^1,2L.Allibert,^1,5J.Siebert,¹S.Charnoz,³S.A.Jacobson,⁴S.N.Raymond
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115325]
¹Institut de Physique du Globe de Paris, Université de Paris, 1 Rue Jussieu, Paris, France
²Museum für Naturkunde, Invalidenstrasse 43, Berlin, Germany
³Michigan State University, Earth and Environmental Sciences, 288 Farm Ln, East Lansing, MI 48824, USA
⁴Laboratoire d’Astrophysique de Bordeaux, Allée Geoffroy St Hilaire, Bordeaux, France
⁵Institut Universitaire de, France
Copyright Elsevier

Impact-induced erosion of the Earth’s early crust during accretion of terrestrial bodies can significantly modify the primordial chemical composition of the Bulk Silicate Earth (BSE, that is, the composition of the crust added to the present-day mantle). In particular, it can be particularly efficient in altering the abundances of elements having a strong affinity for silicate melts (i.e. incompatible elements) as the early differentiated crust was preferentially enriched in those. Here, we further develop an erosion model (EROD) to quantify the effects of collisional erosion on the final composition of the BSE. Results are compared to the present-day BSE composition models and constraints on Earth’s accretion processes are provided. The evolution of the BSE chemical composition resulting from crustal stripping is computed for entire accretion histories of about 50 Earth analogs in the context of the Grand Tack model. The chosen chemical elements span a wide range of incompatibility degrees. We find that a maximum loss of 40wt% can be expected for the most incompatible lithophile elements such as Rb, Th or U in the BSE when the crust is formed from low partial melting rates. Accordingly, depending on both the exact nature of the crust-forming processes during accretion and the accretion history itself, Refractory Lithophile Elements (RLE) may not be in chondritic relative proportions in the BSE. In that case, current BSE estimates may need to be corrected as a function of the geochemical incompatibility of these elements. Alternatively, if RLE are indeed in chondritic relative proportions in the BSE, accretion scenarios that are efficient in affecting the BSE chemical composition should be questioned.

¹Yan Zhuang,^1,2Hao Zhang,¹Pei Ma,¹Te Jiang,³Yazhou Yang,⁴Ralph E.Milliken,^5,2Weibiao Hsu
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115346]
¹School of Earth Sciences, China University of Geosciences, Wuhan, China
²CAS Center for Excellence in Comparative Planetology, Hefei, China
³Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, China
⁴Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, USA
⁵Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, China
Copyright Elsevier

Most solid planetary bodies in the solar system are covered by a layer of fine particles and the topic of light scattering by small particles has been thoroughly studied in the past decades. In contrast, light reflection from intact rocks has received much less attention, though the spectral features of fresh rocks are more diagnostic than that of highly space-weathered regolith grains. As high spatial-resolution spectral images obtained by modern space-borne and in-situ sensors have become available, it is important to understand the spectral feature links between rocks and powders made by crushing the rocks. In this work, we selected 13 terrestrial igneous rocks with a 1 μm absorption feature and measured the visible and near-infrared reflectance spectra of their slabs and powders in three size fractions, 0-45 μm, 90-125 μm, and 450-900 μm. We have found that the spectral characteristics of these samples can be divided into two groups. For slabs with reflectance lower than 0.1 at 0.5 μm, they have less pronounced 1 μm absorption feature. For slabs with reflectance higher than 0.1, they have pronounced 1 μm feature, consistent with that of their powdered counterparts. By using the equivalent-slab and the Hapke model, we obtained the optical constants and single scattering albedo values of the samples. The dependence of single scattering albedo on effective absorption thickness indicates that the differences between the spectral characteristics of rock slabs and powdered samples are likely controlled by the degree of weak surface scattering contributions. We reconstructed the spectrum of a powdered lunar meteorite which best matches the Chang’E-4 rock and found that the reconstructed rock spectra are very close to the rock spectrum observed in suit by Chang’E-4.