Calcium-aluminum-rich inclusions in enstatite chondrites (I): Mineralogy and textures

Timothy J. Fagan*, Alexander N. Krot, Klaus Keil

*この研究の対応する著者

研究成果: Article査読

41 被引用数 (Scopus)

抄録

Like calcium-aluminum-rich inclusions (CAIs) from carbonaceous and ordinary chondrites, enstatite chondrite CAIs are composed of refractory minerals such as spinel, perovskite, Al, Ti-diopside, melilite, hibonite, and anorthitic plagioclase, which may be partially to completely surrounded by halos of Na-(±Cl)-rich minerals. Porous, aggregate, and compact textures of the refractory cores in enstatite chondrite CAIs and rare Wark-Lovering rims are also similar to CAIs from other chondrite groups. However, the small size (<100 μm), low abundance (<1% by mode in thin section), occurrence of only spinel or hibonite-rich types, and presence of primary Ti-(±V)-oxides, and secondry geikelite and Ti, Fe-sulfides distinguish the assemblage of enstatite chondrite CAIs from other groups. The primary mineral assemblage in enstatite chondrite CAIs is devoid of indicators (e.g., oldhamite, osbornite) of low O fugacities. Thus, high-temperature processing of the CAIs did not occur under the reducing conditions characteristic of enstatite chondrites, implying that either (1) the CAIs are foreign to enstatite-chondrite-forming regions or (2) O fugacities fluctuated within the enstatite-chondrite-forming region. In contrast, secondary geikelite and Ti-Fe-sulfide, which replace perovskite, indicate that alteration of perovskite occurred under reducing conditions distinct from CAIs in the other chondrite groups. We have not ascertained whether the reduced alteration of enstatite chondrite CAIs occurred in a nebular or parent-body setting. We conclude that each chondrite group is correlated with a unique assemblage of CAIs, indicating spatial or temporal variations in physical conditions during production or dispersal of CAIs.

本文言語English
ページ(範囲)771-781
ページ数11
ジャーナルMeteoritics and Planetary Science
35
4
DOI
出版ステータスPublished - 2000
外部発表はい

ASJC Scopus subject areas

  • 地球物理学
  • 宇宙惑星科学

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