¹James M. D. Day, ¹Christopher A. Corder, ²Douglas Rumble III, ³Nelly Assayag, ³Pierre Cartigny,⁴Lawrence A. Taylor
¹Geosciences Research Division, Scripps Institution of Oceanography, La Jolla, California, USA
²Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, USA
³Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, UMR 7154 CNRS, Paris, France
⁴Department of Earth and Planetary Sciences, Planetary Geosciences Institute, University of Tennessee, Knoxville, Tennessee, USA

Olivine-dominated (70–80 modal %) achondrite meteorite Lewis Cliff (LEW) 88763 originated from metamorphism and limited partial melting of a FeO-rich parent body. The meteorite experienced some alteration on Earth, evident from subchondritic Re/Os, and redistribution of rhenium within the sample. LEW 88763 is texturally similar to winonaites, has a Δ17O value of −1.19 ± 0.10‰, and low bulk-rock Mg/(Mg+Fe) (0.39), similar to the FeO-rich cumulate achondrite Northwest Africa (NWA) 6693. The similar bulk-rock major-, minor-, and trace-element abundances of LEW 88763, relative to some carbonaceous chondrites, including ratios of Pd/Os, Pt/Os, Ir/Os, and 187Os/188Os (0.1262), implies a FeO- and volatile-rich precursor composition. Lack of fractionation of the rare earth elements, but a factor of approximately two lower highly siderophile element abundances in LEW 88763, compared with chondrites, implies limited loss of Fe-Ni-S melts during metamorphism and anatexis. These results support the generation of high Fe/Mg, sulfide, and/or metal-rich partial melts from FeO-rich parent bodies during partial melting. In detail, however, LEW 88763 cannot be a parent composition to any other meteorite sample, due to highly limited silicate melt loss (0 to <<5%). As such, LEW 88763 represents the least-modified FeO-rich achondrite source composition recognized to date and is distinct from all other meteorites. LEW 88763 should be reclassified as an anomalous achondrite that experienced limited Fe,Ni-FeS melt loss. Lewis Cliff 88763, combined with a growing collection of FeO-rich meteorites, such as brachinites, brachinite-like achondrites, the Graves Nunataks (GRA) 06128/9 meteorites, NWA 6693, and Tafassasset, has important implications for understanding the initiation of planetary differentiation. Specifically, regardless of precursor compositions, partial melting and differentiation processes appear to be similar on asteroidal bodies spanning a range of initial oxidation states and volatile contents.

Reference
Day JMD, Corder CA, Rumble III D, Assayag N, Cartigny P, Taylor LA (2015) Differentiation processes in FeO-rich asteroids revealed by the achondrite Lewis Cliff 88763. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12509]

Published by arrangement with John Wiley&Sons

^1,2Vogel, N., ³Bochsler, P., ³Bühler, F., ^4,5Heber, V. S., ³Grimberg, A., ¹Baur, H., ⁵Horstmann, M., ⁵Bischoff, A., ¹Wieler, R.
¹Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland
²Department of Water Resources and Drinking Water, Eawag, Swiss Federal Institute for Aquatic Research, Dübendorf, Switzerland
³Physikalisches Institut, University of Bern, Bern, Switzerland
⁴Department of Earth, Planetary and Space Sciences, University of California Los Angeles, Los Angeles, California, USA
⁵Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Münster, Germany
⁶Division of Radiation Protection and Safety, Paul Scherrer Institut, OFLC/U103, Villigen PSI, Switzerland

We compare the solar wind (SW) He, Ne, and Ar compositions collected during the Apollo Solar Wind Composition (SWC) experiments (1969–1972; Al- & Pt-foils) and the Genesis mission (2002–2004; so-called DOS targets considered here). While published SW 20Ne/22Ne and 36Ar/38Ar ratios of both data sets agree, differences exist in the 4He/3He, 4He/20Ne, and 20Ne/36Ar ratios. However, 20Ne/36Ar ratios from Apollo-16 Pt-foils, exclusively adopted as SW values by the SWC team, are consistent with the Genesis results. We investigate if the differences indicate a variability of the SW over the course of about 30 yr, or systematic biases of the two data sets, which were collected in different environments and measured several decades apart in different laboratories (University of Bern; ETH Zurich). New measurements of Apollo-15 SWC aluminum foils in Zurich generally agree with the original measurements performed in Bern. Zurich samples show slightly lower 4He concentrations suggesting a few percent of diffusive loss of 4He during storage of the foils. A 3% difference between the He isotopic ratios measured in Bern and in Zurich possibly represents an analytical bias between the laboratories. The low SW 4He/20Ne and 20Ne/36Ar ratios in Apollo-15 Al-foils compared to Genesis data are consistent with a mixture of Genesis-like SW and noble gases from small amounts of lunar dust. Our data suggest that the mean SW He, Ne, and Ar isotopic and elemental compositions have not significantly changed between the overall Apollo and Genesis mission collection periods.

Reference
Vogel N, Bochsler P, Bühler F, Heber VS, Grimberg A, Baur H, Horstmann M, Bischoff A, Wieler R (2015) Similarities and differences between the solar wind light noble gas compositions determined on Apollo 15 SWC foils and on NASA Genesis Targets. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12503]

Published by arrangement with John Wiley&Sons