¹Lidia Pittarello,^2,3Akira Yamaguchi,⁴Julia Roszjar,⁵Vinciane Debaille,^1,4Christian Koeberl,⁶Philippe Claeys
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13284]
¹Department of Lithospheric Research, University of Vienna, Althanstraße 14, A‐1090 Vienna, Austria
²National Institute of Polar Research, 10‐3 Midori‐cho, Tachikawa, Tokyo, 190‐8518 Japan
³Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, 190‐8518 Japan
⁴Natural History Museum Vienna, Burgring 7, A‐1010 Vienna, Austria
⁵Laboratoire G‐Time (Géochimie: Traçage isotopique, minéralogique et élémentaire), Université Libre de Bruxelles, Av. F.D., Roosevelt 50, 1050 Brussels, Belgium
⁶Analytical, Environmental and Geo‐Chemistry (AMGC), Vrije Universiteit Brussel, Pleinlaan 2, B‐1050 Brussels, Belgium
Published by arrangement with John Wiley & Sons

Meteorite fusion crusts are quenched melt layers formed during meteoroid atmospheric entry, mostly preserved as coating on the meteorite surface. Antarctic ureilite Asuka (A) 09368 and H chondrites A 09004 and A 09502 exhibit well preserved thick fusion crusts, characterized by extensive olivine crystallization. As olivine is one of the major components of most meteorites and its petrologic behavior is well constrained, it can be roughly considered as representative for the bulk meteorite. Thus, in this work, the evolution of olivine in fusion crusts of the above‐listed selected samples is investigated. The different shape and chemistry of olivine crystallized in the fusion crust, both as overgrown rim on relic olivine clasts and as new crystals, suggest a general temperature and cooling rate gradient. The occurrence of reverse and oscillatory zoning in individual olivine grains within the fusion crust suggests complex redox reactions. Overall, the investigated fusion crusts exhibit a general oxidation of the relatively reduced initial material. However, evidence of local reduction is preserved. Reduction is likely triggered by the presence of carbon in the ureilite or by overheating during the atmospheric entry. Constraining these processes provides a potential analog for interpreting features observed in cosmic spherules and micrometeorites and for calibrating experiments and numerical models on the formation of fusion crusts.

^1,2Danielle N. Simkus,^2,3José C. Aponte,²Jamie E. Elsila,¹Robert W. Hilts,^2,3Hannah L. McLain,¹Christopher D. K. Herd
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13276]
¹Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2R3 Canada
²Solar System Exploration Division, Code 691, NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA
³Department of Chemistry, Catholic University of America, Washington, DC, 20064 USA
Published by arrangement with John Wiley & Sons

The Tagish Lake carbonaceous chondrite exhibits a unique compositional heterogeneity that may be attributed to varying degrees of aqueous alteration within the parent body asteroid. Previous analyses of soluble organic compounds from four Tagish Lake meteorite specimens (TL5b, TL11h, TL11i, TL11v) identified distinct distributions and isotopic compositions that appeared to be linked to their degree of parent body processing (Herd et al. 2011; Glavin et al. 2012; Hilts et al. 2014). In the present study, we build upon these initial observations and evaluate the molecular distribution of amino acids, aldehydes and ketones, monocarboxylic acids, and aliphatic and aromatic hydrocarbons, including compound‐specific δ13C compositions, for three additional Tagish Lake specimens: TL1, TL4, and TL10a. TL1 contains relatively high abundances of soluble organics and appears to be a moderately altered specimen, similar to the previously analyzed TL5b and TL11h lithologies. In contrast, specimens TL4 and TL10a both contain relatively low abundances of all of the soluble organic compound classes measured, similar to TL11i and TL11v. The organic‐depleted composition of TL4 appears to have resulted from a relatively low degree of parent body aqueous alteration. In the case of TL10a, some unusual properties (e.g., the lack of detection of intrinsic monocarboxylic acids and aliphatic and aromatic hydrocarbons) suggest that it has experienced extensive alteration and/or a distinct organic‐depleted alteration history. Collectively, these varying compositions provide valuable new insights into the relationships between asteroidal aqueous alteration and the synthesis and preservation of soluble organic compounds.

^1,2,3M. D. Suttle,^2,3M. J. Genge,⁴T. Salge,⁵M. R. Lee,¹L. Folco,⁴T. Góral,³S. S. Russell,⁶P. Lindgren
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13279]
¹Dipartimento di Scienze della Terra, Università di Pisa, 56126 Pisa, Italy
²Department of Earth Science and Engineering, Imperial College London, South Kensington, London, SW7 2AZ UK
³Mineral and Planetary Sciences, The Natural History Museum, Cromwell Rd, London, SW7 5BD UK
⁴Imaging and Analysis Centre, Core Research Laboratories, The Natural History Museum, Cromwell Rd, London, SW7 5BD UK
⁵School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ UK
⁶Earth Science and Physical Geography, Lund University, 221 00 Lund, Sweden
Published by arrangement with John Wiley & Sons

We report the discovery of a partially altered microchondrule within a fine‐grained micrometeorite. This object is circular, <10 μm in diameter, and has a cryptocrystalline texture, internal zonation, and a thin S‐bearing rim. These features imply a period of post‐accretion parent body aqueous alteration, in which the former glassy igneous texture was subject to hydration and phyllosilicate formation as well as leaching of fluid‐mobile elements. We compare this microchondrule to three microchondrules found in two CM chondrites: Elephant Moraine (EET) 96029 and Murchison. In all instances, their formation appears closely linked to the late stages of chondrule formation, chondrule recycling, and fine‐grained rim accretion. Likewise, they share cryptocrystalline textures and evidence of mild aqueous alteration and thus similar histories. We also investigate the host micrometeorite’s petrology, which includes an unusually Cr‐rich mineralogy, containing both Mn‐chromite spinel and low‐Fe‐Cr‐rich (LICE) anhydrous silicates. Because these two refractory phases cannot form together in a single geochemical reservoir under equilibrium condensation, this micrometeorite’s accretionary history requires a complex timeline with formation via nonequilibrium batch crystallization or accumulation of materials from large radial distances. In contrast, the bulk composition of this micrometeorite and its internal textures are consistent with a hydrated carbonaceous chondrite source. This micrometeorite is interpreted as a fragment of fine‐grained rim material that once surrounded a larger parent chondrule and was derived from a primitive carbonaceous parent body; either a CM chondrite or Jupiter family comet.