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Cosmochemical study on parent body evolution of chondritic meteorites

球粒陨石母体演化的宇宙化学研究

基本信息

批准号：
08454167
负责人：
EBIHARA Mitsuru
金额：
$ 1.15万
依托单位：
TOKYO METROPOLITAN UNVERSTY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1998
项目状态：
已结题

项目摘要

1. Distribution of rare earth elements, thorium and uraniumThese elements are largely distributed in Ca-phosphate minerals in equilibrated ordinary chondrites. Considering that Ca-phosphates are soluble in acid, chondritic meteorites were separated into acid-soluble and acid-residual phases. Then, rare earth elements, thorium and uranium were precisely determined for the acid-residual phases by inductively-coupled plasma mass spectrometry. The acid-residual phases consist of pyroxene, plagioclase and glass; glass is more abundant than plagioclase in unequilibrated ordinary chondrites. Rare earth contents and their abundance pattern normalized to their cosmic abundance for acid residual phases are correlated with the degree of thermal metamorphism chondrites experienced on the parent body. Similar change was observed for thorium and uranium contents. From these results, it was observed that contents of rare earth elements, thorium and uranium are good parameters for describing the thermal activity chondrites suffered on the parent body(ies). Furthermore, these contents are also correlated with contents of noble gases, especially heavy noble gases, suggesting that these noble gases were released from chondrites and were degassed from the parent body(ies) upon heating due to thermal activity.2. Refractory siderophile element abundances in metallic phases of ordinary chondritesOrdinary chondrites mainly consist of silicates, sulfides and Fe-Ni alloy phases. The weight of Fe-Ni phases ranges from several % up to 20% and siderophile elements are quantitatively distributed in metal phases. Precise determination of refractory siderophile elements revealed that their abundances systematically change from group to group of ordinary chondrites. Such a change was suggested to be caused by the difference in accretion temperature of ordinary chondrite parent bodies.

1.稀土元素、钍和铀的分布这些元素主要分布在平衡的普通辉长岩中的钙磷矿物中。考虑到钙磷酸盐易溶于酸，将钙磷陨石分为酸溶相和酸残相。然后，稀土元素，钍和铀，精确测定的酸残留相电感耦合等离子体质谱法。酸残余相由辉石、斜长石和玻璃组成;在不平衡的普通辉长岩中，玻璃比斜长石更丰富。稀土元素含量和它们的丰度模式归一化为他们的宇宙丰度的酸性残留相与热变质程度经历的母岩。钍和铀的含量也有类似的变化。结果表明，稀土元素、钍和铀的含量是描述母岩热活动特征的较好参数。此外，这些含量还与稀有气体，特别是重稀有气体的含量相关，这表明这些稀有气体是从方解石中释放出来的，并且由于热活动而在加热时从母体中脱气。普通辉长岩金属相中难熔亲铁元素的丰度普通辉长岩主要由硅酸盐、硫化物和Fe-Ni合金相组成。Fe-Ni相的重量范围从几%到20%，亲铁元素定量地分布在金属相中。难熔亲铁元素的精确测定表明，它们的丰度系统地从一组到另一组的普通方解石。这种变化可能是由普通球粒陨石母体的吸积温度差异引起的。