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Mineralogical study of CI carbonaceous chondrite matrix by using electron microscopes

CI碳质球粒陨石基体的电子显微镜矿物学研究

基本信息

批准号：
02640622
负责人：
TOMEOKA Kazushige
金额：
$ 1.09万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

1. We have studied three new CI carbonaceous chondrites(Yamato82162, Yamato-86720, Belgica-7904)from Antarctica by using electron microscopes. Our study reveals that they have many mineralogical features different from non-Antarctic CI chondrites. Two of them are mineralogically more similar to CM chondrites. All of the three chondrites apparently have undergone thermal metamorphism at temperatures 500-600'C Such significant thermal effects have not been known from other CI and CM chiondrites. These results indicate that the new CI chondrites have experienced considerably different formation histories from those for ordinary CI and CM chondrites, and suggest that there was an event in which some CI and CM parent bodies have been heated to significantly high temperatures.2. We have found fracture-filling veins of phyllosilicates in one of the new CI chondrites(Y82162). The finding provides new evidence that the phyllosilicates in CI chondrites were formed by the activity of aqueous solutions on the meteorite parent body, and that phyllosilicate formation overlapped the period of impact brecciation.3. CV type chondrites have been generally considered to have not been affected by aqueous alteration after accretion. However, we have found considerable amounts of phyllosilicates in the Mokoia CV chondrite. Evidence was found that the phyllosilicates in Mokoia were formed by aqueous alteration of olivine and pyroxene. The mechanism to form saponite from olivine is not found from terrestrial. analogues and suggests that the alteration occurred by reaction with the solar nebula in an oxidizing condition.

1.用电子显微镜研究了三种新的南极CI碳质化石（Yamato-82162，Yamato-86720，Belgica-7904）。我们的研究表明，它们具有许多不同于非南极大陆的矿物学特征。其中两种在矿物学上更类似于CM钙钛矿。这三种球粒陨石显然都经历了500- 600 ℃的热变质作用，这种显著的热效应是其它CI和CM球粒陨石所没有的。这些结果表明，新的CI榴辉岩经历了与普通CI榴辉岩和CM榴辉岩截然不同的形成历史，并表明存在一次CI和CM母岩被加热到显著高温的事件.在其中一个新的Cl-辉石岩（Y82162）中发现了层状硅酸盐的充填脉。这一发现提供了新的证据，证明CI陨石中的层状硅酸盐是由水溶液在陨石母体上的活动形成的，层状硅酸盐的形成与撞击角砾岩的形成期重叠.一般认为CV型碳酸盐岩在增生后不受水蚀变的影响。然而，我们已经发现相当数量的层状硅酸盐在Mokoia CV球粒陨石。研究表明，莫科亚层状硅酸盐是由橄榄石和辉石的水蚀变作用形成的。橄榄石形成皂石的机制在陆地上没有发现。类似物，并表明在氧化条件下与太阳星云反应发生的变化。