John T. Wasson^1,2
1Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, California, USA
²Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA

Treysa and Delegate have compositions closely similar to those of IIIAB irons but plot above the IIIAB field on Ir-Au diagrams; for this reason they are designated anomalous members of IIIAB. All refractory siderophiles share this anomaly. Wasson (1999) interpreted the large spread on IIIAB Ir-Au diagrams to result from melt-trapping and generated solid and liquid fractional crystallization tracks; almost all IIIAB irons fall between the tracks. In contrast, Treysa, Delegate, and three other irons (the Treysa quintet) plot beyond the liquid track. Ideal fractional crystallization cannot account for compositions that plot outside the region between the tracks. Possible explanations for the anomalous compositions of the Treysa quintet are that (1) these meteorites did not form in the IIIAB magma or (2) they formed by the mixing of early crystallized solids with a late liquid. The weight of the evidence including cosmic-ray ages favor the second explanation. Although this explanation can account for positions plotting above the liquid track, it requires special circumstances. The infalling blocks must be assimilated and the resulting melt must crystallize quickly into pockets small enough (<1 m) to allow igneous gradients to be leveled by subsequent diffusion. The Treysa quintet shares the region beyond the liquid track with most main-group pallasites (PMG), which may have also originated in the IIIAB body. It appears that Treysa, its relatives, and the PMG were formed in one or more impact events that mixed olivine and solid metal formed near the core-mantle boundary with nearby magma. It is then necessary to cool the melt rapidly; the best way to achieve rapid cooling is by heat exchange with cooler solids. That the Treysa quintet and the PMG can be explained by the same processes operating on late IIIAB magma supports the conclusion that PMG formed on the IIIAB parent asteroid.

Reference
Wasson JT (2016) Formation of the Treysa quintet and the main-group pallasites by impact-generated processes in the IIIAB asteroid. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12635]
Published by arrangement with John Wiley & Sons

E. Dobrică and A. J. Brearley
Department of Earth and Planetary Sciences, University of New Mexico, MSC03-2040, Albuquerque, New Mexico, USA

The diversity of silicate, glassy spherules analogous to chondrules, called microchondrules, and the implications for their presence in unequilibrated ordinary chondrites (UOCs) were investigated using different electron microscope techniques. Our observations show that the abundance of microchondrules in UOCs is much larger than the values proposed by previous studies. We identified two different types of microchondrules, porous and nonporous, embedded within fine-grained matrices and type I chondrule rims. The porous microchondrules are characterized by distinctive textures and chemical compositions that have not been recognized previously. Additionally, we show detailed textures and chemical compositions of protuberances of silicate materials, connected to the chondrules and ending with microchondrules. We suggest that microchondrules and protuberances formed from materials splattered from the chondrules during stochastic collisions when they were still either completely or partially molten. The occurrence and distinct morphologies of microchondrules and protuberances suggest that rather than just a passive flash melting of chondrules, an additional event perturbed the molten chondrules before they underwent cooling. The bulk chemical compositions suggest that (1) nonporous microchondrules and protuberances were formed by splattering of materials that are compositionally similar to the bulk silicate composition of type I chondrules, and (2) the porous microchondrules could represent the splattered melt products of a less evolved, fine-grained dust composition. The preservation of protuberances and microchondrules in the rims suggests that the cooling and accretion rates were exceptionally fast and that they represent the last objects that were formed before the accretion of the parent bodies of OCs.

Reference
Dobrică E and Brearley AJ (2016) Microchondrules in two unequilibrated ordinary chondrites: Evidence for formation by splattering from chondrules during stochastic collisions in the solar nebula. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12633]
Published by arrangement with John Wiley & Sons

N. Meftah^1,2,3, S. Mostefaoui⁴, A. Jambon², E. H. Guedda³ and S. Pont^4
1Faculté des Mathématiques et des Sciences de la Matière, Université Kasdi Merbah, Ouargla, Algeria
²Sorbonne Universités ISTEP UMR 7193, UPMC, Paris Cedex 05, France
³Laboratoire LEVRES et Faculté des Sciences et technologie, Université d’El-Oued, El-Oued, Algeria
⁴IMPMC, Muséum National d’Histoire Naturelle, Paris, France

We report in situ NanoSIMS siderophile minor and trace element abundances in individual Fe-Ni metal grains in the unequilibrated chondrite Krymka (LL3.2). Associated kamacite and taenite of 10 metal grains in four chondrules and one matrix metal were analyzed for elemental concentrations of Fe, Ni, Co, Cu, Rh, Ir, and Pt. The results show large elemental variations among the metal grains. However, complementary and correlative variations exist between adjacent kamacite-taenite. This is consistent with the unequilibrated character of the chondrite and corroborates an attainment of chemical equilibrium between the metal phases. The calculated equilibrium temperature is 446 ± 9 °C. This is concordant with the range given by Kimura et al. (2008) for the Krymka postaccretion thermal metamorphism. Based on Ni diffusivity in taenite, a slow cooling rate is estimated of the Krymka parent body that does not exceed ~1K Myr⁻¹, which is consistent with cooling rates inferred by other workers for unequilibrated ordinary chondrites. Elemental ionic radii might have played a role in controlling elemental partitioning between kamacite and taenite. The bulk compositions of the Krymka metal grains have nonsolar (mostly subsolar) element/Ni ratios suggesting the Fe-Ni grains could have formed from distinct precursors of nonsolar compositions or had their compositions modified subsequent to chondrule formation events.

Reference
Meftah N, Mostefaoui S, Jambon A, Guedda EH and Pont S (2016) Minor and trace element concentrations in adjacent kamacite and taenite in the Krymka chondrite. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12617]
Published by arrangement with John Wiley & Sons

J. W. Aerts¹, A. Elsaesser², W. F. M. Röling¹ and P. Ehrenfreund^2,3
1Molecular Cell Physiology, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands
²Leiden Observatory, Leiden University, Leiden, the Netherlands
³Space Policy Institute, George Washington University, Washington, District of Columbia, USA

The Orgueil meteorite has become one of the most well-studied carbonaceous meteorites, after it fell in France 150 yr ago. Extraterrestrial organic compounds such as amino acids and nucleobases in the parts per billion ranges were identified in Orgueil samples with supporting isotopic analyses. However, speculations of terrestrial contamination such as organic inclusions in the form of microbes and seeds accompanied the analyses of the Orgueil meteorite ever since its fall. By using molecular analysis, we performed DNA extractions and spiking experiments combined with 16S and 18S rRNA gene targeted PCR amplification to quantify the level of terrestrial biocontamination. Our results indicate that terrestrial contamination with DNA was insignificant in the investigated meteorite fraction. We also remeasured and confirmed concentrations of amino acids found in previous studies and conclude that their rather high concentrations and distribution cannot be explained by terrestrial contamination with microorganisms alone. These results represent the first analysis using DNA-directed tools in the analysis of the Orgueil meteorite to determine trace levels of biomarkers.

Reference
Aerts JW, Elsaesser A, Röling WFM and Ehrenfreund P (2016) A contamination assessment of the CI carbonaceous meteorite Orgueil using a DNA-directed approach. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12629]
Published by arrangement with John Wiley & Sons

Diana Bolser¹, Thomas J. Zega^2,3, Abu Asaduzzaman³, Stefan Bringuier³, Steven B. Simon⁴, Lawrence Grossman⁴, Michelle S. Thompson² and Kenneth J. Domanik^1
1Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, USA
²Lunar and Planetary Laboratory, Department of Planetary Sciences, University of Arizona, Tucson, Arizona, USA
³Department of Materials Science & Engineering, University of Arizona, Tucson, Arizona, USA
⁴Department of Geophysical Sciences, University of Chicago, Chicago, Illinois, USA

A coordinated, electron-backscatter-diffraction (EBSD) and transmission electron microscope (TEM) study was undertaken to obtain information on the origin of rims on refractory inclusions in the Allende and Axtell CV3 chondrites. These measurements were supported by theoretical modeling using density functional theory. Crystal-orientation analysis of Wark-Lovering rims via EBSD revealed pyroxene grains with similar crystallographic orientations to one another in both inclusions. An epitaxial relationship between grains within the diopside and anorthite rim layers was observed in Allende. TEM examination of the rims of both samples also revealed oriented crystals at depth. The microstructural data on the rims suggest that grain clusters grew in the form of three-dimensional islands. Density functional theory calculations confirm that formation of oriented grain islands is the result of energy minimization at high temperature. The results point toward condensation as the mode of origin for the rims studied here.

Reference
Bolser D, Zega TJ, Asaduzzaman A, Bringer S, Simon SB, Grossman L, Thompson MS and Domanik KJ (2016) Microstructural analysis of Wark-Lovering rims in the Allende and Axtell CV3 chondrites: Implications for high-temperature nebular processes. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12620]
Published by arrangement with John Wiley & Sons

Motoo Ito¹ and Scott Messenger^2
1Robert M Walker Laboratory for Space Science, EISD/ARES, NASA Johnson Space Center, Houston, Texas, USA
²JAMSTEC, Kochi Institute for Core Sample Research, Nankoku, Kochi, Japan

We have established analytical procedures for quantitative rare earth element (REE) measurements by NanoSIMS 50L ion microprobe with 2–10 μm spatial resolution. Measurements are performed by multidetection using energy filtering under several static magnetic field settings. Relative sensitivity factors and REE oxide/REE element secondary ion ratios that we determined for the NanoSIMS match values previously determined for other ion microprobes. REE measurements of 100 ppm REE glass standards yielded reproducibility and accuracy of 0.5–2.5% and 5–15%, respectively. REE measurements of minerals of an Allende type-A CAI, 7R19-1, were performed using three different methods: spot analysis, line profile, and imaging. These data are in excellent agreement with previous REE measurements of this inclusion by IMS-3f ion microprobe. The higher spatial resolution NanoSIMS measurements provide additional insight into the formation process of this CAI and offer a promising new tool for analysis of fine-grained and complexly zoned materials.

Reference
Ito M and Messenger S (2016) Rare earth element measurements and mapping of minerals in the Allende CAI, 7R19-1, by NanoSIMS ion microprobe. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12623]
Published by arrangement with John Wiley & Sons

¹Scott Harlan et al. (>10)*
¹Planetary Geology Lab, Institute of Geological Sciences, Polish Academy of Sciences, Wrocław, Poland
*Find the extensive, full author and affiliation list on the publishers website

Meteorites have been found on the small Misfits Flat dry lakebed near Stagecoach, Nevada (119.382W, +39.348N). Since the first find on Sept. 22, 2013, a total of 58 stones of weathering stage W2/3 with a combined mass of 339 g have been collected in 19 visits to the area. This small (3.3 × 3.6 km) lakebed is now a newly designated dense collection area (DCA). Most meteorites were found in a small 350 × 180 m area along the north shore and most are fragments of several broken individual stones. Three of these fragments were classified as an LL4/5 of shock stage S2, now named Misfits Flat 001, one of which (stone MF33) fell 8.1 ± 1.3 ka ago based on the 14C terrestrial age, assuming it came from a 20–80 cm diameter meteoroid. In addition, a small darkly crusted meteorite MF34, now named Misfits Flat 002, was found 820 m WSW from the main mass. This meteorite is classified as an LL5 ordinary chondrite with shock stage S4/5. The meteorite is saturated in 14C at 63 dpm kg−1, suggesting it originated from the center of a 0.5 m diameter meteoroid, or deep inside a ~1.0 m meteoroid, less than 300 yr ago. Accounts exist of a fireball seen at 13:15 UT on March 2, 1895, that are consistent with the find location of Misfits Flat 002.

Reference
Harlan S et al. (2016) Meteorites found on Misfits Flat dry lake, Nevada. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12619]
Published by arrangement with John Wiley & Sons

Derek W. G. Sears¹, Hazel Sears¹, Denton S. Ebel², Sean Wallace² andJon M. Friedrich^2,3
1NASA Ames Research Center/BAER Institute, Mountain View, California, USA
²American Museum of Natural History, New York, New York, USA
³Department of Chemistry, Fordham University, New York, New York, USA

X-ray computed tomography has become a popular means for examining the interiors of meteorites and has been advocated for routine curation and for the examination of samples returned by missions. Here, we report the results of a blind test that indicate that CT imaging deposits a considerable radiation dose in a meteorite and seriously compromises its natural radiation record. Ten vials of the Bruderheim L6 chondrite were placed in CT imager and exposed to radiation levels typical for meteorite studies. Half were retained as controls. Their thermoluminescence (TL) properties were then measured in a blind test. Five of the samples had TL data unaltered from their original (~10 cps) while five had very strong signals (~20,000 cps). It was therefore very clear which samples had been in the CT scanner. For comparison, the natural TL signal from Antarctic meteorites is ~5000–50,000 cps. Using the methods developed for Antarctic meteorites, the apparent dose absorbed by the five test samples was calculated to be 83 ± 5 krad, comparable with the highest doses observed in Antarctic meteorites and freshly fallen meteorites. While these results do not preclude the use of CT scanners when scientifically justified, it should be remembered that the record of radiation exposure to ionizing radiations for the sample will be destroyed and that TL, or the related optically stimulated luminescence, are the primary modern techniques for radiation dosimetry. This is particularly important with irreplaceable samples, such as meteorite main masses, returned samples, and samples destined for archive.

Reference
Sears DWG, Sears H, Ebel DS, Wallace S andFriedrich JM (2016) X-ray computed tomography imaging: A not-so-nondestructive technique. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12622]
Published by arrangement with John Wiley & Sons

François L. H. Tissot, Nicolas Dauphas, Lawrence Grossman
Origins Lab, Department of the Geophysical Sciences, and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA.

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

Reference
Tissot FLH, Dauphas N, Grossman L (2016) Origin of uranium isotope variations in early solar nebula condensates. Science Advances e1501400
Link to Article [doi:10.1126/sciadv.1501400]

¹A. Losiak et al. (>10)*
¹Planetary Geology Lab, Institute of Geological Sciences, Polish Academy of Sciences, Wrocław, Poland
*Find the extensive, full author and affiliation list on the publishers website

The estimates of the age of the Kaali impact structure (Saaremaa Island, Estonia) provided by different authors vary by as much as 6000 years, ranging from ~6400 to ~400 before current era (BCE). In this study, a new age is obtained based on 14C dating charred plant material within the proximal ejecta blanket, which makes it directly related to the impact structure, and not susceptible to potential reservoir effects. Our results show that the Kaali crater was most probably formed shortly after 1530–1450 BCE (3237 ± 10 14C yr BP). Saaremaa was already inhabited when the bolide hit the Earth, thus, the crater-forming event was probably witnessed by humans. There is, however, no evidence that this event caused significant change in the material culture (e.g., known archeological artifacts) or patterns of human habitation on Saaremaa.

Reference
Losiak A et al. (2016) Dating a small impact crater: An age of Kaali crater (Estonia) based on charcoal emplaced within proximal ejecta. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12616]
Published by arrangement with John Wiley & Sons