¹Yoshinori Miyazaki,¹Jun Korenaga
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114368]
¹Department of Earth and Planetary Sciences, Yale University, New Haven, CT 06511, USA
Copyright Elsevier

Chondrites are the likely building blocks of Earth, and identifying the group of chondrite that best represents Earth is a key to resolving the state of the early Earth. The origin of chondrites, however, remains controversial partly because of their puzzling major element compositions, some exhibiting depletion in Al, Ca, and Mg. Based on a new thermochemical evolution model of protoplanetary disks, we show that planetesimals with depletion patterns similar to ordinary and enstatite chondrites can originate at 1–2 AU outside where enstatite evaporates. Around the “evaporation front” of enstatite, the large inward flow of refractory minerals, including forsterite, takes place with a high pebble concentration, and the loss of those minerals results in depletion in Al, Ca, and Mg. The fractionation driven by the loss of forsterite would also create a complementary Mg-rich reservoir just inside the depleted region, creating two chemically distinct reservoirs adjacent to each other. The region around the evaporation front of enstatite has the highest dust concentration inside the snow line, and thus the streaming instability is most likely to be triggered therein. Planetesimals with two different major element compositions could naturally be created in the terrestrial region, which could evolve into parent bodies for Earth and chondrites. This can explain why Earth and enstatite chondrites share similar isotopic signatures but have different bulk compositions.

^1,2Noël Chaumard,^1,3Céline Defouilloy,^1,4Andreas T.Hertwig,¹Noriko T.Kita
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.02.012]
¹WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, 1215 W. Dayton Street, Madison, WI 53706-1692, USA
²Fi Group, Direction scientifique, 14 terrasse Bellini, 92800 Puteaux, France
³CAMECA, 29 quai des Grésillons, 92622 Gennevilliers Cedex, France
⁴Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany
Copyright Elsevier

In-situ oxygen three-isotope analyses of chondrules and isolated olivine grains in the Paris (CM) chondrite were conducted by secondary ion mass spectrometry (SIMS). Multiple analyses of olivine and/or pyroxene in each chondrule show indistinguishable Δ17O values, except for minor occurrences of relict olivine grains (and one low-Ca pyroxene). A mean Δ17O value of these homogeneous multiple analyses was obtained for each chondrule, which represent oxygen isotope ratios of the chondrule melt. The Δ17O values of individual chondrules range from –7‰ to –2‰ and generally increase with decreasing Mg# of olivine and pyroxene in individual chondrules. Most type I (FeO-poor) chondrules have high Mg# (∼99) and variable Δ17O values from –7.0‰ to –3.3‰. Other type I chondrules (Mg# ≤97), type II (FeO-rich) chondrules, and two isolated FeO-rich olivine grains have host Δ17O values from –3‰ to –2‰. Eight chondrules contain relict grains that are either 16O-rich or 16O-poor relative to their host chondrule and show a wide range of Δ17O values from –13‰ to 0‰.

The results from chondrules in the Paris meteorite are similar to those in Murchison (CM). Collectively, the Δ17O values of chondrules in CM chondrites continuously increase from –7‰ to –2‰ with decreasing Mg# from 99 to 37. The majority of type I chondrules (Mg# >98) show Δ17O values from –6‰ to –4‰, while the majority of and type II chondrules (Mg# 60-70) show Δ17O values of –2.5‰. The covariation of Δ17O versus Mg# observed among chondrules in CM chondrites may suggest that most chondrules in carbonaceous chondrites formed in a single large region across the snow line where the contribution of 16O-poor ice to chondrule precursors and dust enrichment factors varied significantly.

^1,2A.J.King,¹P.F.Schofield,¹S.S.Russell
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.02.011]
¹Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK
²School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
Copyright Elsevier

The CM carbonaceous chondrite meteorites provide a record of low temperature (<150 °C) aqueous reactions in the early solar system. A number of CM chondrites also experienced short-lived, post-hydration thermal metamorphism at temperatures of ∼200 °C to >750 °C. The exact conditions of thermal metamorphism and the relationship between the unheated and heated CM chondrites are not well constrained but are crucial to understanding the formation and evolution of hydrous asteroids. Here we have used position-sensitive-detector X-ray diffraction (PSD-XRD), thermogravimetric analysis (TGA) and transmission infrared (IR) spectroscopy to characterise the mineralogy and water contents of 14 heated CM and ungrouped carbonaceous chondrites. We show that heated CM chondrites underwent the same degree of aqueous alteration as the unheated CMs, however upon thermal metamorphism their mineralogy initially (300–500 °C) changed from hydrated phyllosilicates to a dehydrated amorphous phyllosilicate phase. At higher temperatures (>500 °C) we observe recrystallisation of olivine and Fe-sulphides and the formation of metal. Thermal metamorphism also caused the water contents of heated CM chondrites to decrease from ∼13 wt% to ∼3 wt% and a subsequent reduction in the intensity of the 3 μm feature in IR spectra. We estimate that the heated CM chondrites have lost ∼15 – >65% of the water they contained at the end of aqueous alteration. If impacts were the main cause of metamorphism, this is consistent with shock pressures of ∼20–50 GPa. However, not all heated CM chondrites retain shock features suggesting that some were instead heated by solar radiation. Evidence from the Hayabusa2 and ORSIRS-REx missions suggest that dehydrated materials may be common on the surfaces of primitive asteroids and our results will support upcoming analysis of samples returned from asteroids Ryugu and Bennu.

^1,2Christy Caudill,^1,2Gordon R. Osinski,³Rebecca N. Greenberger,^1,2Livio L. Tornabene,^1,2Fred J. Longstaffe,^1,2Roberta L. Flemming,^3,4Bethany L. Ehlmann
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13600]
¹Department of Earth Sciences, The University of Western Ontario, 1151 Richmond St, London, Ontario, N6A 5B7 Canada
²Institute for Earth and Space Exploration, The University of Western Ontario, 1151 Richmond St, London, Ontario, N6A 5B7 Canada
³Division of Geological & Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
⁴Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, 91109 USA
Published by arrangement with John Wiley & Sons

The impact melt‐bearing breccias at the Ries impact structure, Germany, host degassing pipes: vertical structures that are inferred to represent conduits along which gases and fluids escaped to the surface, consistent with hydrothermal activity that occurs soon after an impact event. Although the presence of degassing pipes has been recognized within the well‐preserved and long‐studied ejecta deposits at the Ries, a detailed mineralogical study of their alteration mineralogy, as an avenue to elucidate their origins, has not been conducted to date. Through the application of high‐resolution in situ reflectance imaging spectroscopy and X‐ray diffraction, this study shows for the first time that the degassing pipe interiors and associated alteration are comprised of hydrated and hydroxylated silicates (i.e., Fe/Mg smectitic clay minerals with chloritic or other hydroxy‐interlayered material) as secondary hydrothermal mineral phases. This study spatially extends the known effects of impact hydrothermal activity into the ejecta deposits, beyond the crater rim. It has been suggested that the degassing pipes at the Ries are analogous to crater‐related pit clusters observed in impact melt‐bearing deposits on Mars, Ceres, and Vesta. The results of this work may inform on the presence of crustal volatiles and their interaction during the impact process on rocky bodies throughout the solar system. The Mars 2020 Perseverance rover may have the opportunity to investigate impact‐related features in situ; if so, this work suggests that such investigations may provide key information on the origin and formation of clay minerals on Mars as well as hold exciting implications for future Mars exploration.

¹S.Anderson et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13615]
¹School of Earth & Planetary Sciences, Curtin University, GPO Box U1987, Perth, Western Australia, 6845 Australia
Published by arrangement with John Wiley & Sons

Murrili, the third meteorite recovered by the Desert Fireball Network, is analyzed using mineralogy, oxygen isotopes, bulk chemistry, physical properties, noble gases, and cosmogenic radionuclides. The modal mineralogy, bulk chemistry, magnetic susceptibility, physical properties, and oxygen isotopes of Murrili point to it being an H5 ordinary chondrite. It is heterogeneously shocked (S2–S5), depending on the method used to determine it, although Murrili is not obviously brecciated in texture. Cosmogenic radionuclides yield a cosmic ray exposure age of 6–8 Ma, and a pre‐atmospheric meteoroid size of 15–20 cm in radius. Murrili’s fall and subsequent month‐long embedment into the salt lake Kati Thanda significantly altered the whole rock, evident in its Mössbauer spectra, and visual inspection of cut sections. Murrili may have experienced minor, but subsequent, impacts after its formation 4475.3 ± 2.3 Ma, which left it heterogeneously shocked.

¹Josefin Martell,¹Carl Alwmark,^1,2,3Sanna Holm‐Alwmark,¹Paula Lindgren
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13625]
¹Department of Geology, Lund University, Sölvegatan 12, 223 62 Lund, Sweden
²Niels Bohr Institute, University of Copenhagen, Blegdamsvej, 17, 2100 Copenhagen, Denmark
³Natural History Museum Denmark, University of Copenhagen, Øster Voldgade, 5‐7, 1350 Copenhagen K, Denmark
Published by arrangement with John Wiley & Sons

Recognition of impact‐induced deformation of minerals is crucial for the identification and confirmation of impact structures as well as for the understanding of shock wave behavior and crater formation. Shock deformed mineral grains from impact structures can also serve as important geochronometers, precisely dating the impact event. We investigated zircon grains from the Mien impact structure in southern Sweden with the aim of characterizing shock deformation. The grains were found in two samples of impact melt rock with varying clast content, and in one sample of suevitic breccia. We report the first documentation of so‐called “FRIGN zircon” (former reidite in granular neoblastic zircon) from Mien (pre‐erosion diameter 9 km), which confirms that this is an important impact signature also in relatively small impact structures. Furthermore, the majority of investigated zircon grains contain other shock‐related microtextures, most notably granular and microporous textures, that occur more frequently in grains found in the impact melt than in the suevitic breccia. Our findings show that zircon grains that are prime candidates for establishing a new and improved age refinement of the Mien impact structure are present in the impact melt.

¹Kim V. Fendrich,¹Denton S. Ebel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13623]
¹Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, 10024 USA
Published by arrangement with John Wiley & Sons

The size, distribution, abundance, and physical and chemical characteristics of chondritic inclusions are key features that define the chondrite groups. We present statistics on the size and abundance of the macroscopic components (inclusions) in the Murchison (CM2) and Allende (CV3) chondrites and measure their general chemical trends using established X‐ray mapping techniques. This study provides a fine‐scale assessment of the two meteorites and a semiquantitative evaluation of the relative abundances of elements and their distribution among meteorite components. Murchison contains 72% matrix and 28% inclusions; Allende contains 57% and 43%, respectively. A broad range of inclusion sizes and relative abundances has been reported for these meteorites, which demonstrates the necessity for a more standardized approach to measuring these characteristics. Nonetheless, the characteristic mean sizes of inclusions in Allende are consistently larger than those in Murchison. We draw two significant conclusions (1) these two meteorites sampled distinct populations of chondrules and refractory inclusions, and (2) complementary Mg/Si ratios between chondrules and matrix are observed in both Murchison and Allende. Both support the idea that chondrules and matrix within each chondrite group originated in single reservoirs of precursors with approximately solar Mg/Si ratios, providing a constraint on astrophysical models of the origin of chondrite parent bodies.

^1,3Xiandi Zeng,^1,2,4Hong Tang,^1,2,4Xiong Yao Li,¹Xiaoji Zeng,^1,2,4Wen Yu,^1,2,4Jianzhong Liu,⁵Yongliao Zou
Earth and Planetary Science Letters Link to Article [https://doi.org/10.1016/j.epsl.2021.116806]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
²CAS Center for Excellence in Comparative Planetology, Hefei, China
³University of Chinese Academy of Sciences, Beijing 100049, China
⁴Key Laboratory of Space Manufacturing Technology, Chinese Academy of Sciences, Beijing 100094, China
⁵National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
Copyright Elsevier

Determining the characteristics and thermal stability of solar wind-produced OH/H2O is critical to understanding the formation and migration of water on the lunar surface. In this study, terrestrial plagioclase (An50−53) was used as a lunar analogue and was irradiated with 5 keV H+ at a fluence of ∼1×1017 H+/cm2. The irradiated plagioclase was characterized via Fourier transform infrared spectroscopy, nanoscale secondary ion mass spectrometry, Raman spectroscopy, and transmission electron microscopy. The thermal stability of OH/H2O in the irradiated plagioclase was investigated via heating experiments. Our results reveal (1) a ∼100–200 ppm increase in the water content of the irradiated plagioclase; (2) structural hydrous species formation in the plagioclase through H+ implantation, including Type I H2O (∼2.75 μm) and Type II H2O (∼2.90 μm); and (3) the escape of much of the OH/H2O formed by H+ implantation at a temperature equivalent to the highest temperature on the lunar surface. The results of this study can improve our understanding of OH/H2O thermal stability on the lunar surface and provide a baseline for the interpretation of remote sensing observations.

¹J.Rojas,^2,1J.Duprat,¹C.Engrand,³E.Dartois,¹L.Delauche,^1,3M.Godard,²M.Gounelle,^4,5J.D.Carrillo-Sánchez,^4,6P.Pokorný,⁷J.M.C.Plane
Earth and Planetary Science Letters 560, 116794 Link to Article [https://doi.org/10.1016/j.epsl.2021.116794]
¹Université Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France
²IMPMC, CNRS-MNHN-Sorbonne Universités, UMR7590, 57 rue Cuvier, 75005 Paris, France
³ISMO, CNRS, Univ. Paris Saclay, Bât 520, 91405 Orsay, France
⁴Department of Physics, Catholic University of America, 620 Michigan Ave., N.E. Washington, DC 20064, USA
⁵ITM Physics Laboratory, NASA Goddard Space Flight Center, Code 675, 8800 Greenbelt Rd., Greenbelt, MD 20771, USA
⁶Astrophysics Science Division, NASA Goddard Space Flight Center, Code 667, 8800 Greenbelt Rd., Greenbelt, MD, USA
⁷School of Chemistry, Univ. of Leeds, Leeds LS2 9JT, UK
Copyright Elsevier

The annual flux of extraterrestrial material on Earth is largely dominated by sub-millimetre particles. The mass distribution and absolute value of this cosmic dust flux at the Earth’s surface is however still uncertain due to the difficulty in monitoring both the collection efficiency and the exposure parameter (i.e. the area-time product in m2.yr). In this paper, we present results from micrometeorite collections originating from the vicinity of the CONCORDIA Station located at Dome C (Antarctica), where we performed several independent melts of large volumes of ultra-clean snow. The regular precipitation rate and the exceptional cleanliness of the snow from central Antarctica allow a unique control on both the exposure parameter and the collection efficiency. A total of 1280 unmelted micrometeorites (uMMs) and 808 cosmic spherules (CSs) with diameters ranging from 30 to 350 μm were identified. Within that size range, we measured mass fluxes of 3.0 μg.m−2.yr−1 for uMMs and 5.6 μg.m−2.yr−1 for CSs. Extrapolated to the global flux of particles in the 12-700 μm diameter range, the mass flux of dust at Earth’s surface is tons.yr−1 ( and tons.yr−1 of uMMs and CSs, respectively). We indicate the statistical uncertainties expected for collections with exposure parameters in the range of 0.1 up to 105 m2.yr. In addition, we estimated the flux of altered and unaltered carbon carried by heated and un-heated particles at Earth’s surface. The mass distributions of CSs and uMMs larger than 100 μm are fairly well reproduced by the CABMOD-ZoDy model that includes melting and evaporation during atmospheric entry of the interplanetary dust flux. These numerical simulations suggest that most of the uMMs and CSs originate from Jupiter family comets and a minor part from the main asteroid belt. The total dust mass input before atmospheric entry is estimated at 15,000 tons.yr−1. The existing discrepancy between the flux data and the model for uMMs below 100 μm suggests that small fragile uMMs may evade present day collections, and/or that the amount of small interplanetary particles at 1 AU may be smaller than expected.

^1,2,3E.Tatsumi et al. (>10)
Nature Astronomy 5, 39–45 Link to Article [DOI https://doi.org/10.1038/s41550-020-1179-z]
¹Instituto de Astrofísica de Canarias (IAC), University of La Laguna, La Laguna, Spain
²Department of Astrophysics, University of La Laguna, La Laguna, Spain
³The University of Tokyo, Tokyo, Japan

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