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Formation processes of achondrite parent bodies as inferred from meteorites.

从陨石推断无球粒陨石母体的形成过程。

基本信息

批准号：
02405002
负责人：
TAKEDA Hiroshi
金额：
$ 4.61万
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 (A)
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

Achondrites are differentiated meteorites developed on primitive protoplanets, which have been formed by crystallization of totally or partially molten primitive source materials in the early solar system. We have tried to reconstruct their protoplanets on the basis of mineralogy and chemistry of their component materials and deduced their formation conditions. A method of computer image processing techniques (CMA method) has been applied to utilize elemental distribution maps obtained by SEM in terms of RGB color images. The image are stored on MD discs to be used as image database of achondrites.A group of meteorites with achondritic textures, but with signatures of chondritic primitive materials have been related to S-type asteroids most abundant in the main belt asteroids. These meteorites can be formed by partial removal of Al-Ca-rich partial melts and relocation of Fe-Ni-S eutectic melts and crystal growth induced by planetesimal-scale collisions. Two new Antarctic meteorites we studied belong to this group and fill gaps between primitive achondrites and lodranites, stony iron meteorites of one of its kind.Brecciated basalt-like meteorites known as monomict eucrites show quickly grown textures but with homogeneous chemistry of their Mg-Fe distribution in pyroxenes. Application of the CMA method shows that they are products of thermal annealing on a protoplanet. All these eucrites have been classified into type 1 to 6 on the basis of degrees of homogenization of their pyroxenes by the thermal metamorphism related to the cratering events on the parent body.Two new lunar meteorites have been investigated by the CMA method and are turned out to be breccias of thick mare basalts. They include low Ti basalts not too well represented in the Apollo samples. Early crystallized Mg-rich mare components were also identified.

无球粒陨石是发育在原始原行星上的分异陨石，由太阳系早期原始源物质全部或部分熔融结晶而成。我们试图在其组成物质的矿物学和化学基础上重建它们的原行星，并推断它们的形成条件。应用计算机图像处理技术（CMA方法）利用扫描电子显微镜在RGB彩色图像上得到的元素分布图。图像存储在光盘上，作为无球粒的图像数据库。一组具有球粒质结构，但具有球粒质原始物质特征的陨石与主带小行星中最丰富的s型小行星有关。这些陨石可能是由富al- ca部分熔体的部分去除和Fe-Ni-S共晶熔体的重新安置以及星子尺度碰撞引起的晶体生长形成的。我们研究的两颗新的南极陨石属于这一组，填补了原始无球粒陨石和lodranites之间的空白，lodranites是同类中的一种石铁陨石。角化玄武岩类陨石被称为单晶长辉长岩，显示出快速生长的结构，但在辉石中具有均匀的Mg-Fe化学分布。CMA方法的应用表明，它们是原行星上热退火的产物。根据其辉石的均质程度和母岩上陨坑事件的热变质作用，将其划分为1 ~ 6型。用CMA方法研究了两颗新的月球陨石，证实它们是厚海玄武岩的角砾岩。它们包括低钛玄武岩，在阿波罗样品中没有很好地代表。发现了早期结晶的富镁成分。