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

¹Ronny Schoenberg, ¹Alexandra Merdian, ²Chris Holmden, ¹Ilka C. Kleinhanns, ¹Kathrin Haßler, ¹Martin Wille, ¹Elmar Reitter
¹Department of Geosciences, University of Tuebingen, Germany
²Department of Geological Sciences, University of Saskatchewan, Canada

The depletion of chromium in Earth’s mantle (∼2,700 ppm) in comparison to chondrites (∼4,400 ppm) indicates significant incorporation of chromium into the core during our planet’s metal-silicate differentiation, assuming that there was no significant escape of the moderately volatile element chromium during the accretionary phase of Earth. Stable Cr isotope compositions – expressed as the ‰-difference in 53Cr/52Cr from the terrestrial reference material SRM979 (δ53/52CrSRM979 values) – of planetary silicate reservoirs might thus yield information about the conditions of planetary metal segregation processes when compared to chondrites. The stable Cr isotopic compositions of 7 carbonaceous chondrites, 11 ordinary chondrites, 5 HED achondrites and 2 martian meteorites determined by a double spike MC-ICP-MS method are within uncertainties indistinguishable from each other and from the previously determined δ53/52CrSRM979 value of –0.124 ± 0.101 ‰ for the igneous silicate Earth. Extensive quality tests support the accuracy of the stable Cr isotope determinations of various meteorites and terrestrial silicates reported here. The uniformity in stable Cr isotope compositions of samples from planetary silicate mantles and undifferentiated meteorites indicates that metal-silicate differentiation of Earth, Mars and the HED parent body did not cause measurable stable Cr isotope fractionation between these two reservoirs. Our results also imply that the accretionary disc, at least in the inner solar system, was homogeneous in its stable Cr isotopic composition and that potential volatility loss of chromium during accretion of the terrestrial planets was not accompanied by measurable stable isotopic fractionation. Small but reproducible variations in δ53/52CrSRM979 values of terrestrial magmatic rocks point to natural stable Cr isotope variations within Earth’s silicate reservoirs. Further and more detailed studies are required to investigate whether silicate differentiation processes, such partial mantle melting and crystal fractionation, can cause stable Cr isotopic fractionation on Earth and other planetary bodies.

Reference
Schoenberg R, Merdian A, Holmden C, Kleinhanns IC, Haßler K, Wille M, Reitter E (2016) The stable Cr isotopic compositions of chondrites and silicate planetary reservoirs. Geochmica et Cosmochmica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.03.013]
Copyright Elsevier

^1,2Geoffrey H. Howarth, ^3,4Yang Liu, ^3,4Yang Chen, ¹John F. Pernet-Fisher, ¹Lawrence A. Taylor
¹Earth and Planetary Sciences Department, Planetary Geosciences Institute, University of Tennessee, Knoxville, Tennessee, USA
²Department of Geological Sciences, University of Cape Town, Rondebosch, South Africa
³Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
⁴Division of Geology and Planetary Science, California Institute of Technology, Pasadena, California, USA

Apatite is the major volatile-bearing phase in Martian meteorites, containing structurally bound fluorine, chlorine, and hydroxyl ions. In apatite, F is more compatible than Cl, which in turn is more compatible than OH. During degassing, Cl strongly partitions into the exsolved phase, whereas F remains in the melt. For these reasons, the volatile concentrations within apatite are predictable during magmatic differentiation and degassing. Here, we present compositional data for apatite and merrillite in the paired enriched, olivine-phyric shergottites LAR 12011 and LAR 06319. In addition, we calculate the relative volatile fugacities of the parental melts at the time of apatite formation. The apatites are dominantly OH-rich (calculated by stoichiometry) with variable yet high Cl contents. Although several other studies have found evidence for degassing in the late-stage mineral assemblage of LAR 06319, the apatite evolutionary trends cannot be reconciled with this interpretation. The variable Cl contents and high OH contents measured in apatites are not consistent with fractionation either. Volatile fugacity calculations indicate that water and fluorine activities remain relatively constant, whereas there is a large variation in the chlorine activity. The Martian crust is Cl-rich indicating that changes in Cl contents in the apatites may be related to an external crustal source. We suggest that the high and variable Cl contents and high OH contents of the apatite are the results of postcrystallization interaction with Cl-rich, and possibly water-rich, crustal fluids circulating in the Martian crust.

Reference
Howarth GH, Liu Y, Chen Y, Pernet-Fisher JF, Taylor LA (2016) Postcrystallization metasomatism in shergottites: Evidence from the paired meteorites LAR 06319 and LAR 12011. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12576]
Published by arrangement with John Wiley & Sons

¹N. G. Rudraswami, ¹M. Shyam Prasad, ²E. V. S. S. K. Babu,²T. Vijaya Kumar
¹National Institute of Oceanography (Council of Scientific and Industrial Research), Goa, India
²National Geophysical Research Institute (Council of Scientific and Industrial Research), Hyderabad, India

Micrometeorites that pass through the Earth’s atmosphere undergo changes in their chemical compositions, thereby making it difficult to understand if they are sourced from the matrix, chondrules, or calcium–aluminum-rich inclusions (CAIs). These components have the potential to provide evidence toward the understanding of the early solar nebular evolution. The variations in the major element and trace element compositions of 155 different type (scoriaceous, relict bearing, porphyritic, barred, cryptocrystalline, and glass) of S-type cosmic spherules are investigated with the intent to decipher the parent sources using electron microprobe and laser ablation inductively coupled plasma-mass spectrometry. The S-type cosmic spherules appear to show a systematic depletion in volatile element contents, but have preserved their refractory trace elements. The trends in their chemical compositions suggest that the S-type spherules comprise of components from similar parent bodies, that is, carbonaceous chondrites. Large fosteritic relict grains observed in this investigation appear to be related to the fragments of chondrules from carbonaceous chondrites. Furthermore, four spherules (two of these spherules enclose spinels and one comprised entirely of a Ca-Al-rich plagioclase) show enhanced trace element enrichment patterns that are drastically different from all the other 151 cosmic spherules. The information on the chemical composition and rare earth elements (REEs) on cosmic spherules suggest that the partially to fully melted ones can preserve evidences related to their parent bodies. The Ce, Eu, and Tm anomalies found in the cosmic spherules have similar behavior as that of chondrites. Distinct correlations observed between different REEs and types of cosmic spherules reflect the inherited properties of the precursors.

Reference
Rudraswami NG, Prasad MS, Babu EVSSK, Kumar TV (2016) Major and trace element geochemistry of S-type cosmic spherules. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12618]
Published by arrangement with John Wiley & Sons

^1,2Matthias M.M. Meier, ¹Christophe Cloquet,¹Bernard
¹Centre de Recherches Pétrographiques et Géochimiques (CRPG), UMR 7358, Université de Lorraine, CNRS, 54500 Vandœuvre-lès-Nancy, France
²Institute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland

We have measured the concentration, isotopic composition and thermal release profiles of Mercury (Hg) in a suite of meteorites, including both chondrites and achondrites. We find large variations in Hg concentration between different meteorites (ca. 10 ppb to 14’000 ppb), with the highest concentration orders of magnitude above the expected bulk solar system silicates value. From the presence of several different Hg carrier phases in thermal release profiles (150 – 650 °C), we argue that these variations are unlikely to be mainly due to terrestrial contamination. The Hg abundance of meteorites shows no correlation with petrographic type, or mass-dependent fractionation of Hg isotopes. Most carbonaceous chondrites show mass-independent enrichments in the odd-numbered isotopes 199Hg and 201Hg. We show that the enrichments are not nucleosynthetic, as we do not find corresponding nucleosynthetic deficits of 196Hg. Instead, they can partially be explained by Hg evaporation and redeposition during heating of asteroids from primordial radionuclides and late-stage impact heating. Non-carbonaceous chondrites, most achondrites and the Earth do not show these enrichments in vapor-phase Hg. All meteorites studied here have however isotopically light Hg (δ202Hg = ∼-7 to -1) relative to the Earth’s average crustal values, which could suggest that the Earth has lost a significant fraction of its primordial Hg. However, the late accretion of carbonaceous chondritic material on the order of ∼2%, which has been suggested to account for the water, carbon, nitrogen and noble gas inventories of the Earth, can also contribute most or all of the Earth’s current Hg budget. In this case, the isotopically heavy Hg of the Earth’s crust would have to be the result of isotopic fractionation between surface and deep-Earth reservoirs.

Reference
Meier MMM, Cloquet C, Marty B (2016) Mercury (Hg) in meteorites: variations in abundance, thermal release profile, mass-dependent and mass-independent isotopic fractionation. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.03.007]
Copyright Elsevier

^1,2Emmanuel Jacquet, ^3,4Jean-Alix Barrat, ^5,6Pierre Beck, ¹Florent Caste, ⁷Jérôme Gattacceca, ⁷Corinne Sonzogni,^1,8Matthieu Gounelle
¹Institut de Minéralogie de Physique des Matériaux et de Cosmochimie, CNRS & Muséum National d’Histoire Naturelle, UMR 7202, Paris, France
²Canadian Institute for Theoretical Astrophysics, Toronto, Ontario, Canada
³Laboratoire Domaines Océaniques, UMR 6538, Université Européenne de Bretagne, Bretagne, France
⁴CNRS UMR 6538 (Domaines Océaniques), U.B.O.-I.U.E.M., Plouzané Cedex, France
⁵1 Univ. Grenoble Alpes, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Grenoble, France
⁶CNRS, IPAG, Grenoble, France
⁷CEREGE UM 34, CNRS/Université d’Aix-Marseille 3, Aix-en-Provence, France
⁸Institut Universitaire de France, Paris, France

Northwest Africa (NWA) 5958 is a carbonaceous chondrite found in Morocco in 2009. Preliminary chemical and isotopic data leading to its initial classification as C3.0 ungrouped have prompted us to conduct a multitechnique study of this meteorite and present a general description here. The petrography and chemistry of NWA 5958 is most similar to a CM chondrite, with a low degree of aqueous alteration, apparently under oxidizing conditions, and evidence of a second, limited alteration episode manifested by alteration fronts. The oxygen isotopic composition, with ∆’17O = −4.3‰, is more 16O-rich than all CM chondrites, indicating, along with other compositional arguments, a separate parent body of origin. We suggest that NWA 5958 be reclassified as an ungrouped carbonaceous chondrite related to the CM group.

Reference
Jacquet E, Barrat J-A, Beck P, Caste F, Gattacceca J, Sonzogni C, Gounelle M (2016) Northwest Africa 5958: A weakly altered CM-related ungrouped chondrite, not a CI3. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12628]
Published by arrangement with John Wiley & Sons