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

Hsu, Weibiao and Guan, Yunbin and Hua, Xin and Wang, Ying and Leshin, L. A. and Sharp, T. G. (2006) Aqueous alteration of opaque assemblages in the Ningqiang carbonaceous chondrite: Evidence from oxygen isotopes. Earth and Planetary Science Letters, 243 (1-2). pp. 107-114. ISSN 0012-821X. doi:10.1016/j.epsl.2005.12.021.

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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.

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Guan, Yunbin0000-0002-7636-3735
Sharp, T. G.0000-0003-2287-9370
Additional Information:The authors thank H. Yurimoto, A. El Goresy, and an anonymous reviewer for their constructive reviews. This work was supported by Chinese National Natural Science Foundation for Distinguished Young Scholars (Grant No. 40325009), by “One-Hundred-Talent Program” of Chinese Academy of Sciences, by the Minor Planet Foundation of China, and by NASA grant NNG05GH37G (LAL/YG). Xin Hua acknowledges the fellowship support from the K.C. Wong Education Foundation.
Funding AgencyGrant Number
National Natural Science Foundation of China40325009
Chinese Academy of SciencesUNSPECIFIED
Minor Planet Foundation of ChinaUNSPECIFIED
K. C. Wong Education FoundationUNSPECIFIED
Issue or Number:1-2
Record Number:CaltechAUTHORS:20230307-650252000.34
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ID Code:119743
Deposited By: George Porter
Deposited On:12 Mar 2023 22:39
Last Modified:12 Mar 2023 22:39

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