Occurrences, abundances, and compositional variations of cosmic symplectites in the Acfer 094 ungrouped carbonaceous chondrite

• Abe Kenichi

  Department of Natural History Sciences, Hokkaido University

• Sakamoto Naoya

  Isotope Imaging Laboratory, Creative Research Institution Sousei, Hokkaido University

• Krot Alexander N.

  Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Manoa

• Yurimoto Hisayoshi

  Department of Natural History Sciences, Hokkaido University Isotope Imaging Laboratory, Creative Research Institution Sousei, Hokkaido University ISAS/JAXA

抄録

We describe the petrographic occurrences, abundances, and compositional variations of symplectically intergrown Fe,Ni-sulfides and ^17,18O-rich magnetite (Δ¹⁷O ~ 90‰), named cosmic symplectites (COS; Sakamoto et al., 2007), from the Acfer 094 (C3.0) ungrouped carbonaceous chondrite. A total of 314 COS studied in two polished sections of this meteorite are uniformly distributed in its matrix with ~600 ppm surface area abundance. No COS have been identified in the Acfer 094 dark inclusions (chondritic lithic clasts) which appear to have experienced extensive aqueous alteration prior to incorporation into the host meteorite. The structure of COS can be arranged in a hierarchy of four categories (from finer to coarser): (1) symplectite structure composed of nanocrystalline magnetite and Fe,Ni-sulfides, (2) submicron-sized wormy structure composed of nanocrystalline symplectites, (3) micrometer-sized irregular rope-like structure composed of wormy structure, and (4) aggregates of the rope-like structure. COS typically associate with fractured Fe,Ni-sulfides and lack Fe,Ni-metal. Most COS studied have smooth surfaces; four grains contain abundant pores. In a single COS, the pore-rich regions are depleted in sulfur and nickel relative to the pore-free regions, indicating that the former are depleted in Fe,Ni-sulfides. Most COS studied contain similar abundances of Fe,Ni-sulfides and magnetite, whereas Ni/(Fe+Ni) atomic ratio in Fe,Ni-sulfides ranges from 0 to 0.4. The lack of Fe,Ni-metal associated with COS supports the formation process proposed by Seto et al. (2008), i.e., oxidation of Fe,Ni-metal and sulfides by ^17,18O-rich water vapor in the outer part of the protoplanetary disk. The similar abundance ratio for Fe,Ni-sulfide and magnetite cannot be simply explained by oxidation processes of Fe,Ni-sulfide precursors after sulfurization of Fe,Ni-metal precursors for COS formation as proposed by Seto et al. (2008).

収録刊行物

• ＧＥＯＣＨＥＭＩＣＡＬ　ＪＯＵＲＮＡＬ

  ＧＥＯＣＨＥＭＩＣＡＬ　ＪＯＵＲＮＡＬ 51 (1), 3-15, 2017

  一般社団法人日本地球化学会

キーワード

• cosmic symplectite
• magnetite
• Fe,Ni-sulfides
• Acfer 094 carbonaceous chondrite

詳細情報

• CRID: 1390001204553889792
• NII論文ID: 130005317106
• NII書誌ID: AA00654975
• DOI: 10.2343/geochemj.2.0454
• ISSN: 18805973
• ISSN: 00167002
• NDL書誌ID: 028042245
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I028042245
• Web Site: https://www.jstage.jst.go.jp/article/geochemj/51/1/51_2.0454/_pdf
• 本文言語コード: en
• データソース種別:
  • JaLC
  • NDL
  • Crossref
  • CiNii Articles
  • KAKEN
• 抄録ライセンスフラグ: 使用不可