620
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发表时间：
2022
影响因子：
6.5
通讯作者：
Komaki H.
中科院分区：
文献类型：
--
作者：
Enju S.;Kawano H.;Tsuchiyama A.;Kim T. H.;Takigawa A.;Matsuno J.;Komaki H.
嵌入金属和硫化物的玻璃是球粒陨石多孔行星际尘埃粒子(CP-IDP)的主要成分，是太阳系中最原始的物质之一，可能类似于在各种天文环境中观察到的无定形硅酸盐尘埃。宝石的矿物学特征应反映其形成过程和条件。本研究通过系统改变氧化还原条件，在Fe-Mg-Si-O-S含硫体系中进行了合成实验，利用热等离子体系统再现了宝石的矿物学和结构。得到的冷凝物由无定形硅酸盐和含铁纳米包裹体组成。无定形硅酸盐中的铁含量和织构以及纳米颗粒的矿物相与氧化还原条件有关。在氧化条件下，Fe以FeO的形式溶解在无定形硅酸盐中，在中间氧化还原条件下形成Fe-金属纳米颗粒，在还原条件下形成孔雀石(Fe3Si)纳米颗粒。在中等-还原氧化还原条件下，贫铁无定形硅酸盐形成两相织构，具有富镁和富硅的区域，表明熔体阶段液体不混溶。大多数Fe-金属颗粒被FeS包围，并在无定形硅酸盐颗粒表面形成。在中等至轻微氧化还原条件下产生的凝析油与宝石相似，因为它们具有与无定形硅酸盐相似的矿物组合和化学成分，但无定形硅酸盐颗粒内部没有铁金属颗粒。这种结构上的差异可以用本研究中高温硫化作用来解释，而不是在天然宝石形成过程中低温硫化作用。根据在实验产品和宝石中观察到的两种液体结构，我们认为宝石在有限的氧化还原条件下凝聚为硅酸盐熔体，然后在硅酸盐熔体中掺入多个金属颗粒，或者在金属铁硫化之前通过核壳结构的颗粒聚集。在氧化条件下产生的凝析油与原始碳质球粒陨石基质中的类宝石物质相似，表明它们可能是在相对氧化的条件下由星云气体直接凝聚而成。
Glass with embedded metal and sulfides (GEMS), the major components of chondritic-porous interplanetary dust particles (CP-IDPs), is one of the most primitive materials in the Solar System and may be analogous to the amorphous silicate dust observed in various astronomical environments. Mineralogical characteristics of GEMS should reflect their formation process and condition. In this study, synthetic experiments in the sulfur-bearing system of Fe–Mg–Si–O–S were performed with a systematic change in redox conditions using thermal plasma systems to reproduce the mineralogy and textures of GEMS. The resulting condensates were composed of amorphous silicates with Fe-bearing nano-inclusions. The Fe content and texture in the amorphous silicates as well as the mineral phases of the nanoparticles correlate with redox conditions. Fe dissolved in the amorphous silicate as FeO in oxidizing conditions formed Fe-metal nanoparticles in intermediate redox conditions, and gupeiite (Fe3Si) nanoparticles in reducing conditions. In intermediate to reducing redox conditions, Fe-poor amorphous silicate formed a biphasic texture with Mg- and Si-rich regions, indicating liquid immiscibility during the melt phase. Most Fe-metal particles were surrounded by FeS and formed on the surface of amorphous silicate grains. Condensates produced in intermediate to slightly reducing redox conditions resemble GEMS in that they have similar mineral assemblages and chemical compositions to amorphous silicate, except that the Fe-metal grains are absent from the interior of the amorphous silicate grains. This textural difference can be explained by the sulfidation at high temperatures in this study, in contrast to sulfidation occurring at low temperatures in the presence of H2in natural GEMS formation. Based on the two-liquid structures observed in the experimental products and in GEMS, also recognized in infrared spectra, we propose that GEMS condensed as silicate melt under limited redox conditions followed by incorporation of multiple metal grains into the silicate melt or by aggregation of coreshell structured grains before sulfidation of the metallic iron. Condensates produced in oxidizing conditions are similar to GEMS-like material in the matrices of primitive carbonaceous chondrite meteorites, indicating the possibility that they form by direct condensation from nebula gas in relatively oxidizing conditions compared to GEMS.