Calcium isotope constraints on the origin of eucrites and diogenites: The role of magma ocean and magmatism

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 []
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.


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