期刊
GEOCHIMICA ET COSMOCHIMICA ACTA
卷 309, 期 -, 页码 79-95出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.gca.2021.06.017
关键词
U-Pb dating; Metal-silicate mixing; Iron meteorites; Silicate inclusions; Planetesimals; Planetary differentiation
资金
- B-type Strategic Priority Program of the Chinese Academy of Sciences [XDB41000000]
- National Natural Science Foundation of China [41973060, 41773059]
- pre-research Project on Civil Aerospace Technologies - Chinese National Space Administration [D020202, D020302]
- Science and Technology Development Fund of Macau [008/2017/AFJ, 0042/2018/A2, 0105/2020/A3, 0111/2020/A]
- Minor Planet Foundation of China
Silicate-bearing iron meteorites provide insights into the metal-silicate separation and mixing processes of planetesimals. The IIE group, in particular, exhibits complex petrogenesis involving early differentiation and impact-induced dynamic mixing, re-melting, and reduction. Combining X-ray elemental mapping with ion microprobe dating technique reveals distinct groups of phosphates in the Weekeroo Station IIE iron meteorite, shedding light on different formation mechanisms and impact-induced processes.
Silicate-bearing iron meteorites record metal-silicate separation and mixing processes of planetesimals. Of particular interest is the IIE group as its silicate inclusions show great petrological diversity, probably resulting from the complex petrogenesis involving early differentiation and impact-induced dynamic mixing, re-melting, and reduction. These geologic records may have been documented by individual minerals to various extents, which blurs the chronological records on the formation of IIEs. Here, by combining X-ray elemental mapping with ion microprobe dating technique, we show that two groups of phosphates are present in the Weekeroo Station IIE iron meteorite. They have distinct petrography, mineralogy, Th/U ratios, and Pb isotopic compositions, which reflects their different formation mechanisms. One group (Group 1) has a fine-grained, euhedral or acicular habit, suggesting rapid crystallization from a melt during the metal-silicate mixing. By contrast, the other group (Group 2) is intimately associated with the decomposition and reduction of pyroxene under subsolidus conditions. The Group 1 phosphates yield a precise Pb-Pb age of 4528 +/- 11 Ma and they provide the first robust constraint on the timing of impact-induced metal-silicate mixing on the IIE iron meteorite parent body. The Group 2 phosphates, on the other hand, probably record a Pb-Pb age at least 50 Myr younger, and they give insight into the role of subsequent impacts on the alteration of IIE irons. Combining our results with published chronological data suggests that the formation of IIEs irons is consistent with early partial differentiation followed by multiple impact-driven metal-silicate mixing and that most of them were not shielded from subsequent impacts. (C) 2021 Elsevier Ltd. All rights reserved.
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