超碳质南极微陨石（UCAMMs）的STXM-XANES和TEM分析
STXM-XANES and TEM analysis of UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs)
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中文总结 AI 辅助
本研究通过STXM-XANES和TEM分析UCAMMs，发现其含三种OM相及多种矿物，富氮OM或源于原行星盘冰的辐照，矿物学特征暗示早期太阳系存在径向混合，还引发彗星水蚀变的疑问。
中文摘要 AI 辅助
康考迪亚微陨石收藏包含可能起源于彗星的超碳质南极微陨石（UCAMMs）。通过扫描透射X射线显微镜-近边X射线吸收精细结构（STXM-XANES）和（扫描）透射电子显微镜（TEM）对8个UCAMMs的聚焦离子束（FIB）切片进行了研究。UCAMMs中存在三种不同的有机质（OM）相，且小矿物集合体分布于OM中。其中两种OM的光谱特征与碳质球粒陨石的不溶性有机质（IOM）以及星尘（Stardust）任务返回的彗星颗粒的光谱特征相似。第三种OM富氮（氮/原子比最高达0.22），在目前分析的地外OM中仅有少量类似物，如星尘任务收集的彗星颗粒、行星际尘埃粒子（IDPs）以及富士圆顶站附近收集的UCAMMs中的OM。这种富氮OM可能由原行星盘外部区域富氮冰的辐照形成。UCAMMs含有不同含量的矿物，包括富镁结晶硅酸盐、铁（镍）硫化物和铁氧化物，这些矿物可被富硅基质胶结，还观察到次晶质矿物集合体，部分UCAMMs中发现与GEMS形态相似的玻璃质相。该矿物学特征与此前UCAMMs分析结果基本一致，且与被视为彗星尘埃颗粒的球粒状多孔IDPs的矿物学特征接近。本研究中观察到一种具有层状硅酸盐结构的矿物，引发了彗星上是否存在水蚀变的疑问。总体而言，UCAMMs的矿物学和有机质表征表明其形成历史复杂，且早期太阳系存在大规模径向混合，将其矿物组分输送至原行星盘外部区域。
英文摘要
The Concordia micrometeorite collection contains UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) of probable cometary origin. Eight FIB sections of UCAMMs were studied by Scanning Transmission X-ray Microscopy - X-ray Absorption Near Edge Structure and (Scanning)Transmission Electronic Microscopy. Three different phases of organic matter (OM) exist in UCAMMs and small mineral aggregates are distributed in the OM. Two OMs share spectral features with those of insoluble organic matter (IOM) of carbonaceous chondrites and of cometary grains returned by the Stardust mission. The third OM is N-rich (N/C at. ratios up to 0.22) and has only a few equivalents in extraterrestrial OM analyzed so far, such as in cometary particles collected during the Stardust mission, Interplanetary Dust Particles (IDPs) and UCAMMs collected near the Dome Fuji Station. This N-rich OM could have formed by irradiation of N-rich ices in the outer regions of the protoplanetary disk. UCAMMs contain variable amounts of minerals, consisting of crystalline Mg-rich silicates, Fe(Ni) sulfides and Fe oxides, which can be cemented in a Si-rich groundmass. Hypocrystalline mineral assemblages are also observed. Glassy phases showing morphological resemblance to GEMS are also found in some UCAMMs. This mineralogy is mainly consistent with that of previous UCAMM analyses, and is close to what is observed in Chondritic Porous IDPs, which are also considered as cometary dust particles. A mineral exhibiting a phyllosilicate texture has been observed in this work, and raises the question of the possibility of aqueous alteration on comets. Overall, UCAMMs' mineralogical and organic characterization implies a complex formation history of UCAMMs, and the presence of large-scale radial mixing in the early solar system, to transport their mineral components to the outer parts of the protoplanetary disk.
