^1,4A. Jambon, ²V. Sautter, ³J-A. Barrat, ⁵J. Gattacceca, ⁵P. Rochette, ⁴O. Boudouma, ^1,4D. Badia, ^5,6B. Devouard
Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2016.06.032]
¹Sorbonne Universités, UPMC Univ Paris 06, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F-75005 Paris, France
²Museum National d’Histoire Naturelle and UPMC Univ Paris 06, IMPMC, UMR7590 75005 Paris, France
³Université de Brest, CNRS UMR 6538 (Domaines Océaniques), I.U.E.M., Place Nicolas Copernic, 29280 Plouzané, France
⁴CNRS, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F-75005 Paris, France
⁵Aix-Marseille Université, CNRS, CEREGE UM 34, F-13545 Aix-en-Provence cedex 4, France
⁶Université Blaise Pascal, CNRS, Laboratoire Magmas et Volcans UMR 6524, 5 rue Kessler, F-63000 Clermont-Ferrand, France
Copyright Elsevier

Northwest Africa 5790, the latest nakhlite find, is composed of 58 vol.% augite, 6% olivine and 36% vitrophyric intercumulus material. Its petrology is comparable to previously discovered nakhlites but with key differences: (1) Augite cores display an unusual zoning between Mg# 54 and 60; (2) Olivine macrocrysts have a primary Fe-rich core composition (Mg#= 35); (3) the modal proportion of mesostasis is the highest ever described in a nakhlite; (4) It is the most magnetite-rich nakhlite, together with MIL 03346, and exhibits the least anisotropic fabric. Complex primary zoning in cumulus augite indicates resorption due to complex processes such as remobilization of former cumulates in a new magma batch. Textural relationships indicate unambiguously that olivine was growing around resorbed augite, and that olivine growth was continuous while pyroxene growth resumed at a final stage. Olivine core compositions (Mg#= 35) are out of equilibrium with the augite core compositions (Mg# 60-63) and with the previously inferred nakhlite parental magma (Mg#= 29). The presence of oscillatory zoning in olivine and augite precludes subsolidus diffusion that could have modified olivine compositions. NWA 5790 evidences at least two magma batches before eruption, with the implication that melt in equilibrium with augite cores was never in contact with olivine. Iddingsite is absent.

Accordingly, the previous scenarios for nakhlite petrogenesis must be revised. The first primary parent magmas of nakhlites generated varied augite cumulates at depth (Mg# 66 to 60) as they differentiated to different extents. A subsequent more evolved magma batch entrained accumulated augite crystals to the surface where they were partly resorbed while olivine crystallized. Trace element variations indicate unambiguously that they represent consanguineous but different magma batches. The compositional differences among the various nakhlites suggest a number of successive lava flows. To account for all observations we propose a petrogenetic model for nakhlites based on several (at least three) thick flows. Although NWA5790 belongs to the very top of one flow, it should come from the lowest flow sampled, based on the lack of iddingsite.

¹Paul D. Asimow, ²Chaney Lin, ^3,4Luca Bindi, ¹Chi Ma, ^5,6Oliver Tschauner, ⁷Lincoln S. Hollister,⁸Paul J. Steinhardt
Proceedings of the National Academy of Sciences 113 7077–7081 Link to Article [doi: 10.1073/pnas.1600321113]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125;
²Department of Physics, Princeton University, Princeton, NJ 08544;
³Dipartimento di Scienze della Terra, Università degli Studi di Firenze, I-50121 Firenze, Italy;
⁴Consiglio Nazionale delle Ricerche–Istituto di Geoscienze e Georisorse, Sezione di Firenze, I-50121 Firenze, Italy;
⁵Department of Geoscience, University of Nevada, Las Vegas, NV 89154;
⁶High Pressure Science and Engineering Center, University of Nevada, Las Vegas, NV 89154;
⁷Department of Geosciences, Princeton University, Princeton, NJ 08544;
⁸Princeton Center for Theoretical Science, Princeton University, Princeton, NJ 08544

We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl5, (Mg0.75Fe2+0.25)2SiO4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. The compositional range of the icosahedral phase is Al68–73Fe11–16Cu10–12Cr1–4Ni1–2 and extends toward higher Al/(Cu+Fe) and Fe/Cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the Al-Cu-Fe system. The shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors.

¹Richard V. Morris et al. (>10)*
Proceedings of the National Academy of Sciences (2016) 113 7071-7076 Link to Article [doi:10.1073/pnas.1607098113]
¹NASA Johnson Space Center, Houston, TX 77058
*Find the extensive, full author and affiliation list on the publishers Website

Tridymite, a low-pressure, high-temperature (>870 °C) SiO₂ polymorph, was detected in a drill sample of laminated mudstone (Buckskin) at Marias Pass in Gale crater, Mars, by the Chemistry and Mineralogy X-ray diffraction instrument onboard the Mars Science Laboratory rover Curiosity. The tridymitic mudstone has ∼40 wt.% crystalline and ∼60 wt.% X-ray amorphous material and a bulk composition with ∼74 wt.% SiO₂ (Alpha Particle X-Ray Spectrometer analysis). Plagioclase (∼17 wt.% of bulk sample), tridymite (∼14 wt.%), sanidine (∼3 wt.%), cation-deficient magnetite (∼3 wt.%), cristobalite (∼2 wt.%), and anhydrite (∼1 wt.%) are the mudstone crystalline minerals. Amorphous material is silica-rich (∼39 wt.% opal-A and/or high-SiO₂ glass and opal-CT), volatile-bearing (16 wt.% mixed cation sulfates, phosphates, and chlorides−perchlorates−chlorates), and has minor TiO₂ and Fe₂O₃T oxides (∼5 wt.%). Rietveld refinement yielded a monoclinic structural model for a well-crystalline tridymite, consistent with high formation temperatures. Terrestrial tridymite is commonly associated with silicic volcanism, and detritus from such volcanism in a “Lake Gale” catchment environment can account for Buckskin’s tridymite, cristobalite, feldspar, and any residual high-SiO₂ glass. These cogenetic detrital phases are possibly sourced from the Gale crater wall/rim/central peak. Opaline silica could form during diagenesis from high-SiO₂ glass, as amorphous precipitated silica, or as a residue of acidic leaching in the sediment source region or at Marias Pass. The amorphous mixed-cation salts and oxides and possibly the crystalline magnetite (otherwise detrital) are primary precipitates and/or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions, temperatures, and acidities. Anhydrite is post lithification fracture/vein fill.

¹J. Borovička, ²A.A Berezhnoy
Icarus (in Press) Link to Article [doi:10.1016/j.icarus.2016.06.022]
¹Astronomical Institute, Czech Academy of Sciences, Fričova Street 298, CZ-25165 Ondřejov, Czech Republic
²Sternberg Astronomical Institute, Moscow State University, Universitetskij pr., 13, Moscow, 119991 Russia
Copyright Elsevier

We analyzed molecular radiation in the spectra of the very bright Benešov bolide. The Benešov bolide appeared over the Czech Republic on May 7, 1991 and reached an absolute magnitude of –19.5. It was caused by a meteoroid larger than 1 meter. Small meteorites of various mineralogical types were recovered recently (Spurný et al. 2014, Astron. Astrophys. 570, A39). The spectrum of the bolide, recorded on two photographic plates, is probably the richest meteor spectrum ever obtained. It contains hundreds of atomic emission lines, continuous radiation and molecular bands, and covers the whole bolide trajectory from the altitude of 90 km to 20 km. In this paper we focus on identification and analysis of molecular bands. The identification of FeO, CaO, AlO, and MgO, reported earlier (Borovička and Spurný 1996, Icarus 121, 484) was confirmed. In addition, radiation of N2 was probably detected. The oxides were best seen in the wake and in the radiating cloud left at the position of the bolide flare at the altitude of 24.5 km. Trace of N2 was seen only in the meteor at lower altitudes. FeO bands are present in the spectra from the highest altitudes. We suppose that FeO was ablated directly in molecular form at high altitudes. CaO was first detected just below 50 km and its intensity, relatively to FeO, strongly increased toward lower altitudes. AlO, which is similarly refractive as CaO, behaved as FeO rather than CaO at lower altitudes. MgO was observed only in the radiating cloud. The spectrum of the cloud is unique because it contains almost no atomic lines. We compared the data with theoretical calculations of the presence of molecules in the mixture of meteoric vapors and air at various altitudes and temperatures. CN and TiO were not found. The upper limit of CN is in agreement with theory for ordinary chondrite meteoroid. Most of carbon should be in fact present in the form of CO, but CO bands are too weak to be detected. The non-detection of TiO can be explained by the fact that temperature in the wake and the cloud was lower than needed for the presence of TiO bands. However, AlO was found to be about 40 times more abundant than MgO, although comparable abundances are expected. The explanation may be that the abundances are in fact comparable but there are non-equilibrium conditions in the radiating cloud with the excitation temperature of MgO lower than that of AlO. The difference may be caused by higher ablation temperature of Al. Another non-equilibrium effect is the observed difference between the rotational (∼ 1000 K) and vibrational (∼ 3000 K) temperature of AlO molecules. This can be explained by short hydrodynamic timescale and the fact that vibrational relaxation time is significantly longer than rotational relaxation time. The vibrational temperature therefore could not decrease so quickly during the cooling and expansion of the cloud because of insufficient number of collisions. FeO and CaO could not be analyzed in detail, because their molecular constants, especially transition probabilities, are not well known. The increase of the CaO/FeO ratio with decreasing altitude could be, nevertheless, explained in scope of equilibrium chemistry.

¹Fox, V.K., ¹Arvidson, R.E., ¹Guinness, E.A., ²Mclennan, S.M., ¹Catalano, J.G., ³Murchie, S.L., ¹Powell, K.E.
Geophysical Research Letters (in Press) Link to Article [DOI: 10.1002/2016GL069108]
¹Department of Earth and Planetary Sciences Washington University in St. Louis St. Louis, Missouri USA
²Department of Geosciences Stony Brook University Stony Brook, New York USA
³Applied Physics Laboratory The Johns Hopkins University Laurel, Maryland USA

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¹Litvak, M.L. et al. (>10)*
Journal of Geophysical Research E: Planets 121,836-845 Link to Article [DOI: 10.1002/2015JE004960]
¹Space Research Institute, RAS, Moscow, Russian Federation
Published by arrangement with John Wiley & Sons
*Find the extensive, full author and affiliation list on the publishers website

The Dynamic Albedo of Neutron (DAN) instrument on board the Mars Science Laboratory Curiosity rover acquired a series of measurements as part of an observational campaign of the Kimberley area in Gale crater. These observations were planned to assess the variability of bulk hydrogen and neutron-absorbing elements, characterized as chlorine-equivalent concentration, in the geologic members of the Kimberley formation and in surface materials exposed throughout the area. During the traverse of the Kimberley area, Curiosity drove primarily over the “Smooth Hummocky” unit, a unit composed primarily of sand and loose rocks, with occasional stops at bedrock of the Kimberley formation. During the Kimberley campaign, DAN detected ranges of water equivalent hydrogen (WEH) and chlorine-equivalent concentrations of 1.5–2.5 wt % and 0.6–2 wt %, respectively. Results show that as the traverse progressed, DAN observed an overall decrease in both WEH and chlorine-equivalent concentration measured over the sand and loose rocks of the Smooth Hummocky unit. DAN measurements of WEH and chlorine-equivalent concentrations in the well-exposed sedimentary bedrock of the Kimberley formation show fluctuations with stratigraphic position. The Kimberley campaign also provided an opportunity to compare measurements from DAN with those from the Sample Analysis at Mars (SAM) and the Alpha-Particle X-ray Spectrometer (APXS) instruments. DAN measurements obtained near the Windjana drill location show a WEH concentration of ~1.5 wt %, consistent with the concentration of low-temperature absorbed water measured by SAM for the Windjana drill sample. A comparison between DAN chlorine-equivalent concentrations measured throughout the Kimberley area and APXS observations of corresponding local surface targets and drill fines shows general agreement between the two instruments.

¹Le Deit, E. et al. (>10)*
Journal of Geophysical Research E: Planets 121, 784-804 Link to Article [DOI: 10.1002/2015JE004987]
¹Laboratoire de Planétologie et Géodynamique, LPG-Nantes, UMR CNRS 6112, Université de Nantes, Nantes, France
Published by arrangement with John Wiley & Sons
*Find the extensive, full author and affiliation list on the publishers website

The Mars Science Laboratory rover Curiosity encountered potassium-rich clastic sedimentary rocks at two sites in Gale Crater, the waypoints Cooperstown and Kimberley. These rocks include several distinct meters thick sedimentary outcrops ranging from fine sandstone to conglomerate, interpreted to record an ancient fluvial or fluvio-deltaic depositional system. From ChemCam Laser-Induced Breakdown Spectroscopy (LIBS) chemical analyses, this suite of sedimentary rocks has an overall mean K2O abundance that is more than 5 times higher than that of the average Martian crust. The combined analysis of ChemCam data with stratigraphic and geographic locations reveals that the mean K2O abundance increases upward through the stratigraphic section. Chemical analyses across each unit can be represented as mixtures of several distinct chemical components, i.e., mineral phases, including K-bearing minerals, mafic silicates, Fe-oxides, and Fe-hydroxide/oxyhydroxides. Possible K-bearing minerals include alkali feldspar (including anorthoclase and sanidine) and K-bearing phyllosilicate such as illite. Mixtures of different source rocks, including a potassium-rich rock located on the rim and walls of Gale Crater, are the likely origin of observed chemical variations within each unit. Physical sorting may have also played a role in the enrichment in K in the Kimberley formation. The occurrence of these potassic sedimentary rocks provides additional evidence for the chemical diversity of the crust exposed at Gale Crater.

¹Ma, C., ¹Beckett, J.R.
American Mineralogist 101, 1161-1170 Link to Article [DOI: 10.2138/am-2016-5399]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, United States
Copyright: The Mineralogical Society of America

Majindeite (IMA 2012-079), Mg2Mo3O8, is a new mineral, occurring as submicrometer-sized crystals with Ni-Fe and Ru-Os-Ir alloys, ± apatite and Nb-oxide. The observed assemblages are partially or wholly enclosed by MgAl2O4 spinel in a Type B1 Ca-Al-rich inclusion, ACM-2, from the Allende CV3 carbonaceous chondrite. The type majindeite has an empirical formula of (Mg1.57Fe0.43)Mo3.00O8, and a nolanite-type P63mc structure with a = 5.778 Å, c = 9.904 Å, V = 286.35 Å3, and Z = 2, leading to a calculated density of 5.54 g/cm3. Majindeite likely formed during the subsolidus oxidation of Mo-rich precursor phase(s) included in Fe-Ni rich alloys in a system that was open to O, Mg, and Ca, which were derived externally and introduced via cracks, subgrain boundaries, and/or surfaces exposed at the exterior of the spinel. If magnetite existed in the phase assemblage, it was lost due to Fe volatilization prior to the formation of majindeite. The immediate precursor to majindeite was likely kamiokite. Majindeite formed during an oxidation event contemporaneous with or postdating the formation of grossular-rich veins in melilite. Kamiokite, the Fe-rich analog of majindeite, also occurs in ACM-2 but only within phase assemblages that contain magnetite and which are entirely enclosed in melilite ± alteration products. Here, grossular-rich veins are not observed and the coexisting awaruites are more Fe-rich than those observed with majindeite. As with majindeite, the precursors for kamiokite grains were also likely to have been Mo-rich alloys, but the Mo-oxide remained magnetite-saturated throughout the alteration process and therefore remained Fe-rich. © 2016 by Walter de Gruyter Berlin/Boston 2016.

^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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