¹Joke Belza, ^1,2Steven Goderis, ³Jan Smit, ²Frank Vanhaecke, ⁴Kitty Baert, ⁴Herman Terryn, ¹Philippe Claeys
¹Department of Analytical Environmental and Geo-Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, BE-1050 Brussels, Belgium
²Department of Analytical Chemistry, Universiteit Gent, Krijgslaan 281-S12, BE-9000 Ghent, Belgium
³Department of Sedimentology, Vrije Universiteit Amsterdam, de Boelelaan 1085, 1081HV Amsterdam, Netherlands
⁴Department of Electrochemical and Surface Engineering, Vrije Universiteit Brussel, Pleinlaan 2, BE-1050 Brussels, Belgium

Using laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS), we have conducted spatially resolved trace element analysis on fresh, unaltered microtektite glasses linked to the Cretaceous-Paleogene (K-Pg) boundary Chicxulub crater and on their surrounding alteration phases. This unique approach offers the opportunity to study in situ and at high spatial resolution both the mixing of different target lithologies and the variation of the major and trace element budget during the alteration process. In addition, two-dimensional element distribution maps reveal important geochemical information beyond the capabilities of single spot laser drilling. Glasses from two localities in opposite quadrants from the source crater were studied. At the Beloc locality (Haiti), the glass population is dominated by the presence of yellow high-Ca glass and black andesitic glass formed by admixture of carbonate/dolomite/anhydrite platform lithologies with crystalline basement. These glasses alter according to the well-established hydration-palagonitisation model postulated for mafic volcanic glasses. REEs become progressively leached from the glass to below the detection limit for the applied spot size, while immobile Zr, Hf, Nb, and Ta passively accumulate in the process exhibiting both inter-element ratios and absolute concentrations similar to those for the original glass. In contrast, The Arroyo El Mimbral locality (NE Mexico) is characterized by abundant green glass fragments high in Si, Al and alkalis, and low in Mg, Ca, Fe. Low Si black glass is less abundant though similar in composition to the black glass variety at Beloc. The alteration pattern of high-Si, Al green glass at the Mimbral locality is more complex, including numerous competing reaction processes (ion-exchange, hydration, dissolution, and secondary mineral precipitation) generally controlled by the pH and composition of the surrounding fluid. All green, high-Si, Al glasses are hydrated and variably enriched in Sr, Ba, and Cs, indicating preferred adsorption from seawater during hydration. Despite the onset of ion-exchange reactions, which only seem to have affected the alkalis, the trace element composition of the green high-Si, Al glass is still largely representative of the original melt composition. Refining the geochemical signature of (altered) melt lithologies may advance our current understanding of glass stability in the natural environment and provide insight into the origin and emplacement of ejecta material during crater formation.

Reference
Belza J, Goderis S, Smit J, Vanhaecke F, Baert K, Terryn H, Claeys P (2014) High spatial resolution geochemistry and textural characteristics of ‘microtektite’ glass spherules in proximal Cretaceous-Paleogene sections: insights into glass alteration patterns and precursor melt lithologies. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2014.12.013]

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¹P. A. Bland,²G. S. Collins,²T. M. Davison,³N. M. Abreu,⁴F. J. Ciesla,²A. R. Muxworthy, ²J. Moore
¹Department of Applied Geology, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
²Impacts & Astromaterials Research Centre (IARC), Department of Earth Science & Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
³Earth Science Program, Pennsylvania State University—Du Bois Campus, Du Bois, Pennsylvania 15801, USA N. M. Abreu
⁴Department of Geophysical Science, University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60430, USA

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Reference
Bland PA, Collins GS, Davison TM, Abreu NM, Ciesla FJ, Muxworthy AR, Moore J (2014) Pressure–temperature evolution of primordial solar system solids during impact-induced compaction. Nature Communications 5, 5451
Link to Article [doi:10.1038/ncomms6451]

¹K.M. Stack, ²R.E. Milliken
¹Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
²Department of Geological Sciences, Brown University, Providence, RI, 02912

High-resolution mapping by visible and near-infrared orbital spectrometers has revealed a diversity of hydrated mineral deposits on the surface of Mars. Quantitative analysis of mineral abundances within these deposits has the potential to distinguish depositional and diagenetic processes. Such analysis can also provide important constraints on the nature of putative global and local-scale mineralogical transitions on Mars. However, the ability of models to extract quantitative mineral abundances from spectra of mixtures relevant to sedimentary rocks remains largely untested. This is particularly true for clay and sulfate minerals, which often occur as fine-grained components of terrestrial sedimentary rocks and are known to occur in a number of sedimentary deposits on Mars. This study examines the spectral properties of a suite of mixtures containing the Mg-sulfate epsomite mixed with varying proportions of smectitic clay (saponite, nontronite, and montmorrilonite). The goal of this work is to test the ability of checkerboard (linear) and intimate (non-linear) mixing models to obtain accurate estimates of mineral abundances under ideal and controlled laboratory conditions. The results of this work suggest that: (1) spectra of clay-sulfate mixtures can be reproduced by checkerboard and intimate mixing models to within 2% absolute reflectance or single scattering albedo, (2) clay and epsomite abundance can be modeled to within 5 wt.% when particle diameter is optimized, and (3) the lower threshold for modeling clay in spectra of clay-epsomite mixtures is approximately 10 wt.%, below which the models often fail to recognize the presence of clay.

Reference
Stack KM, Milliken RE (2014) Modeling near-infrared reflectance spectra of clay and sulfate mixtures and implications for Mars. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.12.009]

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¹Christopher R. Webster et al. (>10)*
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
*Find the extensive, full author and affiliation list on the publishers website

Reports of plumes or patches of methane in the Martian atmosphere that vary over monthly timescales have defied explanation to date. From in situ measurements made over a 20-month period by the Tunable Laser Spectrometer (TLS) of the Sample Analysis at Mars (SAM) instrument suite on Curiosity at Gale Crater, we report detection of background levels of atmospheric methane of mean value 0.69 ± 0.25 ppbv at the 95% confidence interval (CI). This abundance is lower than model estimates of ultraviolet (UV) degradation of accreted interplanetary dust particles (IDP’s) or carbonaceous chondrite material. Additionally, in four sequential measurements spanning a 60-sol period, we observed elevated levels of methane of 7.2 ± 2.1 (95% CI) ppbv implying that Mars is episodically producing methane from an additional unknown source.

Reference
Webster CR et al. (2014) Mars methane detection and variability at Gale crater. Science (in Press)
Link to Article [Science DOI: 10.1126/science.1261713]

Reprinted with permission from AAAS

^1,2Gerardo Dominguez, ³A. S. Mcleod, ⁴Zack Gainsforth, ³P. Kelly, ⁵Hans A. Bechtel, ⁶Fritz Keilmann, ⁴Andrew Westphal, ²Mark Thiemens, ³D. N. Basov
¹Department of Physics, California State University, San Marcos, San Marcos, California 92096-0001, USA
²Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA
³Department of Physics, University of California, San Diego, La Jolla, California 92093, USA
⁴Space Sciences Laboratory, University of California, Berkeley, Berkeley, California 94720, USA
⁵Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
⁶Ludwig-Maximilians-Universität and Center for Nanoscience, 80539 München, Germany

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Reference
Dominguez G, Mcleod AS, Gainsforth Z, Kelly P, Bechtel HA, Keilmann F, Westphal A, Thiemens M, Basov DN (2014) Nanoscale infrared spectroscopy as a non-destructive probe of extraterrestrial samples. Nature Communications 5, 5445
Link to Article [doi:10.1038/ncomms6445]

¹Paula Lindgren, ²Romy D. Hanna, ^3,4Katherine J. Dobson, ⁵Tim Tomkinson, ¹Martin R. Lee
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
²Jackson School of Geological Sciences, University of Texas, Austin, TX 78712, USA
³Manchester X-ray Imaging Facility, School of Materials, University of Manchester, Manchester M13 9PL, UK
⁴Research Complex at Harwell, Rutherford Appleton Laboratories, Oxfordshire OX11 0FA, UK
⁵Scottish Universities Environmental Research Centre, East Kilbride E75 0QF, UK

Petrographic analysis of eight CM carbonaceous chondrites (EET 96029, LAP 031166, LON 94101, MET 01072, Murchison, Murray, SCO 06043, QUE 93005) by electron imaging and diffraction, and X-ray computed tomography, reveals that six of them have a petrofabric defined by shock flattened chondrules. With the exception of Murchison, those CMs that have a strong petrofabric also contain open or mineralized fractures, indicating that tensional stresses accompanying the impacts were sufficient to locally exceed the yield strength of the meteorite matrix. The CMs studied span a wide range of petrologic subtypes, and in common with Rubin (2012) we find that the strength of their petrofabrics increases with their degree of aqueous alteration. This correspondence suggests that impacts were responsible for enhancing alteration, probably because the fracture networks they formed tapped fluid reservoirs elsewhere in the parent body. Two meteorites that do not fit this pattern are MET 01072 and Murchison; both have a strong petrofabric but are relatively unaltered. In the case of MET 01072, impact deformation is likely to have postdated parent body aqueous activity. The same may also be true for Murchison, but as this meteorite also lacks fractures and veins, its chondrules were most likely flattened by multiple low intensity impacts. Multiphase deformation of Murchison is also revealed by the microstructures of calcite grains, and chondrule-defined petrofabrics as revealed by X-ray computed tomography. The contradiction between the commonplace evidence for impact-deformation of CMs and their low shock stages (most belong to S1) can be explained by most if not all having been exposed to multiple low intensity (i.e., <5 GPa) shock events. Aqueous alteration was enhanced by those impacts that were of sufficient intensity to open high permeability fracture networks that could connect to fluid Reservoirs.

Reference
Lindgren P, Romy D. Hanna, Dobson KJ, Tomkinson T, Lee MR (2015) The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity Impacts. Geochimica et Cosmochimica (in Press)
Link to Article [doi:10.1016/j.gca.2014.09.014]

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^1,2Péter Németh, ^3,4Laurence A. J. Garvie, ⁵Toshihiro Aoki,⁶Natalia Dubrovinskaia, ⁷Leonid Dubrovinsky, ^2,4Peter R. Buseck
¹Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest 1117, Hungary
²Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604, USA
³Center for Meteorite Studies, Arizona State University, Tempe, Arizona 85287-6004, USA Laurence
⁴School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287-1404, USA Laurence
⁵LeRoy Eyring Center for Solid State Science, Arizona State University, Tempe, Arizona 85287-1704, USA
⁶Material Physics and Technology at Extreme Conditions, Laboratory of Crystallography, University of Bayreuth, Bayreuth D-95440, Germany
⁷Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth D-95440, Germany

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Reference
Németh P, Garvie LAJ, Aoki T, Dubrovinskaia N, Dubrovinsky L, Buseck PR (2014) Lonsdaleite is faulted and twinned cubic diamond and does not exist as a discrete material. Nature Communications 5, 5447
Link to Article [doi:10.1038/ncomms6447]

¹Wang, Z., ¹Becker, H., ²Wombacher, F.
¹Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
²Institut für Geologie und Mineralogie, Universität zu Köln, Köln, Germany

Mass fractions of S, Cu, Se, Mo, Ag, Cd, In, Te, Ba, Sm, W and Tl were determined by isotope dilution sector field ICP-MS in the same sample aliquot of reference materials using HF-HNO3 digestion in PFA beakers in pressure bombs and glassy carbon vessels in a high-pressure asher (HPA-S) for comparison. Additionally, Bi was determined by internal standardisation relative to Tl. Because isobaric and oxide interferences pose problems for many of these elements, efficient chromatographic separation methods in combination with an Aridus desolvator were employed to minimise interference effects. Repeated digestion and measurement of geological reference materials (BHVO-1, BHVO-2, SCo-1, MAG-1, MRG-1 and UB-N) gave results with < 5% relative intermediate precision (1s) for most elements, except Bi. Replicates of NIST SRM 612 glass digested on a hot plate were analysed by the same methods, and the results agree with reference values mostly within 2% relative deviation. Data for the carbonaceous chondrites Allende, Murchison, Orgueil and Ivuna are also reported. Digestion in a HPA-S was as efficient as in pressure bombs, but some elements displayed higher blank levels following HPA-S treatment. Pressure bomb digestion yielded precise data for volatile S, Se and Te, but may result in high blanks for W.

Reference
Wang Z, Becker H, Wombacher F (2014) Mass Fractions of S, Cu, Se, Mo, Ag, Cd, In, Te, Ba, Sm, W, Tl and Bi in Geological Reference Materials and Selected Carbonaceous Chondrites Determined by Isotope Dilution ICP-MS. Geostandards and Geoanalytical Research (in Press)
Link to Article [doi: 10.1111/j.1751-908X.2014.00312.x]

Published by arrangement with John Wiley&Sons

¹Alan E. Rubin
¹Institute of Geophysics and Planetary Physics and Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA

Enstatite-rich meteorites include EH and EL chondrites, rare ungrouped enstatite chondrites, aubrites, a few metal-rich meteorites (possibly derived from the mantle of the aubrite parent body), various impact-melt breccias and impact-melt rocks, and a few samples that may be partial-melt residues ultimately derived from enstatite chondrites. Members of these sets of rocks exhibit a wide range of impact features including mineral-lattice deformation, whole-rock brecciation, petrofabrics, opaque veins, rare high-pressure phases, silicate darkening, silicate-rich melt veins and melt pockets, shock-produced diamonds, euhedral enstatite grains, nucleation of enstatite on relict grains and chondrules, low MnO in enstatite, high Mn in troilite and oldhamite, grains of keilite, abundant silica, euhedral graphite, euhedral sinoite, F-rich amphibole and mica, and impact-melt globules and spherules. No single meteorite possesses all of these features, although many possess several. Impacts can also cause bulk REE fractionations due to melting and loss of oldhamite (CaS) – the main REE carrier in enstatite meteorites. The Shallowater aubrite can be modeled as an impact-melt rock derived from a large cratering event on a porous enstatite chondritic asteroid; it may have been shock melted at depth, slowly cooled and then excavated and quenched. Mount Egerton may share a broadly similar shock and thermal history; it could be from the same parent body as Shallowater. Many aubrites contain large pyroxene grains that exhibit weak mosaic extinction, consistent with shock-stage S4; in contrast, small olivine grains in some of these same aubrites have sharp or undulose extinction, consistent with shock stage S1 to S2. Because elemental diffusion is much faster in olivine than pyroxene, it seems likely that these aubrites experienced mild post-shock annealing, perhaps due to relatively shallow burial after an energetic impact event. There are correlations among EH and EL chondrites between petrologic type and the degree of shock, consistent with the hypothesis that collisional heating is mainly responsible for enstatite-chondrite thermal metamorphism. Nevertheless, the apparent shock stages of EL6 and EH6 chondrites tend to be lower than EL3-5 and EH3-5 chondrites, suggesting that the type-6 enstatite chondrites (many of which possess impact-produced features) were shocked and annealed. The relatively young Ar–Ar ages of enstatite chondrites record heating events that occurred long after any 26Al that may have been present initially had decayed away. Impacts remain the only plausible heat source at these late dates. Some enstatite meteorites accreted to other celestial bodies: Hadley Rille (EH) was partly melted when it struck the Moon; Galim (b), also an EH chondrite, was shocked and partly oxidized when it accreted to the LL parent asteroid. EH, EL and aubrite-like clasts also occur in the polymict breccias Kaidun (a carbonaceous chondrite) and Almahata Sitta (an anomalous ureilite). The EH and EL clasts in Kaidun appear unshocked; some clasts in Almahata Sitta may have been extensively shocked on their parent bodies prior to being incorporated into the Almahata Sitta host.

Reference
Rubin AE (2014) Impact features of enstatite-rich meteorites. Chemie der Erde (in Press)
Link to Article [doi:10.1016/j.chemer.2014.09.001]

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^1,2Patrick L. Harner, ¹Martha S. Gilmore
¹Department of Earth and Environmental Sciences, Wesleyan University, 265 Church St., Middletown CT 06459, USA
²Present address: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA

We present visible-near infrared (VNIR, 0.35 to 5 μm) spectra for a suite of hydrous carbonates that may be relevant to the surface of Mars. This includes VNIR spectra for ikaite, nesquehonite, synthetic monohydrocalcite and lansfordite over the 0.35 – 2.5 μm range that are new to the literature. The spectral features of the hydrous carbonates are dominated by absorptions at ∼1.0, 1.2, 1.4–1.5, 1.9 and 2.8μm that are due to overtones and combinations of fundamental water and hydroxyl vibrations. Absorptions due to (CO3)2-, Mg-OH, Fe-OH, and/or water are seen at ∼ 2.3-2.5, 3.4, and 3.9 μm in hydrous Mg and Mg-Fe3+ carbonates containing hydroxyl groups, but are weaker than in the common anhydrous carbonates. When present in the hydrous carbonates, the positions of the centers of the 2.3 μm and/or 2.5 μm absorptions are often shifted relative to the anhydrous carbonates, which may be diagnostic. Some or all of the (CO3)2- absorptions typical of anhydrous carbonates are weak to absent in the hydrous carbonates, and thus this group may be difficult to distinguish from other hydrous minerals like sulfates, phyllosilicates or chlorides in Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data using standard spectral search parameters for anhydrous carbonates. We present strategies for recognizing hydrous carbonates in CRISM data using combinations of spectral parameters that measure the intensity and shape of the water-related absorptions in these minerals.

Reference
Harner PL, Gilmore MS (2014) Visible-Near Infrared Spectra of Hydrous Carbonates, with Implications for the Detection of Carbonates in Hyperspectral data of Mars. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.11.037]

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