Hydrothermal evolution of the morphology, molecular composition, and distribution of organic matter in CR (Renazzo-type) chondrites
Hydrothermal evolution of the morphology, molecular composition, and distribution of organic matter in CR (Renazzo-type) chondrites
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DOI：
10.1111/maps.13045
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发表时间：
2018-05-01
影响因子：
2.2
通讯作者：
Brearley, Adrian J.
中科院分区：
文献类型：
--
作者：
Changela, Hitesh G.;Le Guillou, Corentin;Brearley, Adrian J.
为了更好地约束CR球粒陨石的热液演化，研究了一套CR球粒陨石中有机质的形态、分子组成和分布。从7个CR球粒陨石的基质中提取了多个聚焦离子束切片。扫描透射x射线显微镜和透射电子显微镜显示OM普遍分布在CR基质中。OM主要表现为离散的亚微米圆形或不规则形状的脉状颗粒。通过碳k边x射线吸收近边结构（XANES）鉴定出有机颗粒的两个光谱族：最丰富的一个，类似于不溶性有机物（IOM）残基，包含芳香、羰基和羧基。第二种品种芳香更浓郁，缺乏独特的羰基峰。另一种普遍存在的有机成分与无定形硅酸盐和层状硅酸盐有关。较少芳香族，但富含脂肪族和羧基，这种弥漫性OM被解释为有机化合物通过水流体重新分配的结果。变化最大的CR1 GRO 95577含有更成熟的OM和富含脂肪和羧基的弥漫性OM。这种从CR2s到CR1的演化过程与陆相气页岩的成熟过程相当，包括裂解反应，释放出沥青样、富含脂肪和羧基的化合物以及芳香残基。我们的观察结果支持可溶性OM的增加和后来的IOM聚合，以及IOM的成熟和部分氧化，释放可移动的化合物。GRO 95577的差异明显可归因于热液事件，但水和温度对OM演化的相对作用仍然难以捉摸。
The morphology, molecular composition, and distribution of organic matter (OM) were investigated in a suite of CR chondrites to better constrain its hydrothermal evolution. Multiple focused ion beam sections were extracted from the matrices of seven CR chondrites. Scanning transmission X-ray microscopy and transmission electron microscopy reveal OM ubiquitously distributed across the CR matrices. OM mainly occurs as either discrete submicron rounded or irregularly shaped vein-like particles. Two spectral populations of organic particles were identified by carbon K-edge X-ray absorption near edge structure (XANES): the most abundant one, similar to insoluble organic matter (IOM) residues, contains aromatic, carbonyl, and carboxylic groups. The second population is more aromatic-rich and lacks a distinctive carbonyl peak. An additional, ubiquitous organic component occurs associated with amorphous silicates and phyllosilicates. Less aromatic but aliphatic- and carboxylic-rich, this diffuse OM is interpreted as the result of the redistribution of organic compounds by aqueous fluids. The most altered CR1 GRO 95577 contains a more mature OM and highly aliphatic- and carboxylic-rich diffuse OM. This evolution, from the CR2s to the CR1, is comparable to that of terrestrial gas shale maturation involving cracking reactions, releasing bitumen-like, aliphatic-, and carboxylic-rich compounds, and aromatic residues. Our observations support the accretion of soluble OM and its later polymerization to IOM, as well as the maturation of IOM and its partial oxidation, releasing mobile compounds. The differences in GRO 95577 are clearly attributable to the hydrothermal episode(s), but the relative role of water and temperature on the evolution of OM remains elusive.