Aqueous alteration of opaque assemblages in the Ningqiang carbonaceous chondrite: Evidence from oxygen isotopes

Weibiao Hsu, Yunbin Guan, Xin Hua, Ying Wang, L. A. Leshin, Thomas Sharp

Research output: Contribution to journalArticle

13 Scopus citations

Abstract

Chondrules and matrix of the Ningqiang carbonaceous chondrite contain numerous opaque assemblages (OAs). These OAs are mainly composed of Ni-rich metal, magnetite, sulfides, phosphates with minor amounts of silicates and trace amounts of Pt-metal grains. Their mineral assemblage is very similar to that of OAs found in Allende refractory inclusions. In this study, we performed in situ analyses of O-isotopic compositions of magnetite and whitlockite in OAs and of olivine adjacent to OAs from Ningqiang. O-isotopic compositions of magnetite vary by 16‰ in δ18O and fall on a regression line with a slope of 0.51 and a mean Δ17O of -2.9 ± 0.3 (1σ)‰ in the three-O-isotope diagram. Magnetite grains have consistently higher Δ17O values than their adjacent olivine grains. The mineral chemistry and O-isotopic compositions of OAs in Ningqiang chondrules and matrix are most consistent with the formation of magnetites and whitlockite by aqueous alteration of preexisting metal alloys within a planetary body. Formation of magnetites and phosphates in OAs thus do not constrain processes in the early solar nebula, but rather provide information on metamorphism in a planetary environment.

Original languageEnglish (US)
Pages (from-to)107-114
Number of pages8
JournalEarth and Planetary Science Letters
Volume243
Issue number1-2
DOIs
StatePublished - Mar 15 2006

Keywords

  • Aqueous alteration
  • Ion microprobe
  • Ningqiang carbonaceous chondrite
  • Opaque assemblages
  • Oxygen isotopes

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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