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

¹Ted L. Roush, ^1,2Janice L. Bishop, ^1,2Adrian J. Brown, ¹David F. Blake, ¹Thomas F. Bristow
¹NASA Ames Research Center, Moffett Field, CA 94035-0001
²SETI Institute, Mountain View, CA

Quantitative estimates of clay minerals on the martian surface, via remote sensing observations, provide constraints on activity, timing, duration, and extent of aqueous processes and the geochemical environment in martian history. We describe an analytical study to begin enabling quantitative estimates of phyllosilicates when mixed with martian analog materials. We characterize the chemistry, mineralogy, particle size distribution, and reflectance spectra of the end-member materials: saponite, montmorillonite, pyroxene, and palagonitic soil. Reflectance spectra were obtained for physical mixtures of saponite and montmorillonite with pyroxene, and saponite with palagonitic soil. We analyzed the diagnostic phyllosilicate spectral signatures in the 2.2-2.4 μm wavelength region in detail for the mixtures. This involved fitting the observed ∼2.3 or ∼2.2 μm band depth, associated with the presence of saponite and montmorillonite, respectively, as a function of the abundance of these materials in the mixtures. Based upon the band depth of the spectral features we find that 3-5 wt.% of the clay minerals in the mixture with pyroxene can be recognized and at 25 wt.% their presence is indisputable in the mixtures. When the saponite is mixed with the lower albedo palagonitic soil, its presence is clearly distinguishable via the 1.4 and 2.3 μm features at 25 wt.% abundance. These relationships, between abundance and band depth, provide an ability to quantitatively address the amount of these materials in mixtures. The trends described here provide guidance for estimating t

Reference
Roush TL, Bishop JL, Brown AJ, Blake DF, Bristow TF (2015) Laboratory reflectance spectra of clay minerals mixed with Mars analog materials: Toward enabling quantitative clay abundances from Mars spectra. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.035]
Copyright Elsevier

¹Scott Messenger, ¹Keiko Nakamura-Messenger, ¹Lindsay P. Keller, ^1,2Simon J. Clemett
¹Robert M. Walker Laboratory for Space Science, EIS Directorate, Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, Texas, USA
²ESCG/ERC Inc., Houston, Texas, USA

We performed chemical, mineralogical, and isotopic studies of the first interplanetary dust particles (IDPs) collected in the stratosphere without the use of silicone oil. The collection substrate, polyurethane foam, effectively traps impacting particles, but the lack of an embedding medium results in significant particle fragmentation. Two dust particles found on the collector exhibit the typical compositional and mineralogical properties of chondritic porous interplanetary dust particles (CP-IDPs). Hydrogen and nitrogen isotopic imaging revealed isotopic anomalies of typical magnitude and spatial variability observed in previous CP-IDP studies. Oxygen isotopic imaging shows that individual mineral grains and glass with embedded metal and sulfide (GEMS) grains are dominated by solar system materials. No systematic differences are observed in element abundance patterns of GEMS grains from the dry collection versus silicone oil-collected IDPs. This initial study establishes the validity of a new IDP collection substrate that avoids the use of silicone oil as a collection medium, removing the need for this problematic contaminant and the organic solvents necessary to remove it. Additional silicone oil-free collections of this type are needed to determine more accurate bulk element abundances of IDPs and to examine the indigenous soluble organic components of IDPs.

Reference
Messenger S, Nakamura-Messenger K, Keller LP, Simon J. Clemett SJ (2015) Pristine stratospheric collection of interplanetary dust on an oil-free polyurethane foam Substrate. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12473]
Copyright Elsevier

The most popular papers on Cosmochemistry Papers in May were:

1-Wasserburg GJ, Tripella O, Busso M (2015) Isotope Anomalies in the Fe-group Elements in Meteorites and Connections to Nucleosynthesis in AGB Stars. Astrophysical Journal 805, 7. Link to Article [doi:10.1088/0004-637X/805/1/7]

2-Burkhardt C, Schönbächler M (2015) Intrinsic W nucleosynthetic isotope variations in carbonaceous chondrites: Implications for W nucleosynthesis and nebular vs. parent body processing of presolar materials. Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2015.06.012]

3-Chen Y, Liu Y, Guan Y, Eiler JM, Ma C, Rossman GR, Taylor LC (2015) Evidence in Tissint for recent subsurface water on Mars. Earth and Planetary Science Letters 425, 55–63 Link to Article [doi:10.1016/j.epsl.2015.05.004]

4-McCubbin FM, Jones RH (2015) Extraterrestrial Apatite: Planetary Geochemistry to Astrobiology. Elements 11/3, 183-188 Link to Article [doi: 10.2113/gselements.11.3.183]

5-Xiong MY, Shelobolina ES, Roden EE (2015) Potential for Microbial Oxidation of Ferrous Iron in Basaltic Glass. Astrobiology 15(5), 331-340. Link to Article [doi:10.1089/ast.2014.1233]

¹O. Ruesch, ¹H. Hiesinger, ²E. Cloutis, ³L. Le Corre, ¹J. Kallisch, ²P. Mann, ^4,1K. Markus, ¹K. Metzler, ⁵A. Nathues, ³V. Reddy
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany
²Department of Geography, University of Winnipeg, 515 Portage Avenue Winnipeg, Manitoba R3B 2E9, Canada
³Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395, USA
⁴DLR, Institute of Planetary research, Berlin, Germany
⁵Max-Planck-Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany

The howardite, eucrite and diogenite (HED) meteorites are genetically related and represent the most voluminous group of achondrites. They are the closest analog materials to Vesta and V-type asteroids. Many of these meteorites were the focus of intense petrologic and visible to near infrared spectral studies. As ground-based and orbital observations of basaltic asteroids have increased, an improved understanding of HEDs is needed. For this study, we investigated 24 HED samples, mainly new finds from Northwest Africa (NWA). Visible to near infrared (up to 2.5 μm) spectral measurements under varying illumination and observation geometries were acquired for 4 samples. Phase reddening and bluing (i.e., increase and decrease in spectral slope) is observed for the visible slope as phase angle increase. Monotonic phase reddening can occur for the near infrared slope as phase angle increase. Non-systematic changes with phase angle are found for the band area ratio parameter. At phase angles higher than ∼60°, the decrease of reflectance and decrease of pyroxene bands depth are undistinguishable from admixture of low albedo material to HED samples. To assess the precision of empirical equations relating spectral properties and composition, the pyroxenes, feldspar, and olivine chemistry of the samples was determined. Using previous calibrations, systematic overestimations of the ferrosilite (Fs) and wollastonite (Wo) contents are found, especially in the 15-40 Fs range. To overcome such discrepancies, a new set of empirical equations is proposed. For an application of the new calibration, we selected two compositional end-member areas on Vesta on the basis of their iron content. For the iron-poor terrain we found an average pyroxene composition of Fs30Wo5 and for the iron-rich terrain an average of Fs47Wo14.

Reference
Ruesch O, Hiesinger H, Cloutis E, Le Corre L, Kallisch J, Mann P, Markus K, Metzler K, Nathues A, Reddy V (2015)
Near infrared spectroscopy of HED meteorites: Effects of viewing geometry and compositional variations. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.034]

Copyright Elsevier