^1,2,3Evan E. Groopman, ⁴Larry R. Nittler
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.02.011]
¹Laboratory for Space Science, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
²National Research Council Postdoctoral Fellow at the U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, USA
³Materials Science and Technology Division, U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, USA
⁴Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5251 Broad Branch Rd NW, Washington, DC 20015, USA
Copyright Elsevier

We report correlated XANES, TEM, and NanoSIMS measurements of twelve presolar graphite grains extracted from primitive meteorites and for which isotopic data indicate predominantly Type-II supernovae origins. We find continued evidence for isotopic heterogeneities in presolar graphite grains, including the first observation of a radial gradient in the inferred initial 26Al/27Al within a presolar graphite grain. The XANES spectra of these samples show a variety of minor absorbances near the C K-edge, attributable to vinyl-keto, aliphatic, carboxyl, and carbonate molecules, as well as possible damage during sample preparation. Each sample exhibits homogeneous C K-edge XANES spectra within the graphite, however, showing no correlation with isotopic heterogeneities. Gradients in the isotope ratios of C, N, O, and Al could be due to both processes during condensation, e.g., mixing in stellar ejecta and granular transport, and post-condensation effects, such as isotope dilution and exchange with isotopically normal material in the early Solar System or laboratory, the latter of which is a significant issue for high-density presolar graphite grains. It remains unknown whether the mechanisms behind isotope exchange would also affect the local chemistry and therefore the XANES spectra. Ti L-edge XANES from most Ti-rich subgrains match standard spectra for TiC and potentially TiCN. A rare rutile (TiO2) subgrain has been identified, though it lacks the lowest energy L3 peak typically seen in standard spectra. Ca has also been identified by EDXS in TiC subgrains, likely due to the decay of live 44Ti at the time of formation. Future NanoSIMS measurements will determine the variability of initial 44Ti in TiC subgrains, an important constraint on mixing in the ejecta of the grains’ parent supernovae.

¹Edward A. Cloutis, ¹Victoria Jonatanson, ²Joshua L. Bandfield, ³Elena S. Amador, ⁴Frances Rivera-Hernández, ¹P. Mann, ⁵Stanley A. Mertzman
Planetary and Space Sciences (in Press) Link to Article [http://dx.doi.org/10.1016/j.pss.2017.01.013]
¹Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, Manitoba, Canada R3B 2E9
²Space Science Institute, Boulder, CO 80301, USA
³Department of Earth and Space Sciences, University of Washington, 4000 15th Avenue NE, Seattle, WA 98195-1310, USA
⁴Department of Earth and Planetary Sciences, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA
⁵Department of Earth and Environment, Franklin and Marshall College, Lancaster, PA 17604-2615, USA

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¹Gustavo C.C. Costa, ¹Nathan S. Jacobson, ²Bruce Fegley Jr.
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2017.02.006]
¹NASA Glenn Research Center, 21000 Brookpark Road, MS 106-1, Cleveland, OH, 44135, USA
²Planetary Chemistry Laboratory, McDonnell Center for the Space Sciences, Department of Earth and Planetary Sciences, Washington University in St. Louis, Campus Box 1169, 1 Brookings Dr, St. Louis, MO, 63130-4899, USA
Copyright Elsevier

We describe an experimental and theoretical study of olivine [Mg2SiO4 (Fo) – Fe2SiO4 (Fa)] vaporization. The vaporization behavior and thermodynamic properties of a fosterite-rich olivine (Fo95Fa5) have been explored by high-temperature Knudsen effusion mass spectrometry (KEMS) from 1750 – 2250 K. The gases observed (in order of decreasing partial pressure) are Fe, SiO, Mg, O2 and O. We measured the solidus temperature (∼ 2050 K), partial pressures of individual gases, the total vapor pressure, and thermodynamic activities and partial molal enthalpies of MgO, ‘FeO’, and SiO2 for the Fo95Fa5 olivine. The results are compared to other measurements and models of the olivine system. Our experimental data show olivine vaporizes incongruently. We discuss this system both as a psuedo-binary of Fo-Fa and a psuedo-ternary of MgO-‘FeO’-SiO2. Iron/magnesium molar ratios in the sample before (∼ 0.05) and after (∼ 0.04) vaporization are consistent with the small positive deviations from ideality of fayalite (γ ∼ 1.17) in olivine of the composition studied (e.g., Nafziger & Muan 1967). Our data for olivine + melt confirm prior theoretical models predicting fractional vaporization of Fe relative to Mg from molten silicates (Cameron & Fegley 1987, Schaefer & Fegley 2009, Ito et al. 2015). If loss of silicate atmospheres occurs from hot rocky exoplanets with magma oceans the residual planet may be enriched in magnesium relative to iron.

^1,2Renaud E. Merle, ¹Alexander A. Nemchin, ³Martin J. Whitehouse, ¹Robert T. Pidgeon, ¹Marion L. Grange, ³Joshua F. Snape, ³Fiona Thiessen
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12835]
¹Department of Applied Geology, Curtin University, Perth, Western Australia, Australia
²Research School of Earth Sciences, Australian National University, Acton, Australian Capital Territory, Australia
³Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden
Published by arrangement with John Wiley & Sons

In this paper, we compare the U-Pb zircon age distribution pattern of sample 14311 from the Apollo 14 landing site with those from other breccias collected at the same landing site. Zircons in breccia 14311 show major age peaks at 4340 and 4240 Ma and small peaks at 4110, 4030, and 3960 Ma. The zircon age patterns of breccia 14311 and other Apollo 14 breccias are statistically different suggesting a separate provenance and transportation history for these breccias. This interpretation is supported by different U-Pb Ca-phosphate and exposure ages for breccia 14311 (Ca-phosphate age: 3938 ± 4 Ma, exposure age: ~550–660 Ma) from the other Apollo 14 breccias (Ca-phosphate age: 3927 ± 2 Ma, compatible with the Imbrium impact, exposure age: ~25–30 Ma). Based on these observations, we consider two hypotheses for the origin and transportation history of sample 14311. (1) Breccia 14311 was formed in the Procellarum KREEP terrane by a 3938 Ma-old impact and deposited near the future site of the Imbrium basin. The breccia was integrated into the Fra Mauro Formation during the deposition of the Imbrium impact ejecta at 3927 Ma. The zircons were annealed by mare basalt flooding at 3400 Ma at Apollo 14 landing site. Eventually, at approximately 660 Ma, a small and local impact event excavated this sample and it has been at the surface of the Moon since this time. (2) Breccia 14311 was formed by a 3938 Ma-old impact. The location of the sample is not known at that time but at 3400 Ma, it was located nearby or buried by hot basaltic flows. It was transported from where it was deposited to the Apollo 14 landing site by an impact at approximately 660 Ma, possibly related to the formation of the Copernicus crater and has remained at the surface of the Moon since this event. This latter hypothesis is the simplest scenario for the formation and transportation history of the 14311 breccia.

^1,2Devin L. Schrader, ¹Timothy J. McCoy, ¹Kathryn Gardner-Vandy
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.02.012]
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, 10th& Constitution Avenue NW, Washington, DC 20560-0119, USA.
²Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, USA.
Copyright Elsevier

We studied the petrography, analyzed the chemical compositions, constrained the closure temperatures (via geothermometry), and determined the oxidation states of relict chondrules in Campo del Cielo (IAB iron meteorite), Graves Nunataks (GRA) 98028 (acapulcoite), and Netschaëvo (IIE iron meteorite) to constrain their formation conditions and investigate links to known meteorite groups. Despite having been thermally metamorphosed, mineral phases within relict chondrules retain information about their precursor compositions. The sizes and textures of relict chondrules, and silicate and chromite compositions indicate that Campo del Cielo, GRA 98028, and Netschaëvo had distinct parent bodies that were similar to, but different from, known chondrite groups. To determine the utility of relict chondrule sizes in thermally metamorphosed meteorites, we determined the chondrule size distributions in the LL chondrites Semarkona (LL3.00), Soko-Banja (LL4), Siena (LL5), and Saint-Séverin (LL6), and the H chondrites Clovis (no. 1) (H3.6), Kesen (H4), Arbol Solo (H5), and Estacado (H6). As expected, mean chondrule diameters increase with degree of thermal metamorphism.

We find that Campo del Cielo and GRA 98028 were reduced during thermal metamorphism, consistent with previous studies, indicating that their precursors were initially more FeO-rich than their current compositions. In contrast to previous studies, we find no evidence for reduction of silicates in Netschaëvo. Normal zoning of olivine in Netschaëvo is consistent with crystallization and suggests its silicates are near their primary FeO-contents. The presence of elongated chromite grains along olivine grain boundaries in Netschaëvo indicates formation during thermal metamorphism under oxidizing conditions. Due to the absence of reduction and the composition of chromite being distinct from that of metamorphosed H chondrites, we conclude that Netschaëvo, and by extension the IIE iron meteorites, are not from the H chondrite parent body.

^1,2M.Lugano et al. (>10)*
Nature Astronomy 1, 27 Link to Article [doi:10.1038/s41550-016-0027]
¹Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, 1121 Budapest, Hungary
²Monash Centre for Astrophysics (MoCA), Monash University, Clayton, Victoria 3800, Australia
*Find the extensive, full author and affiliation list on the publishers website

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¹Arya Udry, ²Geoffrey H. Howarth, ³Thomas J. Lapen, ³Minako Righter
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.01.032]
¹Department of Geoscience, University of Nevada Las Vegas, Las Vegas NV, USA
²Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa
³Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, USA
Copyright Elsevier

Northwest Africa (NWA) 7320 is classified as a gabbroic shergottite, the second to be recognized in the martian meteorite record. This interpretation is based on: (1) the calculated bulk-rock rare earth element (REE) concentrations, which show the highest Eu positive anomaly (Eu/Eu∗ = 2.2) of all the shergottites, reflecting accumulation of plagioclase; and (2) the highest modal abundance of maskelynitized plagioclase (50 mod.%) compared to the other shergottites. The three-phase symplectite (fayalite + hedenbergite + silica) is present in NWA 7320 and formed as a result of the breakdown of metastable pyroxene/pyroxenoid margins on coarse-grained pyroxenes. The latter is indicative of metastable overgrowths on pyroxene cores during the final stages of crystallization, followed by relatively slow cooling at subsolidus conditions. The NWA 7320 parental melt originated from an incompatible trace element enriched and oxidized (∼FMQ) source as indicated by Sm–Nd, Lu–Hf isotope systematics, ilmenite-titanomagnetite pairs, the partition coefficient of Cr in pyroxene, and merrillite REE compositions. The Ti/Al ratio of pyroxene in NWA 7320 indicates an initial crystallization depth of 30–70 km (P = 4–9 kbar). However, the largest impact craters on Mars are

¹Marina A. Ivanova, ¹Cyril A. Lorenz, ²Sergey E. Borisovskiy, ¹Andrey A. Burmistrov, ³Dmitriy V. Korost, ¹Alexander V. Korochantsev, ⁴Maria N. Logunova, ¹Sergei I. Shornikov, ⁵Michail I. Petaev
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12839]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences, Moscow, Russia
²Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of Russian Academy of Sciences, Moscow, Russia
³Moscow State University, Moscow, Russia
⁴Mining Museum, St. Petersburg Mining University, St. Petersburg, Russia
⁵Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Published by arrangement with John Wiley & Sons

We investigated the khatyrkite–cupalite holotype sample, 1.2 × 0.5 mm across. It consists of khatyrkite (Cu,Zn)Al2, cupalite (Cu,Zn)Al, and interstitial material with approximate composition (Zn,Cu)Al3. All mineral phases of the holotype sample contain Zn and lack Fe that distinguishes them from khatyrkite and cupalite in the Khatyrka meteorite particles (Bindi et al. 2009, 2011, 2012, 2015; MacPherson et al. 2013; Hollister et al. 2014). Neither highly fractionated natural systems nor geo- or cosmochemical processes capable of forming the holotype sample are known so far. The bulk chemistry and thermal history of khatyrkite–cupalite assemblage in the holotype sample hint for its possible industrial origin. Likewise, the aluminides in the Khatyrka meteorite particles may also be derived from industrial materials and mixed with extraterrestrial matter during gold prospecting in the Listvenitovy Stream valley.

¹Elishevah M.M.E. van Kooten et al. (>10)*
Geochimica et Cosmochmica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.02.002]
¹Centre for Star and Planet Formation and Natural History Museum of Denmark, University of Copenhagen, DK-1350 Copenhagen, Denmark
Copyright Elsevier
*Find the extensive, full author and affiliation list on the publishers website

Primitive meteorites are samples of asteroidal bodies that contain a high proportion of chemically complex organic matter (COM) including prebiotic molecules such as amino acids, which are thought to have been delivered to Earth via impacts during the early history of the Solar System. Thus, understanding the origin of COM, including their formation pathway(s) and environment(s), is critical to elucidate the origin of life on Earth as well as assessing the potential habitability of exoplanetary systems. The Isheyevo CH/CBb carbonaceous chondrite contains chondritic lithic clasts with variable enrichments in 15N believed to be of outer Solar System origin. Using transmission electron microscopy (TEM-EELS) and in situ isotope analyses (SIMS and NanoSIMS), we report on the structure of the organic matter as well as the bulk H and N isotope composition of Isheyevo lithic clasts. These data are complemented by electron microprobe analyses of the clast mineral chemistry and bulk Mg and Cr isotopes obtained by inductively coupled plasma and thermal ionization mass spectrometry, respectively (MC-ICPMS and TIMS). Weakly hydrated (A) clasts largely consist of Mg-rich anhydrous silicates with local hydrated veins composed of phyllosilicates, magnetite and globular and diffuse organic matter. Extensively hydrated clasts (H) are thoroughly hydrated and contain Fe-sulfides, sometimes clustered with organic matter, as well as magnetite and carbonates embedded in a phyllosilicate matrix. The A-clasts are characterized by a more 15N-rich bulk nitrogen isotope composition (δδ15N=200-650‰‰) relative to H-clasts (δδ15N=50-180‰‰) and contain extremely 15N-rich domains with δδ15N <5000‰‰. The D/H ratios of the clasts are correlated with the degree of clast hydration and define two distinct populations, which we interpret as reflecting mixing between D-poor fluid(s) and distinct organic endmember components that are variably D-rich. High-resolution N isotope data of 15N-rich domains show that the lithic clast diffuse organic matter is typically more 15N-rich than globular organic matter. The correlated δδ15N values and C/N ratios of nanoglobules require the existence of multiple organic components, in agreement with the H isotope data. The combined H and N isotope data suggest that the organic precursors of the lithic clasts are defined by an extremely 15N-poor (similar to solar) and D-rich component for H-clasts, and a moderately 15N-rich and D-rich component for A-clasts. In contrast, the composition of the putative fluids is inferred to include D-poor but moderately to extremely 15N-rich H- and N-bearing components. The variable 15N enrichments in H- and A-clasts are associated with structural differences in the N bonding environments of their diffuse organic matter, which are dominated by amine groups in H-clasts and nitrile functional groups in A-clasts. We suggest that the isotopically divergent organic precursors in Isheyevo clasts may be similar to organic moieties in carbonaceous chondrites (CI, CM, CR) and thermally recalcitrant organic compounds in ordinary chondrites, respectively. The altering fluids, which are inferred to cause the 15N enrichments observed in the clasts, may be the result of accretion of variable abundances of NH3 and HCN ices. Finally, using bulk Mg and Cr isotope composition of clasts, we speculate on the accretion regions of the various primitive chondrites and components and the origin of the Solar System’s N and H isotope variability.

^1,2Erin L. Walton, ¹Sabrina McCarthy
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12829]
¹Department of Physical Sciences, MacEwan University, Edmonton, Alberta, Canada
²Department of Earth & Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
Published by arrangement with John Wiley & Sons

The formation of the high-pressure compositional equivalents of olivine and pyroxene has been well-documented within and surrounding shock-induced veins in chondritic meteorites, formed by crystallization from a liquid- or solid-state phase transformation. Typically polycrystalline ringwoodite grains have a narrow range of compositions that overlap with those of their olivine precursors, whereas the formation of iron-enriched ringwoodite has been documented from only a handful of meteorites. Here, we report backscattered electron images, quantitative wavelength-dispersive spectrometry (WDS) analyses, qualitative WDS elemental X-ray maps, and micro-Raman spectra that reveal the presence of Fe-rich ringwoodite (Fa44-63) as fine-grained (500 nm), polycrystalline rims on olivine (Fa24-25) wall rock and as clasts engulfed by shock melt in a previously unstudied L5 chondrite, Dhofar 1970. Crystallization of majorite + magnesiowüstite in the vein interior and metastable mineral assemblages within 35 μm of the vein margin attest to rapid crystallization of a superheated shock melt (>2300 K) from 20─25 GPa to ambient pressure and temperature. The texture and composition of bright polycrystalline ringwoodite rims (Fa44-63; MnO 0.01─0.08 wt%) surrounding dark polycrystalline olivine (Fa8-14; MnO 0.56─0.65 wt%) implies a solid-state transformation mechanism in which Fe was preferentially partitioned to ringwoodite. The spatial association between ringwoodite and shock melt suggests that the rapidly fluctuating thermal regimes experienced by chondritic minerals in contact with shock melt are necessary to both drive phase transformation but also to prevent back-transformation.