A study of crystallization process of CAI using Sr and Ba as tracers

以Sr和Ba为示踪剂的CAI结晶过程研究

基本信息

批准号：
13640492
负责人：
NAGASAWA Hiroshi
金额：
$ 2.24万
依托单位：
GAKUSHUIN UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640492/
关键词：
CAI partialmelting recrystallization melilite gehlenite akermanite アエンデ隕石タイプ-BCAI SBダイヤグラム

项目摘要

Ca, Al-rich inclusions (CAI) in the primitive meteorite are believed to be one of the oldest solid material in the solar system. We have experimentally synthesized CAI analogues to investigate the process of formation of the CAIs. We first synthesized CAIs adding minor amounts of Sr and Ba as tracers, and investigated the order of crystallization of minerals by determining the distribution of Sr and Ba in the samples. It is found that the plot of Sr/Ca vs Ba/Ca ratios as parameters is very useful in describing the process of crystallization of CAIs.Based on the heterogeneous distribution of Oxygen isotopes among the minerals in the CAIs, it is suggested that CAIs cannot have been produced by a single sequence of cooling from a molten state. It is suggested that the heterogeneous distribution observed for CAIs are explained by repeated rapid heating and cooling in the gaseous environment with changing Oxygen isotopeRatios while partially melted. We have performed experiments in which the synthetic CAIs with no Sr and Ba tracers were inserted in a tracer doped Ca, Al-rich melt and cooled to investigate the process of remelting-recrystallization process by determining the distribution of Sr and Ba in the solid products. The plot of Sr/Ca vs Ba/Ca ratios as parameters is found to be a useful tool to describing the remelting-recrystalli-zation processes in this case again.Melilite is a major component mineral of the CAIs and is a solid solution of two end-members, gehlenite( Ca_2Al_2SiO_7) and akermanite (Ca_2MgSi_2O_7). When heated to a temperature between solidus and liquidus, is it expected to separate in to small crystals of solidus composition and the liquid of liquidus composition. We heated synthetic melilite crystals to such a temperature and found that a mosaic structure composed of tiny crystals of gehlenitic melilite and akermanitic glass was produced.

据信，原始陨石中的Ca，富含Al的夹杂物（CAI）是太阳系中最古老的固体物质之一。我们已经实验合成的CAI类似物来研究CAI的形成过程。我们首先合成CAI，将少量的SR和BA作为示踪剂添加，并通过确定样品中SR和BA的分布来研究矿物结晶的顺序。发现SR/CA与BA/CA比作为参数的图在描述CAI的结晶过程非常有用。基于CAI矿物质中氧同位素的异质分布的结晶过程，这表明CAI的氧气同位素的单个冷却状态的单个冷却序列不可能由熔融状态的单个冷却序列产生。建议通过在气态环境中反复加热和冷却来解释CAI所观察到的异质分布，而在部分融化的同时，氧气同位素变化。我们进行了实验，其中将无SR和BA示踪剂的合成CAI插入了掺杂的CA，富含Al al的熔体并冷却以研究通过确定固体产品中SR和BA的分布来研究的过程。发现SR/CA与BA/CA比率作为参数的图是在这种情况下再次描述Remelting-Recrystalli-Zation过程的有用工具。Melilite是CAI的主要组成矿物，并且是两个最终成员的可靠解决方案（CA_2AL_2AL_2SIO_2SIO_7）和akermanite（CA_2AL_2SIO_2MANS）（Ca_2sio_77）（Ca_2sio_7s）。当加热到固相物和液体之间的温度时，预计它将与固体组成的小晶体和液体液体分离。我们将合成的Melilite晶体加热到这样的温度，发现由小葡萄膜的微小晶体和阿基曼氏玻璃组成的镶嵌结构。