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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.

原始陨石中的富Ca、Al包裹体（CAI）被认为是太阳系中最古老的固体物质之一。我们实验合成了CAI类似物，以研究CAI的形成过程。我们首先合成了添加少量Sr和Ba作为示踪剂的CAIs，并通过测定样品中Sr和Ba的分布来研究矿物的结晶顺序。结果表明，Sr/Ca-Ba/Ca比值曲线可以很好地描述CAIs的结晶过程，基于CAIs中矿物间氧同位素的不均匀分布，认为CAIs不可能是由熔融状态的单一冷却过程形成的。这表明，CAIs观察到的不均匀分布解释了反复快速加热和冷却的气体环境中的变化的氧同位素Ratios，而部分熔化。我们已经进行了实验，其中合成的CAIs没有Sr和Ba示踪剂插入示踪剂掺杂的Ca，Al丰富的熔体和冷却的重熔-再结晶过程中，通过确定Sr和Ba在固体产品中的分布进行了研究。Sr/Ca与Ba/Ca比值的关系曲线是描述再熔-再结晶过程的有效工具，黄长石是Ca_2Al_2SiO_7和Ca_2MgSi_2O_7两种端元的固溶体。当加热到固相线和液相线之间的温度时，预期分离成固相线组成的小晶体和液相线组成的液体。我们将合成黄长石晶体加热到这样的温度，发现产生了由钙黄长石和镁黄长石玻璃的微小晶体组成的镶嵌结构。