¹Lingzhi Sun,¹Paul G. Lucey,¹G. Jeff Taylor
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2020JE006445]
¹Hawai‘i Institute of Geophysics and Planetology, Dept. of Earth Sciences, University of Hawai‘i at Manoa, 1680 East‐West Rd., Honolulu, Hi, 96822 USA
Published by arrangement with >John Wiley & Sons

Although lunar soils contain rock and mineral components from the breakdown of a mixture of rock types, a classification based on the abundances of the major silicate minerals plagioclase, olivine, low‐Ca pyroxene (LCP) and high‐Ca pyroxene can be used to evaluate the major compositional classes that are represented within a given soil. We studied the compositional classes for Apollo 15, 16 and 17 soil samples based on the mineral modal abundances derived by X‐ray diffraction (XRD). Using the XRD results as a ground truth, we determined the compositional classes of the Apollo 15, 16 and 17 sampling stations using mineral maps from the Kaguya Multiband Imager (MI), then mapped areas having compositional classes similar to the sampling stations on regional and global scales. Global distribution of compositional classes was also mapped using MI mineral maps, and the major compositional classes of lunar nonmare surfaces are noritic anorthosite (40 %), anorthositic norite (24 %), and anorthosite (23 %). Our maps show that the lunar highlands and the South Pole‐Aitken (SPA) basin are enriched with noritic materials, indicating the widespread occurrence of LCP‐rich and olivine‐poor assemblages. In contrast to the SPA basin and the highlands, the basin rings of Serenitatis, Crisium, Humorum, Nectaris, Orientale and Hertzsprung exhibit higher olivine/pyroxene ratios (>2), and we interpret this signature as reflecting a contribution from olivine‐rich upper mantle components.

¹Paul Frossard,²Zhiguo Guo,²Mary Spencer,¹Maud Boyet,^2,3Audrey Bouvier
Earth and Planetary Science Letters 566, 116968 Link to Article [https://doi.org/10.1016/j.epsl.2021.116968]
¹Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000 Clermont-Ferrand, France
²Department of Earth Sciences, University of Western Ontario, N6A 5B7 London, Ontario, Canada
³Bayerisches Geoinstitut, Universität Bayreuth, 95447 Bayreuth, Germany
Copyright Elsevier

Heterogeneity in isotopic compositions within the protoplanetary disc has been demonstrated for a number of elements measured in extra-terrestrial materials, mostly based on chondrite meteorite analyses. However, precise 182Hf-182W and 26Al-26Mg ages of iron meteorites, achondrites, and chondrules show that chondrites accreted later than achondrites and therefore do not strictly represent the early (<2 Ma) solar system composition. Here we present the Nd mass-independent stable isotopic compositions of a suite of diverse achondrites to better constrain the Nd isotope evolution of the early solar system. Carbonaceous (C) achondrites are indistinguishable from their chondritic counterpart. However, early formed planetesimals as sampled by silicate-rich non-carbonaceous (NC) achondrite meteorites have higher 145Nd/144Nd and 148Nd/144Nd ratios (3.9 < Nd < 11.0 and 9.1 < Nd < 17.9 in part per million deviation, or Nd) compared to NC chondrites (2.7 < Nd < 3.3 and 2.2 < Nd < 8.1). Moreover, the three terrestrial planets for which we have samples available (Earth, Mars, and the Moon) as well as the silicate inclusions from the non-magmatic IIE iron meteorite Miles present a systematic deficit in Nd and Nd compared to early-formed NC achondrites. Unlike chondrites, the Nd anomalies in achondrites are not correlated to the heliocentric distance of accretion of their respective parent bodies as inferred from redox conditions. Chronological constraints on planetesimal accretion suggest that Nd (and other elements such as Mo and Zr) nucleosynthetic compositions of the inner part of the protoplanetary disc significantly changed around 1.5 Ma after Solar System formation due to thermal processing of dust in the protoplanetary disc. This relatively late event coincides with the beginning of chondrule formation or at least their preservation. Terrestrial planets formed subsequently by a complex accretion regime during several million years. Therefore, two scenarios are envisioned considering the reported Nd isotope composition of early planetesimals: 1) Terrestrial planets accreted mostly chondritic material similar in composition to enstatite chondrites, or 2) early planetesimals constitute substantial parts of terrestrial planets building blocks mixed with highly thermally processed material enriched in s-process, still unsampled by meteorites.