Department of Mineralogical Science and Geology, Faculty of Science, Yamaguchi University
Department of Mineralogical Science and Geology, Faculty of Science, Yamaguchi University
抄録(英)
Significant amounts of iron, magnesium and Na (and/or Ca) vacancy are found in meteoritic plagioclases of the Holbrook (L6), Willard (L6), Plainview (H5), ALH-77307,85 (C3) and Allende chondrites and the Juvinas eucrite. Seven components are used in this study, six of which were used already for lunar plagioclases; that is, KAl(Si)_3O_8,NaAl(Si)_3O_8,Ca(Al)_2(Si)_2O_8,(Fe, Mg)(Al)_2(Si)_2O_8,Ca(Fe, Mg)(Al)_3O_8,[ ](Si)_4O_8 and M(MT)O_8,where [ ] means Na and/or Ca vacancy, M=K, Na, Ca, and T=Al, Si. The amounts of components Ca(Fe, Mg)(Si)_3O_8 and (Fe, Mg)(Al)_2(Si)_2O_8 significantly decrease with ordinary An-content. The highest contents of components Ca(Fe, Mg)(Si)_3O_8 and (Fe, Mg)(Al)_2(Si)_2O_8 in this study are obtained as 29(mol%) in the ALH-77307,85 (C3) and 11(mol%) in the Allende (CV3) chondrites, respectively. The largest values of components [ ](Si)_4O_8 and M (MT)O_8 are found in this study as 8(mol%) in the Juvinas eucrite and 12(mol%) in the Allende (CV3) chondrite, respectively. Lower Fe/(Fe+Mg) ratio is characteristic of chondrule in meteorite. The Plainview chondrite showing unique behavior of a considerable variation of the components may indicate a mixture of various parent materials. Small amounts of excess M cations (i.e. M(MT)O_8) are observed mainly in the exsolved regions of plagioclase crystal in meteorite (esp. the Juvinas eucrite and the Holbrook chondrite). A plot of each end-member abundance vs. Ca(Al)_2(Si)_2O_8 may be considered a useful indicator of the formation process of the meteorite.
雑誌書誌ID
AA00733561
雑誌名
Memoirs of National Institute of Polar Research. Special issue
Composition and structural substitution of meteoritic plagioclases (I)
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KJ00000012357
(2.18MB)
概要
