¹Lodders, K.
Springer Proceedings in Physics 219, 165-170 Link to Article [DOI: 10.1007/978-3-030-13876-9_27]
¹Dept. of Earth & Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, Saint Louis, MO 63130, United States

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

¹Marina Martinez,¹Adrian J. Brearley,²Josep M. Trigo‐Rodríguez,¹Jordi Llorca
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13391]
¹Department of Earth & Planetary Sciences, MSC03-2040, University of New Mexico, Albuquerque, New Mexico 87131, USA
²Institute of Space Sciences (CSIC-IEEC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Bellaterra (Barcelona),
Catalonia, Spain
³Institut de Tecniques Energetiques i Centre de Recerca en Nanoenginyeria, Universitat Politecnica de Catalunya, Diagonal 647,
ETSEIB, 08028 Barcelona, Catalonia, Spain
Published by arrangement with John Wiley & Sons

The petrology and mineralogy of shock melt veins in the L6 ordinary chondrite host of Villalbeto de la Peña, a highly shocked, L chondrite polymict breccia, have been investigated in detail using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and electron probe microanalysis. Entrained olivine, enstatite, diopside, and plagioclase are transformed into ringwoodite, low‐Ca majorite, high‐Ca majorite, and an assemblage of jadeite‐lingunite, respectively, in several shock melt veins and pockets. We have focused on the shock behavior of diopside in a particularly large shock melt vein (10 mm long and up to 4 mm wide) in order to provide additional insights into its high‐pressure polymorphic phase transformation mechanisms. We report the first evidence of diopside undergoing shock‐induced melting, and the occurrence of natural Ca‐majorite formed by solid‐state transformation from diopside. Magnesiowüstite has also been found as veins injected into diopside in the form of nanocrystalline grains that crystallized from a melt and also occurs interstitially between majorite‐pyrope grains in the melt‐vein matrix. In addition, we have observed compositional zoning in majorite‐pyrope grains in the matrix of the shock‐melt vein, which has not been described previously in any shocked meteorite. Collectively, all these different lines of evidence are suggestive of a major shock event with high cooling rates. The minimum peak shock conditions are difficult to constrain, because of the uncertainties in applying experimentally determined high‐pressure phase equilibria to complex natural systems. However, our results suggest that conditions between 16 and 28 GPa and 2000–2200 °C were reached.

¹Chi Ma,²Oliver Tschauner,¹John R. Beckett,³Yang Liu,⁴Eran Greenberg,⁴Vitali B. Prakapenka
American Mineralogist 104,1521-1525 Link to Article [https://doi.org/10.2138/am-2019-6999]

¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
²Department of Geoscience, University of Nevada, Las Vegas, Nevada 89154, U.S.A.
³Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, U.S.A.
⁴GSECARS, University of Chicago, Argonne National Laboratory, Chicago, Illinois 60637, U.S.A.
Copyright: The Mineralogical Society of America

Chenmingite (FeCr2O4; IMA 2017-036) is a high-pressure mineral, occurring as micrometer- to submicrometer-sized lamellae within precursor chromite grains along with xieite and Fe,Cr-rich ulvöspinel next to shock-induced melt pockets, from the Tissint martian meteorite. The composition of type chenmingite by electron probe analysis shows an empirical formula of (Fe2+0.75Mg0.23Mn0.02) (Cr1.60Al0.29Fe3+0.06Fe2+0.04Ti0.02)Σ2.01O4. The general and end-member formulas are (Fe,Mg)(Cr,Al)2O4 and FeCr2O4. Synchrotron X-ray diffraction reveals that chenmingite has an orthorhombic Pnma CaFe2O4-type (CF) structure with unit-cell dimensions: a = 9.715(6) Å, b = 2.87(1) Å, c = 9.49(7) Å, V = 264.6(4) Å3, and Z = 4. Both chenmingite and xieite formed by solid-state transformation of precursor chromite under high pressure and high temperature during the Tissint impact event on Mars. The xieite regions are always in contact with melt pockets, whereas chenmingite lamellae only occur within chromite, a few micrometers away from the melt pockets. This arrangement suggests that chenmingite formed under similar pressures as xieite but at lower temperatures, in agreement with experimental studies.

^1,2Aidan J.Ross,^1,2,3,4Hilary Downes,⁵Jason S.Herrin,⁶David W.Mittlefehldt,⁷Munir Humayun,²Caroline Smith
Geochemistry (Chemie der Erde) (In Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125539]
¹UCL/Birkbeck Centre for Planetary Sciences, University College London, Gower St, London, WC1E 6BT, UK
²Dept. of Earth Sciences, Natural History Museum, Cromwell Rd, London, SW7 5BD, UK
³Dept. of Earth and Planetary Sciences, Birkbeck University of London, Malet St., London, WC1E 7HX, UK
⁴Lunar and Planetary Institute/USRA, 3600 Bay Area Blvd, Houston, TX 77058, USA
⁵Earth Observatory of Singapore & Facility for Analysis, Characterisation, Testing, and Simulation, Nanyang Technological University, 639798, Singapore
⁶Astromaterials Research Office, NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, USA
⁷Department of Earth, Ocean and Atmospheric, Science & National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, FL 32310, USA
Copyright Elsevier

Ureilite meteorites contain iron silicide minerals including suessite (Fe,Ni)₃Si, hapkeite (Fe₂Si) and xifengite (Fe₅Si₃). Despite occurring mostly in brecciated varieties presumed to be derived from the regolith of the ureilite parent asteroid, suessite has also been confirmed in one lithology of a dimict ureilite (NWA 1241). In contrast, Si-bearing Fe-metals occur in both brecciated and unbrecciated ureilites, implying that they were formed throughout the ureilite parent asteroid. We examined major, minor and trace element data of Fe-metals in seven brecciated ureilites (DaG 319, DaG 999, DaG 1000, DaG 1023, DaG 1047, EET 83309, and EET 87720) in addition to the dimict ureilite NWA 1241.

In this study we show that the silicides and Si-bearing metals in ureilites have similar siderophile trace element patterns; therefore, the precursors to the silicides were indigenous to the ureilite parent body. Si-free kamacite grains in brecciated ureilites show flatter, more chondritic siderophile element patterns. They may also be derived from the interior of the ureilite parent body, but some may be of exogenous origin (impactor debris), as are rare taenite grains.

On Earth, iron silicides are often formed under high-temperature and strongly reducing conditions (e.g. blast furnaces, lightning strikes). On the Moon, hapkeite (Fe₂Si) and other silicides have been found in the regolith where they were formed by impact-induced space weathering. In the Stardust aerogel, iron silicides derived from comet Wild2 were also formed by an impact-related reduction process. Silicides in ureilite regolith breccias may have formed by similar processes but ureilites additionally contain abundant elemental carbon which probably acted as a reducing agent, thus larger and more abundant silicide grains were formed than in the lunar regolith or cometary material. The origin of suessite in NWA 1241 may be analogous to that of reduced lithologies in the terrestrial mantle, although a regolith origin may also be possible since this sample is shown here to be a dimict breccia.

^1,2,3Jangmi Han,⁴Benjamin Jacobsen,⁵Ming-Chang Liu,¹Adrian J.Brearley,⁴Jennifer E.Matzel,³Lindsay P.Keller
Geochemistry (Chemie der Erde) (In Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125543]
¹Department of Earth and Planetary Sciences, MSC03-2040, University of New Mexico, Albuquerque, NM 87131, USA
²Lunar and Planetary Institute, USRA, 3600 Bay Area Boulevard, Houston, TX 77058, USA
³ARES, NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, USA
⁴Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
⁵Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA
Copyright Elsevier

A coordinated mineralogical and oxygen isotopic study of four fine-grained calcium-, aluminum-rich inclusions (CAIs) from the ALHA77307 CO3.0 carbonaceous chondrite was conducted. Three of the inclusions studied, 05, 1-65, and 2-119, all have nodular structures that represent three major groups, melilite-rich, spinel-rich, and hibonite-rich, based on their primary core mineral assemblages. A condensation origin was inferred for these CAIs. However, the difference in their primary core mineralogy reflects unique nebular environments in which multiple gas-solid reactions occurred under disequilibrium conditions to form hibonite, spinel, and melilite with minor perovskite and Al,Ti-rich diopside. A common occurrence of a diopside rim on the CAIs records a widespread event that marks the end of their condensation as a result of isolation from a nebular gas. An exception is a rare inclusion 2-112 that contains euhedral spinel crystals embedded in melilite, suggesting this CAI had been re-melted. All of the fine-grained CAIs analyzed in ALHA77307 are uniformly ¹⁶O-rich with an average Δ¹⁷O value of ∼−22 ± 5‰ (2σ), indicating no apparent correlation between their textures and oxygen isotopic compositions. We therefore conclude that a prevalent ¹⁶O-rich gas reservoir existed in a region of the solar nebula where CO3 fine-grained CAIs formed, initially by condensation and then later, some of them were reprocessed by melting event(s).

¹A.J.King,¹K.J.H.Phillips,²S.Strekopytov,¹C.Vita-Finzi,¹S.S.Russell
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.09.041]
¹Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, U.K
²Imaging and Analysis Centre, Natural History Museum, Cromwell Road, London SW7 5BD, U.K
Copyright Elsevier

The rare CI carbonaceous chondrites are the most aqueously altered and chemically primitive meteorites but due to their porous nature and high abundance of volatile elements are susceptible to terrestrial weathering. The Ivuna meteorite, type specimen for the CI chondrites, is the largest twentieth-century CI fall and probably the CI chondrite least affected by terrestrial alteration that is available for study. The main mass of Ivuna (BM2008 M1) has been stored in a nitrogen atmosphere at least since its arrival at the Natural History Museum (NHM), London, in 2008 (70 years after its fall) and could be considered the most pristine CI chondrite stone. We report the mineralogy, petrography and bulk elemental composition of BM2008 M1 and a second Ivuna stone (BM1996 M4) stored in air within wooden cabinets. We find that both Ivuna stones are breccias consisting of multiple rounded, phyllosilicate-rich clasts that formed through aqueous alteration followed by impact processing. A polished thin section of BM2008 M1 analysed immediately after preparation was found to contain sulphate-bearing veins that formed when primary sulphides reacted with oxygen and atmospheric water. A section of BM1996 M4 lacked veins but had sulphate grains on the surface that formed in ≤6 years, ∼3 times faster than previous reports for CI chondrite sections. Differences in the extent of terrestrial alteration recorded by BM2008 M1 and BM1996 M4 probably reflect variations in the post-recovery curation history of the stones prior to entering the NHM collection, and indicate that where possible pristine samples of hydrated carbonaceous should be kept out of the terrestrial environment in a stable environment to avoid modification. The bulk elemental composition of the two Ivuna stones show some variability due to their heterogeneous nature but in general are similar to previous analyses of CI chondrites. We combine our elemental abundances with literature values to calculate a new average composition for the Ivuna meteorite, which we find is in good agreement with existing compilations of element compositions in the CI chondrites and the most recent solar photospheric abundances.

¹Johannes M.Meusburger,¹Martin Ende,¹Philipp Matzinger,¹Dominik Talla,¹Ronald Miletich,¹Manfred Wildner
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.113459]
¹Institut für Mineralogie und Kristallographie, Althanstraße 14, 1090 Wien, Austria
Copyright Elsevier

The high-pressure behaviour of hydrated magnesium sulfate kieserite, MgSO₄⋅H₂O, has been investigated on isothermal compression at T = 295 K up to 8.3 GPa hydrostatic pressure. The crystal properties of synthetic endmember single crystals were investigated using a high-pressure diamond anvil cell by means of in-situ X-ray diffraction and vibrational spectroscopy methods. The experimental study reveals a second-order phase transition from the monoclinic (C2/c) α-phase to a triclinic (P 1¯) β-form at a transition pressure of 2.72 GPa. Elastic properties as determined from precise lattice parameters yield static elasticities as described by third-order Birch-Murnaghan equations of state with V₀ = 355.5(4) ų, K₀ = 48.1(5) GPa, K’ = 8.1(6) for the low-pressure polymorph (α-MgSO₄⋅H₂O), and V₀ = 355.8(1.8) ų, K₀ = 49.3(5.5) GPa, K’ = 4.8(1.0) for the high-pressure polymorph (β-MgSO₄⋅H₂O). The nature of the phase transition and its reversibility on pressure release make it seem unlikely that the β-polymorph can be recovered at surface conditions on any icy satellite, although in the context of impact events it is proposed to exist, but only on a limited time scale before re-transforming to α-MgSO₄⋅H₂O. With respect to the icy mantles of Ganymede and Callisto, the depth profile of Ganymede following the established thermal gradients suggest a stability field only for α-MgSO₄⋅H₂O being relevant to the presumable conditions in the icy mantle. In contrast, the depth profile for Callisto, as corresponding to maximum pressures of approximately 5 GPa, crosses the α-to-β-transition boundary and make the high-pressure polymorph a promising candidate rock-forming mineral for the deep icy mantle of the outermost Galilean moon. In particular the material parameters reported for the α and β form of MgSO₄⋅H₂O are fundamental to compute the icy mantle dynamics and accurately determine the radial density structure in models of Ganymede and Callisto.

¹Emily J.Foote,¹David A.Paige,²Michael K.Shepard,³Jeffrey R.Johnson,⁴Stuart Biggar
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.113456]
¹University of California Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, CA 90095-1567
²Bloomsburg University, 400 E. Second St., Bloomsburg, PA 17815, Bloomsburg, PA
³Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Road, 200-W230, Laurel, MD 20723-6005
⁴College of Optical Sciences, University of Arizona, 1630 E. University Blvd., P.O. Box 210094, Tucson, AZ 85721-0094
Copyright Elsevier

We have acquired a comprehensive laboratory bidirectional measurements of Apollo 11 and Apollo 16 lunar soil samples and have successfully fit photometric models to the laboratory data and have determined the solar spectrum averaged hemispheric reflectance as a function of incidence angle. The Apollo 11 (sample 10084) and 16 (sample 68810) soil samples are two representative end member samples from the Moon, dark lunar maria and bright lunar highlands. We used our solar spectrum averaged albedos in a thermal model and compared our model-calculated normal bolometric infrared emission curves with those measured by the LRO Diviner Lunar Radiometer Experiment. We found excellent agreement at the Apollo 11 site, but at the Apollo 16 site, we found that the albedos we measured in the laboratory were 33% brighter than those required to fit the Diviner infrared data. We attribute this difference at Apollo 16 to increased compaction and decreased maturity of the laboratory sample relative to the natural lunar surface, and to local variability in surface albedos at the Apollo 16 field area that are below the spatial resolution of Diviner.

¹Gregory J.Archer,¹Gregory A.Brennecka,² Philipp Gleißner,³Andreas Stracke,²Harry Becker,¹Thorsten Kleine
Earth and Planetary Science Letters 528, 115841 Link to Article [https://doi.org/10.1016/j.epsl.2019.115841]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
²Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstrasse 74-100, 12249 Berlin, Germany
³Institut für Mineralogie, University of Münster, Corrensstrasse 24, 48149 Münster, Germany
Copyright Elsevier

We report ¹⁸²W and ¹⁴²Nd isotopic compositions, ¹⁸⁷Re–¹⁸⁷Os systematics, and abundances of highly siderophile elements (HSE: Re, Os, Ir, Ru, Rh, Pt, Pd, and Au) for a suite of komatiites and basalts from the ∼3.3Ga Ruth Well Formation and the ∼3.45Ga Warrawoona Group of the Pilbara Craton, Western Australia. The ¹⁸²W compositions from all samples are indistinguishable from each other, and more radiogenic than modern bulk silicate Earth, with a mean μ¹⁸²W value of +9.1±4.2 (2SD). By contrast, the ¹⁴²Nd values for all samples are indistinguishable from each other and terrestrial standards, with a mean μ¹⁴²Nd value of −1.6±3.2 (2SD). The ¹⁴⁶Sm–¹⁴²Nd and ¹⁸⁷Re–¹⁸⁷Os systematics are consistent with chondritic Sm/Nd and Re/Os ratios in the mantle source during the lifetime of ¹⁸²Hf, and the observed ¹⁸²W excesses therefore cannot be accounted for by early Hf–W fractionation by magma ocean processes, neither by silicate liquid-crystal fractionation nor by high P–T metal-silicate equilibration. The estimated abundances of HSE in the mantle source, however, are significantly lower than modern bulk silicate Earth, with only 51±9% (1SD) of modern bulk silicate Earth abundances. These results are consistent with a partial lack of late-accreted material within the Pilbara source at ∼3.3Ga to account for the ¹⁸²W excesses. Further, widespread ¹⁸²W excesses of similar magnitude in other Archean mantle-derived rocks worldwide strongly suggests that a common process, most likely incomplete addition of late-accreted material, was responsible. The apparent mismatch between late-accreted ¹⁸²W–HSE systematics for some other localities likely reflects either the inherent difficulties associated with estimating source HSE abundances, and/or dissociation of W and HSE by mantle processes. Finally, the combined average ¹⁸²W–HSE systematics of Archean samples indicate that the pre-late accretion BSE likely had a μ¹⁸²W value similar to that of the lunar mantle, which strongly suggests post-giant impact Earth–Moon equilibration and indicates that the Moon formed after ¹⁸²Hf extinction.

¹Hill, P.J.A.,¹Banerjee, N.R.,^1,2Ali, A.,¹Jabeen, I.,¹Osinski, G.R.,¹Longstaffe, F.J.
Journal of Mass Spectrometry 54, 667-675 Link to Article [DOI: 10.1002/jms.4381]
¹Department of Earth Sciences and Centre for Planetary Science and Exploration, The University of Western Ontario, 1151 Richmond Street N, London, ON N6A 5B7, Canada
²Earth Sciences Research Centre (ESRC), Sultan Qaboos University (SQU), Al-Khoudh, Muscat, Oman

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