¹Almansa-Villatoro, M.V.
Journal of Egyptian Archaeology 105, 73-81 Link to Article [DOI: 10.1177/0307513319899948]
¹Brown University, United States

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Maria Eugenia Varela
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.1353]
¹Instituto de Ciencias Astronómicas de la Tierra y del Espacio (ICATE)‐CONICET, Avenida España 1512 sur, J5402DSP San Juan, Argentina
Published by arrangement with John Wiley & Sons

Five silica‐rich objects (SRO) from Acfer 182 were studied. They have cryptocrystalline textures characterized by micro‐emulsion and amoeboid patterns that point toward the coexistence of pyroxene‐ and silica‐normative liquids that were quenched. Both objects have variable contents of refractory lithophile elements. Their positive Yb versus La correlation around primordial values suggests a cosmochemical process (e.g., a gas/liquid condensation) as responsible for SRO formation. The bulk trace element abundances of amoeboid‐ and emulsion‐type SRO as well as their fractionation do not support an origin through high temperature processes. Conversely, their formation might have taken place while cooling of the nebular gas in two different chondrule‐forming regions characterized by having different evolution paths. Cooling of these dust‐enriched regions might lead to the condensation of pyroxene‐rich liquids first, followed by formation of Mg‐rich and SiO₂‐rich liquids, provided irradiation and annealing were active in these regions. Irradiation could be the process involved both in the formation of cristobalite (with annealing ~1200 K) and in triggering a spinoidal decomposition causing unmixing of the enstatite liquid into two coexisting phases, such as Mg‐rich and SiO₂‐rich liquids, the precursors of the SRO in Acfer 182. Formation of emulsion‐ and amoeboid‐type objects may be the result of exposing those chondrule‐forming regions to different degrees of radiation.

¹G.Alemanno,¹A.Maturilli,¹J.Helbert,¹M.D’Amore
Earth and Planetary Science Letters 546, 116424 Link to Article [https://doi.org/10.1016/j.epsl.2020.116424]
¹Institute for Planetary Research, German Aerospace Center DLR, Rutherfordstr. 2, 12489 Berlin, Germany
Copyright Elsevier

Recent orbital data revealed the presence of hydrated minerals on the surfaces of asteroids, mainly through the identification and the study of the 3-μm spectral absorption band (Hamilton et al., 2019; Kitazato et al., 2019). The presence of an absorption feature around 3-μm on planetary bodies’ surfaces is indicative of the presence of OH-bearing minerals. This band has been widely detected on carbonaceous chondrites but its appearance and its shape are diverse indicating different composition and/or the occurrence of subsequent alteration events. In this work, we present the results of laboratory experiments performed at the Planetary Spectroscopy Laboratory (PSL) of the German Aerospace Center (DLR) to study the spectral behaviour of the 3-μm spectral features in the Mg-OH minerals with thermal variation. It has been suggested that thermal alteration processes, can darken the surfaces of carbonaceous chondrites, thus decreasing the appearance and visibility of the spectral features around 3 μm. Thermal alteration processes are consistent with the scenario currently proposed to explain the formation of 162173 Ryugu asteroid (Sugita et al., 2019). The Near Infrared Spectrometer (NIRS3) on the Hayabusa2 mission detected a weak and narrow absorption feature centred at 2.72 μm across the entire observed surface of the C-type asteroid (Kitazato et al., 2019). However, the collected spectra from the Ryugu surface show no other absorption features in the 3-μm region. To investigate this point further and analyze the variation of the spectral features around 3-μm with thermal alteration, we studied the Mg-rich phyllosilicates serpentine and saponite in two different situations: 1) thermal alteration at increasing temperature – the samples were heated at steps of 100 °C, starting from 100 °C up to 700 °C, for 4 hours each; 2) long time heating at constant temperature – samples were kept constantly at ∼250 °C for 1 month (1st step), then cooled down and measured in reflectance. This long heating process has been repeated at the same temperature of 250 °C for 2 months (2nd step). The results obtained show an important variation of phyllosilicates spectral bands with temperature and provide useful data for the interpretation of past and future mission small bodies collected surface spectra.

^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.

¹Carolyn A.Crow,²Sarah A.Crowther,³Kevin D.McKeegan,²Grenville Turner,⁴Henner Busemann,²Jamie D.Gilmour
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.06.019]
¹Department of Geological Sciences, University of Colorado Boulder
²School of Earth and Environmental Sciences, The University of Manchester
³Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles
⁴ETH Zürich
Copyright Elsevier

We demonstrate a new way of investigating the processing of the lunar surface (and other planetary regoliths) that combines Xe_S-Xe_N ages (based on uranium fission) in individual zircons with their xenon isotopic record of solar wind and cosmic ray exposure. We report the first xenon isotopic analyses of individual lunar zircons (from Apollo 14 soil and breccias samples). Parallel analyses of a suite of zircons from the Vredefort impact structure in South Africa revealed Xe_S-Xe_N ages that agree well with U-Pb systematics, suggesting that the diffusion kinetics of xenon and lead in zircon are similar in the pressure-temperature environment of sub-basin floors. In contrast, all Apollo 14 zircons examined exhibit Xe_S-Xe_N ages markedly younger than the associated U-Pb and ²⁰⁷Pb-²⁰⁶Pb ages, and soil zircons with ²⁰⁷Pb-²⁰⁶Pb ages greater than 3900 Ma produced an abundance of Xe_S-Xe_N ages <1000 Ma. The young ages cannot be explained by thermal neutron irradiation on the lunar surface, and diurnal heating is unlikely to cause preferential loss of xenon. As such these young soil zircon ages likely record regolith gardening processes. The breccia zircons typically record older ages, >2400 Ma, suggesting that these samples may be useful for investigating ancient events and regolith processing at an earlier epoch. However, none of the zircons contain xenon from now-extinct ²⁴⁴Pu implying that either the samples have completely degassed since ∼3900 Ma or that the initial Pu/U ratio of the Moon is lower than that on Earth. We also describe a methodology for conducting component deconvolution that can be applied to multi-isotopes systems beyond xenon. We have also determined new xenon isotopic yields from rare earth element spallation in the lunar environment and high precision yields for neutron induced fission of ²³⁵U in geologic samples.

¹A.Stephant,^1,2M.Anand,³R.Tartèse,¹X.Zhao,¹G.Degli-Alessandrini,¹I.A.Franchi
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.06.017]
¹School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
²Department of Earth Sciences, The Natural History Museum, London, SW7 5BD, UK
³Department of Earth and Environmental Sciences, The University of Manchester, Manchester, M13 9PL, UK
Copyright Elsevier

Since the discovery of water (a term collectively used for the total H, OH and H₂O) in samples derived from the lunar interior, heterogeneity in both water concentration and its hydrogen isotopic ratio has been documented for various lunar phases. However, most previous studies have focused on measurements of hydrogen in apatite, which typically forms during the final stages of melt crystallisation. To better constrain the abundance and isotopic composition of water in the lunar interior, we have targeted melt inclusions (MIs), in mare basalts, that are trapped during the earliest stages of melt crystallisation. Melt inclusions are expected to have suffered minimal syn- or post-eruption modification processes, and, therefore, should provide more accurate information about the history of H in the lunar interior. Here, we report H^–/¹⁸O^– measurements as calibrated water concentrations, and hydrogen isotope ratios obtained by secondary ion mass spectrometry (SIMS) in a large set of basaltic MIs from Apollo mare basalts 10020, 10058, 12002, 12004, 12008, 12020, 12040, 14072 and 15016. Our results demonstrate that partially crystallised MIs from lunar basalts and their parental melts were influenced by a variety of processes such as hydrogen diffusion, degassing and assimilation of material affected by solar-wind implantation. Deconvolution of these processes show that lunar basaltic parental magmas were heterogeneous and had a broadly chondritic hydrogen isotopic composition with δD values varying between -200 and +200 ‰.

¹Dustin Trail,²Mélanie Barboni,³Kevin D.McKeegan
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.06.018]
¹Department of Earth & Environmental Sciences, University of Rochester, Rochester, NY 14627, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ USA
³Department of Earth, Planetary, and Space Sciences, University of California – Los Angeles, Los Angeles CA, 90095 USA
Copyright Elsevier

Lunar samples collected during Apollo missions are typically impact-related breccias or regolith that contain amalgamations of rocks and minerals with various origins (e.g., products of igneous differentiation, mantle melting, and/or impact events). The largest intact pre-Nectarian (∼≥3.92 Ga) fragments of igneous rock contained within the breccia and regolith rarely exceed 1 cm in size, and they often show evidence for impact recrystallization. This widespread mixing of disparate materials makes unraveling the magmatic history of pre-Nectarian period fraught with challenges. To address this issue, we combine U-Pb geochronology of Apollo 14 zircons (²⁰⁷Pb-²⁰⁶Pb ages from 3.93 to 4.36 Ga) with zircon trace element chemistry and thermodynamic models. Zircon crystallization temperatures are calculated with Ti-in-zircon thermometry after presenting new titania and silica activity models for lunar melts. We also present rare earth element (REE), P, actinide, and Mg+Fe+Al concentrations. While REE patterns and P yield little information about the parent melt origins of these out-of-context grains, U and Th concentrations are highly variable among pre-4.2 Ga zircons when compared to younger grains. Thus, the distribution of heat-producing radioactive elements in melt sources pervading the early lunar crust was heterogenous. Melt composition variation is confirmed by zircon Al concentrations and thermodynamic modeling that reveal at least two dominant magma signatures in the pre-4.0 Ga zircon population. One inferred magma type has a high alumina activity. This magma likely assimilated Feldspathic Highlands Terrane (FHT) anorthosites, though impact-generated melts of an alumina-rich target rock is a viable alternative. The other magma signature bears more similarities to KREEP basalts from the Procellarum KREEP Terrane (PKT), reflecting lower apparent alumina activities. Melt diversity seems to disappear after 4.0 Ga, with zircon recording magma compositions that largely fall in-between the two main groups found for pre-4.0 Ga samples. We interpret <4 Ga zircons to have formed from a mixture of PKT- and FHT-like rocks, consistent with the upper ∼15 km of the crust being thoroughly mixed and re-melted by basin-forming impacts during the pre-Nectarian period.