¹Jérôme Aléon,²Alice Aléon-Toppani,³Bernard Platevoet,³Jacques-Marie Bardintzeff,⁴Kevin D. McKeegan, ⁵François Brisset
Proceedings of the National Academy of Sciences of the United States of Americs (PNAS) (in Press) Link to Article [DOI:
https://doi.org/10.1073/pnas.1919550117]
¹Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, UMR 7590, Sorbonne Université, Museum National d’Histoire Naturelle, CNRS, Université Pierre et Marie Curie, Institut de Recherche pour le Développement, 75005 Paris, France;
²Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France;
³Université Paris-Saclay, Sciences de la Terre, Volcanologie-Planétologie, UMR CNRS 8148 Geosciences Paris Sud, F-91405 Orsay, France;
⁴Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095-1567;
⁵Université Paris-Saclay, CNRS, Institut de Chimie Moléculaire et des Matériaux d’Orsay, 91405 Orsay Cedex, France

Recent isotopic and paleomagnetic data point to a possible connection between carbonaceous chondrites and differentiated planetary materials, suggesting the existence, perhaps ephemeral, of transitional objects with a layered structure whereby a metal-rich core is enclosed by a silicate mantle, which is itself overlain by a crust containing an outermost layer of primitive solar nebula materials. This idea has not received broad support, mostly because of a lack of samples in the meteoritic record that document incipient melting at the onset of planetary differentiation. Here, we report the discovery and the petrologic–isotopic characterization of UH154-11, a ferroan trachybasalt fragment enclosed in a Renazzo-type carbonaceous chondrite (CR). Its chemical and oxygen isotopic compositions are consistent with very-low-degree partial melting of a Vigarano-type carbonaceous chondrite (CV) from the oxidized subgroup at a depth where fluid-assisted metamorphism enhanced the Na content. Its microdoleritic texture indicates crystallization at an increasing cooling rate, such as would occur during magma ascent through a chondritic crust. This represents direct evidence of magmatic activity in a carbonaceous asteroid on the verge of differentiating and demonstrates that some primitive outer Solar System objects related to icy asteroids and comets underwent a phase of magmatic activity early in the Solar System. With its peculiar petrology, UH154-11 can be considered the long-sought first melt produced during partial differentiation of a carbonaceous chondritic planetary body, bridging a previously persistent gap in differentiation processes from icy cometary bodies to fully melted iron meteorites with isotopic affinities to carbonaceous chondrites.

¹Max Collinet,¹Timothy L. Grove
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13471]
¹Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, 02139 Massachusetts, USA
Published by arrangement with John Wiley & Sons

Ureilites are carbon‐rich ultramafic achondrites that have been heated above the silicate solidus, do not contain plagioclase, and represent the melting residues of an unknown planetesimal (i.e., the ureilite parent body, UPB). Melting residues identical to pigeonite‐olivine ureilites (representing 80% of ureilites) have been produced in batch melting experiments of chondritic materials not depleted in alkali elements relative to the Sun’s photosphere (e.g., CI, H, LL chondrites), but only in a relatively narrow range of temperature (1120 ºC–1180 ºC). However, many ureilites are thought to have formed at higher temperature (1200 ºC–1280 ºC). New experiments, described in this study, show that pigeonite can persist at higher temperature (up to 1280 ºC) when CI and LL chondrites are melted incrementally and while partial melts are progressively extracted. The melt productivity decreases dramatically after the exhaustion of plagioclase with only 5–9 wt% melt being generated between 1120 ºC and 1280 ºC. The relative proportion of pyroxene and olivine in experiments is compared to 12 ureilites, analyzed for this study, together with ureilites described in the literature to constrain the initial Mg/Si ratio of the UPB (0.98–1.05). Experiments are also used to develop a new thermometer based on the partitioning of Cr between olivine and low‐Ca pyroxene that is applicable to all ureilites. The equilibration temperature of ureilites increases with decreasing Al₂O₃ and Wo contents of pyroxene and decreasing bulk REE concentrations. The UPB melted incrementally, at different fO₂, and did not cool significantly (0 ºC–30 ºC) prior to its disruption. It remained isotopically heterogenous, but the initial concentration of major elements (SiO₂, MgO, CaO, Al₂O₃, alkali elements) was similar in the different mantle reservoirs.

¹Connor D.Hilton, ¹Richard J.Walker
Earth and Planetary Science Letters 540, 116248 Link to Article [https://doi.org/10.1016/j.epsl.2020.116248]
¹Department of Geology, University of Maryland, College Park, MD 20742, USA
Copyright Elsevier

The origin of the IAB main group (MG) iron meteorites is explored through consideration of 182W isotopic compositions, thermal modeling of 26Al decay, and mass independent (nucleosynthetic) Mo isotopic compositions of planetesimals formed in the noncarbonaceous (NC) protosolar isotopic reservoir. A refined 182W model age for the meteorites Campo del Cielo, Canyon Diablo, and Nantan suggests that the IAB-MG parent body underwent some form of metal-silicate segregation as early as 5.3 ± 0.4 Myr after calcium-aluminum rich inclusion (CAI) formation or as late as 13.8 ± 1.4 Myr after CAI formation. If melting of the IAB-MG occurred prior to 7 Myr after CAI formation, it was likely driven by 26Al decay for a parent body radius >40 km. Otherwise, additional heat from impact is required for melting metal this late in Solar System history. If melting was partially or wholly the result of internal heating, a thermal model of 26Al decay heat production constrains the accretion age of the IAB-MG parent body to ∼1.7 ± 0.4 Myr after CAI formation. If melting was, instead, dominantly caused by impact heating, thermal modeling suggests the parent body accreted more than 2 Myr after CAI formation. Comparison of Mo mass independent isotopic compositions of the IAB-MG to other NC bodies with constrained accretion ages suggests that the Mo isotopic composition of the NC reservoir changed with time, and that the IAB-MG parent body accreted between 2 to 3 Myr after CAI formation, thus requiring an origin by impact. The relationship between nucleosynthetic Mo isotopic compositions and accretion ages of planetesimals from the NC reservoir suggests that isotopic heterogeneity developed from either addition of s-process material to, or removal of coupled r-/p-process material from the NC reservoir.

^1,2Janne Blichert-Toft,³Christa Göpel,³Marc Chaussidon,^1,2F.Albarède
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.04.006]
¹Laboratoire de Géologie de Lyon, École Normale Supérieure de Lyon, CNRS UMR 5276, Université de Lyon, 46 Allée d’Italie, 69007 Lyon, France
²Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, Houston, TX 77005, USA
³Université de Paris, Institut de Physique du Globe de Paris, CNRS, 1 Rue Jussieu, 75005 Paris, France
Copyright Elsevier

Lead isotope compositions were measured on both single and combined chondrules from the CV3 carbonaceous chondrite Allende with the goal of determining the range of Th/U implied by the radiogenic 208Pb*/206Pb* values. All samples were aggressively acid step-leached to separate radiogenic from primordial lead. It is found that apparent Th/U varies both between individual chondrules and between the different leaching fractions of each chondrule or group of chondrules. Specifically, the apparent Th/U ratio deviates from the planetary value (3.876), varying spectacularly from 0.65 to 14.6. Variations between leachates and residues disclose the existence of internal heterogeneities, while inter-chondrule variations reveal the presence of external heterogeneities. Three main explanations for the observed Th-U fractionation that are not mutually exclusive prevail: (1) uranium species, notably UO and UO₂, coexisted in the nebular gas at high temperature, whereas Th existed exclusively as ThO₂; (2) chondrules interacted with an exotic oxidized vapor; and (3) chondrules represent melt of dust of different origins, a hypothesis dictated by the evidence of internal heterogeneity. The extent to which the measured apparent Th/U variability is due to each of these particular processes is difficult to assess, but the existence of substantial Th/U heterogeneity, especially within, but also among, single (or pooled) chondrules from the same chondrite calls for caution when Pb-Pb linear arrays, or mixing lines, are assigned isochronous significance.

^1,2James Wampler,³Mark Thiemens,³Shaobo Cheng,³Yimei Zhu,^1,2Ivan K. Schuller
Proceedings of the National Academy of Sciences of the United States of America (PNAS) (in Press) Link to Article [https://doi.org/10.1073/pnas.1918056117]
¹Department of Physics, University of California San Diego, La Jolla, CA 92093;
²Center for Advanced Nanoscience, University of California San Diego, La Jolla, CA 92093;
³Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093;
⁴Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, NY 11973

Meteorites can contain a wide range of material phases due to the extreme environments found in space and are ideal candidates to search for natural superconductivity. However, meteorites are chemically inhomogeneous, and superconducting phases in them could potentially be minute, rendering detection of these phases difficult. To alleviate this difficulty, we have studied meteorite samples with the ultrasensitive magnetic field modulated microwave spectroscopy (MFMMS) technique [J. G. Ramírez, A. C. Basaran, J. de la Venta, J. Pereiro, I. K. Schuller, Rep. Prog. Phys. 77, 093902 (2014)]. Here, we report the identification of superconducting phases in two meteorites, Mundrabilla, a group IAB iron meteorite [R. Wilson, A. Cooney, Nature 213, 274–275 (1967)] and GRA 95205, a ureilite [J. N. Grossman, Meteorit. Planet. Sci. 33, A221–A239 (1998)]. MFMMS measurements detected superconducting transitions in samples from each, above 5 K. By subdividing and remeasuring individual samples, grains containing the largest superconducting fraction were isolated. The superconducting grains were then characterized with a series of complementary techniques, including vibrating-sample magnetometry (VSM), energy-dispersive X-ray spectroscopy (EDX), and numerical methods. These measurements and analysis identified the likely phases as alloys of lead, indium, and tin.

¹Jack Wisdom
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13463]
¹Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139 USA
Published by arrangement with John Wiley & Sons

In Wisdom (2017), I presented new simulations of meteorite transport from the chaotic zones associated with major resonances in the asteroid belt: the ν6 secular resonance, the 3:1 mean motion resonance with Jupiter, and the 5:2 mean motion resonance with Jupiter. I found that the observed afternoon excess (the fact that approximately twice as many meteorites fall in the afternoon as in the morning) of the ordinary chondrites is consistent with chaotic transport from the 3:1 resonance, contradicting prior reports. Here I report an additional study of the transport of meteorites from ν6 secular resonance and the 3:1 mean motion resonance. I use an improved integration algorithm, and study the evolution of more particles. I confirm that the afternoon excess of the ordinary chondrites is consistent with transport from the 3:1 resonance.

¹Lei Song,¹Jiao Xu,² Hong Tang,¹ Jiquan Liu,²Jianzhong Liu,²Xiongyao Li,¹Shuqian Fan
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113810]
¹Chongqing Key Laboratory of Additive Manufacturing Technology and System, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, No.266 Fangzheng Avenue, Beibei District, Chongqing 400714, PR China
²Center for Lunar & Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, 99 Lincheng West Road, Guiyang 550081, PR China
Copyright Elsevier

Lunar regolith in-situ utilization receives increasing attentions due to development of lunar exploration research. The complex composition of lunar regolith leads to its complicated phase reaction and composition evolution at high temperature, whereas few studies focus on the alteration of physicochemical properties for simulated lunar regolith at high temperature. This paper focuses on physicochemical variation characteristics and magnetic transformation for high-Ti type basalt lunar regolith simulant CLRS-2 during vacuum sintering process. Importantly, the effect of heat-treatment on magnetic properties of CLRS-2 and the magnetic properties difference between high-Ti and low-Ti type basalt lunar regolith simulant have been investigated. The results would help us understand how the micro-morphology and chemical composition of ilmenite change in lunar regolith during sintering process. What can be inferred is that the ions substitution between ilmenite and other minerals or amorphous phase would occur during sintering process of lunar regolith at high temperature in vacuum, which would lead to the evaporation of Fe-containing components. Besides, the results of micro-hardness indicate that the ilmenite content difference between CLRS-1 and CLRS-2 have no influence on the micro-hardness of the sintered samples, while the density of samples and the sintering condition such as temperature have a greater influence.

¹Kevin Righter,²Alexander P. Holmwood
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13465]
¹NASA Johnson Space Center, 2101 NASA Parkway, Houston, Texas, 77058 USA
²Department of Geosciences, Hamilton College, Clinton, New York, 13323 USA
Published by arrangement with John Wiley & Sons

The Allan Hills 76005 polymict eucrite pairing group consists of 15 paired masses recovered during six different field seasons in the Transantarctic Mountains. Although this group has been well studied in general, most of the meteorites contain a significant portion of dark clasts that have not been well characterized. The Dawn mission to Vesta discovered dark materials that provide insight into its evolution. The ALH dark clasts are thus of great interest to understanding the evolution of Vesta. Here, 45 different dark clasts from 15 different thin sections from the pairing group are characterized in detail to better understand their nature and origin. Five different textural types of dark clasts are recognized among this group—skeletal, vitrophyric, pilotaxitic, fan spherulitic, and troilite‐silica‐plagioclase‐rich clasts with aphyric or blobby textures. Mineralogy of the clasts is dominated by plagioclase and pyroxene, with minor troilite, silica, ilmenite, chromite, and rare Fe‐Ni metal. All of the textures can be produced by rapid cooling rates on the order of 60–2500°C h⁻¹. Bulk compositions of the clasts are demonstrably eucritic, and not chondritic, howarditic, or diogenitic. The combination of mineralogy, composition, and textures strongly suggests that the dark clasts are eucritic impact melts. Several craters on Vesta have associated orange deposits that have been proposed as impact melt breccias. The ALH pairing group may thus represent material that originated near Oppia or Octavia craters.

¹Noriyuki Kawasaki,¹Sohei Wadaa,²Changkun Park,³Naoya Sakamoto,^1,3,4Hisayoshi Yurimoto
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.03.045]
¹Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan
²Division of Earth-System Sciences, Korea Polar Research Institute, Incheon 21990, Republic of Korea
³Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo 001-0021, Japan
⁴Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara 252-5210, Japan
Copyright: Elsevier

Fine-grained Ca-Al-rich inclusions (FGIs) in CV chondrites are suggested to be condensates formed directly from the solar nebular gas. Al−Mg mineral isochrons of seven FGIs from reduced CV chondrites Efremovka, Vigarano, Thiel Mountains 07007, and Northwest Africa 8613 were obtained via in situ Al–Mg isotope measurements using secondary ion mass spectrometry. The slopes of the mineral isochrons for seven FGIs exhibit statistically significant variations in initial ²⁶Al/²⁷Al ratios, (²⁶Al/²⁷Al)₀, ranging from (5.19 ± 0.17) to (3.35 ± 0.21) × 10⁻⁵, which correspond to a relative age spread of 0.44 ± 0.07 Myr. Inferred upper limit of (²⁶Al/²⁷Al)₀ for the FGIs is identical to the Solar System (²⁶Al/²⁷Al)₀ of ∼5.2 × 10⁻⁵as determined by whole-rock Al–Mg isochron studies for CAIs in CV chondrites. The intercepts of the mineral isochrons, the initial ²⁶Mg/²⁴Mg ratios the FGIs formed with, are consistent with Mg-isotope evolution path of a solar-composition nebular gas. The observed variations in (²⁶Al/²⁷Al)₀ for FGIs are essentially similar to those (∼5.2 to ∼4.2 × 10⁻⁵) for coarse-grained, igneous CAIs of CV chondrites that are formed by melting and solidification. If ²⁶Al was distributed homogeneously in the forming region, then our data indicate that thermal processes of condensation and melting for CAI formation occurred contemporaneously and continued for at least ∼0.4 Myr at the very beginning of the Solar System. Alternatively, the observed variations in (²⁶Al/²⁷Al)₀ also indicate the possibility of heterogeneous distributions of ²⁶Al in the forming region, corresponding to a range of over at least 3.4 × 10^–5 < (²⁶Al/²⁷Al)₀ < 5.2 × 10^–5.

¹Connor D. Hilton,¹Richard D. Ash,¹Philip M. Piccoli,²David A. Kring,³Timothy J. McCoy,¹Richard J. Walker
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13464]
¹Department of Geology, University of Maryland, College Park, Maryland, 20742 USA
²Lunar and Planetary Institute, USRA, Houston, Texas, 77058 USA
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, 20560 USA
Published by arrangement with John Wiley & Sons

Previous studies attributed the origin of metal veins penetrating graphite nodules in the Canyon Diablo IAB main group iron meteorite to condensation from vapor or melting of host metal. Abundances of 16 siderophile elements measured in kamacite within vein and host meteorite are most consistent with an origin by melting of the host metal followed by fractional crystallization of the liquid. The presence of the veins within graphite nodules may be explained by impact, as peak shock temperatures, and thus the most likely areas to undergo metal melting are at metal–graphite interfaces. The origin of the veins is constrained by Re‐Os chronometry to have occurred early (>4 Ga) in solar system history.