^1,2Šárka Jonášová, ^1,3Lukáš Ackerman, ¹Karel Žák, ^1,2Roman Skála, ¹Jana Ďurišová, ^4,5Alexander Deutsch, ³Tomáš Magna
Geochmica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2016.06.031]
¹Institute of Geology, The Czech Academy of Sciences, Rozvojová 269, CZ-165 00 Prague 6, Czech Republic
²Faculty of Science, Charles University, Albertov 6, CZ-128 43, Prague 2, Czech Republic
³Czech Geological Survey, Klárov 3, CZ-118 21 Prague 1, Czech Republic
⁴Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany
⁵Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Corrensstr. 24, D-48149 Münster, Germany
Copyright Elsevier

Internal structure and element chemistry including contents of highly siderophile elements (HSE) and Os isotope ratios have been studied in target rocks and several groups of impact glasses of the Zhamanshin impact structure, Kazakhstan. These include larger irregularly-shaped fragments and blocks of impact glass (zhamanshinite), and three types of tektite-like splash-form glasses, part of fallback ejecta. These glassy objects typically are up to 30 mm large and are shaped as teardrops, irregularly bent and curved glass rods and fibers. They can be subdivided into acidic types (irghizites; typically 69–76 wt.% SiO2), basic splash-forms (typically 53–56 wt.% SiO2), and rarely occurring highly inhomogeneous composites with abundant mineral inclusions. A comparison with the target rocks shows that zhamanshinites and basic splash-forms usually have no detectable admixture of the projectile matter, indicated by major and trace elements as well as highly siderophile element contents, with an exception of one sample containing Fe-, Cr-, Ni- and Ti-enriched particles and elevated HSE contents. In contrast, irghizites exhibit clear admixture of the projectile matter, which was incorporated by complex processes accompanied by strong element fractionations. Microscopic investigations confirm that irghizites were formed mainly by coalescence of smaller molten glass droplets sized typically below 1 mm. Irghizites exhibit significant enrichments in Ni, Co and Cr, whose concentrations are locally enriched in the rims of the original small droplets. A portion of these elements and also part of Fe and Mn and other elements were derived from the impactor, most likely a Ni-rich carbonaceous chondrite. The contents of HSE are low and strongly fractionated, with moderate depletions of Pt and Pd and strong depletions of other HSE with respect to chondritic element ratios. Osmium shows the strongest depletion, likely related to the presence of oxygen in the post-impact atmosphere causing strong Os loss through volatilization. One composite splash-form contains Fe–Ni–S inclusions and exhibits a less fractionated HSE pattern suggesting the lowest degree of melting, volatilization and condensation. The observed structural and microchemical features of irghizites are interpreted to reflect variable proportions of the uppermost target sediments and the projectile matter, with HSE element ratios influenced by evaporation and condensation processes, and differences in volatility of individual HSE elements and/or their compounds. Two possible pathways of incorporation of the projectile matter into the irghizites include either re-condensation of evaporated projectile matter on the surface of glass droplets, or incorporation of less chemically fractionated microparticles dispersed by the explosion.

¹Basu Sarbadhikari, A., ¹Marhas, K.K., ¹Sameer,¹Goswami, J.N.
Current Science 110, 1536-1538 Link to Article [DOI: 10.18520/cs/v110/i8/1536-1539]
¹Physical Research Laboratory, Ahmedabad, India

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¹Parnell, J., ¹Salter, N., ¹West, P.
Earth and Environmental Science Transactions of the Royal Society of Edinburgh
(in Press) Link to Article [DOI: 10.1017/S1755691016000037]
¹School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK

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¹Ivanova, M.A.
Geochemistry International 54, 387-402 Link to Article [DOI: 10.1134/S0016702916050037]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, Russian Federation

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¹Devin L. Schrader, ¹Kazuhide Nagashima, ¹Alexander N. Krot, ¹Ryan C. Ogliore, ²Qing-Zhu Yin, ³Yuri Amelin, ⁴Claudine H. Stirling, ⁴Angela Kaltenbach
Geochimica et Cosmochmica Acta (in Press)   Link to Article [doi:10.1016/j.gca.2016.06.023]
¹Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
²Department of Earth and Planetary Sciences, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA
³Research School of Earth Sciences, Australian National University, Canberra 2601, Australia
⁴Department of Chemistry and Centre for Trace Element Analysis, University of Otago, PO Box 56, Dunedin 9054, New Zealand
Copyright Elsevier

We report on the mineralogy, petrography, and in situ measured oxygen- and magnesium-isotope compositions of eight porphyritic chondrules (seven FeO-poor and one FeO-rich) from the Renazzo-like carbonaceous (CR) chondrites Graves Nunataks 95229, Grosvenor Mountains 03116, Pecora Escarpment 91082, and Queen Alexandra Range 99177, which experienced minor aqueous alteration and very mild thermal metamorphism. We find no evidence that these processes modified the oxygen- or Al-Mg isotope systematics of chondrules in these meteorites. Olivine, low-Ca pyroxene, and plagioclase within an individual chondrule have similar O-isotope compositions, suggesting crystallization from isotopically uniform melts. The only exceptions are relict grains in two of the chondrules; these grains are 16O-enriched relative to phenocrysts of the host chondrules. Only the FeO-rich chondrule shows a resolvable excesses of 26Mg, corresponding to an inferred initial 26Al/27Al ratio [(26Al/27Al)0] of (2.5±1.6)×10−6 (±2SE). Combining these results with the previously reported Al-Mg isotope systematics of CR chondrules (Nagashima et al., 2014, Geochem. J.48, 561), 7 of 22 chondrules (32%) measured show resolvable excesses of 26Mg; the presence of excess 26Mg does not correlate with the FeO content of chondrule silicates. In contrast, virtually all chondrules in weakly metamorphosed (petrologic type 3.0–3.1) unequilibrated ordinary chondrites (UOCs), Ornans-like carbonaceous (CO) chondrites, and the ungrouped carbonaceous chondrite Acfer 094 show resolvable excesses of 26Mg. The inferred (26Al/27Al)0 in CR chondrules with resolvable excesses of 26Mg range from (1.0±0.4)×10−6 to (6.3±0.9)×10−6, which is typically lower than (26Al/27Al)0 in the majority of chondrules from UOCs, COs, and Acfer 094. Based on the inferred (26Al/27Al)0, three populations of CR chondrules are recognized; the population characterized by low (26Al/27Al)0 (<3×10−6) is dominant. There are no noticeable trends with major and minor element or O-isotope compositions between these populations. The weighted mean (26Al/27Al)0 of 22 CR chondrules measured is (1.8±0.3)×10−6. An apparent agreement between the 26Al-26Mg ages (using weighted mean value) and the revised (using 238U/235U ratio for bulk CR chondrites of 137.7789±0.0085) 207Pb-206Pb age of a set of chondrules from CR chondrites (Amelin et al., 2002, Science297, 1678) is consistent with the initial 26Al/27Al ratio in the CR chondrite chondrule-forming region at the canonical level (∼5.2×10−5), allowing the use of 26Al-26Mg systematics as a chronometer for CR chondrules. To prove chronological significance of 26Al for CR chondrules, measurements of Al-Mg and U-Pb isotope systematics on individual chondrules are required. The presence of several generations among CR chondrules indicates some chondrules that accreted into the CR chondrite parent asteroid avoided melting by later chondrule-forming events, suggesting chondrule-forming processes may have occurred on relatively limited spatial scales. Accretion of the CR chondrite parent body occurred at > View the MathML source4.0-0.3+0.5 Ma after the formation of CAIs with the canonical 26Al/27Al ratio, although rapid accretion after formation of the major population of CR chondrules is not required by our data.

¹Pang, R.-L.,¹Zhang, A.-C.,¹Wang, S.-Z.,¹Wang, R.-C., ²Yurimoto, H.
Scientific Reports 6, Article number 26063 Link to Article [DOI: 10.1038/srep26063]
¹State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, China
²Department of Natural History Sciences, Hokkaido University, Sapporo, Japan

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¹Ruzié-Hamilton, L., ¹Clay, P.L., ¹Burgess, R., ^2,3Joachim, B.,²Ballentine, C.J., ¹Turner, G.
Chemical Geology 437, 77-87 Link to Article [DOI: 10.1016/j.chemgeo.2016.05.003]
¹School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Rd, Manchester, United Kingdom
²Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, United Kingdom
³Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck, Austria

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¹Kenny, G.G.,²Whitehouse, M.J.,¹Kamber, B.S.
Geology 44, 435-438 Kink to Article [DOI: 10.1130/G37898.1]
¹Department of Geology, School of Natural Sciences, Trinity College Dublin, Dublin, Ireland
²Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden

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¹Andreas Morlok, ¹Aleksandra Stojic, ¹Iris Weber, ¹Harald Hiesinger, ²Michael Zanetti, ³Joern Helbert
Icarus (in Press) Link to Article [doi:10.1016/j.icarus.2016.06.013]
¹Institut für Planetologie, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
²University of Western Ontario, 1151 Richmond St, London, Ontario, Canada N6A 3K7
³Institute for Planetary Research, DLR, Rutherfordstrasse 2, 12489 Berlin, Germany
Copyright Elsevier

We have analyzed 14 impact melt glass samples, covering the compositional range from highly felsic to mafic/basaltic, as part of our effort to provide mid-infrared spectra (7-14 µm) for MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer), an instrument onboard of the ESA/JAXA BepiColombo mission.

Since Mercury was exposed to many impacts in its history, and impact glasses are also common on other bodies, powders of tektites (Irghizite, Libyan Desert Glass, Moldavite, Muong Nong, Thailandite) and impact glasses (from the Dellen, El’gygytgyn, Lonar, Mien, Mistastin, and Popigai impact structures) were analyzed in four size fractions of (0-25, 25-63, 93-125 and 125-250 µm) from 2.5-19 µm in bi-directional reflectance. The characteristic Christiansen Feature (CF) is identified between 7.3 µm (Libyan Desert Glass) and 8.2 µm (Dellen). Most samples show mid-infrared spectra typical of highly amorphous material, dominated by a strong Reststrahlen Band (RB) between 8.9 µm (Libyan Desert Glass) and 10.3 µm (Dellen). Even substantial amounts of mineral fragments hardly affect this general band shape.

Comparisons of the SiO2 content representing the felsic/mafic composition of the samples with the CF shows felsic/intermediate glass and tektites forming a big group, and comparatively mafic samples a second one. An additional sign of a highly amorphous state is the lack of features at wavelengths longer than ∼15 µm. The tektites and two impact glasses, Irghizite and El’gygytgyn respectively, have much weaker water features than most of the other impact glasses.

For the application in remote sensing, spectral features have to be correlated with compositional characteristics of the materials. The dominating RB in the 7-14 µm range correlates well with the SiO2 content, the Christiansen Feature shows similar dependencies. To distinguish between glass and crystalline phases of the same chemical composition, a comparison between CF the SCFM index (SiO2/(SiO2+CaO+FeO+MgO)) (Walter and Salisbury, 1989) is useful, if chemical compositional data are also available.

^1,2,3Bezaeva, N.S.,^2,4Chareev, D.A.,⁵Rochette, P.,⁶Kars, M.,⁶Gattacceca, J.,⁷Feinberg, J.M.,⁸Sadykov, R.A.,³Kuzina, D.M.,⁸Axenov, S.N.
Physics of the Earth and Planetary Interiors 257, 79-90     Link to Article [DOI: 10.1016/j.pepi.2016.05.009]
¹Faculty of Physics, M.V. Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation
²Ural Federal University, 19 Mira Str., Ekaterinburg, Russian Federation
³Kazan Federal University, 18 Kremlyovskaya Str., Kazan, Russian Federation
⁴Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Moscow Region, Russian Federation
⁵Aix-Marseille Université, CNRS, IRD, CEREGE UM34, Technopôle de l’Environnement Arbois-Mediterranée, BP80, Aix-en-Provence, France
⁶Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku, Japan
⁷Institute for Rock Magnetism, Dept. of Earth Sciences, University of Minnesota, Minneapolis, United States
⁸Institute for Nuclear Research, Russian Academy of Sciences, Prospekt 60-letiya Oktiabria 7a, Moscow, Russian Federation

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