Alteration processes of carbonaceous chondrite parent bodies

碳质球粒陨石母体的蚀变过程

基本信息

批准号：
06403001
负责人：
TOMEOKA Kazushige
金额：
$ 17.41万
依托单位：
Kobe University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

(1) Various types of dark inclusions (DIs) in CV chondrites have been studied in detail by using scanning electron microscopy equipped with an energy dispersive X-ray spectrometer. DIs have been been thought to be primary aggregates of condensates from the solar nebula. However, from all the DIs studied our study revealed evidence that they were affected by aqueous alteration and stbsequant dehydration on the meteorite parent body. The compositional and mineralogical features of DIs indicate that they were probably derived from their host CV chondrites. These results suggest that water and heat source existed in the CV parent body and that aqueous alteration and thermal metamorphism occurred actively.(2) Ca-Al-rich inclusions (CAIs) in four Antarctic CO3 chondrites and four non-Antarctic CO3 chondrites have been studied in detail. Nepheline was found to occur in CAIs in all the CO3 chondrites. Nepheline is formed by replacing mainly melilite and anorthite, indicating it to have an alte … More ration origin. Previously the alteration was thought to have occurred by reaction with the solar nebular gas before accretion. Our study shows that the amount of nepheline increases in the same order as that of metamorphic grade of the CO chondrites. This result suggests that the alteration of CAIs is related to the metamoprhism of the host meteortes, thus it occurred on the meteorite parent body rather than in the solar nebula.(3) In order to better understand the aqueous alteration processes and conditions, we did hydrothermal alteration experiments of the Allende CV3 chondrites. Various alteration mineralogy and textures were produced that resemble those in CI and CM chondrites. Based on the results, we can understand the details of mineralogical and chemical changes that occurred during aqueous alteration of the meteorites.(4) In order to gain our knowledge about the shock histroy of carbonaceous chondrites, we performed shock recovery experiments of the Murchison CM,Yamato 791717 CO and Allende. CV chondrites and studied the recovered samples in detail by using a scanning electron microscope. The meteorite samples were shocked at 5,10,20,25,30,35, and 40 GPa. The carbonaceous chondrites of type CM and CO have not experienced shock pressures higher than 25 GPa. The experimental results indicate that chondrules were flattened at pressures higher than 10 Gpa. The degree of chondrule flattening increases in accordance with the intensity of shock pressure. The experiments also reveal mineralogical and chemical changes that occur in the pressure range between 20 and 40 GPa. Less

(1) 使用配备能量色散 X 射线光谱仪的扫描电子显微镜对 CV 球粒陨石中的各种类型的暗包裹体 (DI) 进行了详细研究，但 DI 被认为是来自太阳星云的凝聚体的主要聚集体。，从我们研究的所有 DI 中，我们的研究揭示了它们受到陨石母体水蚀变和连续脱水影响的证据。 DIs的特征表明它们可能源自其宿主CV球粒陨石。这些结果表明CV母体中存在水和热源，并且水蚀变和热变质作用活跃。(2)富Ca-Al包裹体(CAI)。）对四种南极 CO3 球粒陨石和四种非南极 CO3 球粒陨石进行了详细研究，发现霞石存在于所有 CO3 的 CAI 中。霞石主要是通过取代黄长石和钙长石而形成的，这表明它有一个替代的起源。我们的研究表明，霞石的数量增加了。与 CO 球粒陨石的变质程度相同，这一结果表明 CAI 的变化与宿主陨石的变质有关。因此，它发生在陨石母体上，而不是在太阳星云中。(3)为了更好地了解水蚀变过程和条件，我们对阿连德CV3球粒陨石进行了热液蚀变实验，产生了各种类似的蚀变矿物学和结构。根据这些结果，我们可以了解陨石在水蚀变过程中发生的矿物学和化学变化的细节。（4）为了了解碳质球粒陨石的冲击历史，我们对 Murchison CM、Yamato 791717 CO 和 Allende 球粒陨石进行了冲击恢复实验，并使用扫描电子显微镜详细研究了回收的陨石样品。、10、20、25、30、35和40 GPa CM和CO型碳质球粒陨石没有经历过冲击。实验结果表明，球粒在压力高于 10 Gpa 时会变平。实验还揭示了在压力范围内发生的矿物学和化学变化。 20 至 40 GPa 之间。