¹C. Lefebvre, ²A. Catalá-Espí, ¹P. Sobron, ¹A. Koujelev, ¹R. Léveillé
¹Space Science and Technology, Canadian Space Agency, 6767, route de l׳aéroport, Saint-Hubert, Canada J3Y 8Y9
²Unidad Asociada UVa-CSIC, Avd. Francisco Vallés, Parque Tecnológico de Boecillo, E-47151 Boecillo, Valladolid, Spain

We demonstrate that Laser-Induced Breakdown Spectroscopy (LIBS) is capable of identifying the presence of natural rock coatings, and we define LIBS signatures of complex multi-layered coatings. This is illustrated by detailed LIBS analysis, in Mars-simulated conditions, of a rock collected in the Svalbard Islands, and which is analogous to some altered Martian rocks. The sample is a basaltic rock with sub-mm Ca–Mg–Fe–Si rich mineral coatings. LIBS elemental analysis of several distinct regions on the surface of the rock demonstrates the variability of chemical compositions of the various coatings, which is confirmed by complementary scanning electron microscope (SEM) analysis. Furthermore, the LIBS analysis as a function of the depth at different locations shows chemical variability, indicative of penetration through thin coatings of varying composition. Fine-scale, three-dimensional LIBS analysis is of interest for identifying and characterizing coatings on martian rocks, likely originating from aqueous processes, providing a rapid chemical composition as a function of the layers and further understanding of the formation of the deposits and on planetary evolution.

Reference
Lefebvre C, Catalá-Espí A, Sobron P, Koujelev A, Léveillé R (2016) Depth-resolved chemical mapping of rock coatings using Laser-Induced Breakdown Spectroscopy: Implications for geochemical investigations on Mars. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2016.04.003]
Copyright Elsevier

¹G. Bilalbegović
¹Department of Physics, Faculty of Science, University of Zagreb, Bijenička 32, 10000 Zagreb, Croatia

Cement mineral tobermorite was formed in hydrothermal experiments on alternation of calcium-aluminum-rich inclusions (CAIs) in carbonaceous chondrite meteorites. Unidentified bands at 14 μm were measured for CAIs and the matrix of the Allende meteorite sample, as well as for Hektor and Agamemnon asteroids. The presence of cement nanoparticles may explain the feature at 14 μm

Reference
Bilalbegović G (2016) A note on cement in asteroids. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.04.029]
Copyright Elsevier

¹Claire L. McLeod, ¹Alan D. Brandon, ^2,3,4Vera. A. Fernandes,⁵Anne H. Peslier, ⁶Jörg Fritz, ¹Thomas Lapen, ¹John T. Shafer, ⁷Alan R. Butcher, ⁸Anthony J. Irving
¹University of Houston, Department of Earth and Atmospheric Sciences, 4800 Calhoun Road, Houston TX, 77004, USA
²Museum für Naturkunde, Leibniz Institute for Research on Evolution and Biodiversity, Invalidenstrasse 43, 10115, Berlin, Germany
³The Centre for Earth Evolution and Dynamics, University of Oslo, Norway
⁴Institute for the Development of New Technologies (UNINOVA), New University of Lisbon, Portugal
⁵Jacobs, NASA-Johnson Space Center, Mail Code XI3, Houston TX, 77058, USA
⁶Saalbau Weltraum Projekt, Wilhelmstrasse 38, 64646 Heppenheim, Germany
⁷FEI Company, Eindhoven, The Netherlands
⁸University of Washington, Department of Earth and Space Sciences, Seattle, WA, 98195, USA

Lunar granulitic meteorites provide new constraints on the composition and evolution of the lunar crust as they are potentially derived from outside the Apollo and Luna landing sites. Northwest Africa (NWA) 3163, the focus of this study, and its paired stones NWA 4881 and NWA 4483, are shocked granulitic noritic anorthosites. They are petrographically and compositionally distinct from the Apollo granulites and noritic anorthosites. Northwest Africa 3163 is REE-depleted by an order of magnitude compared to Apollo granulites and is one of the most trace element depleted lunar samples studied to date. New in-situ mineral compositional data and Rb-Sr, Ar-Ar isotopic systematics are used to evaluate the petrogenetic history of NWA 3163 (and its paired stones) within the context of early lunar evolution and the bulk composition of the lunar highlands crust. The NWA 3163 protolith was the likely product of reworked lunar crust with a previous history of heavy REE depletion. The bulk feldspathic and pyroxene-rich fragments have 87Sr/86Sr that are indistinguishable and average 0.699282±0.000007. A calculated source model Sr TRD age of 4.340 ± 0.057 Ga is consistent with 1) the recently determined young FAS (Ferroan Anorthosite) age of 4.360 ± 0.003 Ga for FAS 60025, 2) 142Nd model ages for the closure of the Sm-Nd system for the mantle source reservoirs of the Apollo mare basalts (4.355-4.314 Ga) and 3) a prominent age peak in the Apollo lunar zircon record (c. 4.345 Ga). These ages are ∼100 Myr younger than predicted timescales for complete LMO crystallization (∼10 Myrs after Moon formation, Elkins-Tanton et al., 2011). This supports a later, major event during lunar evolution associated with crustal reworking due to magma ocean cumulate overturn, serial magmatism, or a large impact event leading to localized or global crustal melting and/or exhumation. The Ar-Ar isotopic systematics on aliquots of paired stone NWA 4881 are consistent with an impact event at ⩾3.5 Ga. This is inferred to record the event that induced granularization of NWA 3163 (and paired rocks). A later event is also recorded at ∼ 2 Ga by Ar-Ar isotopes, and would be consistent with an increase in the number of impacts on the lunar surface at this time (Fernandes et al., 2013) . Northwest Africa 3163 and its paired stones therefore record a c. 2.4 Gyr record of lunar crustal production, metamorphism, brecciation, impacts and eventual ejection from the lunar surface.

Reference
McLeod CL, Brandon AD, Fernandes VD, Peslier AH, Fritz J, Lapen T, Shafer JT, Butcher AR, Irving AJ (2016) Constraints on Formation and Evolution of the Lunar Crust from Feldspathic Granulitic Breccias NWA 3163 and 4881. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.04.032]
Copyright Elsevier

^1,2Matthew J. Genge
¹Impact and Astromaterials Research Centre (IARC), Department of Earth Science and Engineering, Imperial College London, London, UK
²Department of Mineralogy, The Natural History Museum, London, UK

The Earth’s extraterrestrial dust flux includes a wide variety of dust particles that include FeNi metallic grains. During their atmospheric entry iron micrometeoroids melt and oxidize to form cosmic spherules termed I-type spherules. These particles are chemically resistant and readily collected by magnetic separation and are thus the most likely micrometeorites to be recovered from modern and ancient sediments. Understanding their behavior during atmospheric entry is crucial in constraining their abundance relative to other particle types and the nature of the zodiacal dust population at 1 AU. This article presents numerical simulations of the atmospheric entry heating of iron meteoroids to investigate the abundance and nature of these materials. The results indicate that iron micrometeoroids experience peak temperatures 300–800 K higher than silicate particles explaining the rarity of unmelted iron particles which can only be present at sizes of

Reference
Genge, MJ (2016) The origins of I-type spherules and the atmospheric entry of iron micrometeoroids. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12645]
Published by arrangement with John Wiley & Sons

¹James M. D. Day, ^2,3Lin Qiu, ²Richard D. Ash, ²William F. McDonough, ⁴Fang-Zhen Teng, ²Roberta L. Rudnick,⁵Lawrence A. Taylor
¹Geosciences Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
²Department of Geology, University of Maryland, College Park, Maryland, USA
³Department of Geology and Geophysics, Yale University, New Haven, Connecticut, USA
⁴Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA
⁵Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA

Lithium isotope and abundance data are reported for Apollo 15 and 17 mare basalts and the LaPaz low-Ti mare basalt meteorites, along with lithium isotope data for carbonaceous, ordinary, and enstatite chondrites, and chondrules from the Allende CV3 meteorite. Apollo 15 low-Ti mare basalts have lower Li contents and lower δ7Li (3.8 ± 1.2‰; all uncertainties are 2 standard deviations) than Apollo 17 high-Ti mare basalts (δ7Li = 5.2 ± 1.2‰), with evolved LaPaz mare basalts having high Li contents, but similar low δ7Li (3.7 ± 0.5‰) to Apollo 15 mare basalts. In low-Ti mare basalt 15555, the highest concentrations of Li occur in late-stage tridymite (>20 ppm) and plagioclase (11 ± 3 ppm), with olivine (6.1 ± 3.8 ppm), pyroxene (4.2 ± 1.6 ppm), and ilmenite (0.8 ± 0.7 ppm) having lower Li concentrations. Values of δ7Li in low- and high-Ti mare basalt sources broadly correlate negatively with 18O/16O and positively with 56Fe/54Fe (low-Ti: δ7Li ≤4‰; δ56Fe ≤0.04‰; δ18O ≥5.7‰; high-Ti: δ7Li >6‰; δ56Fe >0.18‰; δ18O <5.4‰). Lithium does not appear to have acted as a volatile element during planetary formation, with subequal Li contents in mare basalts compared with terrestrial, martian, or vestan basaltic rocks. Observed Li isotopic fractionations in mare basalts can potentially be explained through large-degree, high-temperature igneous differentiation of their source regions. Progressive magma ocean crystallization led to enrichment in Li and δ7Li in late-stage liquids, probably as a consequence of preferential retention of 7Li and Li in the melt relative to crystallizing solids. Lithium isotopic fractionation has not been observed during extensive differentiation in terrestrial magmatic systems and may only be recognizable during extensive planetary magmatic differentiation under volatile-poor conditions, as expected for the lunar magma ocean. Our new analyses of chondrites show that they have δ7Li ranging between −2.5‰ and 4‰. The higher δ7Li in planetary basalts than in the compilation of chondrites (2.1 ± 1.3‰) demonstrates that differentiated planetary basalts are, on average, isotopically heavier than most chondrites.

Reference
Day JMD, Qiu L, Ash RD, McDonough WF, Teng F-Z, Rudnick RL, Taylor LA (2016) Evidence for high-temperature fractionation of lithium isotopes during differentiation of the Moon. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12643]
Published by arrangement with John Wiley & Sons

¹Mikhail Yu. Zolotov, ²Mikhail V. Mironenko
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, USA
²Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19 Kosygin Str., Moscow 119991, Russia

Numerical chemical models for water-basalt interaction have been used to constrain the formation of stratified mineralogical sequences of Noachian clay-bearing rocks exposed in the Mawrth Vallis region and in other places on cratered martian highlands. The numerical approaches are based on calculations of water-rock type chemical equilibria and models which include rates of mineral dissolution. Results show that the observed clay-bearing sequences could have formed through downward percolation and neutralization of acidic H2SO4-HCl solutions. A formation of weathering profiles by slightly acidic fluids equilibrated with current atmospheric CO2 requires large volumes of water and is inconsistent with observations. Weathering by solutions equilibrated with putative dense CO2 atmospheres leads to consumption of CO2 to abundant carbonates which are not observed in clay stratigraphies. Weathering by H2SO4-HCl solutions leads to formation of amorphous silica, Al-rich clays, ferric oxides/oxyhydroxides, and minor titanium oxide and alunite at the top of weathering profiles. Mg-Fe phyllosilicates, Ca sulfates, zeolites, and minor carbonates precipitate from neutral and alkaline solutions at depth. Acidic weathering causes leaching of Na, Mg, and Ca, from upper layers and accumulation of Mg-Na-Ca sulfate-chloride solutions at depth. Neutral MgSO4 type solutions dominate in middle parts of weathering profiles and could occur in deeper layers owing to incomplete alteration of Ca minerals and a limited trapping of Ca to sulfates. Although salts are not abundant in the Noachian geological formations, the results suggest the formation of Noachian salty solutions and their accumulation at depth. A partial freezing and migration of alteration solutions could have separated sulfate-rich compositions from low-temperature chloride brines and contributed to the observed diversity of salt deposits. A Hesperian remobilization and release of subsurface MgSO4 type solutions into newly-formed depressions could account for formation of massive layered sulfate deposits through freezing or evaporation. This scenario explains the observed deficiency of salts in Noachian formations, a paucity of Hesperian phyllosilicates, and the occurrence of sulfate deposits in Valles Marineris troughs, chaotic terrains, and some craters of the Hesperian age.

Reference
Zolotov MY, Mironenko MV (2016) Chemical models for martian weathering profiles: Insights into formation of layered phyllosilicate and sulfate deposits. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.04.011]
Copyright Elsevier

^1,2Martin Schmieder, ^1,2David A. Kring, ³Timothy D. Swindle, ⁴Jade C. Bond,⁵Carleton B. Moore
¹Lunar and Planetary Institute, Houston, Texas, USA
²NASA Solar System Exploration Research Virtual Institute
³Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
⁴Department of Astrophysics, School of Physics, University of New South Wales, Sydney, New South Wales, Australia
⁵Center for Meteorite Studies, Arizona State University, Tempe, Arizona, USA

The Gao-Guenie H5 chondrite that fell on Burkina Faso (March 1960) has portions that were impact-melted on an H chondrite asteroid at ~300 Ma and, through later impact events in space, sent into an Earth-crossing orbit. This article presents a petrographic and electron microprobe analysis of a representative sample of the Gao-Guenie impact melt breccia consisting of a chondritic clast domain, quenched melt in contact with chondritic clasts, and an igneous-textured impact melt domain. Olivine is predominantly Fo80–82. The clast domain contains low-Ca pyroxene. Impact melt-grown pyroxene is commonly zoned from low-Ca pyroxene in cores to pigeonite and augite in rims. Metal–troilite orbs in the impact melt domain measure up to ~2 mm across. The cores of metal orbs in the impact melt domain contain ~7.9 wt% of Ni and are typically surrounded by taenite and Ni-rich troilite. The metallography of metal–troilite droplets suggest a stage I cooling rate of order 10 °C s−1 for the superheated impact melt. The subsolidus stage II cooling rate for the impact melt breccia could not be determined directly, but was presumably fast. An analogy between the Ni rim gradients in metal of the Gao-Guenie impact melt breccia and the impact-melted H6 chondrite Orvinio suggests similar cooling rates, probably on the order of ~5000–40,000 °C yr−1. A simple model of conductive heat transfer shows that the Gao-Guenie impact melt breccia may have formed in a melt injection dike ~0.5–5 m in width, generated during a sizeable impact event on the H chondrite parent asteroid.

Reference
Schmieder M, Kring DA, Swindle TD, Bond JC, Moore CB (2016) The Gao-Guenie impact melt breccia—Sampling a rapidly cooled impact melt dike on an H chondrite asteroid? Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12642]
Published by arrangement with John Wiley & Sons

^1,2Francis M. McCubbin, ³Jeremy W. Boyce, ²Poorna Srinivasan, ²Alison R. Santos, ⁴Stephen M. Elardo, ⁵Justin Filiberto, ⁴Andrew Steele,²Charles K. Shearer
¹NASA Johnson Space Center, Houston, Texas, USA
²Institute of Meteoritics, Department of Earth & Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
³Department of Earth & Space Sciences, University of California Los Angeles, Los Angeles, California, USA
⁴Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, USA
⁵Department of Geology, Southern Illinois University, Carbondale, Illinois, USA

We conducted a petrologic study of apatite within 12 Martian meteorites, including 11 shergottites and one basaltic regolith breccia. These data were combined with previously published data to gain a better understanding of the abundance and distribution of volatiles in the Martian interior. Apatites in individual Martian meteorites span a wide range of compositions, indicating they did not form by equilibrium crystallization. In fact, the intrasample variation in apatite is best described by either fractional crystallization or crustal contamination with a Cl-rich crustal component. We determined that most Martian meteorites investigated here have been affected by crustal contamination and hence cannot be used to estimate volatile abundances of the Martian mantle. Using the subset of samples that did not exhibit crustal contamination, we determined that the enriched shergottite source has 36–73 ppm H2O and the depleted source has 14–23 ppm H2O. This result is consistent with other observed geochemical differences between enriched and depleted shergottites and supports the idea that there are at least two geochemically distinct reservoirs in the Martian mantle. We also estimated the H2O, Cl, and F content of the Martian crust using known crust-mantle distributions for incompatible lithophile elements. We determined that the bulk Martian crust has ~1410 ppm H2O, 450 ppm Cl, and 106 ppm F, and Cl and H2O are preferentially distributed toward the Martian surface. The estimate of crustal H2O results in a global equivalent surface layer (GEL) of ~229 m, which can account for at least some of the surface features on Mars attributed to flowing water and may be sufficient to support the past presence of a shallow sea on Mars’ surface.

Reference
McCubbin FM, Boyce JW, Srinivasan P, Santos AR, Elardo SM, FilibertoJ, Steele A, Shearer CK (2016) Heterogeneous distribution of H2O in the Martian interior: Implications for the abundance of H2O in depleted and enriched mantle sources. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12639]
Published by arrangement with John Wiley & Sons

¹Hugues Leroux, ¹Damien Jacob, ²Maya Marinova, ^3,4Roger H. Hewins, ^3,4,5Brigitte Zanda, ³Sylvain Pont, ⁶Jean-Pierre Lorand, ⁷Munir Humayun
¹Unité Matériaux et Transformations, University of Lille & CNRS, Villeneuve d’Ascq, France
²Institut Chevreul, University of Lille & CNRS, Villeneuve d’Ascq, France
³Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Université, Muséum National d’Histoire Naturelle, UPMC Université Paris 06, IRD & CNRS, Paris, France
⁴Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
⁵Institut de Mécanique Céleste et de Calcul des Ephémérides, Observatoire de Paris, Paris Cedex, France
⁶Laboratoire de Planétologie et Géodynamique, Université de Nantes, Nantes, France
⁷Department of Earth, Ocean & Atmospheric Science and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, USA

Northwest Africa (NWA) 7533 is a Martian regolith breccia. This meteorite (and its pairings) offers a good opportunity to study (near-) surface processes that occurred on early Mars. Here, we have conducted a transmission electron microscope study of medium- and coarse-grained (a few tens to hundreds of micrometers) Ca-rich pyroxene clasts in order to define their thermal and shock histories. The pyroxene grains have a high-temperature (magmatic) origin as revealed by the well-developed pigeonite–augite exsolution microstructure. Exsolution lamella characteristics (composition, thickness, and spacing) indicate a moderately slow cooling. Some of the pyroxene clasts display evidence for local decomposition into magnetite and silica at the submicron scale. This phase decomposition may have occurred at high temperature and occurred at high oxygen fugacity at least 2–3 log units above the QFM buffer, after the formation of the exsolution lamellae. This corresponds to oxidizing conditions well above typical Martian magmatic conditions. These oxidizing conditions seem to have prevailed early and throughout most of the history of NWA 7533. The shock microstructure consists of (100) mechanical twins which have accommodated plastic deformation. Other pyroxene shock indicators are absent. Compared with SNC meteorites that all suffered significant shock metamorphism, NWA 7533 appears only mildly shocked. The twin microstructure is similar from one clast to another, suggesting that the impact which generated the (100) twins involved the compacted breccia and that the pyroxene clasts were unshocked when they were incorporated into the NWA 7533 breccia.

Reference
Leroux H, Jacob D, Marinova M, Hewins RH, Zanda B, Pont S, Lorand J-P, Humayun M (2016) Exsolution and shock microstructures of igneous pyroxene clasts in the Northwest Africa 7533 Martian meteorite. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12637]
Published by arrangement with John Wiley & Sons

^1,2Arshad Ali, ¹Iffat Jabeen, ³David Gregory, ⁴Robert Verish,¹Neil R. Banerjee
¹Department of Earth Sciences & Centre for Planetary Science and Exploration, Western University, London, Ontario, Canada
²Earth Sciences Research Centre (ESRC), Sultan Qaboos University, Muscat, Sultanate of Oman
³St. Thomas, Ontario, Canada
⁴Meteorite-Recovery Lab, Escondido, California, USA

We report precise triple oxygen isotope data of bulk materials and separated fractions of several Shergotty–Nakhla–Chassigny (SNC) meteorites using enhanced laser-assisted fluorination technique. This study shows that SNCs have remarkably identical Δ17O and a narrow range in δ18O values suggesting that these meteorites have assimilated negligibly small surface materials (<5%), which is undetectable in the oxygen isotope compositions reported here. Also, fractionation factors in coexisting silicate mineral pairs (px-ol and mask-ol) further demonstrate isotopic equilibrium at magmatic temperatures. We present a mass-dependent fractionation line for bulk materials with a slope of 0.526 ± 0.016 (1SE) comparable to the slope obtained in an earlier study (0.526 ± 0.013; Franchi et al. 1999). We also present a new Martian fractionation line for SNCs constructed from separated fractions (i.e., pyroxene, olivine, and maskelynite) with a slope of 0.532 ± 0.009 (1SE). The identical fractionation lines run above and parallel to our terrestrial fractionation line with Δ17O = 0.318 ± 0.016‰ (SD) for bulk materials and 0.316 ± 0.009‰ (SD) for separated fractions. The conformity in slopes and Δ17O between bulk materials and separated fractions confirm oxygen isotope homogeneity in the Martian mantle though recent studies suggest that the Martian lithosphere may potentially have multiple oxygen isotope reservoirs.

Reference
Ali A, Jabeen I, Gregory D, Verish R, Banerjee NR (2016) New triple oxygen isotope data of bulk and separated fractions from SNC meteorites: Evidence for mantle homogeneity of Mars. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12640]
Published by arrangement with John Wiley & Sons