¹John P. Breen,^2,3Alan E. Rubin,^1,2,3John T. Wasson
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12685]
¹Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA
²Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA
³Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, USA
Published by arrangement with John Wiley & Sons

Group-IIIE iron meteorites can be ordered into four categories reflecting increasing degrees of shock alteration. Weakly shocked samples (Armanty, Colonia Obrera, Coopertown, Porto Alegre, Rhine Villa, Staunton, and Tanokami Mountain) have haxonite within plessite, unrecrystallized kamacite grains containing Neumann lines or possessing the ɛ structure, and sulfide inclusions typically consisting of polycrystalline troilite with daubréelite exsolution lamellae. The only moderately shocked sample is NWA 4704, in which haxonite has been partially decomposed to graphite; the majority of the kamacite in NWA 4704 is recrystallized, and its sulfide inclusions were partly melted. Strongly shocked samples (Cachiyuyal, Kokstad, and Paloduro) contain graphite and no haxonite, suggesting that pre-existing haxonite fully decomposed. Also present in these rocks are recrystallized kamacite and melted troilite. Residual heat from the impact caused annealing and recrystallization of kamacite as well as the decomposition of haxonite into graphite. Severely shocked samples (Aliskerovo and Willow Creek) have sulfide-rich assemblages consisting of fragmental and subhedral daubréelite crystals, 1–4 vol% spidery troilite filaments, and 30–50 vol% low-Ni kamacite grains, some of which contain up to 6.0 wt% Co; haxonite in these inclusions has fully decomposed to graphite. The wide range of impact effects in IIIE irons is attributed to one or more major collision(s) on the parent asteroid that affected different group members to different extents depending on their proximity to the impact point.

¹Wataru Fujiya, ²Peter Hoppe,^2,3Ulrich Ott
Meteoritics & Planetary Science (in Press)        Link to Article [DOI: 10.1111/maps.12686]
¹College of Science, Ibaraki University, Ibaraki, Japan
²Max Planck Institute for Chemistry, Mainz, Germany
³University of West Hungary, Szombathely, Hungary
Published by arrangement with John Wiley & Sons

We report the B abundances and isotopic ratios of two olivine grains from the S-type asteroid Itokawa sampled by the Hayabusa spacecraft. Olivine grains from the Dar al Gani (DaG) 989 LL6 chondrite were used as a reference. Since we analyzed polished thin sections in both cases, we expect the contribution from the solar wind B (rich in 10B) to be minimal because the solar wind was implanted only within very thin layers of the grain surface. The Itokawa and DaG 989 olivine grains have homogeneous B abundances (~400 ppb) and 11B/10B ratios compatible with the terrestrial standard and bulk chondrites. The observed homogeneous B abundances and isotopic ratios of the Itokawa olivine grains are likely the result of thermal metamorphism which occurred in the parent asteroid of Itokawa, which had a similar composition as LL chondrites. The chondritic B isotopic ratios of the Itokawa samples suggest that they contain little cosmogenic B (from cosmic-ray spallation reactions) rich in 10B. This observation is consistent with the short cosmic-ray exposure ages of Itokawa samples inferred from the small concentrations of cosmogenic 21Ne. If other Itokawa samples have little cosmogenic B as well, the enrichment in 10B found previously on the surface of another Itokawa particle (as opposed to the bulk grain study here) may be attributed to implanted solar wind B.

^1,2J. A. Arnold, ¹T. D. Glotch, ³P. G. Lucey, ⁴E. Song,^2,5I. R. Thomas, ²N. E. Bowles, ⁶B. Greenhagen
Journal of Geophysical Research Planets (in Press) Link to Article [DOI: 10.1002/2015JE004874]
¹Stony Brook University, Stony Brook, NY
²Oxford University, Oxford, UK
³Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, HI
⁴Jet Propulsion Laboratory, Pasadena, CA
⁵Belgian Institute for Space Aeronomy, Brussels, Belgium
⁶John Hopkins University Applied Physics Laboratory, Laurel, MD
Published by arrangement with John Wiley & Sons

We place upper limits on lunar olivine abundance using mid infrared (5-25 µm) (MIR) data from the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment (Diviner) along with effective emissivity spectra of mineral mixtures in a simulated lunar environment. Olivine-bearing, pyroxene-poor lithologies have been identified on the lunar surface with visible-near infrared (VNIR) observations. Since the Kaguya Spectral Profiler (SP) VNIR survey of olivine-rich regions [Yamamoto et al., 2010] is the most complete to date, we focus this work on exposures identified by that study. We first confirmed the locations with VNIR data from the Moon Mineralogy Mapper (M3) instrument. We then developed a Diviner olivine index from our laboratory data which, along with M3 and Lunar Reconnaissance Orbiter Camera (LROC) wide angle camera (WAC) data, was used to select the geographicarea over which Diviner emissivity data were extracted. We calculate upper limits on olivine abundance for these areas using laboratory emissivity spectra of anorthite-forsterite mixtures acquired under lunar-like conditions.

We find that these exposures have widely varying olivine content. In addition, after applying an albedo-based space weathering correction to the Diviner data, we find that none of the areas are unambiguously consistent with concentrations of forsterite exceeding 90 wt%, in contrast to the higher abundance estimates derived from VNIR data.

¹Christelle Briois et al. (>10)*
Planetary and Space Science (in Press) Link to Article [doi:10.1016/j.pss.2016.06.012]
¹LPC2E, UMR CNRS 7328, Université d’Orléans, Orléans Cedex 2, France
*Find the extensive, full author and affiliation list on the publishers website

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

¹Genesis Berlanga,¹Charles A. Hibbitts, ²Driss Takir, ³M. Darby Dyar, ³Elizabeth Sklute
Icarus (in Press) Link to Article [doi:10.1016/j.icarus.2016.06.020]
¹Johns Hopkins Applied Physics Laboratory
²USGS Astrogeology Science Center
³Mount Holyoke College Department of Astronomy
Copyright Elsevier

Previous studies have identified carbon dioxide (CO2) on the surfaces of Jovian and Galilean satellites in regions of non-ice material that are too warm for CO2 ice to exist. CO2 ice would quickly sublimate if not retained by a less-volatile material. To ascertain what non-ice species may be responsible for stabilizing this CO2, we performed CO2 gas adsorption experiments on thirteen powdered CM, CI, and CV carbonaceous chondrite meteorites. Reflectance spectra of the ν3 feature associated with adsorbed CO2 near 4.27 μm were recorded. Results show that many meteorites adsorbed some amount of CO2, as evidenced by an absorption feature that was stable over several hours at ultra-high vacuum (UHV) and high vacuum, (1.0×10−8 and 1.0×10−7 Torr, respectively). Ivuna, the only CI chondrite studied, adsorbed significantly more CO2 than the others. We found that CO2 abundance did not vary with ‘water’ abundance, organics, or carbonates as inferred from the area of the 3-μm band, the 3.2-3.4 μm C-H feature, and the ∼3.8-μm band respectively, but did correlate with hydrous/anhydrous phyllosilicate ratios. Furthermore, we did not observe CO2 ice because the position of the CO2 feature was generally shifted 3-10 nm from that of the 4.27 μm absorption characteristic of ice. The strongest compositional relationship observed was a possible affinity of CO2 for total FeO abundance and complex clay minerals, which make up the bulk of the CI chondrite matrix. This finding implies that the most primitive refractory materials in the Solar System may also act as reservoirs of CO2, and possibly other volatiles, delivering them to parts of the Solar System where their ices would not be stable.

¹Tabb C. Prissel, ¹Stephen W. Parman, ¹James W. Head
American Mineralogist 101, 1624-1635, Link to Article [doi:10.2138/am-2016-5581]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, Rhode Island 02912, U.S.A.
Copyright: The Mineralogical Society of America

Two competing hypotheses suggest lunar Mg-suite parental melts formed: (1) by shallow-level partial melting of a hybridized source region (containing ultramafic cumulates, plagioclase-bearing rocks, and KREEP), producing a plagioclase-saturated, MgO-rich melt, or (2) when plagioclase-undersaturated, MgO-rich melts were brought to plagioclase saturation during magma-wallrock interactions within the anorthositic crust. To further constrain the existing models, phase equilibria experiments have been performed on a range of Mg-suite parental melt compositions to investigate which composition can best reproduce two distinct spinel populations found within the Mg-suite troctolites—chromite-bearing (FeCr2O4) troctolites and the more rare pink spinel (MgAl2O4 or Mg-spinel) troctolites (PST).

Phase equilibria experiments at 1 atm pressure were conducted under reducing conditions Embedded Image and magmatic temperatures (1225–1400 °C) to explore the spinel compositions produced from melts predicted by the models above. Additionally, the experimental data are used to calculate a Sp-Ol, Fe-Mg equilibrium exchange coe to cient to correct natural spinel for sub-solidus re-equilibration with olivine in planetary samples: Sp-Ol Embedded Image (R2 = 0.956). Melts from each model (≥50% normative anorthite) produce olivine, plagioclase, and Mg-spinel compositionally consistent with PST samples. However, chromite was not produced in any of the experiments testing current Mg-suite parental melt compositions. The lack of chromite in the experiments indicates that current estimates of Mg-suite parental melts can produce Mg-spinel bearing PST, but not chromite-bearing troctolites and dunites. Instead, model calculations using the MAGPOX equilibrium crystallization program predict chromite production from plagioclase-undersaturated melts (<20% normative anorthite). If so, experimental and model results suggest chromite in Mg-suite crystallized from plagioclase-undersaturated parental melts, whereas Mg-spinel in the PST is an indicator of magma-wallrock interactions within the lunar crust (a mechanism that increases the normative anorthite contents of initially plagioclase-undersaturated Mg-suite parental melts, eventually producing Mg-spinel). The constraints for magmatic chromite crystallization suggest Mg-suite parental melts were initially plagioclase-undersaturated. In turn, a plagioclase-undersaturated Mg-suite parent is consistent with mantle overturn models that predict Mg-suite parent magmas resulted from decompression melting of early ultramafic cumulates produced during the differentiation of a global lunar magma ocean.

¹Allan H. Treiman, ^2,3Jeremy W. Boyce, ⁴James P. Greenwood, ²John M. Eiler, ⁵Juliane Gross, ²Yunbin Guan, ²Chi Ma, ²Edward M. Stolper
American Mineralogist 101, 1596-1603    Link to Article [doi:10.2138/am-2016-5582]
¹Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, U.S.A.
²Division of Geological & Planetary Sciences, Caltech, 1200 East California Boulevard, Pasadena, California 91125, U.S.A.
³Department of Earth, Planetary, and Space Sciences, UCLA, California 90095, U.S.A.
⁴Department of Earth & Environmental Sciences, Wesleyan University, Middletown, Connecticut 06459, U.S.A.
⁵Department of Earth and Planetary Sciences, Rutgers University, 610 Taylor Road, Piscataway, New Jersey 08854, U.S.A.
Copyright: The Mineralogical Society of America

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^1,2Bethany L. Ehlmann et al. (>10)*
American Mineralogist 101, 1527-1542 Link to Article [DOI: 10.2138/am-2016-5574]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, U.S.A.
*Find the extensive, full author and affiliation list on the publishers website
Copyright: The Mineralogical Society of America

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¹Z. W. Hu, ²R. P. Winarski
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12674]
¹XNano Sciences Inc., Huntsville, Alabama, USA
²Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, USA
Published by arrangement with John Wiley & Sons

Unlocking the 3-D structure and properties of intact chondritic porous interplanetary dust particles (IDPs) in nanoscale detail is challenging, which is also complicated by atmospheric entry heating, but is important for advancing our understanding of the formation and origins of IDPs and planetary bodies as well as dust and ice agglomeration in the outer protoplanetary disk. Here, we show that indigenous pores, pristine grains, and thermal alteration products throughout intact particles can be noninvasively visualized and distinguished morphologically and microstructurally in 3-D detail down to ~10 nm by exploiting phase contrast X-ray nanotomography. We have uncovered the surprisingly intricate, submicron, and nanoscale pore structures of a ~10-μm-long porous IDP, consisting of two types of voids that are interconnected in 3-D space. One is morphologically primitive and mostly submicron-sized intergranular voids that are ubiquitous; the other is morphologically advanced and well-defined intragranular nanoholes that run through the approximate centers of ~0.3 μm or lower submicron hollow grains. The distinct hollow grains exhibit complex 3-D morphologies but in 2-D projections resemble typical organic hollow globules observed by transmission electron microscopy. The particle, with its outer region characterized by rough vesicular structures due to thermal alteration, has turned out to be an inherently fragile and intricately submicron- and nanoporous aggregate of the sub-μm grains or grain clumps that are delicately bound together frequently with little grain-to-grain contact in 3-D space.

¹Benton C. Clark et al. (>10)*
American Mineralogist 101 (7) 1515-1526   Link to Article [DOI: 10.2138/am-2016-5575]
¹Space Science Institute, 4750 Walnut, Boulder, Colorado 80301, U.S.A.
*Find the extensive, full author and affiliation list on the publishers website
Copyright: The Mineralogical Society of America

In the search for evidence of past aqueous activity by the Mars Exploration Rover Opportunity, fracture-filling veins and rock coatings are prime candidates for exploration. At one location within a segment of remaining rim material surrounding Endeavour Crater, a set of “boxwork” fractures in an outcrop called Esperance are filled by a bright, hydrated, and highly siliceous (SiO2 ~ 66 wt%) material, which has overall a montmorillonite-like chemical composition. This material is partially covered by patches of a thin, dark coating that is sulfate-rich (SO3 ~ 21 wt%) but also contains significant levels of Si, Fe, Ca, and Mg. The simultaneous presence of abundant S, Si, and Fe indicates significant mineralogical complexity within the coating. This combination of vein and coating compositions is unlike previous analyses on Mars. Both materials are heterogeneously eroded, presumably by eolian abrasion. The evidence indicates at least two separate episodes of solute precipitation from aqueous fluids at this location, possibly widely separated in time. In addition to the implications for multiple episodes of alteration at the surface of the planet, aqueous chemical environments such as these would have been habitable at the time of their formation and are also favorable for preservation of organic material.