Kristin Leftwich^1,*, David L. Bish¹ and C.H. Chen²

¹Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, U.S.A.
²Indiana University Molecular Structure Center, Indiana University, Bloomington, Indiana 47405, U.S.A.

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Reference
Leftwich K, Bish DL and Chen CH (2013) Crystal structure and hydration/dehydration behavior of Na2Mg(SO4)2·16H2O: A new hydrate phase observed under Mars-relevant conditions. American Mineralogist 98:1772-1778.
[doi:10.2138/am.2013.4509]

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Juan A. Sanchez^a,*, Vishnu Reddy^b,1, Michael S. Kelley^c,1,2, Edward A. Cloutis^d, William F. Bottke^e, David Nesvorný^e, Michael P. Lucas^f, Paul S. Hardersen^g,1, Michael J. Gaffey^g,1, Paul A. Abell^h,1, Lucille Le Corre^b

^aMax Planck Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany
^bPlanetary Science Institute, 1700 East Fort Lowell Road, Tucson, Arizona 85719, USA
^cDepartment of Geology and Geography, Georgia Southern University, Statesboro, USA
^dDepartment of Geography, University of Winnipeg, Winnipeg, Manitoba, Canada
^eSouthwest Research Institute and NASA Lunar Science Institute, Boulder, USA
^fDepartment of Earth and Planetary Sciences, University of Tennessee, USA
^gDepartment of Space Studies, University of North Dakota, Grand Forks, USA
^hNASA Johnson Space Center, Houston, Texas, USA
¹Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement No. NNX-08AE38A with the National Aeronautics and Space Administration, Science Mission Directorate, Planetary Astronomy Program.
²Planetary Science Division, Science Mission Directorate, NASA Headquarters, Washington, DC 20546, USA.

Olivine-dominated asteroids are a rare type of objects formed either in nebular processes or through magmatic differentiation. The analysis of meteorite samples suggest that at least 100 parent bodies in the main belt experienced partial or complete melting and differentiation before being disrupted. However, only a few olivine-dominated asteroids, representative of the mantle of disrupted differentiated bodies, are known to exist. Due to the paucity of these of objects in the main belt their origin and evolution have been a matter of great debate over the years. In this work we present a detailed mineralogical analysis of twelve olivine-dominated asteroids. We have obtained near-infrared (NIR) spectra (0.7 to 2.4 μm) of asteroids (246) Asporina, (289) Nenetta, (446) Aeternitas, (863) Benkoela, (4125) Lew Allen and (4490) Bamberry. Observations were conducted with the Infrared Telescope Facility (IRTF) on Mauna Kea, Hawai’i. This sample was complemented with spectra of six other olivine-dominated asteroids including (354) Eleonora, (984) Gretia, (1951) Lick, (2501) Lohja, (3819) Robinson and (5261) Eureka obtained by previous workers. Within our sample we distinguish two classes, one that we call pure-olivine asteroids, which are those whose spectra only exhibit the 1 μm feature, and another referred to as olivine-rich asteroids, whose spectra exhibit the 1 μm feature and a weak (Band II depth ~4%) 2 μm feature. For the pure-olivine asteroids the olivine chemistry was found to range from ~Fo₄₉ to Fo₇₀, consistent with the values measured for brachinites and R chondrites. In the case of the olivine-rich asteroids we determined their olivine and low-Ca pyroxene abundance using a new set of spectral calibrations derived from the analysis of R chondrites spectra. We found that the olivine abundance for these asteroids varies from 0.68 to 0.93, while the fraction of low-Ca pyroxene to total pyroxene ranges from 0.6 to 0.9. A search for dynamical connections between the olivine-dominated asteroids and asteroid families found no genetic link (of the type core-mantel-crust) between these objects.

Reference
Sanchez JA, Reddy V, Kelley MS, Cloutis CA, Bottke WF, Nesvorný D, Lucas MP, Hardersen PS, Gaffey MJ, Abell PA and Le Corre L (in press) Olivine-dominated Asteroids: Mineralogy and Origin. Icarus
[doi:10.1016/j.icarus.2013.10.006]
Copyright Elsevier

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Stephen M. Seddio^1,*, Bradley L. Jolliff¹, Randy L. Korotev¹ and Ryan A. Zeigler²

¹Department of Earth and Planetary Sciences and the McDonnell Center for Space Sciences, Washington University, St. Louis, Missouri 63130, U.S.A.
²Astromaterials and Exploration Science Directorate, NASA, Johnson Space Center, mail code KT, 2101 NASA Pkwy, Houston, Texas 77058, U.S.A.

We currently seek a copyright agreement with American Mineralogist to display abstracts of their cosmochemistry related publications.

Reference
Seddio SM, Jolliff BL, Korotev RJ and Zeigler RA (2013) Petrology and geochemistry of lunar granite 12032,366-19 and implications for lunar granite petrogenesis. American Mineralogist 98:1697-1713.
[doi:10.2138/am.2013.4330]

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Tomohiro Usui^1,2,*, Hikaru Iwamori¹

¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan
²Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA

Dawn has recently revealed that the surface of Vesta is heterogeneously covered by polymictic regoliths represented by mixtures of howardite, eucrite, and diogenite (HED) meteorites. Mixing relations of the HED suite are examined here using a new computational statistical approach of independent component analysis (ICA). We performed eight-component ICA (Si, Ti, Al, Cr, Fe, Mn, Mg, and Ca) for 209 HED bulk-rock compositions. The ICA results indicate that the HED bulk-rock compositions can be reduced into three independent components (IC) and these IC vectors can reasonably explain compositional variation, petrographic observations, and the mixing relations of the HED suite. The IC-1 vector represents a eucrite variation that extends from cumulate eucrite toward main-group (MG) and incompatible-element enriched eucrites. The IC-2 vector represents a compositional variation of howardites that extends from diogenites to MG-eucrites, indicating the well-known two-component mixing trend of diogenite and eucrite. The IC-3 vector represents a compositional variation defined by diogenites and olivine-bearing diogenites, suggesting mixing of olivine and orthopyroxene. Among the three ICs, the diogenite-eucrite mixing trend IC-2 is most statistically robust and dominates the compositional variations of the HED suite. Our ICA study further indicates that the combination of only three elements (Mg, Si, and Fe) approximates the eight-component ICA model, and that the limited number of resolvable γ-ray spectra obtained by the Dawn mission possibly discriminates olivine lithologies from the olivine-free regolith breccias on the surface of Vesta.

Reference
Usui T and Iwamori H (in press) Mixing relations of the howardite-eucrite-diogenite suite: A new statistical approach of independent component analysis for the Dawn mission. Meteoritics & Planetary Science
[doi:10.1111/maps.12205]
Published by arrangement with John Wiley & Sons

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M. L. Grange^1,*, A. A. Nemchin^1,2, R. T. Pidgeon¹

¹Department of Applied Geology, Western Australian School of Mines, Curtin University, Perth, Australia
²Swedish Museum of Natural History, Stockholm, Sweden

Zircon and phosphate grains from matrix and quartz-monzodiorite (QMD) clasts in two thin sections of Apollo 15 impact melt breccia 15405 were investigated using optical microscopy, scanning electron microscopy, Raman spectroscopy, and ion microprobe U-Pb analyses. U-Pb results for zircon grains with well-defined cathodoluminescence zoning define the primary (i.e., magmatic) crystallization age as 4330 ± 6 Ma (2σ). One zircon consists of a preserved inner part surrounded by a porous polycrystalline (“granular”) mixture of zircon and baddeleyite, indicating incomplete reaction of the zircon with melt. Previous work showed that this microstructure could form at pressures above 60 GPa and a temperature close to ~1700°C and is evidence of an impact-related melting event. The U-Pb system of this grain indicates a resetting event at 1940 ± 10 Ma, interpreted as the age of this impact (impact #1). Other zircon and phosphate grains also have disturbed U-Pb systems, showing an even younger reset event (impact #2) at 1407 ± 57 Ma. Evidence of impact is supported by microstructures of zircon and baddeleyite such as secondary rims. These impacts are tentatively identified as those having formed Autolycus and Aristillius craters.

Reference
Grange ML, Nemchin AA and Pidgeon RT (in press) The effect of 1.9 and 1.4 Ga impact events on 4.3 Ga zircon and phosphate from an Apollo 15 melt breccia. Journal of Geophysical Research – Planets
[doi:10.1002/jgre.20167]
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Richard A. Kerr

We currently seek a copyright agreement with Science to display abstracts of their cosmochemistry related publications.

Reference
Kerr RA (in press) Roving Into Martian Waters. Science
[doi:10.1126/science.342.6156.304]

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Gainsforth et al. (>>10)^*

^*Find the extensive, full author and affiliation list on the publishers website.

Using synchrotron-based X-ray diffraction measurements, we identified crystalline material in two particles of extraterrestrial origin extracted from the Stardust Interstellar Dust Collector. The first particle, I1047,1,34 (Hylabrook), consisted of a mosaiced olivine grain approximately 1 µm in size with internal strain fields up to 0.3%. The unit cell dimensions were a = 4.85 ± 0.08 Å, b  =  10.34 ± 0.16 Å, c  =  6.08 ± 0.13 Å (2σ). The second particle, I1043,1,30 (Orion), contained an olivine grain ≈ 2 µm in length and >500 nm in width. It was polycrystalline with both mosaiced domains varying over ≈ 20º and additional unoriented domains, and contained internal strain fields < 1%. The unit cell dimensions of the olivine were a = 4.76 ± 0.05 Å, b  =  10.23 ± 0.10 Å, c  =  5.99 ± 0.06 Å (2σ), which limited the olivine to a forsteritic composition  >Fo₆₅ (2σ). Orion also contained abundant spinel nanocrystals of unknown composition, but unit cell dimension a  = 8.06 ± 0.08 Å (2σ). Two additional crystalline phases were present and remained unidentified. An amorphous component appeared to be present in both these particles based on STXM and XRF results reported elsewhere.

Reference
Gainsforth et al. (in press) Stardust Interstellar Preliminary Examination VIII: Identification of crystalline material in two interstellar candidates. Meteoritics & Planetary Science
[doi:10.1111/maps.12148]
Published by arrangement with John Wiley & Sons

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Bechtel et al. (>>10)^*

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Under the auspices of the Stardust Interstellar Preliminary Examination, picokeystones extracted from the Stardust Interstellar Dust Collector were examined with synchrotron Fourier transform infrared (FTIR) microscopy to establish whether they contained extraterrestrial organic material. The picokeystones were found to be contaminated with varying concentrations and speciation of organics in the native aerogel, which hindered the search for organics in the interstellar dust candidates. Furthermore, examination of the picokeystones prior to and post X-ray microprobe analyses yielded evidence of beam damage in the form of organic deposition or modification, particularly with hard X-ray synchrotron X-ray fluorescence. From these results, it is clear that considerable care must be taken to interpret any organics that might be in interstellar dust particles. For the interstellar candidates examined thus far, however, there is no clear evidence of extraterrestrial organics associated with the track and/or terminal particles. However, we detected organic matter associated with the terminal particle in Track 37, likely a secondary impact from the Al-deck of the sample return capsule, demonstrating the ability of synchrotron FTIR to detect organic matter in small particles within picokeystones from the Stardust interstellar dust collector.

Reference
Bechtel et al. (in press) Stardust Interstellar Preliminary Examination III: Infrared spectroscopic analysis of interstellar dust candidates. Meteoritics & Planetary Science
[doi:10.1111/maps.12125]
Published by arrangement with John Wiley & Sons

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Stroud et al. (>>10)^*

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The Stardust Interstellar Preliminary Examination team analyzed thirteen Al foils from the NASA Stardust interstellar collector tray in order to locate candidate interstellar dust (ISD) grain impacts. Scanning electron microscope (SEM) images reveal that the foils possess abundant impact crater and crater-like features. Elemental analyses of the crater features, with Auger electron spectroscopy, SEM-based energy dispersive X-ray (EDX) spectroscopy, and scanning transmission electron microscope-based EDX spectroscopy, demonstrate that the majority are either the result of impacting debris fragments from the spacecraft solar panels, or intrinsic defects in the foil. The elemental analyses also reveal that four craters contain residues of a definite extraterrestrial origin, either as interplanetary dust particles or ISD particles. These four craters are designated level 2 interstellar candidates, based on the crater shapes indicative of hypervelocity impacts and the residue compositions inconsistent with spacecraft debris.

Reference
Stround et al. (in press) Stardust Interstellar Preliminary Examination XI: Identification and elemental analysis of impact craters on Al foils from the Stardust Interstellar Dust Collector. Meteoritics & Planetary Science
[doi:10.1111/maps.12136]
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Bashar Baghdadi^1,*, Gaston Godard², Albert Jambon¹

¹UPMC Paris 6, Institut des Sciences de la Terre Paris, Paris Cedex 05, France
²Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris-Diderot, Paris Cedex 05, France

Northwest Africa 3164 is a coarse-grained angrite that shows reaction coronas, a unique character among achondrites. Olivine (Fo₅₇; 1.2 wt% CaO), fassaitic clinopyroxene, anorthite, and spinel account for 46–47, 28–29, 8–13, and 4–8 vol%, respectively; kamacite is an accessory phase. The spinel grains in contact with clinopyroxene are bounded by discontinuous 20 μm thick coronas of anorthite and olivine, indicating the reaction Cpx + Spl → Ol + An (R1). In addition, irregular coronas of clinopyroxene and spinel developed around the primary anorthite in contact with primary olivine, during the reaction Ol + An → Cpx + Spl (R2). R2 also generated clinopyroxene and spinel films between the secondary olivine and anorthite coronas produced during R1, implying that R1 preceded R2. Both are metamorphic reactions that developed in the solid state. Finally, the coronas are cross cut by μm-thick veinlets due to a late shock. A mass-balance study shows that R2 is almost the reverse of R1. The P–T metamorphic evolution of the rock, modeled by calculating a P–T isochemical diagram, indicates an equilibrium T of 940 ± 120 °C at P < 0.9 GPa for the initial assemblage, followed by an increase of T up to approximately 1000–1200 °C during reaction R1 and a subsequent cooling during R2. Several causes are envisaged to account for this metamorphic evolution. Contact metamorphism due to a hot magmatic intrusion in the angrite parent body is favored, as similar metamorphic coronas are well known in metamorphic terrestrial rocks. In addition to differentiation and magmatism, there is now evidence for metamorphism in the angrite parent body, which would have been a large asteroid or a planetary-sized body.

Reference
Baghdadi B, Godard G and Jambon A (in press) Evolution of the angrite parent body: Implications of metamorphic coronas in NWA 3164. Meteoritics & Planetary Science
[doi:10.1111/maps.12202]
Published by arrangement with John Wiley & Sons

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