¹Michael T. Thorpe,¹A. Deanne Rogers,²Thomas F. Bristow,¹Cong Pan
¹Department of Geosciences, State University of New York at Stony Brook University, Stony Brook, NY, USA
²NASA Ames Research Center, Moffett Field, CA

Thermal emission spectroscopy is used to determine the mineralogy of sandstone and mudstone rocks as part of an investigation of linear spectral mixing between sedimentary constituent phases. With widespread occurrences of sedimentary rocks on the surface of Mars, critical examination of the accuracy associated with quantitative models of mineral abundances derived from thermal emission spectra of sedimentary materials is necessary. Though thermal emission spectroscopy has been previously proven to be a viable technique to obtain quantitative mineralogy from igneous and metamorphic materials, sedimentary rocks, with natural variation of composition, compaction, and grain size, have yet to be examined. In this work, we present an analysis of the thermal emission spectral (~270-1650 cm−1) characteristics of a suite of 13 sandstones and 14 mudstones. X-ray diffraction and traditional point counting procedures were all evaluated in comparison with thermal emission spectroscopy. Results from this work are consistent with previous thermal emission spectroscopy studies and indicate that bulk rock mineral abundances can be estimated within 11.2 % for detrital grains (i.e., quartz and feldspars) and 14.8 % for all other mineral phases present in both sandstones and mudstones, in comparison to common in situ techniques used for determining bulk rock composition. Clay-sized to fine silt-sized grained phase identification is less accurate, with differences from the known ranging from ~5-24% on average. Nevertheless, linear least squares modeling of thermal emission spectra is an advantageous technique for determining abundances of detrital grains and sedimentary matrix, and for providing a rapid classification of clastic rocks.

Reference
Thorpe MT, Rogers AD, Bristow TF, Pan C (2015) Quantitative Compositional Analysis of Sedimentary Materials Using Thermal Emission Spectroscopy: 1. Application to Sedimentary Rocks. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004863]
Published by arrangement with John Wiley & Sons

^1,2,3S. Goderis, ³A.D. Brandon, ⁴B. Mayer, ⁴M. Humayun
¹Earth System Science, Vrije Universiteit Brussel, Brussels, Belgium
²Department of Analytical Chemistry, Ghent University, Ghent, Belgium
³Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA
⁴National High Magnetic Field Laboratory and Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, FL, USA

Ubiquitous nucleosynthetic isotope anomalies relative to the terrestrial isotopic composition in Mo, Ru, and other elements are known from both bulk chondrites and differentiated meteorites, but Os isotope ratios reported from such meteorites have been found to be indistinguishable from the terrestrial value. The carriers of s- and r-process Os must thus have been homogeneously distributed in the solar nebula. As large Os isotope anomalies are known from acid leachates and residues of primitive chondrites, the constant relative proportions of presolar s- and r-process carriers in such chondrites must have been maintained during nebular processes. It has long been assumed that partial melting of primitive chondrites would homogenize the isotopic heterogeneity carried by presolar grains. Here, ureilites, carbon-rich ultramafic achondrites dominantly composed of olivine and low-Ca pyroxene, are shown to be the first differentiated bulk Solar System materials for which nucleosynthetic Os isotope anomalies have been identified. These anomalies consist of enrichment in s-process Os heterogeneously distributed in different ureilites. Given the observed homogeneity of Os isotopes in all types of primitive chondrites, this Os isotope variability among ureilites must have been caused by selective removal of s-process-poor Os host phases, probably metal, during rapid localized melting on the ureilite parent body. While Mo and Ru isotope anomalies for all meteorites measured so far exhibit s-process deficits relative to the Earth, the opposite holds for the Os isotope anomalies in ureilites reported here. This might indicate that the Earth preferentially accreted olivine-rich restites and inherited a s-process excess relative to smaller meteorite bodies, consistent with Earth’s high Mg/Si ratio and enrichment of s-process nuclides in Mo, Ru, and Nd isotopes. Our new Os isotope results imply that caution must be used when applying nucleosynthetic isotope anomalies as provenance indicators between different classes of meteorites.

Reference
Goderis S, Brandon AD, Mayer B, Humayun M (2015) s-Process Os isotope enrichment in ureilites by planetary processing. Earth and Planetary Science Letters 431, 110–118
Link to Article [doi:10.1016/j.epsl.2015.09.021]
Copyright Elsevier

¹Evelyn Füri, ^2,3Peter H. Barry, ²Lawrence A. Taylor, ¹Bernard Marty
¹Centre de Recherches Pétrographiques et Géochimiques, CNRS-UL, 15 rue Notre Dame des Pauvres, BP 20, 54501 Vandoeuvre-lès-Nancy, France
²Planetary Geosciences Institute, Department of Earth Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, USA
³Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, UK

Nitrogen and noble gas (Ne–Ar) abundances and isotope ratios, determined by step-wise CO2 laser-extraction, static-mass spectrometry analysis, are reported for bulk fragments and mineral separates of ten lunar mare basalts (10020, 10057, 12008, 14053, 15555, 70255, 71557, 71576, 74255, 74275), one highland breccia (14321), and one ferroan anorthosite (15414). The mare basalt sub-samples 10057,183 and 71576,12 contain a large amount of solar noble gases, whereas neon and argon in all other samples are purely cosmogenic, as shown by their 21Ne/22Ne ratios of ≈0.85 and 36Ar/38Ar ratios of ≈0.65. The solar-gas-free basalts contain a two-component mixture of cosmogenic 15N and indigenous nitrogen ((<0.5 ppm). Mare basalt 74255 and the olivine fraction of 15555,876 record the smallest proportion of ¹⁵N_cosm; therefore, their δ¹⁵Nδ15N values of −0.2 to +26.7‰+26.7‰ (observed at the low-temperature steps) are thought to well represent the isotopic composition of indigenous lunar nitrogen. However, δ¹⁵Nδ15N values ≤−30‰≤−30‰ are found in several basalts, overlapping with the isotopic signature of Earth’s primordial mantle or an enstatite chondrite-like impactor. While the lowest δ¹⁵Nδ15N values allow for nitrogen trapped in the Moon’s interior to be inherited from the proto-Earth and/or the impactor, the more ¹⁵N-enriched compositions require that carbonaceous chondrites provided nitrogen to the lunar magma ocean prior to the solidification of the crust. Since nitrogen can efficiently be incorporated into mafic minerals (olivine, pyroxene) under oxygen fugacities close to or below the iron-wustite buffer (Li et al., 2013), the mare basalt source region is likely characterized by a high nitrogen storage capacity. In contrast, anorthosite 15414 shows no traces of indigenous nitrogen, suggesting that nitrogen was not efficiently incorporated into the lunar crust during magma ocean Differentiation.

Reference
Füri E, Barry PH, Taylor LA, Marty B (2015) Indigenous nitrogen in the Moon: Constraints from coupled nitrogen–noble gas analyses of mare basalts. Earth and Planetary Science Letters 431, 195–205
Link to Article [doi:10.1016/j.epsl.2015.09.022]
Copyright Elsevier

Paul R. Renne^1,2, Courtney J. Sprain^1,2, Mark A. Richards², Stephen Self², Loÿc Vanderkluysen³, Kanchan Pande^4
11Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA.
²Department of Earth and Planetary Science, University of California–Berkeley, Berkeley, CA 94720, USA.
³Department of Biodiversity, Earth and Environmental Science, Drexel University, Philadelphia, PA 19104, USA.
⁴Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India.

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Reference
Renne PR, Sprain CJ, Richards MA, Self S, Vanderkluysen L, Pande K (2015) State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact. Science 6256:76-78.
Link to Article [doi:10.1126/science.aac7549]

Lujendra Ojha¹, Mary Beth Wilhelm^1,2, Scott L. Murchie³, Alfred S. McEwen⁴, James J. Wray¹, Jennifer Hanley⁵, Marion Massé⁶ & Matt Chojnacki^4
1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 30308, USA
²Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, California 94035, USA
³Applied Physics Laboratory, Laurel, Maryland 20723, USA
⁴Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA
⁵Department of Space Studies, Southwest Research Institute, Boulder, Colorado 80302, USA
⁶Laboratoire de Planétologie et Géodynamique, Nantes 44322, France

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Reference
Ojha L, Wilhelm MB, Munchie SL, McEwen AS, Wray JJ, Hanley J, Massé M & Chojnacki M (2015) Spectral evidence for hydrated salts in recurring slope lineae on Mars. Nature Geoscience 8 (in press).
Link to Article [doi:10.1038/ngeo2546]

Diane T. Wetzel¹, Erik H. Hauri², Alberto E. Saal¹ & Malcolm J. Rutherford^1
1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA
²Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC 20015, USA

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Reference
Wetzel DT, Hauri EH, Saal AE & Rutherford MJ (2015) Carbon content and degassing history of the lunar volcanic glasses. Nature Geoscience 8:755–758.
Link to Article [doi:10.1038/ngeo2511]

Bruno Scaillet
Bruno Scaillet is at Institut des Sciences de la Terre d’Orléans, CNRS/Université d’Orléans/BRGM, 1a Rue de la Férollerie 45071, Orléans, France

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Reference
Scaillet B (2015) Planetary science: Carbon in the Moon. Nature Geoscience 8:747–748.
Link to Article [doi:10.1038/ngeo2530]

H. Leroux^a, P. Cuvillier^a, B. Zanda^b, R.H. Hewins^b
aUnité Matériaux et Transformations, Université Lille 1 & CNRS, 59655 Villeneuve d’Ascq, France
^bInstitut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Universités, Muséum National d’Histoire Naturelle, UPMC Université Paris 06, UMR CNRS 7590, IRD UMR 206, 57 rue Cuvier, 75231 Paris, France

The Paris meteorite is a weakly altered CM chondrite that has been discovered recently (Hewins et al. 2014). Its matrix offers the opportunity to search for well-preserved pristine pre-accretional material, as well as to study the earliest stages of aqueous alteration in the CM parent body. The study of the matrix of Paris has been conducted by analytical transmission electron microscopy on focused ion beam sections extracted from matrix areas showing different degrees of aqueous alteration.

The least altered matrix sample consists of amorphous silicate grains, a few hundreds of nm in size, separated from one another by an abundant porosity. The amorphous silicates enclose numerous Fe-sulfide nanograins and their average composition is close to the chondritic composition. They share many similarities with GEMS (glass with embedded metal and sulfides) grains present in chondritic-porous interplanetary dust particles and with primitive type 3.0 carbonaceous chondrites. This first discovery of GEMS-like texture in a CM chondrite suggests that GEMS grains could have been the building blocks of the CM matrices.

In more aqueously altered samples, pronounced microstructural heterogeneities were detected at the micrometer scale. The matrix consists mostly of a mixture of amorphous material and Fe-rich, spongy to fine-fibrous, poorly crystalline phyllosilicates. The porosity fraction is significantly reduced and the mixed amorphous-fibrous material frequently forms a continuous groundmass. The close association between these two material types suggests a replacement mechanism due to aqueous alteration. Chemical compositions correlate strongly with the microstructure. The amorphous material has a composition close to the chondritic value while the fine-fibrous phyllosilicate material is Fe-enriched. This Fe enrichment is found to be continuous from weakly to more heavily altered areas, in which the fibrous morphology is coarser and better crystalline. Cronstedtite with intercalated tochilinite is also found, but in pore spaces. This chemical evolution, concomitant with the maturation of the phyllosilicates, demonstrates that the early aqueous fluids that interacted with silicates in the matrix were enriched in Fe. This composition is probably the consequence of the preferential dissolution of metal and iron sulfides during the first stages of alteration. The enrichment of phyllosilicates in Mg seen in more altered CM chondrites is not observed in Paris.

Reference
Leroux H, Cuvillier P, Zanda B and Hewins RH (2015) GEMS-like material in the matrix of the Paris meteorite and the early stages of alteration of CM chondrites. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.09.019]
Copyright Elsevier

V. Adibekyan¹, N. C. Santos^1,2, P. Figueira¹, C. Dorn³, S. G. Sousa¹, E. Delgado-Mena¹, G. Israelian^4,5, A. A. Hakobyan⁶ and C. Mordasini^3
1Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
²Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
³Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
⁴Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
⁵Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁶Byurakan Astrophysical Observatory, 0213 Byurakan, Aragatsotn province, Armenia

Aims. The main goal of this work is to study element ratios that are important for the formation of planets of different masses.
Methods. We study potential correlations between the existence of planetary companions and the relative elemental abundances of their host stars. We use a large sample of FGK-type dwarf stars for which precise Mg, Si, and Fe abundances have been derived using HARPS high-resolution and high-quality data.
Results. A first analysis of the data suggests that low-mass planet host stars show higher [Mg/Si] ratios, while giant planet hosts present [Mg/Si] that is lower than field stars. However, we found that the [Mg/Si] ratio significantly depends on metallicity through Galactic chemical evolution. After removing the Galactic evolution trend only the difference in the [Mg/Si] elemental ratio between low-mass planet hosts and non-hosts was present in a significant way. These results suggest that low-mass planets are more prevalent around stars with high [Mg/Si].
Conclusions. Our results demonstrate the importance of Galactic chemical evolution and indicate that it may play an important role in the planetary internal structure and composition. The results also show that abundance ratios may be a very relevant issue for our understanding of planet formation and evolution.

Reference
Adibekyan V, Santos NC, Figueira P, Dorn C, Sousa SG, Delgado-Mena E, Israelian G, Hakobyan AA and Mordasini C (2015) From stellar to planetary composition: Galactic chemical evolution of Mg/Si mineralogical ratio. Astronomy & Astrophysics 581:L2.
Link to Article [doi:10.1051/0004-6361/201527059]

V. Alí-Lagoa, M. Delbo’, and G. Libourel
Laboratoire Lagrange, UMR7293, Université de la Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, F-06304 Nice Cedex 4, France

The so-called “early activity” of comet 67P/Churyumov–Gerasimenko has been observed to originate mostly in parts of the concave region or “neck” between its two lobes. Since activity is driven by the sublimation of volatiles, this is a puzzling result because this area is less exposed to the Sun and is therefore expected to be cooler on average. We used a thermophysical model that takes into account thermal inertia, global self-heating, and shadowing, to compute surface temperatures of the comet. We found that, for every rotation in the 2014 August–December period, some parts of the neck region undergo the fastest temperature variations of the comet’s surface precisely because they are shadowed by their surrounding terrains. Our work suggests that these fast temperature changes are correlated to the early activity of the comet, and we put forward the hypothesis that erosion related to thermal cracking is operating at a high rate on the neck region due to these rapid temperature variations. This may explain why the neck contains some ice—as opposed to most other parts of the surface—and why it is the main source of the comet’s early activity. In a broader context, these results indicate that thermal cracking can operate faster on atmosphereless bodies with significant concavities than implied by currently available estimates.

Reference
Alí-Lagoa V, Delbo’ M and Libourel G (2015) Rapid temperature changes and the early activity on comet 67P/Churumov-Gerasimenko. Astrophysical Journal – Letters 811:L22.
Link to Article [doi:10.1088/2041-8205/810/2/L22]