Parent body thermal metamorphism is an important process that alters the structure of organic matter in the parent asteroid of meteorites. Increasing and progressing thermal metamorphism results in carbonization and graphitization of carbonaceous matter in the parent body. Such modifications in the carbon structures can be studied by Raman microspectroscopy, thanks to its high sensitivity to structure and bonding within carbonaceous molecules. We have characterized polyaromatic carbonaceous matter in a total of 24 Antarctic CV3 and CO3 chondrites using micro-Raman imaging spectroscopy in an effort to better understand parent body thermal metamorphism and assess its effects on the carbon structures. Raman spectral parameters of the first-order carbon peaks (D and G) were extracted from at least 200 spectra for each meteorite and were compared to deduce relationships that yield information regarding the thermal metamorphism conditions. We also show, for the first time, spectral trends and relations of the second-order carbon peaks (2D and D+G) within the 2500–3200 cm−1 with thermal metamorphic history. The second-order peaks appear to contain information that is lacking in the first-order peaks. Based on the second-order carbon peak parameters, we tentatively classify four CV3 chondrites into subtypes, and reclassify another. Peak metamorphic temperatures of the investigated meteorites have been estimated based on the width of the D band as well as the calculated Raman spectral curvature. Estimated temperatures appear to correlate well with the assigned petrologic types. We have calculated higher peak metamorphic temperatures for the CV3 chondrites than for the considered CO3 chondrites and further showed that the peak metamorphic temperatures of CV3oxA chondrites are higher than those of CV3oxB, indicating possibly different metamorphic conditions for the two oxidized subtypes. We observe that there is a relatively larger temperature increase going from CO3.2 to CO3.4 (150 °C increase) compared to CO3.4–CO3.6 (20 °C), which may indicate that the graphitization and structural ordering of carbon reach a critical temperature regime around petrologic type CO3.3.

中文翻译：

---

从多芳族有机碳的一阶和二阶拉曼峰推断南极CV3和CO3球粒陨石的热变质历史

母体热变质是改变陨石母体小行星中有机物结构的重要过程。热变质的增加和进行会导致母体中碳质物质的碳化和石墨化。由于碳结构对碳质分子内的结构和键合反应高度敏感，因此可以通过拉曼光谱研究碳结构的这种修饰。为了更好地了解母体热变质并评估其对碳结构的影响，我们使用微拉曼成像光谱法对了总共24个南极CV3和CO3球粒陨石中的多芳族碳质物质进行了表征。从每个陨石的至少200个光谱中提取一阶碳峰（D和G）的拉曼光谱参数，并将其进行比较，以推导得出有关热变质条件的信息的关系。我们还首次显示了具有热变质历史的2500–3200 cm-1内的二阶碳峰（2D和D + G）的光谱趋势和关系。二阶峰似乎包含一阶峰中缺少的信息。基于二阶碳峰参数，我们将四个CV3球粒陨石暂定为亚型，然后将另一个重分类。已根据D波段的宽度以及计算出的拉曼光谱曲率估算了所研究陨石的峰值变质温度。估计的温度似乎与分配的岩石学类型很好地相关。我们已经计算出CV3球粒陨石的峰值变质温度高于考虑的CO3球粒陨石的峰值变质温度，并且进一步表明CV3oxA球粒陨石的峰值变质温度高于CV3oxB的峰值变质温度，表明两种氧化亚型的变质条件可能不同。我们观察到，与CO3.4-CO3.6（20°C）相比，从CO3.2到CO3.4的温度升高相对较大（升高150°C），这可能表明石墨化和结构有序化。碳达到岩石学类型CO3.3附近的临界温度范围。我们已经计算出CV3球粒陨石的峰值变质温度高于考虑的CO3球粒陨石的峰值变质温度，并且进一步表明CV3oxA球粒陨石的峰值变质温度高于CV3oxB的峰值变质温度，表明两种氧化亚型的变质条件可能不同。我们观察到，与CO3.4-CO3.6（20°C）相比，从CO3.2到CO3.4的温度升高幅度更大（升高150°C），这可能表明碳的石墨化和结构有序化碳达到岩石学类型CO3.3附近的临界温度范围。我们已经计算出CV3球粒陨石的峰值变质温度高于考虑的CO3球粒陨石的峰值变质温度，并且进一步表明CV3oxA球粒陨石的峰值变质温度高于CV3oxB的峰值变质温度，表明两种氧化亚型的变质条件可能不同。我们观察到，与CO3.4-CO3.6（20°C）相比，从CO3.2到CO3.4的温度升高幅度更大（升高150°C），这可能表明碳的石墨化和结构有序化碳达到岩石学类型CO3.3附近的临界温度范围。