^1,2,3,4Zhongchen Wu, ⁴Alian Wang, ^1,3Zongcheng Ling
Earth and Planetary Science Letters (in Press) Link to Article [doi:10.1016/j.epsl.2016.07.044]
¹Institute of Space Science, Shandong University, Weihai 264209, PR China
²Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
³Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Shandong University, Weihai 264209, PR China
⁴Dept. Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St. Louis, 63130, USA
Copyright Elsevier

We report a study where the molecular spectral features of nine anhydrous and hydrous oxygen chlorides were analyzed both under Mars atmospheric pressure and temperature conditions in a Planetary Environment and Analysis Chamber (PEACh) and, for comparison, under ambient laboratory conditions. The goal is to understand the effect of Mars environmental conditions (mainly temperature T and CO2 pressure P) on their spectral features as determined by both Raman and NIR spectroscopy. These results will be used for in situ simultaneous identification of the View the MathML sourceClO4− and other intermediate oxygen chloride products generated during a dynamic electrostatic discharge (ESD) experiment. We have three major findings from the first phase of this study: (1) the ν1ν1 Raman peak position is the most sensitive parameter for identifying the cation speciation in perchlorates (e.g., Na, Mg, Ca), the hydration state of magnesium perchlorate (e.g., Mg(ClO4)2 ⋅ xH2O, x=0,2,4,6x=0,2,4,6), and the degree of oxidation of sodium oxygen chlorides (e.g., NaClOy, y=1,2,3,4y=1,2,3,4); (2) ν1ν1 Raman peak positions of most tested hydrous and anhydrous oxygen chlorides show no detectable changes within the tested T and P ranges relevant to the environmental conditions at Mars surface and shallow subsurface, but water Raman peaks of the hydrated salts change following T decreases; (3) under the P & T conditions relevant to current surface and shallow subsurface at Mars mid-latitude regions, both Mg(ClO4)2 ⋅ 6H2O and Ca(ClO4)2 ⋅ 2H2O are stable against dehydration, while NaClO4 ⋅ H2O dehydrates, with a dehydration rate that is a function of T which was quantified by in situ NIR spectroscopy. These results are useful for the interpretations of the data from current orbital remote sensing (Vis-NIR spectra) and from future landed missions (Raman spectra). Furthermore, we have designed a set of systematic ESD experiments to be conducted in PEACh for studying the pathways and the rates of oxygen chloride generation from chloride salts, as a potential mechanism to form oxygen chlorides during Martian dust storm. The results of the current study will be used for in situ simultaneous identification of the View the MathML sourceClO4− and other intermediate oxygen chloride products generated during a dynamic ESD experiment.

¹L.V.Forman et al. (>10)*
Earth and Planetary Science Letters 452, 133–145 Link to Article [doi:10.1016/j.epsl.2016.07.050]
¹Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
Copyright Elsevier

The CV3 Allende is one of the most extensively studied meteorites in worldwide collections. It is currently classified as S1—essentially unshocked—using the classification scheme of Stöffler et al. (1991), however recent modelling suggests the low porosity observed in Allende indicates the body should have undergone compaction-related deformation. In this study, we detail previously undetected evidence of impact through use of Electron Backscatter Diffraction mapping to identify deformation microstructures in chondrules, AOAs and matrix grains. Our results demonstrate that forsterite-rich chondrules commonly preserve crystal-plastic microstructures (particularly at their margins); that low-angle boundaries in deformed matrix grains of olivine have a preferred orientation; and that disparities in deformation occur between chondrules, surrounding and non-adjacent matrix grains. We find heterogeneous compaction effects present throughout the matrix, consistent with a highly porous initial material. Given the spatial distribution of these crystal-plastic deformation microstructures, we suggest that this is evidence that Allende has undergone impact-induced compaction from an initially heterogeneous and porous parent body. We suggest that current shock classifications (Stöffler et al., 1991) relying upon data from chondrule interiors do not constrain the complete shock history of a sample.

¹James A. D. Connolly
Journal of Geophysical Research Planets (in Press) Link to Article [DOI: 10.1002/2016JE005059]
¹Earth Sciences Department, Swiss Federal Institute of Technology, Zurich, Switzerland
Published by arrangement with John Wiley & Sons

This work explores the use of several van der Waals (vW) type equations of state (EoS) for predicting vaporous phase relations and speciation in the Si-O system, with emphasis on the azeotropic boiling curve of SiO2-rich liquid. Comparison with the observed Rb and Hg boiling curves demonstrates that prediction accuracy is improved if the a-parameter of the EoS, which characterizes vW forces, is constrained by ambient pressure heat capacities. All EoS considered accurately reproduce metal boiling curve trajectories, but absent knowledge of the true critical compressibility factor, critical temperatures remain uncertain by ~500 K. The EoS plausibly represent the termination of the azeotropic boiling curve of silica-rich liquid by a critical point across which the dominant Si oxidation state changes abruptly from the tetravalent state characteristic of the liquid to the divalent state characteristic of the vapor. The azeotropic composition diverges from silica toward metal-rich compositions with increasing temperature. Consequently, silica boiling is divariant and atmospheric loss after a giant impact would enrich residual silicate liquids in reduced silicon. Two major sources of uncertainty in the boiling curve prediction are: the heat capacity of silica liquid, which may decay during depolymerization from the near-Dulong Petit Limit heat capacity of the ionic liquid to values characteristic of the molecular liquid; and the unknown liquid affinity of silicon monoxide. Extremal scenarios for these uncertainties yield critical temperatures and compositions of 5200-6200 K and Si1.1O2-Si1.4O2. The lowest critical temperatures are marginally consistent with shock experiments and are therefore considered to be more realistic.

¹Z. Y. Cheng, ²D. C. Fernández-Remolar, ^3,4,5M. R. M. Izawa, ⁴D. M. Applin, ⁶M. Chong Díaz, ⁷M. T. Fernandez-Sampedro, ⁷M. García-Villadangos, ⁸T. Huang, ^8,9L. Xiao, ⁷V. Parro
Journal of Geophysical Research Biogeosciences (in Press) Link to Article [DOI: 10.1002/2016JG003439]
¹Planetary Science Institute, School of Earth Sciences, China University of Geosciences, Wuhan, China
²Environmental Science Centre, British Geological Survey, Keyworth, UK
³Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada
⁴Hyperspectral Optical Sensing for Extraterrestrial Reconnaissance Laboratory, Department of Geography, University of Winnipeg, Winnipeg, Manitoba, Canada
⁵Planetary Science Institute, Tucson, Arizona, USA
⁶Department of Geological Sciences, Universidad Católica del Norte, Antofagasta, Chile
⁷Centro de Astrobiologia (INTA-CSIC), Torrejon de Ardoz, Spain
⁸Planetary Science Institute, School of Earth Sciences, China University of Geosciences, Wuhan, China
⁹Space Science Institute, Macau University of Science and Technology, Macau, China

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¹Heather C. Watson, ²Frank Richter, ²Ankun Liu, ³Gary R. Huss
Earth and Planetary Science Letters 451, 159–167 Link to Article [doi:10.1016/j.epsl.2016.06.030]
¹Union College, Schenectady, NY, United States
²University of Chicago, United States
³University of Hawai‘i at Mānoa, United States
Copyright Elsevier

Mass-dependent, kinetic fractionation of isotopes through processes such as diffusion can result in measurable isotopic signatures. When these signatures are retained in geologic materials, they can be used to help interpret their thermal histories. The mass dependence of the diffusion coefficient of isotopes 1 and 2 can be written as (D1/D2)=(m2/m1)β(D1/D2)=(m2/m1)β, where D1D1 and D2D2 are the diffusion coefficients of m1m1 and m2m2 respectively, and β is an empirical coefficient that relates the two ratios. Experiments have been performed to measure β in the Fe–Ni alloy system. Diffusion couple experiments between pure Fe and Ni metals were run in a piston cylinder at 1300–1400 °C and 1 GPa. Concentration and isotopic profiles were measured by electron microprobe and ion microprobe respectively. We find that a single β coefficient of β=0.32±0.04β=0.32±0.04 can describe the isotopic effect in all experiments. This result is comparable to the isotope effect determined in many other similar alloy systems. The new β coefficient is used in a model of the isotopic profiles to be expected during the Widmanstätten pattern formation in iron meteorites. The results are consistent with previous estimates of the cooling rate of the iron meteorite Toluca. The application of isotopic constraints based on these results in addition to conventional cooling rate models could provide a more robust picture of the thermal history of these early planetary bodies.

¹J. Mortimer, ¹A.B. Verchovsky, ^1,2M. Anand
Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2016.08.006]
¹Planetary and Space Sciences, Department of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
²Department of Earth Sciences, The Natural History Museum, London, SW7 5BD, UK
Copyright Elsevier

Simultaneous static-mode mass spectrometric measurements of nitrogen, carbon, helium, neon, and argon, extracted from the same aliquot of sample by high-resolution stepped combustion, have been made for a suite of five lunar soils.

Noble gas isotope ratios show that the majority of noble gases are derived from a solar wind source; for example, at peak release temperatures of 500-600 °C, 21Ne/22Ne = 0.0313 ± 0.0007 to 0.0333 ± 0.0007, and 20Ne/22Ne = 11.48 ± 0.05 to 12.43 ± 0.07, with values at the lowest temperature steps less fractionated during implantation from, and therefore even closer to, solar values (21Ne/22NeSW = 0.03361 ± 0.00018 and 20Ne/22NeSW = 14.001 ± 0.042 (Pepin et al., 2012)). Despite the co-release of nitrogen and solar wind argon, measured nitrogen isotopic signatures at each temperature step, whilst variable, are significantly more enriched in 15N compared to the measured solar wind nitrogen value from the Genesis mission. Therefore, mixing between a 15N-enriched non-solar planetary nitrogen source with solar wind nitrogen is required to explain the measured isotopic values from the stepped combustion analysis of lunar soils. Binary mixing calculations, made under different assumptions about the degree of loss of solar wind 36Ar, reveal that the majority (up to 98%) of the nitrogen released is derived from a non-solar source. The range of modelled non-solar end-member nitrogen compositions required to satisfy the measured δ15N values varies between samples and temperature steps from +5 ‰ up to +300 ‰, or between +87 ‰ and +160 ‰ for bulk samples. This range of modelled isotopic compositions for the non-solar source of nitrogen encompasses measured values for several different groups of carbonaceous chondrite, as well as IDPs.

¹D.J. Cherniak, ¹E.B. Watson, ²R. Trappisch, ³J.B. Thomas, ⁴D. Chaussende
Geochimica et Cosmochmica Acta (in Press) Link to Article
[doi:10.1016/j.gca.2016.08.007]
¹Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180 USA
²Department of the Geophysical Sciences, The University of Chicago, and Chicago Center for Cosmochemistry, Chicago, IL 60637 USA
³Department of Earth Sciences, Syracuse University, Syracuse, NY 13244 USA
⁴Laboratoire des Matériaux et du Génie Physique, CNRS – Grenoble INP, 3 parvis Louis Néel, BP, 257, 38016 Grenoble, France
Copyright Elsevier

Diffusion of helium has been characterized in silicon carbide of cubic and hexagonal (4H and 6H) forms. Polished sections of SiC were implanted with 3He at 100 keV at a dose of 1×1015/cm2. The implanted SiC samples were sealed under vacuum in silica glass ampoules, and annealed in 1-atm furnaces. 3He distributions following all experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. For He diffusion in cubic SiC and 4H hexagonal SiC we obtain the following Arrhenius relations:

Dcubic=1.83×10-6exp(-254±10kJmol-1/RT)m2sec-1Dcubic=1.83×10-6exp(-254±10kJmol-1/RT)m2sec-1

D4H=4.78×10-7exp(-255±29kJmol-1/RT)m2sec-1D4H=4.78×10-7exp(-255±29kJmol-1/RT)m2sec-1

While He diffusion is considerably slower in SiC than in many silicate phases, He retentivity may be limited under some conditions. For example, helium will be lost from SiC grains over much shorter timescales than potential survival times of SiC presolar grains in the solar nebula. When exposed to impact heating followed by slow cooling, nearly complete loss of He from SiC grains near the site of impact will occur within several hours to a few days. For SiC grains at greater distance from impact sites, He would be better retained, depending on the rapidity of cooling. At tens of km away from a large impactor, where peak T would be ∼800K, SiC grains would lose about 50% of their He if the grains cooled within a few thousand years, and 5% if they cooled within a few tens of years. At greater distances where heating is more modest (500K and lower), SiC grains would be quite retentive of He even for cases of very slow cooling. Helium would also be retained in cases of impact heating followed by very rapid cooling. For these short heating pulses, 10 μm diameter SiC grains would retain more than 50% of their He for peak heating temperatures of 2173, 1973 and 1773K for durations of 3, 10 and 60 seconds, respectively.

¹Alexander Hubbard
Monthly Notices of the Royal Astronomical Society 460, 1163-1172 Linkt to Article [doi: 10.1093/mnras/stw1005]
¹Department of Astrophysics, American Museum of Natural History, New York, NY 10024-5192, USA

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

¹Frans J. M. Rietmeijer
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12695]
¹Department of Earth and Planetary Sciences, MSC03-2040, University of New Mexico, Albuquerque, New Mexico, USA
Published by arrangement with John Wiley & Sons

¹Maartje F. Hamers,¹Gill M. Pennock,²Marco Herwegh,¹Martyn R. Drury
Meteoritics & Planetary Science (in Press)   Link to Article [DOI: 10.1111/maps.12711]
¹Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, the Netherlands
²Institute of Geological Sciences, University of Bern, Bern, Switzerland
Published by arrangement with John Wiley & Sons

Planar deformation features (PDFs) in quartz are one of the most reliable and most widely used forms of evidence for hypervelocity impact. PDFs can be identified in scanning electron microscope cathodoluminescence (SEM-CL) images, but not all PDFs show the same CL behavior: there are nonluminescent and red luminescent PDFs. This study aims to explain the origin of the different CL emissions in PDFs. Focused ion beam (FIB) thin foils were prepared of specific sample locations selected in composite color SEM-CL images and were analyzed in a transmission electron microscope (TEM). The FIB preparation technique allowed a direct, often one-to-one correlation between the CL images and the defect structure observed in TEM. This correlation shows that composite color SEM-CL imaging allows distinction between amorphous PDFs on one hand and healed PDFs and basal Brazil twins on the other: nonluminescent PDFs are amorphous, while healed PDFs and basal Brazil twins are red luminescent, with a dominant emission peak at 650 nm. We suggest that the red luminescence is the result of preferential beam damage along dislocations, fluid inclusions, and twin boundaries. Furthermore, a high-pressure phase (possibly stishovite) in PDFs can be detected in color SEM-CL images by its blue luminescence.