¹J.D. Toner, ¹D.C. Catling, ² B. Light
¹University of Washington, Box 351310, Dept. Earth & Space Sciences, Seattle, WA 98195, USA
²Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, Washington, USA

The Wet Chemistry Laboratory (WCL) on the Mars Phoenix Lander measured ions in a soil-water extraction and found Na+, K+, H+ (pH), Ca2+, Mg2+, View the MathML sourceSO42-,ClO4-, and Cl–. Equilibrium models offer insights into salt phases that were originally present in the Phoenix soil, which dissolved to form the measured WCL solution; however, there are few experimental datasets for single cation perchlorates (View the MathML sourceClO4-), and none for mixed perchlorates, at low temperatures, which are needed to build models. In this study, we measure ice and salt solubilities in binary and ternary solutions in the Na-Ca-Mg-ClO4 system, and then use this data, along with existing data, to construct a low-temperature Pitzer model for perchlorate brines. We then apply our model to a nominal WCL solution. Previous studies have modeled either freezing of a WCL solution or evaporation at a single temperature. For the first time, we model evaporation at subzero temperatures, which is relevant for dehydration conditions that might occur at the Phoenix site. Our model indicates that a freezing WCL solution will form ice, KClO4, hydromagnesite (3MgCO3·Mg(OH)2·3H2O), calcite (CaCO3), meridianiite (MgSO4·11H2O), MgCl2·12H2O, NaClO4·2H2O, and Mg(ClO4)2·6H2O at the eutectic (209 K). The total water held in hydrated salt phases at the eutectic is ∼1.2 wt. %, which is much greater than hydrated water contents when evaporation is modeled at 298.15 K (∼0.3 wt. %). Evaporation of WCL solutions at lower temperatures (down to 210 K) results in lower water activities and the formation of more dehydrated minerals, e.g. kieserite (MgSO4·H2O) instead of meridianiite. Potentially habitable brines, with awaw>0.6, can occur when soil temperatures are above 220 K and when the soil liquid water content is greater than 0.4 wt. % (View the MathML source100×gH2Ogsoil-1). In general, modeling indicates that mineral assemblages derived from WCL-type solutions are characteristic of the soil temperature, water content, and water activity conditions under which they formed, and are useful as indicators of past environmental conditions.

Reference
Toner JD, Catling DC, Light B (2015) A revised Pitzer model for low-temperature soluble salt assemblages at the Phoenix Site, Mars. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.06.011]

Copyright Elsevier

^1,2Z. Kanuchova, ³R. Brunetto, ^4,5D. Fulvio, ^1,2G. Strazzulla
¹Astronomical Institute of Slovak Academy of Sciences, SK-05960 T. Lomnica, Slovakia
²INAF-Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania, Italy
³Institut d’Astrophysique Spatiale (IAS), Université Paris-Sud, UMR 8617 – CNRS INSU, Bât 121, F-91405 Orsay, France
⁴Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, 07743 Jena, Germany
⁵Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marquês de São Vicente 225, 22451-900, Rio de Janeiro, RJ, Brazil

Asteroid surface space weathering has been investigated both observationally and experimentally, mostly focusing on the effects on the visible-near infrared (VNIR, 0.4-2.5 μm) spectral range. Here we present laboratory near-ultraviolet (NUV, 200-400 nm) reflectance spectra of ion irradiated (30-400 keV) silicates and meteorites as a simulation of solar wind ion irradiation. These results show that the induced alteration can reproduce the spread observed in the VNIR vs. NUV slope diagram for S-type asteroids. In particular, the well-known spectral reddening effect induced in the VNIR range is accompanied by a less known but stronger bluing effect at NUV wavelengths. Such trend was previously identified by Hendrix and Vilas (2006) but only based on the comparison between observations and laboratory spectra of lunar materials. We attribute the NUV bluing, analogously to the VNIR reddening, to the formation of iron nanoparticles accompanied by structural modifications (amorphization) of surface silicates. We expect the evidence of weathering processes in the NUV part of spectra before these effects become observable at longer wavelengths, thus searching for the space weathering effects in the NUV range would allow establishing the extent of space weathering for very young asteroidal families.
It will be important to include in future studies the NUV range both in the observations of specific classes of objects (e.g. the Vestoids) and in the laboratory spectra of meteorites and terrestrial analogues before and after space weather processing.

Reference
Kanuchova Z, Brunetto R, Fulviod D, Strazzulla G (2015) Near-ultraviolet Bluing after Space Weathering of Silicates and Meteorites. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.030]

Copyright Elsevier

¹N. Van Roosbroek, ¹V. Debaille, ²L. Pittarello, ^2,3S. Goderis, ⁴M. Humayun, ⁵L. Hecht, ⁶F. Jourdan, ⁷M. J. Spicuzza, ³F. Vanhaecke, ²Ph. Claeys
¹Laboratoire G-Time, Université Libre de Bruxelles, Brussels, Belgium
²Earth System Science, Vrije Universiteit Brussel, Brussels, Belgium
³Department of Analytical Chemistry, Ghent University, Ghent, Belgium
⁴Department of Earth, Ocean & Atmospheric Science and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, USA
⁵Museum für Naturkunde, Leibniz-Institut für Evolutions-und Biodiversitätsforschung, Berlin, Germany
⁶Department of Applied Geology & JdL CMS, Western Australian Argon Isotope Facility, Curtin University of Technology, Perth, WA, Australia
⁷Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, USA

A 435 kg piece of the Mont Dieu iron meteorite (MD) contains cm-sized silicate inclusions. Based on the concentration of Ni, Ga, Ge, and Ir (8.59 ± 0.32 wt%, 25.4 ± 0.9 ppm, 61 ± 2 ppm, 7.1 ± 0.4 ppm, respectively) in the metal host, this piece can be classified as a IIE nonmagmatic iron. The silicate inclusions possess a chondritic mineralogy and relict chondrules occur throughout the inclusions. Major element analysis, oxygen isotopic analysis (Δ17O = 0.71 ± 0.02‰), and mean Fa and Fs molar contents (Fa15.7 ± 0.4 and Fs14.4 ± 0.5) indicate that MD originated as an H chondrite. Because of strong similarities with Netschaëvo IIE, MD can be classified in the most primitive subgroup of the IIE sequence. 40Ar/39Ar ages of 4536 ± 59 Ma and 4494 ± 95 Ma obtained on pyroxene and plagioclase inclusions show that MD belongs to the old (~4.5 Ga) group of IIE iron meteorites and that it has not been perturbed by any subsequent heating event following its formation. The primitive character of MD sheds light on the nature of its formation process, its thermal history, and the evolution of its parent body.

Reference
Van Roosbroek N, Debaille V, Pittarello L, Goderis S, Humayun M, Hecht L, Jourdan F, Spicuzza MJ, Vanhaecke F, Claeys Ph (2015) The formation of IIE iron meteorites investigated by the chondrule-bearing Mont Dieu meteorite. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12463]

Published by arrangement with John Wiley & Sons

^1,2,3Erica R. Jawin, ¹Sebastien Besse,⁴Lisa R. Gaddis,⁵Jessica M. Sunshine,³James W. Head, ¹Sara Mazrouei
¹European Space Research and Technology Center, Noordwijk, Netherlands.
²Department of Astronomy, Mount Holyoke College, 50 College Street, South
Hadley, MA 01075, USA.
³Department of Earth, Environmental, and Planetary Sciences, Brown University,
Providence, Rhode Island, USA.
⁴USGS Astrogeology Science Center, Flagstaff, Arizona, USA.
⁵Department of Astronomy, University of Maryland, College Park, Maryland, USA

The localized lunar dark mantle deposits (DMDs) in Alphonsus, J. Herschel, and Oppenheimer craters were analyzed using VIS-NIR spectroscopy data from the Moon Mineralogy Mapper. Spectra of these localized DMDs were analyzed for compositional and mineralogical variations within the deposits and were compared with nearby mare basalt units. Spectra of the three localized DMDs exhibited mafic absorption features indicating iron-rich compositions, although the DMDs were spectrally distinct from nearby mare basalts. All of the DMDs contained spectral signatures of glassy materials, suggesting the presence of volcanic glass in varying concentrations across the individual deposits. In addition, the albedo and spectral signatures were variable within the Alphonsus and Oppenheimer crater DMDs, suggesting variable deposit thickness and/or variations in the amount of mixing with the local substrate. Two previously unidentified localized DMDs were discovered to the northeast of Oppenheimer crater. The identification of high concentrations of volcanic glass in multiple localized DMDs in different locations suggests that the distribution of volcanic glass across the lunar surface is much more widespread than has been previously documented. The presence of volcanic glass implies an explosive, vulcanian eruption style for localized DMDs, as this allows volcanic glass to rapidly quench, inhibiting crystallization, compared to the larger hawaiian-style eruptions typical of regional DMD emplacement where black beads indicate a higher degree of crystallization. Improved understanding of the local and global distribution of volcanic glass in lunar DMDs will further constrain lunar degassing and compositional evolution throughout lunar volcanic history.

Reference
Jawin ER, Besse S, LR Gaddis, Sunshine JM, Head JW, Mazrouei S (2015) Examining spectral variations in localized lunar dark mantle deposits. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004759]

Published by arrangement with John Wiley and Sons

^1,2Francis M. McCubbin,^2,3Rhian H. Jones
¹Institute of Meteoritics, University of New Mexico
Albuquerque, NM 87131, USA
²Department of Earth and Planetary Sciences, University of New Mexico
³School of Earth, Atmospheric and Environmental Sciences, University of Manchester
Manchester, M13 9PL, UK

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

Reference
McCubbin FM, Jones RH (2015) Extraterrestrial Apatite: Planetary Geochemistry to Astrobiology. Elements 11/3, 183-188
Link to Article [doi: 10.2113/gselements.11.3.183]

^1,2Enrico Bonatti, ^2,3Dee Breger, ⁴Tommaso Di Rocco, ¹Fulvio Franchi, ¹Luca Gasperini, ¹Alina Polonia, ⁵John Anfinogenov, ⁶Yana Anfinogenova
¹Istituto di Scienze Marine, CNR, U.O.S. Bologna, via Gobetti 101, 40129, Bologna, Italy
²Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA
³Micrographic Arts, P.O. Box 3088, Saratoga Springs 12866, NY, USA
⁴Geowissenschaftliches Zentrum, Abteilung Isotopengeologie, Georg-August-Universität, Goldschmidtstraβe 1, D-37077 Göttingen, Germany
⁵Faculty of Geology and Geography, National Research Tomsk State University, 36 Lenin Avenue, Tomsk, 634050, Russia
⁶Institute of Physics and Technology, National Research Tomsk Polytechnic University, 30 Lenin Avenue, Tomsk, 634050, Russia

An exotic meter-size quartzitic boulder known as John’s Stone was found by John Anfinogenov in 1972 buried in permafrost close to the epicenter of the 1908 Tunguska blast in a region of Siberia dominated by Permian-Triassic Siberian Trap basalts. The boulder is made almost entirely of well-cemented quartz grains, mostly around 100μm in size; it contains zones with coarser or finer grain sizes. Rare zircon and rutile crystals are scattered within the quartz matrix. Quartz is often dissected by strain lamellae. The rock contains abundant scattered internal vugs rimmed by euhedral quartz crystals. We cannot exclude that John’s Stone is a fragment of a Permian granite-derived sandstone unit. However, based on structure, mineralogy and chemistry the quartzitic boulder may have originated due to silica deposition from hydrothermal solutions that had reacted with basaltic rocks. Anfinogenov et al. (2014) interpreted features observed in the permafrost at the base of the boulder as indicating it impacted from above, suggesting the boulder may be a meteorite, possibly of Martian origin, given the reported presence on Mars of silica-rich deposits. Triple oxygen isotope ratios determined on two samples of the quartzite reveal a terrestrial rather than a Martian meteorites composition. Oxygen isotope data suggest also that the precipitation of SiO2 could have occurred in equilibrium with hydrothermal water (δ18Ow ≈ -19.5 ‰) at the temperature of about 50°C. The thermal event that generated the quartzite may be related either to the century-old Tunguska event, or, more probably, to Permian-Triassic Siberian Traps magmatism, although an extraterrestrial origin cannot be completely ruled out.

Reference
Bonatti E, Breger D, Di Roccod T, Franchi F, Gasperini L, Polonia A, Anfinogenov J, Anfinogenova Y (2015)
Origin of John’s Stone: A quartzitic boulder from the site of the 1908 Tunguska (Siberia) Explosion. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.018]

Copyright Elsevier

¹A. Kereszturi, ²S. Ormandi, ²S. Jozsa
¹Research Center for Astronomy and Earth Sciences, Konkoly Astronomical Institute, Budapest, Hungary
²Department of Petrology and Geochemistry, Faculty of Science, Hungarian Academy of Sciences, Eötvös Lorand University of Sciences, Budapest, Hungary

In analyzing a thin section of the NWA 6604 CK4 meteorite, only altered chondrules and various components that are probably left behind the destruction of former chondrules can be observed. We suggest that melting, grain size decrease, resorption of the original chondrules, and crystallization of opaque minerals were the main processes that destroyed the chondrules. Four different events could be identified as having occurred during this alteration. First, opaques crystallized along former fractures producing chains of separated grains. Later, opaques and Ca-rich minerals crystallized together in veins and large melt pockets; this was the strongest recrystallization phase involving the largest volume of melt. This occurred along different fractures than the first phase above. During the third phase, only Ca-rich plagioclase crystallized along thin veins, and in a fourth phase, fractures formed again, partly along those formed during the second phases but without substantial mineral infill. Two simple possible case models should be considered for this meteorite: alteration by purely impact-driven processes or mainly by melt-driven processes. Although for CK4 chondrites, the shock-produced alteration driven by impact is the more accepted and widespread approach, melting is also compatible with the observed textural characteristics of chondrule destruction. During melting, recrystallization took place producing iron-rich minerals earlier and Ca-Si-rich ones later. The penetration of melts into veins contributed in the chondrule destruction. The stress directions also changed during these alterations, and minerals that formed later filled differently oriented fractures than the earlier ones. From our observations, we favor a view where heat-driven melting and recrystallization produced the destruction and uniform mineralogy in the sample.

Reference
Kereszturi A, Ormandi S, Jozsa S (2015) Possible melting produced chondrule destruction in NWA 6604 CK4 chondrite. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12458]

Published by arrangement with John Wiley&Sons

^1,2A. Yamaguchi, ³J. A. Barrat, ⁴N. Shirai, ^1,4M. Ebihara
¹National Institute of Polar Research, Tachikawa, Tokyo, Japan
²Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, Japan
³U.B.O.-I.U.E.M., CNRS UMR 6538, Plouzané Cedex, France
⁴Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo, Japan

We performed a petrological and geochemical study of an olivine diogenite, Northwest Africa (NWA) 5480. NWA 5480 is a crystalline stone, but shows a heterogeneous texture. Olivine aggregates and grains of olivine and chromite display resorption textures set in a crystalline pyroxene matrix. Large olivine aggregates are penetrated by pyroxene matrix. Flow textures are observed near olivine aggregates. Olivine, chromite, and pyroxene show minor chemical zoning, implying relatively rapid cooling. NWA 5480 contains a significant amount of platinum group elements with chondritic relative proportions. All this evidence supports that NWA 5480 is an impact-melt breccia from a target composed of olivine and pyroxene-rich lithologies. Such impact melt would have formed by melting crustal materials, possibly during one of the impacts that formed the South Pole basins on Vesta.

Reference
Yamaguchi A, BarratJA, Shirai N, Ebihara M (2015) Petrology and geochemistry of Northwest Africa 5480 diogenite and evidence for a basin-forming event on Vesta. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12470]

Published by arrangement with John Wiley&Sons

^1,2Christoph Burkhardt,²Maria Schönbächler
¹Institute of Geochemistry and Petrology, Clausiusstrasse 25, ETH Zürich, CH-8092 Zürich, Switzerland
²Origins Laboratory, Department of Geophysical Sciences, The University of Chicago, IL 60637, USA

The progressive dissolution of the carbonaceous chondrites Orgueil (CI1), Murchison (CM2) and Allende (CV3) with acids of increasing strength reveals correlated W isotope variations ranging from 3.5 ε182W and 6.5 ε183W in the initial leachate (acetic acid) to –60 ε182W and –40 ε183W in the leachate residue. The observed variations are readily explained by variable mixing of s-process depleted and s-process enriched components. One W s-process carrier is SiC, however, the observed anomaly patterns and mass-balance considerations require at least on additional s-process carrier, possibly a silicate or sulfide. The data reveal well-defined correlations, which provide a test for s-process nucleosynthesis models. The correlations demonstrate that current models need to be revised and highlight the need for more precise W isotope data of SiC grains. Furthermore the correlations provide a mean to disentangle nucleosynthetic and radiogenic contributions to 182W (ε182Wcorrected= ε182Wmeasured –(1.41±0.05) × ε183Wmeasured; ε182Wcorrected= ε182Wmeasured –(–0.12±0.06) × ε184Wmeasured), a prerequisite for the successful application of the Hf-W chronometer to samples with nucleosynthetic anomalies.

The overall magnitude of the W isotope variations decreases in the order CI1>CM2>CV3. This can be interpreted as the progressive thermal destruction of an initially homogeneous mixture of presolar grains by parent-body processing. However, not only the magnitude but also the W anomaly patterns of the three chondrites are different. In particular leach step 2, that employs nitric acid, reveals a s-deficit signature for Murchison, but a s-excess for Orgueil and Allende. This could be the result of redistribution of anomalous W into a new phase by parent-body alteration, or, the fingerprint of dust processing in the solar nebula. Given that the thermal and aqueous alteration of Murchison is between the CI and CV3 chondrites, parent-body processing is probably not the sole cause for creating the different patters. Small-scale nebular redistribution of anomalous W may have played a role as well. Similar nebular processes possibly acted differently on specific carrier phases and elements, resulting in the diverse nucleosynthetic signatures observed in planetary materials today.

Reference
Burkhardt C, Schönbächler M (2015) Intrinsic W nucleosynthetic isotope variations in carbonaceous chondrites: Implications for W nucleosynthesis and nebular vs. parent body processing of presolar materials.
Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.06.012]
Copyright Elsevier

¹Jean Bollard, ¹James N. Connelly, ¹Martin Bizzarro
¹Centre for Star and Planet Formation, Natural History Museum of Denmark, Copenhagen, Denmark

The CB chondrites are metal-rich meteorites with characteristics that sharply distinguish them from other chondrite groups. Their unusual chemical and petrologic features and a young formation age of bulk chondrules dated from the CBa chondrite Gujba are interpreted to reflect a single-stage impact origin. Here, we report high-precision internal isochrons for four individual chondrules of the Gujba chondrite to probe the formation history of CB chondrites and evaluate the concordancy of relevant short-lived radionuclide chronometers. All four chondrules define a brief formation interval with a weighted mean age of 4562.49 ± 0.21 Myr, consistent with its origin from the vapor-melt impact plume generated by colliding planetesimals. Formation in a debris disk mostly devoid of nebular gas and dust sets an upper limit for the solar protoplanetary disk lifetime at 4.8 ± 0.3 Myr. Finally, given the well-behaved Pb-Pb systematics of all four chondrules, a precise formation age and the concordancy of the Mn-Cr, Hf-W, and I-Xe short-lived radionuclide relative chronometers, we propose that Gujba may serve as a suitable time anchor for these systems.

Reference
Bollard J, Connelly JN, Bizzarro M (2015) Pb-Pb dating of individual chondrules from the CBa chondrite Gujba: Assessment of the impact plume formation model. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12461]

Published by arrangement with John Wiley&Sons