⁵D. Schwander, ^2,3,4L. Kööp, ¹T. Berg, ⁵G. Schönhense, ^2,3,4P.R. Heck, ^2,3,4,5A.M. Davis, ^1,6,7U. Ott
¹Institut für Physik, Johannes Gutenberg-Universität, Staudingerweg 7, D-55128 Mainz, Germany
²Department of the Geophysical Sciences, The University of Chicago, Chicago, IL, United States
³Chicago Center for Cosmochemistry, The University of Chicago, Chicago, IL, United States
⁴Robert A. Pritzker Center for Meteoritics and Polar Studies, Field Museum of Natural History, Chicago, IL, United States
⁵Enrico Fermi Institute, The University of Chicago, Chicago, IL, United States
⁶University of West Hungary, H-9700 Szombathely, Hungary
⁷Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, D-55128 Mainz, Germany

Ca, Al-rich inclusions (CAIs) often contain numerous refractory metal nuggets (RMNs), consisting of elements like Os, Ir, Mo, Pt and Ru. The nuggets are usually thought to have formed by equilibrium condensation from a gas of solar composition, simultaneously with or prior to oxide and silicate minerals. However, the exact mechanisms responsible for their extremely variable compositions, small sizes and associations with CAI minerals remain puzzling. Expanding on previous work on chemically separated RMNs, we have studied a large number of RMNs within their host CAIs from three different meteorite types, i.e., the highly primitive chondrite Acfer 094, Allende (CV3ox) and Murchison (CM2). Our results show several inconsistencies between the observed features and a direct condensation origin, including a lack of correlated abundance variations in the refractory metals that is expected from variations in condensation temperature. Instead, we show that most RMN features are consistent with RMN formation by precipitation from a CAI liquid enriched in refractory metals. This scenario is additionally supported by the common occurrence of RMNs in CAIs with clear melt crystallization textures as well as the occurrence of synthetic RMNs with highly variable compositions in run products from Schwander et al. (2015). In some cases, the sizes of meteoritic RMNs correlate with the sizes of their host minerals in CAIs, which indicates common cooling rates.

Reference
Schwander D, Kööp L, Berg T, Schönhense G, Heck PR, Davis AM, Ott U (2015) Formation of refractory metal nuggets and their link to the history of CAIs. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.07.014]

Copyright Elsevier

^1,2,3Kasia Biron, ^1,2Sylvie Derenne, ³François Robert, ⁴Jean-Noël Rouzaud
¹CNRS, UMR 7619 METIS, Paris, France
²Sorbonne Universités, UPMC Univ Paris 06, CNRS, EPHE, UMR 7619 METIS, Paris, France
³IMPMC, CNRS/MNHN UMR 7202, Paris, France
⁴Laboratoire de Géologie, ENS/CNRS UMR 8538, Paris, France

Based on the statistical model proposed for the molecular structure of the insoluble organic matter (IOM) isolated from the Murchison meteorite, it was recently proposed that, in the solar T-Tauri disk regions where (photo)dissociation of gaseous molecules takes place, aromatics result from the cyclization/aromatization of short aliphatics. This hypothesis is tested in this study, with n-alkanes being submitted to high-frequency discharge at low pressure. The contamination issue was eliminated using deuterated precursor. IOM was formed and studied using solid-state nuclear magnetic resonance, pyrolysis coupled to gas chromatography and mass spectrometry, RuO4 oxidation, and high-resolution transmission electron microscopy. It exhibits numerous similarities at the molecular level with the hydrocarbon backbone of the natural IOM, reinforcing the idea that the initial precursors of the IOM were originally chains in the gas. Moreover, a fine comparison between the chemical structure of several meteorite IOM suggests either that (i) the meteorite IOMs share a common precursor standing for the synthetic IOM or that (ii) the slight differences between the meteorite IOMs reflect differences in their environment at the time of their formation i.e., related to plasma temperature that, in turn, dictates the dissociation–recombination rates of organic fragments.

Reference
Biron K, Derenne S, Robert F, Rouzaud J-N (2015) Toward an experimental synthesis of the chondritic insoluble organic matter. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12477]

Published by arrangement with John Wiley & Sons

¹Charles A Schambeau, ¹Yanga R. Fernández, ²Carey M. Lisse, ³Nalin Samarasinha, ⁴Laura M. Woodney
¹Department of Physics, University of Central Florida, Orlando, FL 32816, USA
²Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723
³Planetary Science Institute, Tucson, AZ 85719, USA
⁴Department of Physics, California State University San Bernardino, San Bernardino, CA 92407

We present a new analysis of Spitzer observations of comet 29P/Schwassmann-Wachmann 1 taken on UT 2003 November 21, 23, and 24, similar to a previous investigation of the observations (Stansberry et al., 2004), but using the most recent Spitzer data pipeline products and intensive image processing techniques. Analysis of images from the IRAC 5.8 & 8.0 μμm bands and the MIPS 24.0 & 70.0 μμm bands resulted in photometry measurements of the nucleus after a suite of coma modeling and removal processes were implemented. SW1 was not identified in the 5.8 μμm image from the previous work so its incorporation into this analysis is entirely new. Using the Near Earth Asteroid Thermal Model ( Harris, 1998) resulted in a nucleus radius measurement of R = View the MathML source30.2-2.9+3.7 km and an infrared beaming parameter value of View the MathML sourceη=0.99-0.19+0.26. We also measured an infrared geometric albedo, p5.8p5.8 = 0.5 ±± 0.5. Extrapolating a 0.04 V-band albedo and using a normalized reflectivity gradient S′=14.94±1.09S′=14.94±1.09 [% (1000 Å)−1] ( Duffard et al., 2014) we recover an infrared albedo of p5.8p5.8 = 0.31 in the near infrared consistent with the value recovered from thermal modeling. The dust composition extracted from IRS spectra are very comet-like, containing mainly amorphous ferromagnesian silicates (but with a minority of crystalline silicates as well), water ice, and metal sulfides.

Reference
Schambeau CA, Fernández YR, Lisse CM, Samarasinha N, Woodney LM (2015) A New Analysis of Spitzer Observations of Comet 29P/Schwassmann-Wachmann 1. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.038]
Copyright Elsevier

¹V. Sautter et al. (>10)*
¹IMPMC, Muséum d’Histoire Naturelle, 75005 Paris, France

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

Reference
Sautter V et al. (2015) In situ evidence for continental crust on early Mars. Nature Geoscience (in Press)
Link to Article [doi:10.1038/ngeo2474]

¹Stephen M. Seddio, ¹Randy L. Korotev, ¹Bradley L. Jolliff, ¹Alian Wang
¹Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St. Louis, Missouri 63130, U.S.A.

Granitic lunar samples largely consist of granophyric intergrowths of silica and K-feldspar. The identification of the silica polymorph present in the granophyre can clarify the petrogenesis of the lunar granites. The presence of tridymite or cristobalite would indicate rapid crystallization at high temperature. Quartz would indicate crystallization at low temperature or perhaps intrusive, slow crystallization, allowing for the orderly transformation from high-temperature silica polymorphs (tridymite or cristobalite). We identify the silica polymorphs present in four granitic lunar samples from the Apollo 12 regolith using laser Raman spectroscopy. Typically, lunar silica occurs with a hackle fracture pattern. We did an initial density calculation on the hackle fracture pattern of quartz and determined that the volume of quartz and fracture space is consistent with a molar volume contraction from tridymite or cristobalite, both of which are less dense than quartz. Moreover, we analyzed the silica in the granitic fragments from Apollo 12 by electron-probe microanalysis and found it contains up to 0.7 wt% TiO2, consistent with initial formation as the high-temperature silica polymorphs, which have more open crystal structures that can more readily accommodate cations other than Si. The silica in Apollo 12 granitic samples crystallized rapidly as tridymite or cristobalite, consistent with extrusive volcanism. The silica then inverted to quartz at a later time, causing it to contract and fracture. A hackle fracture pattern is common in silica occurring in extrusive lunar lithologies (e.g., mare basalt). The extrusive nature of these granitic samples makes them excellent candidates to be similar to the rocks that compose positive relief silicic features such as the Gruithuisen Domes.

Reference
Seddio SM, Korotev RL, Jolliff BL, Wang A (2015) Silica polymorphs in lunar granite: Implications for granite petrogenesis on the Moon. American Mineralogist 100, 1533-1543
Link to Article [doi: 10.2138/am-2015-5058]

Copyright : The American Mineralogical Society

¹Franck Poitrasson, ¹Thomas Zambardi
¹Laboratoire Géosciences Environnement Toulouse, CNRS UMR 5563 – UPS – IRD, 14-16, avenue Edouard Belin, 31400 Toulouse, France

A comparison between lunar and terrestrial igneous rocks reveals that Si isotope compositions become slightly, though significantly enriched in heavy isotopes from basalts to granites as a function of the rock SiO2 concentration and/or tectosilicate content. This is interpreted as the result of a global igneous differentiation process that leads to an increased amount of tectosilicates in the rocks. This relationship of increasing degree of melt polymerization with increasing silicon isotope composition is particularly apparent in lunar rocks. The terrestrial trend, however, is more scattered. Given the sensitivity of Si isotopes to water-rock interactions, it is likely that the more erratic terrestrial trend reveals the involvement of water that does not occur on the Moon. Hence, Si isotopes appear to reflect the occurrence of low temperature water-rock interaction products, like clay minerals, in the source of peraluminous leucogranites. Conversely, the heavy silicon isotope composition of some andesites possibly trace the input of fluids involved in subduction zones and/or interaction of the oceanic crust with isotopically heavy seawater before subduction.

Reference
Poitrasson F, Zambardi T (2015) An Earth-Moon silicon isotope model to track silicic magma origins. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.07.005]

Copyright Elsevier

¹Reto Gieré, ²Wolfhard Wimmenauer, ²Hiltrud Müller-Sigmund, ³Richard Wirth, ⁴Gregory R. Lumpkin, ⁵Katherine L. Smith
¹Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6316, U.S.A.
²Institut für Geo- und Umweltnaturwissenschaften, Albert-Ludwigs-Universität, 79104 Freiburg, Germany
³GeoForschungsZentrum Potsdam, Department 4, Telegrafenberg, 14473 Potsdam, Germany
⁴Institute of Materials Engineering, ANSTO, Private Mail Bag 1, Menai, New South Wales 2234, Australia
⁵International Relations, ANSTO, P.O. Box 2001, Kirrawee DC, New South Wales 2232, Australia

Using transmission electron microscopy we show that planar deformation lamellae occur within quartz in the substrate of a rock fulgurite, i.e., a lightning-derived glass. These lamellae exist only in a narrow zone adjacent to the quartz/fulgurite boundary and are comparable to planar deformation features (“shock lamellae”) caused by hypervelocity impacts of extra-terrestrial objects. Our observations strongly suggest that the lamellae described here have been formed as a result of the fulgurite-producing lightning strike. This event must have generated a transient pressure pulse, whose magnitude, however, is uncertain at this stage.

Reference
Gieré R, Wimmenauer W, Müller-Sigmund H, Wirth R, Lumpkin GR, Smith KL (2015) Lightning-induced shock lamellae in quartz. American Mineralogist 100, 1645-1648
Link to Article [doi: 10.2138/am-2015-5218]

Copyright: The Mineralogical Society of America

¹Leslie Hsu, ¹Kerstin A. Lehnert, ¹Andrew Goodwillie, ²John W. Delanob, ³James B. Gill, ⁴Maurice A. Tivey, ¹Vicki L. Ferrini, ¹Suzanne M. Carbotte, ¹Robert A. Arko
¹Geoinformatics Center, Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, USA
²Department of Chemistry, University at Albany (SUNY), Albany, NY 12222, USA
³Department of Earth and Planetary Sciences, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA
⁴Woods Hole Oceanographic Institution, 266 Woods Hole Rd., MS #22, Woods Hole, MA 02543, USA

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

Reference
Hsu L, Lehnert KA, Goodwillie A, Delano JW, Gill JB, Tivey MA, Ferrini VL, Carbotte SM, Arko RA (2015) Rescue of long-tail data from the ocean bottom to the Moon: IEDA Data Rescue Mini-Awards. GeoResJ 6, 108–114
Link to Article [doi:10.1016/j.grj.2015.02.012]

¹M. E. Varela, ²P. Sylvester, ³F. Brandstätter, ⁴A. Engler
¹Instituto de Ciencias Astronómicas de la Tierra y del Espacio (ICATE), San Juan, Argentina
²Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada
³Mineralogisch-Petrographische Abteilung, Naturhistorisches Museum, Wien, Austria
⁴Institute of Earth Sciences, Department of Mineralogy and Petrology, University of Graz, Graz, Austria

Sixteen nonporphyritic chondrules and chondrule fragments were studied in polished thin and thick sections in two enstatite chondrites (ECs): twelve objects from unequilibrated EH3 Sahara 97158 and four objects from equilibrated EH4 Indarch. Bulk major element analyses, obtained with electron microprobe analysis (EMPA) and analytical scanning electron microscopy (ASEM), as well as bulk lithophile trace element analyses, determined by laser ablation inductively coupled plasma–mass spectrometry (LA-ICP-MS), show that volatile components (K2O + Na2O versus Al2O3) scatter roughly around the CI line, indicating equilibration with the chondritic reservoir. All lithophile trace element abundances in the chondrules from Sahara 97158 and Indarch are within the range of previous analyses of nonporphyritic chondrules in unequilibrated ordinary chondrites (UOCs). The unfractionated (solar-like) Yb/Ce ratio of the studied objects and the mostly unfractionated refractory lithophile trace element (RLTE) abundance patterns indicate an origin by direct condensation. However, the objects possess subchondritic CaO/Al2O3 ratios; superchondritic (Sahara 97158) and subchondritic (Indarch) Yb/Sc ratios; and chondritic-normalized deficits in Nb, Ti, V, and Mn relative to RLTEs. This suggests a unique nebular process for the origin of these ECs, involving elemental fractionation of the solar gas by the removal of oldhamite, niningerite, and/or another phase prior to chondrule condensation. A layered chondrule in Sahara 97158 is strongly depleted in Nb in the core compared to the rim, suggesting that the solar gas was heterogeneous on the time scales of chondrule formation. Late stage metasomatic events produced the compositional diversity of the studied objects by addition of moderately volatile and volatile elements. In the equilibrated Indarch chondrules, this late process has been further disturbed, possibly by a postaccretional process (diffusion?) that preferentially mobilized Rb with respect to Cs in the studied objects.

Reference
Varela ME, Sylvester P, Brandstätter F, Engler A (2015) Nonporphyritic chondrules and chondrule fragments in enstatite chondrites: Insights into their origin and secondary processing. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12468]

Published by arrangement with John Wiley&Sons

¹M. R. Lee, ²I. MacLaren, ²S. M. L. Andersson, ³A. Kovács, ^1,4T. Tomkinson, ⁴D. F. Mark, ⁵C. L. Smith
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK
²SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, UK
³Ernst Ruska-Centrum für Mikroskopie und Spektroskopie mit Elektronen, Forschungszentrum Jülich GmbH, Jülich, Germany
⁴Scottish Universities Environmental Research Centre, East Kilbride, UK
⁵Department of Earth Sciences, Natural History Museum, London, UK

The nakhlite meteorites are clinopyroxenites that are derived from a ~1300 million year old sill or lava flow on Mars. Most members of the group contain veins of iddingsite whose main component is a fine-grained and hydrous Fe- and Mg-rich silicate. Siderite is present in the majority of veins, where it straddles or cross-cuts the Fe-Mg silicate. This carbonate also contains patches of ferric (oxy)hydroxide. Despite 40 years of investigation, the mineralogy and origins of the Fe-Mg silicate is poorly understood, as is the paragenesis of the iddingsite veins. Nanometer-scale analysis of Fe-Mg silicate in the Nakhla meteorite by electron and X-ray imaging and spectroscopy reveals that its principal constituents are nanoparticles of opal-A. This hydrous and amorphous phase precipitated from acidic solutions that had become supersaturated with respect to silica by dissolution of olivine. Each opal-A nanoparticle is enclosed within a ferrihydrite shell that formed by oxidation of iron that had also been liberated from the olivine. Siderite crystallized subsequently and from solutions that were alkaline and reducing, and replaced both the nanoparticles and olivine. The fluids that formed both the opal-A/ferrihydrite and the siderite were sourced from one or more reservoirs in contact with the Martian atmosphere. The last event recorded by the veins was alteration of the carbonate to a ferric (oxy)hydroxide that probably took place on Mars, although a terrestrial origin remains possible. These results support findings from orbiter- and rover-based spectroscopy that opaline silica was a common product of aqueous alteration of the Martian crust.

Reference
Lee MR, MacLaren I, Andersson SML, Kovács A, Tomkinson T, Mark DF, Smith CL (2015) Opal-A in the Nakhla meteorite: A tracer of ephemeral liquid water in the Amazonian crust of Mars. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12471]
Published by Arrangement with John Wiley&Sons