Mineralogical study of CI carbonaceous chondrite matrix by using electron microscopes

1.利用电子显微镜对南极三种新的CI碳质球粒陨石(Yamato82162、Yamato-86720、Belgica-7904)进行了研究。研究表明，它们具有许多不同于非南极CI球粒陨石的矿物学特征。其中两个在矿物学上更类似于CM球粒陨石。这三种球粒陨石显然都经历了500-600℃的热变质作用，这种显著的热效应在其他CI和CM球粒陨石中是未知的。这些结果表明，新的CI球粒陨石经历了与普通CI和CM球粒陨石相当不同的形成历史，并表明存在一些CI和CM母体被加热到显著高温的事件。我们在一个新的CI球粒陨石(Y82162)中发现了层状硅酸盐的裂缝充填脉。这一发现为CI球粒陨石中的层状硅酸盐形成于陨石母体上的水溶液活动提供了新的证据，并且层状硅酸盐的形成与撞击角砾岩的时期重叠。CV型球粒陨石一般被认为在增生后不受水蚀变的影响。然而，我们在莫科亚CV球粒陨石中发现了相当数量的层状硅酸盐。有证据表明，莫科亚中的层状硅酸盐是由橄榄石和辉石的水蚀变形成的。在陆地上没有发现橄榄石形成皂石的机制。并表明这种变化是在氧化条件下与太阳星云发生反应而发生的。

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.