地学前缘 ›› 2009, Vol. 16 ›› Issue (1): 134-145.

• 论文 • 上一篇    下一篇

动态高压下陨石矿物的冲击熔融和分离结晶及其地球化学意义

  

  1. 中国科学院 广州地球化学研究所, 广东 广州 510640

  • 出版日期:2009-02-02 发布日期:2009-02-02
  • 作者简介:谢先德(1934—),男,研究员,俄罗斯科学院院士,矿物学专业,从事近代矿物学、高压矿物学和天体矿物学研究。E-mail: xdxie@gzb.ac.cn
  • 基金资助:

    国家自然科学基金项目(40772030)

Shock melting and fractional crystallization of meteorite minerals under dynamic highpressures and their geochemical significance

  1. Guangzhou Insitiute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China

  • Online:2009-02-02 Published:2009-02-02

PDF (PC)

776

摘要：

应用近代微束矿物学分析测试技术,对在中国陨落的随州、寺巷口和岩庄等三块球粒陨石中矿物的冲击熔融和分离结晶作用进行了较系统的研究。查明存在有硅酸盐单矿物熔体、硅酸盐矿物混合熔体和全岩熔体三种组成不同的冲击熔体。研究结果显示:(1)三种熔融相与未熔相之间在主成分和微量元素组成上没有明显差别,说明它们是原地熔融的产物,但在较大的冲击熔块中,也发现冲击熔融作用引发了一部分元素,如亲铁元素、硒元素和轻重稀土元素的分异现象;(2)查明Al2O3、Cr2O3、Na2O和CaO等优先进入从冲击熔体结晶的辉石常压相或辉石的高压相——镁铁榴石(属地幔过渡带矿物)中;(3)Al元素能进入阿基莫石(即辉石的钛铁矿结构相,属下地幔矿物)中,以固熔体形式稳定下来。ELNES的测定查明,其氧化铁组分中Fe3+/∑Fe的比值高达067(3);(4)陨石全岩熔体中硅酸盐相与金属硫化物相之间为完全不混熔,后者以孤立的共结体团块产于硅酸盐熔体之中,除Zn、Na、Cr、Co和Cu在硫化物相中和Na在金属相中有明显富集外,其他元素的浓度则无明显变化;(5)在寺巷口陨石熔脉的金属硫化物共结团块内发现了FeNi金属硫化铁磁铁矿组合,进一步证实了S和O等轻元素可以加入到以FeNi金属为主要组成的地核成分中去;(6)在岩庄陨石的FeNi金属硫化铁共结体团块的硫化铁内发现了Na、Mn和Fe的磷酸盐矿物小球体,说明P和Na、Mn等元素也能成为地核的组成元素。以上研究在行星演化、地幔矿物学和地球化学,以及陨石学研究上均有着重要的科学意义。

关键词: 陨石矿物; 高温高压; 冲击熔融; 分离结晶; 元素配分

Abstract:

Abstract:  We have systematically studied the shock melting and the fractional crystallization of minerals in the three Chinese fallen chondrites, the Suizhou, the Sixiangkou and the Yanzhuang chondrite, using modern micromineralogical techniques. It was revealed that there exist three types of shockinduced melts, namely, the monomineral silicatemelt, the mixed silicatemineralmelt, and the wholerock melt. The research results may be summed up as follows. (1)No obvious differences in major and trace element constituents between the melted and unmelted phases, implying that they are the products of insitu melting. However, the shock melting process did cause the differentiation of some siderophile elements, of light and heavy rare earth elements, and of the element Se in some large melt pockets. (2)Al2O3, Cr2O3, Na2O, and CaO preferentially entered into pyroxene or its highpressure polymorphic majorite (main mineral phase in Earths transition zone), both of which were crystallized from the shock induced silicate melts. (3)The element Al may enter into akimotoite, the ilmenitestructured polymorph of pyroxene and one of the mineral phases in lower mantle, and stabilized as the solid solution. The ELNES analyses revealed that the Fe3+/∑Fe ratio for akimotoite is as high as 067(3). (4)The complete immiscibility of silicate and metalsulfide phases is observed in the whole rock melt, and the latter occurs in the silicate melt as isolated eutectic nodules. No significant differences were found in the concentrations of elements in the melted and unmelted phases, except the Zn,Na,Cr,Co and Cu enrichment in molten sulfide phase and the Na enrichment in molten metal phase. (5)The presence of the FeNi metaltroilitemagnetite assemblage in a melt vein of Sixiangkou chondrite implies that the light elements of S and O may be involved in the Earths core in which FeNi metal is the main mineral composition. (6)Some spherules of Na, Mn and Fe phosphates were observed in the FeNiFeS eutectic nodules in the Yanzhuang chondrite, indicating that the elements of P, Na and Mn may be also involved in the Earths core. The above mentioned phenomena are of important significance in the study of planet evolution, in the Earths mantle mineralogy and geochemistry, as well as in meteoritics itself.

Key words:

Key words: meteorite mineral; high pressure and temperature; shock melting; fractional crystallization; element partitioning

中图分类号: