Metallographic Cooling Rate and Petrogenesis of the Recently Found Huoyanshan Iron Meteorite Shower

1,2Nian Wang,3,4Guiqin Wang,1,2Ting Zhang,1Lixin Gu,1Chi Zhang,1Sen Hu,5Bingkui Miao,1,2Yangting Lin
Journal of Geophysical Research (Planets) (In Press) Link to Article [https://doi.org/10.1029/2021JE006847]
1Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
2University of Chinese Academy of Sciences, Beijing, 100049 China
3State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640 China
4CAS Center for Excellence in Comparative Planetology, China
5Key Laboratory of Geological Engineering Center of Guangxi Province, Guilin University of Technology, Guilin, 541004 China
Published by arrangement with John Wiley & Sons

The Huoyanshan iron meteorite shower, recently found in the Gobi Desert of Hami, Xinjiang, China, has very high Ni (21.1 wt%) content and low Au (2.0 ppm), Ir (0.02 ppm), Ge (1.7 ppm), and Ga (1.1 ppm) contents, and was classified into IAB-sLH subgroup. The iron has a finest octahedrite structure of Widmanstätten pattern (the intergrowth of kamacite (α) and taenite (γ)) with plessite matrix, and euhedral schreibersite (Sch) crystals exclusively enclosed in kamacite bands. The textural features suggest the following formation process: γ→γ + Sch →γ+ Sch + α, and then γ→α2 + γ. The metallographic cooling rate of Huoyanshan iron was determined to be 3–50 °C/Myr using both the taenite Ni profile-matching and taenite central Ni content methods, with the bandwidths corrected for crystallographic orientation by electron backscatter diffraction (EBSD). The cooling rate of Huoyanshan is consistent with other sLH and confirms the slow cooling history of the IAB low-Au subgroups. The slow cooling rates of non-magmatic irons required immediate re-accretion with a thick brecciated fragments layer in the parent body after the impact melting event. The depleted but unfractionated Re, Os, Ir, Ru, and Pt and the enriched Pd and Au abundances of Huoyanshan iron and other sLH subgroup show complementary feature to that of refractory metal nuggets in Ca-, Al-rich inclusions (CAIs), which could be explained by extracting the metallic Fe-Ni with HSE predominantly remained in CAIs from a CAI-bearing asteroid. The very high Ni content of sLH subgroup suggests a highly oxidized parental asteroid, but non-carbonaceous chondrite based on Mo isotopic compositions (Worsham et al., 2017). We propose that the Huoyanshan iron and other sLH subgroup were produced by impact melting of a LL like and CAI-bearing asteroid, followed by fast burying of thick and porous silicate breccia.

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