¹Christian Vollmer,¹Stella Rombeck,²Julia Roszjar,³Adam R. Sarafian,¹Stephan Klemme
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13453]
¹Institut für Mineralogie, Westfälische Wilhelms‐Universität Münster, Corrensstrasse 24, D‐48149 Münster, Germany
²Department of Mineralogy and Petrography, Natural History Museum Vienna, Burgring 7, 1010 Vienna, Austria
³Science and Technology Division, Corning Incorporated, 21 Lynn Morse Rd., Painted Post, New York, New York, 14870 USA
Published by arrangement with John Wiley & Sons

We report on the petrography and mineralogy of five Yamato polymict eucrites to better constrain the formation and alteration of crustal material on differentiated asteroids. Each sample consists of different lithic clasts that altogether form four dominant textures and therefore appear to originate from closely related petrological areas within Vesta′s crust. The textures range from subophitic to brecciated, porphyritic, and quench‐textured, that differ from section to section. Comparison with literature data for these samples is therefore difficult, which stresses that polymict eucrites are extremely complex in their petrography and investigation of only one thick section may not be representative for the host rock. We also show that sample Y‐793548 consists of more than one lithic unit and must therefore be classified as polymict instead of monomict. The variety and nature of lithic textures in the investigated Yamato meteorites indicate shock events, intense post‐magmatic thermal annealing, and secondary alteration. These postmagmatic features occur in different intensities, varying from clast to clast or among coexisting mineral fragments on a small, local scale. Several clasts within the eucrites studied have been modified by late‐stage alteration processes that caused deposition of Fe‐rich olivine and Fe enrichment along cracks crosscutting pyroxene crystals. However, formation of these secondary phases seems to be independent of the degree of thermal metamorphism observed within every type of clast, which would support a late‐stage metasomatism model for their formation.

¹O. Pravdivtseva,²F. L. H. Tissot,³N. Dauphas,¹S. Amari
Nature Astronomy(In Press) Link to Article [DOIhttps://doi.org/10.1038/s41550-019-1000-z]
¹Physics Department and McDonnell Center for the Space Sciences, Washington University, Saint Louis, MO, USA
²The Isotoparium, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
³Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, Chicago, IL, USA

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

¹Dominika Kalasová,¹Tomáš Zikmund,²Pavel Spurný,³Jakub Haloda,²Jiří Borovička,¹Jozef Kaiser
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13460]
¹CEITEC – Central European Institute of Technology, Brno University of Technology, Purkyňova 123, Brno, Czech Republic
²Astronomical Institute of the Czech Academy of Sciences, Fričova 298, 25165 Ondřejov, Czech Republic
³Czech Geological Survey, Geologická 6, 152 00 Prague, Czech Republic
Published by arrangement with John Wiley & Sons

A very bright and long bolide was observed over the eastern part of the Czech Republic during late local evening on December 9, 2014. This bolide was recorded by professional instruments in the Czech part of the European Fireball Network. Three meteorites weighing in total 87 g were found in the predicted area and were named Žďár nad Sázavou. The complete material composition of the meteorite was obtained from one cut‐off piece using petrography, mineralogy, and scanning electron microscopy (together with X‐ray energy dispersive spectroscopy and wavelength dispersive spectroscopy). X‐ray computed tomography (CT) was applied on all pieces for the determination of their grain and bulk density, digitization of shape, and examination of the structural homogeneity. CT has proved its important role for nondestructive exploration of brecciated meteorites formed by distinct lithologies or petrological types. In this article, we discuss its limits in terms of structural and material resolution based on the correlation of state‐of‐the‐art CT data and SEM images. Furthermore, we introduce a new way of air cavity quantification, which distinguishes the natural porosity of meteorite and cracks related to erosion processes. This helps to discuss the presence of weathering products based on comparison of the meteorite pieces found at different times after impact.

¹E. Dobrică,¹A. J. Brearley
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13458]
¹Department of Earth and Planetary Sciences, MSC03‐2040, 1 University of New Mexico, Albuquerque, New Mexico, 87131‐0001 USA
Published by Arrangement with John Wiley & Sons

We have investigated the fine‐grained matrix of the least‐altered unequilibrated ordinary chondrite (UOC) Semarkona (LL3.00) using different electron microscope techniques. Unlike previous studies, which found that the matrix of Semarkona was extensively altered to phyllosilicates, we have discovered the widespread occurrence of much more pristine amorphous silicates in the sample that we have studied. Detailed TEM study shows that these materials occur pervasively in the matrix as (1) continuous groundmass; (2) distinct, circular to subrounded features, which contain nanometric‐size sulfides and carbides; or (3) distinct objects containing parallel, linear features composed of sulfides and voids. These amorphous silicates have many textural and compositional similarities to the occurrences of amorphous silicates found in pristine carbonaceous chondrites (CCs); however, minor differences were also identified. Most of the textural and chemical differences suggest that these materials formed at different times and locations in the solar nebula, compared to matrix materials in CCs. Nevertheless, their occurrence suggests that the amorphous silicates in Semarkona formed by similar processes to those proposed for amorphous silicates in CCs, that is, rapid cooling that favored disequilibrium condensation of material evaporated during chondrule‐forming events. In addition, the occurrence of minimally altered amorphous silicates in Semarkona demonstrates that the effects of aqueous alteration, which have been widely described in this meteorite, are not pervasive. Instead, our new observations demonstrate that aqueous alteration has affected Semarkona heterogeneously and that locally, regions of much more pristine matrix that have escaped extensive alteration are still preserved within this meteorite. Such materials provide significant new insights into the pristine characteristics of ordinary chondrite matrix material that has not been previously available.

^1,2Patrick J. A. Hill,^1,3Gordon R. Osinski,^1,3Neil R. Banerjee
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13457]
¹Department of Earth Sciences, University of Western Ontario, 1151 Richmond Street, London, Ontario, N6A 5B7 Canada
²Department of Earth and Atmospheric Sciences, University of Alberta, 1‐26 Earth Sciences Building, Alberta, T6G 2E3 Canada
³Institute for Earth and Space Exploration, University of Western Ontario, 1151 Richmond Street, London, Ontario, N6A 5B7 Canada
Published by arrangement with John Wiley & Sons

By analyzing impact glass, the evolution of the impact melt at the Mistastin Lake impact structure was investigated. Impact glass clasts are present in a range of impactites, including polymict breccias and clast‐rich impact melt rock, and from a variety of settings within the crater. From the glass clasts analyzed, three petrographic subtypes of impact glass were identified based on their clast content, prevalence of schlieren, color, texture, and habit. Several alteration phases were also observed replacing glass and infilling vesicles; however, textural observations and quantified compositional data allowed for the identification of pristine impact glass. Although the various types of glasses show significant overlap in their major oxide composition, several subtle variations in the major oxide chemistry of the glass were observed. To investigate this variation, a least‐squares mixing model was implemented utilizing the composition of the glass and the known target rock chemistry to model the initial melt composition. Additionally, image analysis of the glass clasts was used to investigate whether the compositional variations correlated to textural difference in the lithologies. We propose that the textural and compositional dichotomy observed is a product of the evolution, assimilation, and emplacement of the glass. The dichotomy is reflective of the melt either being ballistically emplaced (group 2 glasses: occurring in melt‐poor polymict breccias at lowermost stratigraphic position outside the transient crater) or the result of late‐stage melt flows (group 1 glasses, occurring in melt‐bearing polymict breccias and impact melt rocks at higher stratigraphic positions outside the transient crater).

^1,2Zoltán Váci,^1,2Carl B. Agee,³Munir Humayun,^1,2Karen Ziegler,²Yemane Asmerom,²Victor Polyak,⁴Henner Busemann,⁴Daniela Krietsch,⁵Matthew Heizler,⁶Matthew E. Sanborn,⁶Qing‐Zhu Yin
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13456]
¹Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, 87131 USA
²Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, 87131 USA
³National High Magnetic Field Laboratory, Department of Earth Ocean & Atmospheric Science, Florida State University, Tallahassee, Florida, 32310 USA
⁴Institute of Geochemistry and Petrology, ETH Zürich, 8092 Zurich, Switzerland
⁵New Mexico Bureau of Geology, New Mexico Institute of Mining and Technology, Socorro, New Mexico, 87801 USA
⁶Department of Earth and Planetary Sciences, University of California, Davis, Davis, California, 95616 USA
Published by arrangement with John Wiley & Sons

Northwest Africa (NWA) 11042 is a heavily shocked achondrite with medium‐grained cumulate textures. Its olivine and pyroxene compositions, oxygen isotopic composition, and chromium isotopic composition are consistent with L chondrites. Sm‐Nd dating of its primary phases shows a crystallization age of 4100 ± 160 Ma. Ar‐Ar dating of its shocked mineral maskelynite reveals an age of 484.0 ± 1.5 Ma. This age coincides roughly with the breakup event of the L chondrite parent body evident in the shock ages of many L chondrites and the terrestrial record of fossil L chondritic chromite. NWA 11042 shows large depletions in siderophile elements (<0.01×CI) suggestive of a complex igneous history involving extraction of a Fe‐Ni‐S liquid on the L chondrite parent body. Due to its relatively young crystallization age, the heat source for such an igneous process is most likely impact. Because its mineralogy, petrology, and O isotopes are similar to the ungrouped achondrite NWA 4284 (this work), the two meteorites are likely paired and derived from the same parent body.

¹Cosette M. Gilmour,¹Christopher D. K. Herd
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13436]
¹Department of Earth and Atmospheric Sciences, University of Alberta, 1‐26 Earth Sciences Building, Edmonton, AB, T6G 2E3 Canada
Published by arrangement with John Wiley & Sons

Platinum group element (PGE) concentrations have been determined in situ in ordinary chondrite kamacite and taenite grains via laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS). Results demonstrate that PGE concentrations in ordinary chondrite metal (kamacite and taenite) are similar among the three ordinary chondrite groups, in contrast to previous bulk metal studies in which PGE concentrations vary in the order H < L < LL. PGE concentrations are higher in taenite than kamacite, consistent with preferential PGE partitioning into taenite. PGE concentrations vary between and within metal grains, although average concentrations in kamacite broadly agree with results from bulk studies. The variability of PGE concentrations in metal decreases with increasing petrologic type; however, variability is still evident in most type six ordinary chondrites, suggesting that equilibration of PGEs does not occur between metal grains, but rather within individual metal grains via self‐diffusion during metamorphism. The constant average PGE concentrations within metal grains across different ordinary chondrite groups are consistent with the formation of metal via nebular condensation prior to the accretion of ordinary chondrite parent bodies. Post‐condensation effects, including heating during chondrule‐formation events, may have affected some element ratios, but have not significantly affected average metal PGE concentrations.

^1,2J. S. New,^1,3R. A. Mathies,²M. C. Price,²M. J. Cole,^1,3M. Golozar,²V. Spathis,²M. J. Burchell,¹A. L. Butterworth
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13448]
¹Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, California, 94720 USA
²School of Physical Sciences, University of Kent, Canterbury, Kent, CT2 7NH UK
³Department of Chemistry, University of California, Berkeley, California, 94720 USA
Published by arrangement with John Wiley & Sons

The presence and accessibility of a sub‐ice‐surface saline ocean at Enceladus, together with geothermal activity and a rocky core, make it a compelling location to conduct further, in‐depth, astrobiological investigations to probe for organic molecules indicative of extraterrestrial life. Cryovolcanic plumes in the south polar region of Enceladus enable the use of remote in situ sampling and analysis techniques. However, efficient plume sampling and the transportation of captured organic materials to an organic analyzer present unique challenges for an Enceladus mission. A systematic study, accelerating organic ice‐particle simulants into soft inert metal targets at velocities ranging 0.5–3.0 km s⁻¹, was carried out using a light gas gun to explore the efficacy of a plume capture instrument. Capture efficiency varied for different metal targets as a function of impact velocity and particle size. Importantly, organic chemical compounds remained chemically intact in particles captured at speeds up to ~2 km s⁻¹. Calibration plots relating the velocity, crater, and particle diameter were established to facilitate future ice‐particle impact experiments where the size of individual ice particles is unknown.

^1,2,3Marc Neveu,⁴Christopher H.House,^2,3,5Scott T.Wieman
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113714]
¹Department of Astronomy, University of Maryland, 4296 Stadium Dr., College Park, MD 20742, USA
²Planetary Environments Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Rd., Greenbelt, MD 20770, USA
³Center for Research in Space Science and Technology, NASA Goddard Space Flight Center, 8800 Greenbelt Rd., Greenbelt, MD 20770, USA
⁴Department of Geosciences, Pennsylvania State University, 503 Deike Building, University Park, PA 16802, USA
⁵Center for Space Sciences and Technology, University of Maryland, Baltimore County, 1000 Hilltop Cir., Baltimore, MD 21250, USA
Copyright Elsevier

Clark et al. [Clark, R.N., Brown, R.H., Cruikshank, D.P., Swayze, G.A., 2019. Icarus, 321, 791–802] reported an extremely low value of the ¹²C/¹³C ratio in CO₂ ice on Phoebe, a likely captured moon of Saturn. Unless Phoebe did not form in the solar system, we interpret this value as indication that Phoebe accreted surface carbon from a region of the protosolar nebula where ¹³C was enriched due to self-shielding of ¹²CO from photodissociation. This could imply that Phoebe is also enriched in ^17,18O relative to most solar system objects sampled to date. Phoebe and other objects that may have sampled these ¹³C-rich regions, such as Pallas or Triton, may provide the opportunity to directly measure isotopic fractionations in endmembers of the self-shielded solar nebula.

¹Lukáš Ackerman,¹Karel Žák,¹Roman Skála,¹Jan Rejšek,¹Šárka Křížová,²Josh Wimpenny,³Tomáš Magna
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.02.025]
¹Institute of Geology of the Czech Academy of Sciences, Rozvojová 269, CZ-165 00 Praha 6, Czech Republic
²Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
³Czech Geological Survey, Klárov 3, CZ-118 21 Praha 1, Czech Republic
Copyright Elsevier

The Australasian tektite (AAT) strewn field is the largest strewn field on the Earth with about ∼10–30% coverage, both land and ocean, but a clearly identified source impact crater is absent despite the young age of AAT of ca. 790 ka. A genetic link between the Australasian tektites and their unequivocal parental materials is therefore largely impossible to establish. Nevertheless, the nature of the parental materials and the extent of volatilization can be constrained using the splash form tektites, carrying the chemical signatures of high-temperature processes, and the layered (so-called Muong Nong-type) tektites, which are less chemically homogenized and exceptionally abundant in the AAT field. New high-precision Sr, Nd and Pb isotopic measurements were obtained for a chemically and petrographically well-characterized suite of AAT, which included the Muong Nong-type (MN-AAT) with precisely known field locations in Laos and splash forms (SF-AAT) from different parts of the strewn field. In addition, optically dark and light zones of the MN-AAT were also separately analyzed. Homogeneous ε_Nd values from −11.8 to −11.2, combined with a narrow range of two-stage Nd model ages from 1.67 to 1.72 Ga for the entire AAT suite, point to a well-mixed source, in terms of REE, of the crustal segment from which the sedimentary material for tektites was ultimately derived. The Sr isotopic data largely overlap for SF-AAT and MN-AAT (⁸⁷Sr/⁸⁶Sr = 0.71636–0.72021) and indicate Paleozoic to Mesozoic sedimentary parentage. However, late Neogene to early Quaternary re-deposition and formation of a thick silt-sized sedimentary section with vertical stratification is required to comply with ¹⁰Be data. Lead isotope systematics documents at least three different components which can perhaps be represented by different mineral phases, such as feldspar, zircon, organic matter adsorbed on young sediments etc., sorted during fluvial transport and final deposition. In addition, the SF-AAT have systematically lower Pb contents than the MN-AAT, and generally show isotopically heavier Pb isotopic ratios. This is theoretically consistent with a preferential volatilization of lighter Pb isotopes during evaporation and considerably larger Pb loss from SF-AAT when compared to MN-AAT. Nevertheless, further experimental work would be necessary to unambiguously distinguish kinetic fractionation from source mixing.