¹Yassir A. ABDU,²Abbasher M. GISMELSEED,³Atta G. ATTAELMANAN,⁴Muawia H. SHADDAD,⁵Frank C. HAWTHORNE
Meteoritics & Planetary Science (in Press) Link to Article [doi: 10.1111/maps.13988]
¹Department of Applied Physics and Astronomy, University of Sharjah, Sharjah, United Arab Emirates
²Department of Physics, Sultan Qaboos University, Muscat, Oman
³College of Arts, Sciences and Information Technology, University of Khorfakkan, Khorfakkan, United Arab Emirates
⁴Department of Physics, University of Khartoum, Khartoum, Sudan
⁵Department of Earth Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
Published by arrangement with John Wiley and Sons

The crystal structures of orthopyroxene (En86.3Fs8.6Wo5.1, space group Pbca) and pigeonite (En81.7Fs8.8Wo9.5, space group P21/c) from the Almahata Sitta ureilite (fragment#051) have been refined to R1 indices of 3.10% and 2.53%, respectively, using single-crystal X-ray diffraction data. The unit formulas were calculated from electron microprobe analysis, and the occupancies at the M1 and M2 sites were refined for both pyroxenes from the single-crystal diffraction data. The results indicate a rather disordered intracrystalline Fe2+-Mg cation distribution over the M1 and M2 sites, with a closure temperature of 726(±55)°C for orthopyroxene and 704(±110)°C for pigeonite, suggesting fast cooling of these pyroxenes. The Mössbauer spectrum of the Fe-Ni metal particles of Almahata Sitta ureilite (fragment#051) is dominated by two overlapping magnetic sextets that are assigned to Fe atoms in Si-bearing kamacite, and arise from two different nearest-neighbor configurations of Fe* (=Fe+Ni) and Si atoms in the bcc structure of kamacite; (8F*, 0Si) and (7Fe*, 1Si). In addition, the spectrum shows weak absorption peaks that are attributed to the presence of small amounts of cohenite [(Fe,Ni)3C], schreibersite [(Fe,Ni)3P], and an Fe-oxide/hydroxide phase. The fast cooling of pyroxene to the closure temperature (after equilibration at ~1200°C) and the incorporation of Si in kamacite can be interpreted as due to a shock event that took place on the meteorite parent body, consistent with the proposed formation history of ureilites parent body where a fast cooling has occurred at a later stage of its formation.

^1,2Yongli Xue,^2,3,4Jinting Kang,^5,4Shiyong Liao,⁶Runlian Pang,^2,3,4Huimin Yu,^2,3,4Zifu Zhao,⁷Zhaofeng Zhang,⁸Bingkui Miao,^5,3,4 Weibiao Hsu,^2,3,4Fang Huang 
Earth and Planetary Science Letters 613, 118171 Link to Article [https://doi.org/10.1016/j.epsl.2023.118171]
¹Key Laboratory of Gemological Design and Testing, School of Jewelry and Art Design, Wuzhou University, Wuzhou, 543002, China
²CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
³Deep Space Exploration Laboratory, University of Science and Technology of China, Hefei 230026, China
⁴CAS Center for Excellence in Comparative Planetology, USTC, Hefei 230026, Anhui, China
⁵Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China
⁶State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China
⁷Research Center for Planetary Science, Chengdu University of Technology, Chengdu, 610059, China
⁸Institution of Meteorites and Planetary Materials Research, Key Laboratory of Planetary Geological Evolution, Guilin University of Technology, Guilin 541006, China
Copyright Elsevier

Howardite-Eucrite-Diogenite (HED) meteorites represent a large suit of crustal and sub-crustal rocks from the Vesta. This work presents systematic examination of the Ca isotope data on multiple varieties of HED meteorites for a better understanding of the magmatic evolution of the Vesta. Falls and finds possess similar Ca isotope compositions, and no correlation is observed between �44/40Ca and (Sr/Eu*)_n, indicating that terrestrial weathering effect on Ca isotopes is insubstantial. According to the data in literature, the inner solar system may have a homogeneous �44/40Ca and the average of inner solar system bodies (‰0.97±0.03‰) can approximate the composition of bulk silicate Vesta (BSV). Basaltic eucrites define a cluster in �44/40Ca (‰0.95±0.07‰, 2SD, N=15) that is higher than the terrestrial mid-ocean ridge basalts (‰∼0.85‰). Combined with partial melting and magma ocean differentiation modeling, the Ca isotope signatures suggest that eucrites represent the residual melts evolved from a magma ocean formed by primordial Vesta’s moderate-to-high degree melting (20-100%). Diogenites have distinguishingly higher �44/40Ca (‰1.18±0.15‰, 2SD, N=7) than the basaltic eucrites, which displays a negative correlation with the 1000×Lu/Ti ratio and a positive correlation with 1/Ca. However, magma ocean crystallization can only explain diogenites with �44/40Ca higher than 1.17‰, suggesting that diogenites have complicated petrogenesis and are not necessarily cogenetic with eucrites. Diogenites with ‰�44/40Ca<1.17‰ may result from magma-ocean-cumulate partial melts intruding the eucritic crust. Mixing models suggest that the eucritic component in these diogenites may be less than 10%. Two howardites have lower �44/40Ca of ‰0.80±0.04‰ and ‰0.86±0.05‰ than eucrites and diogenites. This signature may reflect the addition of carbonaceous chondritic materials due to impact brecciation.