Elephant Moraine 96029, a very mildly aqueously altered and heated CM carbonaceous chondrite: Implications for the drivers of parent body processing
Elephant Moraine 96029, a very mildly aqueously altered and heated CM carbonaceous chondrite: Implications for the drivers of parent body processing
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大象冰碛 96029，一种非常轻微的水蚀和加热的 CM 碳质球粒陨石：对母体加工驱动因素的影响
DOI：
10.1016/j.gca.2016.05.008
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发表时间：
2016
影响因子：
5
通讯作者：
Lee M
中科院分区：
文献类型：
--
作者：
Lee M
大象冰川(EET)96029是一种CM碳质球粒陨石风化角砾岩，具有异常温和的水蚀变、后期加热和陆地风化的证据。球粒陨石和细粒基质中层状硅酸盐和碳酸盐的存在表明，这块陨石的母体发生了水蚀变。表明水介质加工在非常早期阶段就被阻止的特征包括低镁铁比的基质，其介观稳定性包含玻璃和/或淬火微晶的球粒陨石，以及富钙铝包裹体。与其他CM球粒陨石相比，EET 96029还富含Fe、Ni金属，在南极风化过程中被针铁矿部分取代之前存在更多的Fe、Ni金属。综合来看，这些特性表明EET 96029是迄今描述的水分变化最小的CMS之一(CM2.7)，因此为了解其母体的原始组成提供了新的见解。在水蚀变之后，当陨石仍在母体风化层中时，通过撞击或太阳辐射将其加热到∼400-600摄氏度。加热导致蛇纹石的非晶化和脱羟化，托奇林石被磁铁矿取代，基质中的硫损失，以及包括有机纳米球在内的有机物的结构改变。样品之间氧同位素组成和水/羟基含量的显著差异表明，陨石含有经历了不同加热强度的岩性。EET 96029可能比许多其他CM陨石更能代表母体陨石的真实性质，因此可以帮助解释即将进行的研究和返回C复合体小行星样本的任务的结果。
Elephant Moraine (EET) 96029 is a CM carbonaceous chondrite regolith breccia with evidence for unusually mild aqueous alteration, a later phase of heating and terrestrial weathering. The presence of phyllosilicates and carbonates within chondrules and the fine-grained matrix indicates that this meteorite was aqueously altered in its parent body. Features showing that water-mediated processing was arrested at a very early stage include a matrix with a low magnesium/iron ratio, chondrules whose mesostasis contains glass and/or quench crystallites, and a gehlenite-bearing calcium- and aluminium-rich inclusion. EET 96029 is also rich in Fe,Ni metal relative to other CM chondrites, and more was present prior to its partial replacement by goethite during Antarctic weathering. In combination, these properties indicate that EET 96029 is one of the least aqueously altered CMs yet described (CM2.7) and so provides new insights into the original composition of its parent body. Following aqueous alteration, and whilst still in the parent body regolith, the meteorite was heated to ∼400–600 °C by impacts or solar radiation. Heating led to the amorphisation and dehydroxylation of serpentine, replacement of tochilinite by magnetite, loss of sulphur from the matrix, and modification to the structure of organic matter that includes organic nanoglobules. Significant differences between samples in oxygen isotope compositions, and water/hydroxyl contents, suggests that the meteorite contains lithologies that have undergone different intensities of heating. EET 96029 may be more representative of the true nature of parent body regoliths than many other CM meteorites, and as such can help interpret results from the forthcoming missions to study and return samples from C-complex asteroids.
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