^1,2Li‐Lin Huang,^1,2Bing‐Kui Miao,^1,2Guo‐Zhu Chen,^1,2Hui‐Min Shao,³Zi‐Yuan Ouyang
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13495]
¹Institution of Meteorites and Planetary Materials Research, Guilin University of Technology, Guilin, 541004 China
²Key Laboratory of Planetary Geological Evolution, Guilin University of Technology, Guilin, 541004 China
³Key Laboratory of Lunar and Deep Space Exporation, CAS, Beijing, 100101 China
Published by arrangement with John Wiley & Sons

Some of the tridymite in the monomict Northwest Africa (NWA) 11591 eucrite are found to have sulfide‐rich replacement textures (SRTs) to varying degrees. The SRTs of tridymite in NWA 11591 are characterized by the distribution of loose porous regions with aggregates of quartz and minor troilite grains along the rims and fractures of the tridymite, and we propose a new mechanism for the origin of this texture. According to the volume and density conversion relationship, the quartz in the SRT of tridymite with a hackle fracture pattern was transformed from tridymite. We suggest that the primary tridymite grains are affected by the S‐rich vapors along the rims and fractures, leading to the transformation of tridymite into quartz. In addition, the S‐rich vapors reacted with Fe2+, which was transported from the relict tridymite and/or the adjacent Fe‐rich minerals, and/or the S‐rich vapors react with the exotic metallic Fe to form troilite grains. The sulfurization in NWA 11591 most likely occurred during the prolonged subsolidus thermal metamorphism in the shallow crust of Vesta and might be an open, relatively high temperature (>800 °C) process. Sulfur would be an important component of the metasomatic fluid on Vesta.

^1,2Zelia Dionnet et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13538]
¹DIST‐Università Parthenope, Napoli, Italy
²INAF‐IAPS, Roma, Italy
Published by arrangement with John Wiley & Sons

In the near future, a new generation of sample return missions (Hayabusa2, OSIRIS‐REx, MMX, etc.) will collect samples from small solar system bodies. To maximize the scientific outcome of laboratory studies and minimize the loss of precious extraterrestrial samples, an analytical sequence from less destructive to more destructive techniques needs to be established. In this work, we present a combined X‐ray and IR microtomography applied to five Itokawa particles and one fragment of the primitive carbonaceous chondrite Paris. We show that this analytical approach is able to provide a 3‐D physical and chemical characterization of individual extraterrestrial particles, using the measurement of their 3‐D structure and porosity, and the detection of mineral and organic phases, and their spatial co‐localization in 3‐D. We propose these techniques as an efficient first step in a multitechnique analytical sequence on microscopic samples collected by space missions.

¹Naoki Shirai et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13480]
¹Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo, 192‐0397 Japan
Published by arrangement with John Wiley & Sons

Chemical compositions of materials used for new sample holders (vertically aligned carbon nanotubes [VACNTs] and polyimide film), which were developed for the analysis of Hayabusa2‐return samples, were determined by instrumental neutron activation analysis and/or instrumental photon activation analysis, to estimate contamination effects from the sample holders. The synthetic quartz plate used for the sample holders was also analyzed. Ten elements (Na, Al, Cr, Mn, Fe, Ni, Eu, W, Au, and Th) and 14 elements (Na, Al, K, Sc, Ti, Cr, Zn, Ga, Br, Sb, La, Eu, Ir, and Au) could be detected in the VACNTs and polyimide film, respectively. The VACNT data show that contamination by this material with respect to the Murchison meteorite is negligible in terms of the elemental ratios (e.g., Fe/Mn, Na/Al, and Mn/Cr) used for the classification of meteorites due to the extremely low density of VACNTs. However, for the Au/Cr ratio, even small degrees (1.7 wt%) of contamination by VACNTs will change the Au/Cr ratio. Elemental ratios used for the classification of meteorites are only influenced by large amounts of contamination (>60 wt%) of polyimide film, which is unlikely to occur. In contrast, detectable effects on Ti isotopic compositions are caused by >0.1 and >0.3 wt% contamination by VACNTs and polyimide film, respectively, and Hf isotopic changes are caused by >0.1 wt% contamination by VACNTs. The new sample holders (VACNTs and polyimide film) are suitable for chemical classification of Hayabusa2‐return samples, because of their ease of use, applicability to multiple analytical instruments, and low contamination levels for most elements.

¹Nicolas P.Walte,²Giulio F.D.Solferino,³Gregor J.Golabek,³Danielle Silva Souza,³Audrey Bouvier
Earth and Planetary Science Letters 546, 116419 Link to Article [https://doi.org/10.1016/j.epsl.2020.116419]
¹Heinz Meier-Leibnitz Centre for Neutron Science (MLZ), Technical University Munich, 85748 Garching, Germany
²Department of Earth Sciences, Royal Holloway University of London, TW20 0EX Egham, United Kingdom
³Bayerisches Geoinstitut (BGI), University of Bayreuth, 95447 Bayreuth, Germany
Copyright Elsevier

Pallasites, stony-iron meteorites predominantly composed of olivine crystals and Fe-Ni metal, are samples of the interior of early solar system bodies and can thus provide valuable insights into the formation of terrestrial planets. However, pallasite origin is controversial, either sampling the core-mantle boundary or the shallower mantle of planetesimals that suffered an impact. We present high strain-rate deformation experiments with the model system olivine + FeS melt ± gold melt to investigate pallasite formation and the evolution of their parent bodies and compare the resulting microstructures to two samples of Seymchan pallasite. Our experiments reproduced the major textural features of pallasites including the different olivine shapes, olivine aggregates, and the distribution of the metal and sulfide phases. These results indicate that pallasites preserve evidence for a two-stage formation process including inefficient core-mantle differentiation and an impact causing disruption, metal melt injection, and fast cooling within months to years. Olivine aggregates, important constituents of angular pallasites, are reinterpreted as samples of a partially differentiated mantle containing primordial metallic melt not stemming from the impactor. The long-term retention of more than 10 vol% of metal melt in a silicate mantle sampled by olivine aggregates indicates high effective percolation thresholds and inefficient metal-silicate differentiation in planetesimals not experiencing a magma ocean stage.