¹Harry Y. McSween Jr.
¹Department of Earth and Planetary Sciences and Planetary Geoscience Institute, University of Tennessee, Knoxville, Tennessee 37996-1410, U.S.A.

Petrologic investigations of martian rocks have been accomplished by mineralogical, geochemical, and textural analyses from Mars rovers (with geologic context provided by orbiters), and by laboratory analyses of martian meteorites. Igneous rocks are primarily lavas and volcaniclastic rocks of basaltic composition, and ultramafic cumulates; alkaline rocks are common in ancient terranes and tholeiitic rocks occur in younger terranes, suggesting global magmatic evolution. Relatively uncommon feldspathic rocks represent the ultimate fractionation products, and granitic rocks are unknown. Sedimentary rocks are of both clastic (mudstone, sandstone, conglomerate, all containing significant igneous detritus) and chemical (evaporitic sulfate and less common carbonate) origin. High-silica sediments formed by hydrothermal activity. Sediments on Mars formed from different protoliths and were weathered under different environmental conditions from terrestrial sediments. Metamorphic rocks have only been inferred from orbital remote-sensing measurements. Metabasalt and serpentinite have mineral assemblages consistent with those predicted from low-pressure phase equilibria and likely formed in geothermal systems. Shock effects are common in martian meteorites, and impact breccias are probably widespread in the planet’s crustal rocks. The martian rock cycle during early periods was similar in many respects to that of Earth. However, without plate tectonics Mars did not experience the thermal metamorphism and flux melting associated with subduction, nor deposition in subsided basins and rapid erosion resulting from tectonic uplift. The rock cycle during more recent time has been truncated by desiccation of the planet’s surface and a lower geothermal gradient in its interior. The petrology of Mars is intriguingly different from Earth, but the tried-and-true methods of petrography and geochemistry are clearly translatable to another world.

Reference
McSween Jr. HY (2015) Petrology on Mars. American Mineralogist 100, 2380-2395
Link to Article [doi: 10.2138/am-2015-5257]

Copyright: The Mineralogical Society of America

¹Maria Eugenia Varela,²Ernst Zinner
¹Instituto de Ciencias Astronómicas de la Tierra y del Espacio (ICATE), San Juan, Argentina
²Laboratory for Space Sciences and the Physics Department, Washington University, St. Louis, Missouri, USA

Glass-bearing inclusions hosted by different mineral phases in SNC meteorites provide important information on the conditions that prevailed during formation of early phases and/or on the composition of the primary trapped liquids/melts of these rocks. Although extensive previous work has been reported on such inclusions, several questions are still unresolved. We performed a chemical and petrographic study of the constituents (glasses and mineral assemblage) of glassy and multiphase inclusions in Shergotty and Chassigny. We focused on obtaining accurate trace element contents of glasses and co-existing minerals and discussing their highly variable REE contents. Our results reveal an unusual geochemistry of trace element contents that appear to be independent of their major element compositions. Chemical equilibrium between phases inside inclusions as well as between glasses and host minerals could not be established. The LREE contents of glasses in glass inclusions can vary by up to two orders of magnitude. The depletion in trace element abundances shown by glasses seem to be inconsistent with these phases being residual melts. The light lithophile element contents of glasses are highly variable with enrichment in incompatible elements (e.g., Be, Sr, Ba, and LREE) indicating some processes involving percolation of fluids. All of these features are incompatible with glass-bearing inclusions in the host minerals acting as closed systems preserving unmodified primary liquids/melts. Glass-bearing inclusions in Shergotty and Chassigny appear to have been altered (as was the rock itself) by different postformational processes (e.g., shock, metamorphism, metasomatic [?] fluids) that affected these meteorites with different degree of intensity. Our results indicate that these inclusions could not preserve a reliable sample of the primary trapped melt.

Reference
Varela ME, Zinner E (2015) Glass-bearing inclusions in Shergotty and Chassigny: Consistent samples of a primary trapped melt? Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12566]
Publsihed by arrangement with John Wiley & Sons

¹Julie E. M. McGeoch,²Malcolm W. McGeoch

¹Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA
²PLEX LLC, Fall River, Massachusetts, USA

It has been proposed that exothermic gas phase polymerization of amino acids can occur in the conditions of a warm dense molecular cloud to form hydrophobic polymer amide (HPA) (McGeoch and McGeoch 2014). In a search for evidence of this presolar chemistry Allende and Murchison meteorites and a volcano control were diamond burr-etched and Folch extracted for potential HPA yielding 85 unique peaks in the meteorite samples via matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI TOF/MS). The amino acids after acid hydrolysis in Allende were below the level of detection but many of the Allende peaks via the more sensitive MALDI/TOF analysis could be fitted to a polymer combination of glycine, alanine, and alpha-hydroxyglycine with high statistical significance. A similar significant fit using these three amino acids could not be applied to the Murchison data indicating more complex polymer chemistry.

Reference
McGeoch JEM, McGeoch MW (2015) Polymer amide in the Allende and Murchison meteorites. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12558]

Published by arrangement with John Wiley & Sons

^1,2Penelope J. Wozniakiewicz, ³Hope A. Ishii, ^1,2Anton T. Kearsley, ³John P. Bradley, ¹Mark. C. Price, ¹Mark J. Burchell, ⁴Nick Teslich,¹Mike J. Cole
¹School of Physical Science, Centre for Astrophysics and Planetary Sciences, University of Kent, Canterbury, UK
²Department of Earth Sciences, Impacts & Astromaterials Research Centre (IARC), Natural History Museum, London, UK
³Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, Honolulu, Hawai’i, USA
⁴Lawrence Livermore National Laboratory, Livermore, California, USA

Comet 81P/Wild 2 samples returned by NASA’s Stardust mission provide an unequalled opportunity to study the contents of, and hence conditions and processes operating on, comets. They can potentially validate contentious interpretations of cometary infrared spectra and in situ mass spectrometry data: specifically the identification of phyllosilicates and carbonates. However, Wild 2 dust was collected via impact into capture media at ~6 km s−1, leading to uncertainty as to whether these minerals were captured intact, and, if subjected to alteration, whether they remain recognizable. We simulated Stardust Al foil capture conditions using a two-stage light-gas gun, and directly compared transmission electron microscope analyses of pre- and postimpact samples to investigate survivability of lizardite and cronstedtite (phyllosilicates) and calcite (carbonate). We find the phyllosilicates do not survive impact as intact crystalline materials but as moderately to highly vesiculated amorphous residues lining resultant impact craters, whose bulk cation to Si ratios remain close to that of the impacting grain. Closer inspection reveals variation in these elements on a submicron scale, where impact-induced melting accompanied by reducing conditions (due to the production of oxygen scavenging molten Al from the target foils) has resulted in the production of native silicon and Fe- and Fe-Si-rich phases. In contrast, large areas of crystalline calcite are preserved within the calcite residue, with smaller regions of vesiculated, Al-bearing calcic glass. Unambiguous identification of calcite impactors on Stardust Al foil is therefore possible, while phyllosilicate impactors may be inferred from vesiculated residues with appropriate bulk cation to Si ratios. Finally, we demonstrate that the characteristic textures and elemental distributions identifying phyllosilicates and carbonates by transmission electron microscopy can also be observed by state-of-the-art scanning electron microscopy providing rapid, nondestructive initial mineral identifications in Stardust residues.

Reference
Wozniakiewicz PJ, Ishii HA, Kearsley AT, Bradley JP, Price MC, Burchell MJ, Teslich N, Cole MJ (2015) The survivability of phyllosilicates and carbonates impacting Stardust Al foils: Facilitating the search for cometary water. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12568]

Published by arrangement with John Wiley & Sons

¹Ebbe N. Bak, ²Svend J. Knak Jensen, ¹Per Nørnberg, ^1,3Kai Finster
¹Department of Bioscience, Aarhus University, Ny Munkegade 116, Building 1540, 8000 Aarhus C, Denmark
²Department of Chemistry, Aarhus University, Langelandsgade 140, Building 1511, 8000 Aarhus C, Denmark
³Stellar Astrophysics Center, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, Building 1520, 8000 Aarhus C, Denmark

The only organic compounds that have been detected in the Martian soil are simple chlorinated compounds released from heated surface material. However, the sources of the organic carbon are in dispute. Wind abraded silicates, which are widespread on the Martian surface, can sequester atmospheric methane which generates methylated silicates and thus could provide a mechanism for accumulation of reduced carbon in the surface soil. In this study we show that thermal volatilization of methylated silicates in the presence of perchlorate leads to the production of chlorinated methane. Thus, methylated silicates could be a source of the organic carbon released as chlorinated methane upon thermal volatilization of Martian soil samples. Further, our experiments show that the ratio of the different chlorinated compounds produced is dependent on the mass ratio of perchlorate to organic carbon in the soil.

Reference
Bak EN, Knak Jensen SJ, Nørnberg P, Finster K (2015) Methylated silicates may explain the release of chlorinated methane from Martian soil. Earth & Planetary Science Letters (in Press)
Link to Article [doi:10.1016/j.epsl.2015.10.044]
Copyright Elsevier

¹Fang, C.M., ¹Van Huis, M.A., ²Sluiter, M.H.F. 
¹Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, Utrecht, Netherlands
²Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, Delft, Netherlands

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

Reference
Fang CM, Van Huis MA, Sluiter MHF (2015) Formation, structure and magnetism of the γ-(Fe,M)23C6 (M = Cr, Ni) phases: A first-principles study. Acta Materialia 103, 273-279
Link to Article [DOI: 10.1016/j.actamat.2015.08.078]

¹J.F. Snape, ^1,2A.A. Nemchin, ²M.L. Grange, ¹J.J. Bellucci, ¹F. Thiessen, ¹M.J. Whitehouse
¹Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden
²Department of Applied Geology, Curtin University, Perth, WA 6845, Australia

The U-Pb systems of apatite and merrillite grains within four separate Apollo 14 impact melt breccia samples were analysed by secondary ion mass spectrometry. No systematic difference was identified between the 207Pb/206Pb ages of the apatites and merrillites. A combined 207Pb/206Pb age of 3927±2 Ma (95% conf.) is determined for three of these samples (14305,103: 3926±4 Ma; 14306,150: 3926±6 Ma; 14314,13: 3929±4 Ma). By combining these data with the ages previously obtained for zircons in Apollo 12 impact melt breccia fragments and the lunar meteorite SaU 169, a weighted average age of 3926±2 Ma (95% conf.) is obtained, which is attributed to the formation of the Imbrium basin. An age of 3943±5 Ma is determined for the fourth breccia (14321,134), which is similar to ages of 3946±15 Ma and 3958±19 Ma, obtained from several older phosphates in 14305,103 and 14314,13. The weighted average of these three older ages is 3944±4 Ma (95% conf.). This is indistinguishable to the age (3938±4 Ma; 2σ) obtained for a different Apollo 14 impact melt breccia in a previous study. After investigating likely sources for this older ∼3940 Ma age, we conclude that the Humorum or Serenitatis basin forming events are likely candidates. The potential identification of two large impact events within ∼15 Myrs has important implications for the rate of lunar bombardment around 3.95-3.92 Ga. This study demonstrates the importance of high-precision age determinations for interpreting the impact record of the Moon, as documented in lunar samples.

Reference
Snape SF, Nemchin AA, Grange ML, Bellucci JJ, Thiessen F, Whitehouse MJ (2015) Phosphate ages in Apollo 14 breccias: Resolving multiple impact events with high precision U-Pb SIMS analyses. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.11.005]
Copyright Elsevier

^1,2K.R. Bermingham, ^1,3K. Mezger, ¹E.E. Scherer, ⁴M. Horan, ⁴R. Carlson, ^1,5D. Upadhyay, ^1,6T. Magna,⁷A. Pack
¹Institut für Mineralogie, Westfälische Wilhelms-Universität, Corrensstraße 24, 48149 Münster, Germany
²Isotope Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD-20740 USA
³Institut für Geologie, Universität Bern, Baltzerstrasse 1 + 3, 3012 Bern, Switzerland
⁴Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road NW, Washington DC 20015 USA
⁵Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, 721302, Kharagpur, India
⁶Czech Geological Survey, Klárov 3, 11821 Prague 1, Czech Republic
⁷Geowissenschaftliches Zentrum, Georg-August-Universität, Goldschmidtstraße 1, 37077 Göttingen, Germany

Several nucleosynthetic processes contributed material to the Solar System; however, the relative contributions of each process, the timing of their input into the solar nebula, and how well these components were homogenized in the solar nebula remain only partially constrained. The Ba isotope system is particularly useful in addressing these issues because Ba contains isotopes are synthesized through three nucleosynthetic processes (s-, r-, p-process). In this study, high precision Ba isotope analyses of 22 different whole rock chondrites and achondrites (carbonaceous chondrites, ordinary chondrites, enstatite chondrites, Martian meteorites, and eucrites) were performed to constrain the distribution of Ba isotopes on the regional scale in the Solar System. A melting method using aerodynamic levitation and CO2-laser heating was used to oxidize SiC, a primary carrier of Ba among presolar grains in carbonaceous chondrites. Destruction of these grains during the fusion process enabled the complete digestion of these samples. The Ba isotope data presented here are thus the first for which complete dissolution of the bulk meteorite samples was certain. Enstatite chondrites, ordinary chondrites, and all achondrites measured here possess Ba isotope compositions that are not resolved from the terrestrial Ba isotope composition. Barium isotope anomalies are evident in most of the carbonaceous chondrites analyzed, but the 135Ba anomalies are generally smaller than previously reported for similarly sized splits of CM2 meteorites. Variation in the size of the 135Ba anomaly is also apparent in fused samples from the same parent body (e.g., CM2 meteorites) and in different pieces from the same meteorite (e.g., Orgueil, CI). Here, we investigate the potential causes of variability in 135Ba, including the contribution of radiogenic 135Ba from the decay of 135Cs and incomplete homogenization of the presolar components on the

Reference
Bermingham KR,Mezger K,Scherer EE, Horan M,Carlson R, Upadhyay D, Magna T,Pack A (2015) Barium Isotope Abundances in Meteorites and Their Implications for Early Solar System Evolution. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.11.006]

Copyright Elsevier

¹D. J. Wilson, ¹B. T. Gänsicke, ²D. Koester, ¹O. Toloza, ¹A. F. Pala, ¹E. Breedt,³S. G. Parsons
¹Department of Physics, University of Warwick, Coventry CV4 7AL, UK
²Institut für Theoretische Physik und Astrophysik, University of Kiel, D-24098 Kiel, Germany
³Departamento de Física y Astronomía, Universidad de Valparaíso, Avenida Gran Bretaña 1111, Valparaíso 2360102, Chile

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

Reference
Wilson DJ, Gänsicke BT, Koester D, Toloza O, Pala AF, Breedt E, Parsons SG (2015) The composition of a disrupted extrasolar planetesimal at SDSS J0845+2257 (Ton 345). Monthly Notices of the Royal Astronomical Society 451, 3237-3248.
Link to Article [doi: 10.1093/mnras/stv1201]

^1,2,6Lydia J. Hallis, ^1,2Gary R. Huss, ²Kazuhide Nagashima, ^1,2G. Jeffrey Taylor, ³Sæmundur A. Halldórsson, ³David R. Hilton, ⁴Michael J. Mottl, ^1,5Karen J. Meech
¹NASA Astrobiology Institute, Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822-1839, USA.
²Hawai’i Institute of Geophysics and Planetology, Pacific Ocean Science and Technology (POST) Building, University of Hawai’i, 1680 East-West Road, Honolulu, HI 96822, USA.
³Scripps Institution of Oceanography, University California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0244, USA.
⁴Department of Oceanography, University of Hawai’i, Marine Sciences Building 304, 1000 Pope Road, Honolulu, HI 96822, USA.
⁵Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA.
⁶School of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lillybank Gardens, Glasgow G12 8QQ, UK.

The hydrogen-isotope [deuterium/hydrogen (D/H)] ratio of Earth can be used to constrain the origin of its water. However, the most accessible reservoir, Earth’s oceans, may no longer represent the original (primordial) D/H ratio, owing to changes caused by water cycling between the surface and the interior. Thus, a reservoir completely isolated from surface processes is required to define Earth’s original D/H signature. Here we present data for Baffin Island and Icelandic lavas, which suggest that the deep mantle has a low D/H ratio (δD more negative than –218 per mil). Such strongly negative values indicate the existence of a component within Earth’s interior that inherited its D/H ratio directly from the protosolar nebula.

Reference
Hallis LJ, Huss GR, Nagashima K, Taylor GJ, Halldórsson SA, Hilton DR, Mottl MJ, Meech KJ (2015)Evidence for primordial water in Earth’s deep mantle. Science 350, 795-797.
Link to Article [DOI: 10.1126/science.aac4834]
Reprinted with permission by AAAS