Moe Matsuoka^a, Tomoki Nakamura^a, Yuki Kimura^b, Takahiro Hiroi^c, Ryosuke Nakamura^d, Satoshi Okumura^a, Sho Sasaki^e
aDivision of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Aoba, Sendai, Miyagi 980-8578, Japan
^bInstitute of Low Temperature Science, Hokkaido University, Sapporo, Hokkaido 060-0819, Japan
^cDepartment of Geological Sciences, Brown University, Providence, RI 02912, USA
^dNational Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
^eDepartment of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan

We performed pulse-laser irradiation experiments of a primitive meteorite to simulate space weathering by micrometeorite bombardments on C-type asteroids. Pellets of powdered Murchison CM2 chondrite were set in vacuum and exposed to pulse laser with a diameter of 0.5 mm and delivered energies of 5, 10 and 15 mJ. We measured reflectance spectra of unirradiated and irradiated surfaces of the pellets. During analysis the pellet was heated to approximately 100°C and purged in N2 gas in order to reduce absorption of ambient water. The spectra become darker and bluer with increasing laser energies. Their UV reflectance increases and 0.7- and 3-μm band depths decrease from 0 to 15 mJ. The spectral bluing observed in our experiments reproduces the bluing occurred during space weathering of C-type asteroids. High-resolution observation by a transmission electron microscope showed that the laser heating causes preferential melting and evaporation in FeS-rich fine-grained portions, which results in dispersion and deposition of numerous FeS-rich amorphous silicate particles 20-1000 nm in size on the surface of the pellet. In addition, at the laser-irradiated but unmelted areas, heat-induced amorphization and decomposition of serpentine occur. These mineralogical changes make the reflectance spectra of the Murchison CM chondrite darker and bluer.

Reference
Matsuok M, Tomoki Nakamura T, Kimura Y, Hiroi T, Nakamura R, Okumura S, Sho Sasaki S (2015) Pulse-laser irradiation experiments of Murchison CM2 chondrite for reproducing space weathering on C-type asteroids. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.02.029]

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Kelsey D. Hargrove^a, Josh Emery^b, Humberto Campins^a, Michael S.P. Kelley^c
a Physics Department, University of Central Florida, Orlando, FL 32816
^b Earth and Planetary Science Dept. and Planetary Geosciences Institute, University of Tennessee, Knoxville, TN 37996
^c Department of Astronomy, University of Maryland, College Park, MD 20742-2421

Many members of the Themis family show evidence of hydration in the form of oxidized iron in phyllosilicates (Florczak et al. 1999), and OH-bearing minerals (Takir and Emery 2012). The largest member, (24) Themis, has H2O ice covering its surface (Campins et al., 2010 and Rivkin and Emery, 2010). We have investigated the second largest Themis-family asteroid, (90) Antiope, which Castillo-Rogez and Schmidt (2010) predict to have a composition that includes water ice and organics. We obtained 2-4-μm spectroscopy of (90) Antiope in 2006 and 2008, and we find an absorption in the 3-μm region clearly present in our 2008 spectrum and likely in our 2006 spectrum. Both spectra have rounded, bowl-shaped absorptions consistent with those due to water ice as in the spectrum of (24) Themis, but do not uniquely identify water ice. We also present and compare Spitzer 8-12-μm mid-infrared spectra of (24) Themis and (90) Antiope. We find that (90) Antiope is lacking a “fairy castle” dusty surface, which is in contrast to (24) Themis, other Themis family members (Licandro et al. 2012), and Jupiter Trojans (e.g. Emery et al. 2006). We conclude that the surface structure of (90) Antiope is most similar to Cybele asteroid (121) Hermione (Hargrove et al. 2012).

Reference
Hargrove KD, Emery J, Michael HC, Kelley SP (2015) Asteroid (90) Antiope: Another Icy Member of the Themis Family? Icarus (in Press)
Link to Article [doi:10.1016/j.gca.2015.03.007]

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¹Agnès Elmaleh,^1,2Franck Bourdelle,¹Florent Caste,¹Karim Benzerara,³Hugues Leroux,
⁴Bertrand Devouard
¹Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Université Pierre et Marie Curie, Sorbonne Universités, CNRS UMR 7590, MNHN, IRD UR 206, Campus Jussieu, 4 Place Jussieu, Boîte Courrier 115, 75252 Paris Cedex 05, France Paris, France
²GeoRessources, Université de Lorraine, CNRS UMR 7359, FST, rue Jacques Callot, BP 70239, 54506 Vandoeuvre-lès-Nancy, France
³Unité Matériaux et Transformations, Université Lille 1, CNRS UMR 8207, 59655 Villeneuve d’Ascq, France
⁴CEREGE UM34, Aix-Marseille Université, CNRS UMR 7330, Europôle Méditerranéen de l’Arbois – Avenue Louis Philibert, BP 80, 13545 Aix en Provence cedex 04, France

Fe-rich serpentines are an abundant product of the early aqueous alteration events that affected the parent bodies of CM carbonaceous chondrites. Alteration assemblages in these meteorites show a large chemical variability and although water-rock interactions occurred under anoxic conditions, serpentines contain high amounts of ferric iron. To date very few studies have documented Fe valence variations in alteration assemblages of carbonaceous chondrites, limiting the understanding of the oxidation mechanisms. Here, we report results from a nanoscale study of a calcium-aluminum-rich inclusion (CAI) from the Murray chondrite, in which alteration resulted in Fe import and Ca export by the fluid phase and in massive Fe-rich serpentines formation. We combined scanning and transmission electron microscopies and scanning transmission X-ray microscopy for characterizing the crystal chemistry of Fe-serpentines. We used reference minerals with known crystallographic orientations to quantify the Fe valence state in Fe-rich serpentines using X-ray absorption spectroscopy at the Fe L2,3-edges, yielding a robust methodology that would prove valuable for studying oxidation processes in other terrestrial or extra-terrestrial cases of serpentinization. We suggest that aqueous Fe2+ was transported to the initially Fe-depleted CAI, where local changes in pH conditions, and possibly mineral catalysis by spinel promoted the partial oxidation of Fe2+ into Fe3+ by water and the formation of Fe-rich serpentines close to the cronstedtite endmember. Such mechanisms produce H2, which opens interesting perspectives as hydrogen may have reacted with carbon species, or escaped and yield increasingly oxidizing conditions in the parent asteroid. From the results of this nanoscale study, we also propose transformations of the initial cronstedtite, destabilized by later input of Al- and Mg-rich solutions, leading to Fe2+ leaching from serpentines, as well as to random serpentine-chlorite interstratifications. Such transformations towards polysomatic assemblages that are un-equilibrated from the structural, chemical and redox point of views are probably controlled by the various rates of alteration of primary minerals, but also by porosity gradients, as in terrestrial hydrothermal systems. We suggest that the proposed mechanisms may have played a role in the early formation of (Fe2+,Fe3+)-rich serpentines documented in CM chondrites, as well as in their transformation with on-going alteration towards Fe-poorer compositions inferred from previous petrologic, mineralogical and magnetic studies of CM chondrites.

Reference
Elmaleh A, Bourdelle F, Caste F, Benzerara K, Leroux H, Devouard B (2015) Formation and transformations of Fe-rich serpentines by asteroidal aqueous alteration processes: A nanoscale study of the Murray chondrite. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.03.007]

Copyright Elsevier

^1,4M. D. Hopkins,^1,2,3S. J. Mojzsis
¹Department of Geological Sciences, NASA Lunar Science Institute Center for Lunar Origin and Evolution (CLOE), University of Colorado, UCB 399, 2200 Colorado Avenue, Boulder, CO, 80309-0399, USA
²Laboratoire de Géologie de Lyon, École Normale Supérieure de Lyon, CNRS UMR 5276, Université Claude Bernard Lyon 1, 46 Allée d’Italie, 69007, Lyon, France
³Research Center for Astronomy and Earth Sciences, Institute for Geological and Geochemical Research, Hungarian Academy of Sciences, 45 Budaörsi Street, Budapest, 1112, Hungary
⁴Department of Earth Science, Santa Monica College, 1900 Pico Boulevard, Santa Monica, CA, 90405, USA

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

Reference
Hopkins MD, Mojzsis SJ (2015) A protracted timeline for lunar bombardment from mineral chemistry, Ti thermometry and U–Pb geochronology of Apollo 14 melt breccia zircons. Contributions to Mineralogy and Petrology 169:30
Link to Article [DOI 10.1007/s00410-015-1123-x]

¹Donald S. Burnett et al. (>10)*
¹California Institute of Technology, Pasadena, CA, USA
*Find the extensive, full author and affiliation list on the publishers Website

Ion microprobe elemental and isotopic determinations can be precise but difficult to quantify. Error is introduced when the reference material and the sample to be analysed have different compositions. Mitigation of such ‘matrix effects’ is possible using ion implants. If a compositionally homogeneous reference material is available which is ‘matrix-appropriate’ (i.e., close in major element composition to the sample to be analysed, but having an unknown concentration of the element, E, to be determined) then ion implantation can be used to introduce a known amount of an E isotope, calibrating the E concentration and producing a matrix-appropriate calibrator. Nominal implant fluences (ions cm−2) are inaccurate by amounts up to approximately 30%. However, ion implantation gives uniform fluences over large areas; thus, it is possible to ‘co-implant’ an additional reference material of any bulk composition having known amounts of E, independently calibrating the implant fluence. Isotope ratio measurement standards can be produced by implanting two different isotopes, but permil level precision requires postimplant calibration of the implant isotopic ratio. Examples discussed include (a) standardising Li in melilite; (b) calibrating a 25Mg implant fluence using NIST SRM 617 glass and (c) using Si co-implanted with 25Mg alongside NIST SRM 617 to produce a calibrated measurement of Mg in Si.

Reference
Burnett DS et al. (2015) Ion Implants as Matrix-Appropriate Calibrators for Geochemical Ion Probe Analyses. Geostandards and Geoanalytical Research (in Press)
Link to Article [DOI: 10.1111/j.1751-908X.2014.00318.x]

Published by arrangement with John Wiley&Sons

¹Gwenaël Hervé,¹Stuart A. Gilder,²Cassandra L. Marion,^2,3Gordon R. Osinski,¹Jean Pohl,¹Nikolai Petersen,⁴Paul J. Sylvester
¹Department of Earth and Environmental Sciences, Ludwig Maximilians Universität, Munich, Germany
²Department of Earth Sciences & Centre for Planetary Science and Exploration, University of Western Ontario, Canada
³Department of Physics and Astronomy, University of Western Ontario, Canada
⁴Department of Geosciences, Texas Tech University, 125 Science Building, Lubbock, TX 79409-1053, USA

We carried out an integrated rock magnetic and paleomagnetic study of the ∼36 Ma Mistastin Lake (Labrador, Canada) meteorite impact structure in order to investigate whether energy from the collision influenced the geodynamo and to assess the effects of shock on the magnetic properties of the target basement rocks. Stepwise demagnetization of 114 specimens isolates a well-defined magnetization component throughout the crater whose overall mean deviates slightly from the expected direction for North America at the time of impact. Paleointensity results from seven samples meeting stringent selection criteria show no significant difference with a global compilation from 40 to 30 Ma. The combined results, including those from a ∼80 m-thick profile of an impact melt unit (Discovery Hill), lend no support that the impact caused an aberration of the geodynamo within a few centuries of a bolide collision that created the ∼28 km-diameter crater. Both titanium-rich and titanium-poor titanomagnetite carry the magnetic remanence in the impact melt rocks; their relative proportions, compositions and domain states are cooling rate dependent. Magnetic hysteresis parameters of the magnetite-bearing anorthositic basement rocks reveal systematic changes as a function of distance from the crater’s center with an increasing prevalence of single domain-like grains toward the center. Changes with radial distance are also found in the character of the Verwey transition in magnetite. Basement rocks were thermally overprinted when lying less than a meter from the impact melt rocks; Mesoproterozoic basement rocks more than a meter below the impact melt rocks hold similar magnetization directions to those expected from a 1500 Ma result for Laurentia. No evidence exists that shock heating of the basement rocks exceeded 200 °C at distances of 6–7 km from the crater’s center.

Reference
Hervé G, Gilder SA, Marion CL, Osinski GR, Pohl J, Petersen N, Sylvester PJ (2015) Paleomagnetic and rock magnetic study of the Mistastin Lake impact structure (Labrador, Canada): Implications for geomagnetic perturbation and shock effects. Earth and Planetary Science Letters (in Press)
Link to Article [doi:10.1016/j.epsl.2015.02.011]

Copyright Elsevier

¹Emily Dixon,¹Andrew Elwood Madden,²Elisabeth M. Hausrath,¹Megan Elwood Madden
¹School of Geology and Geophysics, University of Oklahoma, Norman, OK, USA
²Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV, USA

Jarosite flow-through dissolution experiments were conducted in ultrapure water (UPW), pH 2 sulfuric acid, and saturated NaCl and CaCl2 brines at 295-298 K to investigate how hydrologic variables may affect jarosite preservation and reaction products on Mars. K+ based dissolution rates in flowing UPW did not vary significantly with flow rate, indicating that mineral surface reactions control dissolution rates over the range of flow rates investigated. In all of the solutions tested, hydrologic variables do not significantly affect extent of jarosite alteration; therefore jarosite is equally likely to be preserved in flowing or stagnant waters on Mars. However, increasing flow rate did affect the mineralogy and accumulation of secondary reaction products. Iron release rates in dilute solutions increased as the flow rate increased, likely due to nanoscale iron (hydr)oxide transport in flowing water. Anhydrite formed in CaCl2 brine flow-through experiments despite low temperatures, while metastable gypsum and bassanite were observed in batch experiments. Therefore, observations of the hydration state of calcium sulfate minerals on Mars may provide clues to unravel past salinity and hydrologic conditions as well as temperatures and vapor pressures.

Reference
Dixon E, Madden AE, Hausrath EM, Madden ME (2015) Assessing hydrodynamic effects on jarosite dissolution rates, reaction products, and preservation on Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004779]

Published by arrangement with John Wiley&Sons

¹Timothy A. Goudge,¹John F. Mustard,¹James W. Head,²Caleb I. Fassett,¹Sandra M. Wiseman
¹DepDepartment of Astronomy, Mount Holyoke College, South Hadley, MA, USA
²Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA

We present results from geomorphic mapping and visible to near-infrared spectral analyses of the Jezero crater paleolake basin and its associated watershed. The goal of this study is to understand the provenance of the sedimentary deposits within this open-basin lake using a source-to-sink approach. Two fan deposits located within the basin have distinct visible to near-infrared mineralogic signatures measured by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). The northern fan is spectrally characterized by a mixture of Mg-rich carbonate and olivine, while the western fan is characterized by Fe/Mg-smectite (e.g., saponite or nontronite) with variable amounts of Mg-rich carbonate and olivine in isolated exposures. The watersheds of these deposits contain a variety of geomorphic units that are likely to have supplied sediment to the Jezero crater paleolake, as the fluvial valleys that fed the basin incise these units. The geomorphic units include exposures of Fe/Mg-smectite-, olivine-, and Mg-rich carbonate-bearing terrain. We show that the difference in fan deposit mineralogy is a function of the areal exposure of the major geomorphic units within their watersheds. This indicates that the spectrally dominant aqueous alteration minerals in the fan deposits are primarily detrital, or transported, in nature and did not form in situ. We conclude that the aqueous alteration of the units in the watershed occurred prior to the fluvial activity that carved the valleys of the Jezero crater paleolake system, and that the two periods of aqueous activity are not genetically related.

Reference
Goudge TA, Mustard JF, Head JW, Fassett CI, Wiseman SM (2015) Assessing the Mineralogy of the Watershed and Fan Deposits of the Jezero Crater Paleolake System, Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004782]

Published by arrangement with John Wiley&Sons

^1,2C. Freissinet et al. (>10)*
¹Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA
²NASA Postdoctoral Program, (NPP), Oak Ridge Associated Universities, Oak Ridge, Tennessee, USA
*Find the extensive, full author and affiliation list on the publishers website

The Sample Analysis at Mars (SAM) instrument [Mahaffy et al., 2012] onboard the Mars Science Laboratory (MSL) Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater [Grotzinger et al., 2012]. Central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration and long-term preservation. This will guide the future search for biosignatures [Summons et al., 2011]. Here we report the definitive identification of chlorobenzene (150–300 parts per billion by weight (ppbw)) and C2 to C4 dichloroalkanes (up to 70 ppbw) with the SAM gas chromatograph mass spectrometer (GCMS), and detection of chlorobenzene in the direct evolved gas analysis (EGA) mode, in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay. When combined with GCMS and EGA data from multiple scooped and drilled samples, blank runs and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in SAM. We conclude that these chlorinated hydrocarbons are the reaction products of martian chlorine and organic carbon derived from martian sources (e.g. igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets or interplanetary dust particles.

Reference
Freissinet C et al. (2015) Organic molecules in the Sheepbed Mudstone, Gale Crater, Mars. Journal of Geophysical Research, Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004737]

Published by arrangement with John Wiley&Sons

¹Abu Asaduzzaman,¹Krishna Muralidharan,²Jibamitra Ganguly
¹Materials Science and Engineering, University of Arizona, Tucson, Arizona, USA
²Department of Geoscience, University of Arizona, Tucson, 85721, USA

Using density functional theory, we have examined the hydration mechanism of olivine with the objective of understanding the reaction pathways toward the formation of crystalline serpentine and brucite. It is found that further supply of water beyond saturation of the adsorption sites on olivine surfaces leads to the formation of amorphous brucite and serpentine molecules, with the latter forming in the subsurface domain. The calculated activation energy for this process is ~25 kJ mol−1, which permits formation of the amorphous materials well within the life span of the solar nebula. In addition, molecular dynamic simulations show that the adsorbed water in olivine is stable at least up to 900 K—a finding that is in accord with independent experimental studies. Thus, adsorption plus subsurface reaction of H2O in olivine could have taken place at temperatures considerably higher than the stability limit of hydrous minerals in the nebular condition. Using the DFT derived enthalpy of adsorption data, and reasonable approximation for the entropy of adsorption, we have calculated the fractional coverage of the reactive surface sites of olivine grains of spherical geometry by adsorbed water, and the corresponding ocean equivalent water (OEW) that could have been accreted into the Earth. These results suggest that adsorption and the associated subsurface hydroxylation of olivine grains might have been responsible for a significant fraction of the Earth’s water budget. The adsorption of water into olivine crystals in the solar nebula might also have led to the delivery of water to other planetary bodies.

Reference
Asaduzzaman A, Muralidharan K, Ganguly J (2015) Incorporation of water into olivine during nebular condensation: Insights from density functional theory and thermodynamics, and implications for phyllosilicate formation and terrestrial water inventory. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12409]

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