新疆库木塔格004号陨石球粒类型研究及其在球粒分类体系的应用

THE RESEARCH OF CHONDRULES TYPES OF KUMTAG 004 CHONDRITE FROM XINJIANG AND THE APPLICATION OF CHONDRULES CLASSIFICATION SCHEMES

球粒是球粒陨石的主要组分,目前球粒分类体系主要有3种,即结构分类、FeO-SiO2分类和M-FeO-CaO分类。球粒结构分类过于依赖结构与形态,而与化学成分联系不紧密。FeO-SiO2分类体系和M-FeO-CaO分类体系在传统的结构分类体系基础上加入了矿物化学分类参数,这有利于进一步研究太阳星云演化的物理化学过程。但与结构分类相比,很少利用FeO-SiO2和M-FeO-CaO分类体系对陨石球粒进行分类。本次所研究陨石为中国新发现的沙漠陨石富集区——新疆库木塔格沙漠004号陨石(L4,S4,W3),在对其中的球粒进行了详细普查和研究的基础上,分别利用3种分类体系对该陨石中的球粒进行分类,并进一步探讨了FeO-SiO2分类和M-FeO-CaO分类方法优缺点与应用范围。通过对比分析,提出了后两种分类方法的改进意见:针对FeO-SiO2分类体系,提出以硅酸盐中FeO=7.5%(wt%)为I型和Ⅱ型球粒分界线,SiO2=47%及53%(wt%)为A型、AB型和B型球粒分界线。FeO-SiO2分类体系不仅能应用于斑状球粒,也适用非斑状球粒。对M-FeO-CaO分类体系依据辉石组分(FeO及CaO,单位wt%)对A1型(FeO<1,CaO>1)、A2型(FeO≈1—3,CaO<0.5)、A5型(FeO≈11—14,CaO≈0.3—0.9)和B型(FeO>3,CaO<0.5)球粒的类型区间进行了初步划分。

Chondrules are the main constituents of chondrites .There are 3 main kinds of classification schemes of chon-drules currently, i.e., texture, FeO-SiO2 and M-FeO-CaO.The texture classification depends on texture and mor-phology highly but chemical composition unclosely .The FeO-SiO2 and M-FeO-CaO classification schemes introduce mineral chemical criteria onto traditional texture taxonomic scheme and provide further insight into the physical -chemical process occurring in the solar nebula .But the practical applications are too few for the latter two schemes . The chondrules in Kumtag 004 （L4, S4, W3） from the new desert meteorites enrichment region-Kumtag desert of Xinjiang have been classified based on the three classification schemes after observing structure and analyzing com -position.Then we discuss the advantages and disadvantages of the FeO-SiO2 and M-FeO-CaO classification schemes and the application range .For the FeO-SiO2 taxonomic scheme that can be applied to porphyritic chondrules as well as non-porhyritic chondrules , we suggest that FeO =7.5% （ wt%） is the boundary between type I and Ⅱ chon-drules and so are 47%and 53%（ SiO2 , wt%） for type A, AB and B chondrules .A approximate partition is pro-posed for the type A1（FeO1）, A2（FeO≈1-3,CaO3,CaO〈0.5） chondrules for the M-FeO-CaO classification scheme based on the pyroxene （FeO and CaO , wt%） .