^1,2Enrico Bonatti, ^2,3Dee Breger, ⁴Tommaso Di Rocco, ¹Fulvio Franchi, ¹Luca Gasperini, ¹Alina Polonia, ⁵John Anfinogenov, ⁶Yana Anfinogenova
¹Istituto di Scienze Marine, CNR, U.O.S. Bologna, via Gobetti 101, 40129, Bologna, Italy
²Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA
³Micrographic Arts, P.O. Box 3088, Saratoga Springs 12866, NY, USA
⁴Geowissenschaftliches Zentrum, Abteilung Isotopengeologie, Georg-August-Universität, Goldschmidtstraβe 1, D-37077 Göttingen, Germany
⁵Faculty of Geology and Geography, National Research Tomsk State University, 36 Lenin Avenue, Tomsk, 634050, Russia
⁶Institute of Physics and Technology, National Research Tomsk Polytechnic University, 30 Lenin Avenue, Tomsk, 634050, Russia

An exotic meter-size quartzitic boulder known as John’s Stone was found by John Anfinogenov in 1972 buried in permafrost close to the epicenter of the 1908 Tunguska blast in a region of Siberia dominated by Permian-Triassic Siberian Trap basalts. The boulder is made almost entirely of well-cemented quartz grains, mostly around 100μm in size; it contains zones with coarser or finer grain sizes. Rare zircon and rutile crystals are scattered within the quartz matrix. Quartz is often dissected by strain lamellae. The rock contains abundant scattered internal vugs rimmed by euhedral quartz crystals. We cannot exclude that John’s Stone is a fragment of a Permian granite-derived sandstone unit. However, based on structure, mineralogy and chemistry the quartzitic boulder may have originated due to silica deposition from hydrothermal solutions that had reacted with basaltic rocks. Anfinogenov et al. (2014) interpreted features observed in the permafrost at the base of the boulder as indicating it impacted from above, suggesting the boulder may be a meteorite, possibly of Martian origin, given the reported presence on Mars of silica-rich deposits. Triple oxygen isotope ratios determined on two samples of the quartzite reveal a terrestrial rather than a Martian meteorites composition. Oxygen isotope data suggest also that the precipitation of SiO2 could have occurred in equilibrium with hydrothermal water (δ18Ow ≈ -19.5 ‰) at the temperature of about 50°C. The thermal event that generated the quartzite may be related either to the century-old Tunguska event, or, more probably, to Permian-Triassic Siberian Traps magmatism, although an extraterrestrial origin cannot be completely ruled out.

Reference
Bonatti E, Breger D, Di Roccod T, Franchi F, Gasperini L, Polonia A, Anfinogenov J, Anfinogenova Y (2015)
Origin of John’s Stone: A quartzitic boulder from the site of the 1908 Tunguska (Siberia) Explosion. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.018]

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¹A. Kereszturi, ²S. Ormandi, ²S. Jozsa
¹Research Center for Astronomy and Earth Sciences, Konkoly Astronomical Institute, Budapest, Hungary
²Department of Petrology and Geochemistry, Faculty of Science, Hungarian Academy of Sciences, Eötvös Lorand University of Sciences, Budapest, Hungary

In analyzing a thin section of the NWA 6604 CK4 meteorite, only altered chondrules and various components that are probably left behind the destruction of former chondrules can be observed. We suggest that melting, grain size decrease, resorption of the original chondrules, and crystallization of opaque minerals were the main processes that destroyed the chondrules. Four different events could be identified as having occurred during this alteration. First, opaques crystallized along former fractures producing chains of separated grains. Later, opaques and Ca-rich minerals crystallized together in veins and large melt pockets; this was the strongest recrystallization phase involving the largest volume of melt. This occurred along different fractures than the first phase above. During the third phase, only Ca-rich plagioclase crystallized along thin veins, and in a fourth phase, fractures formed again, partly along those formed during the second phases but without substantial mineral infill. Two simple possible case models should be considered for this meteorite: alteration by purely impact-driven processes or mainly by melt-driven processes. Although for CK4 chondrites, the shock-produced alteration driven by impact is the more accepted and widespread approach, melting is also compatible with the observed textural characteristics of chondrule destruction. During melting, recrystallization took place producing iron-rich minerals earlier and Ca-Si-rich ones later. The penetration of melts into veins contributed in the chondrule destruction. The stress directions also changed during these alterations, and minerals that formed later filled differently oriented fractures than the earlier ones. From our observations, we favor a view where heat-driven melting and recrystallization produced the destruction and uniform mineralogy in the sample.

Reference
Kereszturi A, Ormandi S, Jozsa S (2015) Possible melting produced chondrule destruction in NWA 6604 CK4 chondrite. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12458]

Published by arrangement with John Wiley&Sons

^1,2A. Yamaguchi, ³J. A. Barrat, ⁴N. Shirai, ^1,4M. Ebihara
¹National Institute of Polar Research, Tachikawa, Tokyo, Japan
²Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, Japan
³U.B.O.-I.U.E.M., CNRS UMR 6538, Plouzané Cedex, France
⁴Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo, Japan

We performed a petrological and geochemical study of an olivine diogenite, Northwest Africa (NWA) 5480. NWA 5480 is a crystalline stone, but shows a heterogeneous texture. Olivine aggregates and grains of olivine and chromite display resorption textures set in a crystalline pyroxene matrix. Large olivine aggregates are penetrated by pyroxene matrix. Flow textures are observed near olivine aggregates. Olivine, chromite, and pyroxene show minor chemical zoning, implying relatively rapid cooling. NWA 5480 contains a significant amount of platinum group elements with chondritic relative proportions. All this evidence supports that NWA 5480 is an impact-melt breccia from a target composed of olivine and pyroxene-rich lithologies. Such impact melt would have formed by melting crustal materials, possibly during one of the impacts that formed the South Pole basins on Vesta.

Reference
Yamaguchi A, BarratJA, Shirai N, Ebihara M (2015) Petrology and geochemistry of Northwest Africa 5480 diogenite and evidence for a basin-forming event on Vesta. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12470]

Published by arrangement with John Wiley&Sons

^1,2Christoph Burkhardt,²Maria Schönbächler
¹Institute of Geochemistry and Petrology, Clausiusstrasse 25, ETH Zürich, CH-8092 Zürich, Switzerland
²Origins Laboratory, Department of Geophysical Sciences, The University of Chicago, IL 60637, USA

The progressive dissolution of the carbonaceous chondrites Orgueil (CI1), Murchison (CM2) and Allende (CV3) with acids of increasing strength reveals correlated W isotope variations ranging from 3.5 ε182W and 6.5 ε183W in the initial leachate (acetic acid) to –60 ε182W and –40 ε183W in the leachate residue. The observed variations are readily explained by variable mixing of s-process depleted and s-process enriched components. One W s-process carrier is SiC, however, the observed anomaly patterns and mass-balance considerations require at least on additional s-process carrier, possibly a silicate or sulfide. The data reveal well-defined correlations, which provide a test for s-process nucleosynthesis models. The correlations demonstrate that current models need to be revised and highlight the need for more precise W isotope data of SiC grains. Furthermore the correlations provide a mean to disentangle nucleosynthetic and radiogenic contributions to 182W (ε182Wcorrected= ε182Wmeasured –(1.41±0.05) × ε183Wmeasured; ε182Wcorrected= ε182Wmeasured –(–0.12±0.06) × ε184Wmeasured), a prerequisite for the successful application of the Hf-W chronometer to samples with nucleosynthetic anomalies.

The overall magnitude of the W isotope variations decreases in the order CI1>CM2>CV3. This can be interpreted as the progressive thermal destruction of an initially homogeneous mixture of presolar grains by parent-body processing. However, not only the magnitude but also the W anomaly patterns of the three chondrites are different. In particular leach step 2, that employs nitric acid, reveals a s-deficit signature for Murchison, but a s-excess for Orgueil and Allende. This could be the result of redistribution of anomalous W into a new phase by parent-body alteration, or, the fingerprint of dust processing in the solar nebula. Given that the thermal and aqueous alteration of Murchison is between the CI and CV3 chondrites, parent-body processing is probably not the sole cause for creating the different patters. Small-scale nebular redistribution of anomalous W may have played a role as well. Similar nebular processes possibly acted differently on specific carrier phases and elements, resulting in the diverse nucleosynthetic signatures observed in planetary materials today.

Reference
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]
Copyright Elsevier

¹Jean Bollard, ¹James N. Connelly, ¹Martin Bizzarro
¹Centre for Star and Planet Formation, Natural History Museum of Denmark, Copenhagen, Denmark

The CB chondrites are metal-rich meteorites with characteristics that sharply distinguish them from other chondrite groups. Their unusual chemical and petrologic features and a young formation age of bulk chondrules dated from the CBa chondrite Gujba are interpreted to reflect a single-stage impact origin. Here, we report high-precision internal isochrons for four individual chondrules of the Gujba chondrite to probe the formation history of CB chondrites and evaluate the concordancy of relevant short-lived radionuclide chronometers. All four chondrules define a brief formation interval with a weighted mean age of 4562.49 ± 0.21 Myr, consistent with its origin from the vapor-melt impact plume generated by colliding planetesimals. Formation in a debris disk mostly devoid of nebular gas and dust sets an upper limit for the solar protoplanetary disk lifetime at 4.8 ± 0.3 Myr. Finally, given the well-behaved Pb-Pb systematics of all four chondrules, a precise formation age and the concordancy of the Mn-Cr, Hf-W, and I-Xe short-lived radionuclide relative chronometers, we propose that Gujba may serve as a suitable time anchor for these systems.

Reference
Bollard J, Connelly JN, Bizzarro M (2015) Pb-Pb dating of individual chondrules from the CBa chondrite Gujba: Assessment of the impact plume formation model. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12461]

Published by arrangement with John Wiley&Sons

¹J. Borovička et al. (>10)*
¹Astronomical Institute of the Czech Academy of Sciences, Ondřejov, Czech Republic

The Križevci H6 meteorite was recovered on the basis of fireball data obtained by the cameras of the Croatian Meteor Network. The fireball, which occurred on February 4, 2011, 23:20:40 UT, was also observed by meteor cameras in Slovenia and by the Autonomous Fireball Observatory in Martinsberg, Austria, which belongs to the European Fireball Network. Here, we present detailed data on fireball trajectory, velocity, deceleration, light curve, and orbit. We also modeled the atmospheric fragmentation of the meteoroid on the basis of the light curve and deceleration. The initial mass of the meteoroid was between 25–100 kg, most probably about 50 kg. Severe fragmentation occurred at heights of approximately 60 and 31 km, under dynamic pressures of 0.1 and 3 MPa, respectively. The peak absolute magnitude of −13.7 was reached during the second severe fragmentation event. The recovered 291 g meteorite was probably the only fragment with a terminal mass exceeding 100 g. The orbit had a low inclination of 0.6 degrees, perihelion distance 0.74 AU, and semimajor axis 1.54 AU. Križevci can be ranked among the 10 best documented meteorite falls.

Reference
Borovička J et al. (2015) The instrumentally recorded fall of the Križevci meteorite, Croatia, February 4, 2011. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12469]

Published by arrangement with John Wiley and Sons

^1,2Mutsumi Komatsu, ¹Timothy J. Fagan, ³Takashi Mikouchi, ⁴Michail I. Petaev, ⁵Michael E. Zolensky
¹Department of Earth Sciences, Waseda University, Tokyo, Japan
²Waseda Institute for Advanced Study, Waseda University, Tokyo, Japan
³Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
⁴Department of Earth and Planetary Sciences, Harvard University and Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA
⁵NASA Johnson Space Center, Astromaterials Research and Exploration Science (ARES), Houston, Texas, USA

MnO/FeO ratios in olivine from amoeboid olivine aggregates (AOAs) reflect conditions of nebular condensation and can be used in concert with matrix textures to compare metamorphic conditions in carbonaceous chondrites. LIME (low-iron, Mn-enriched) olivine was identified in AOAs from Y-81020 (CO3.05), Kaba (CV~3.1), and in Y-86009 (CV3), Y-86751 (CV3), NWA 1152 (CR/CV3), but was not identified in AOAs from Efremovka (CV3.1–3.4) or Allende (CV>3.6). According to thermodynamic models of nebular condensation, LIME olivine is stable at lower temperatures than Mn-poor olivine and at low oxygen fugacities (dust enrichment <10× solar). Although this set of samples does not represent a single metamorphic sequence, the higher subtypes tend to have AOA olivine with lower Mn/Fe, suggesting that Mn/Fe decreases during parent body metamorphism. Y-81020 has the lowest subtype and most forsteritic AOA olivine (Fo>95) in our study, whereas Efremovka AOAs are slightly Fe-rich (Fo>92). AOA olivines from Kaba are mostly forsteritic, but rare Fe-rich olivine precipitated from an aqueous fluid. A combination of precipitation of Fe-rich olivine and diffusion of Fe into primary olivine grains resulted in iron-rich compositions (Fo97–59) in Allende AOAs. Variations from fine-grained, nonporous matrix toward higher porosity and coarser lath-like matrix olivine can be divided into six stages represented by (1) Y-81020, Efremovka, NWA 1152; (2) Y-86751 lithology B; (3) Y-86009; (4) Kaba; (5) Y-86751 lithology A; (6) Allende. These stages are inferred to represent general degree of metamorphism, although the specific roles of thermally driven grain growth and diffusion versus aqueous dissolution and precipitation remain uncertain.

Reference
Komatsu M, Fagan TJ, Mikouchi T, Petaev MI, Zolensky ME (2015) LIME silicates in amoeboid olivine aggregates in carbonaceous chondrites: Indicator of nebular and asteroidal processes. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12460]

Published by arrangement with John Wiley&Sons

¹Ryuji Okazaki et al. (>10)*
¹Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, 33, Hakozaki, Higashi-ku 812-8581, Fukuoka, Japan
*Find the extensive, full author and affiliation list on the publishers website

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

Reference
Okazaki R et al. (2015) Mineralogy and noble gas isotopes of micrometeorites collected from Antarctic snow. Earth, Planets and Space 2015, 67:90
Link to Article [doi:10.1186/s40623-015-0261-8]

¹Hans-Peter Gail, ¹Stephan Henke, ^2,3Mario Trieloff
¹Institut für Theoretische Astrophysik, Zentrum für Astronomie, Universität Heidelberg, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
e-mail: gail@uni-heidelberg.de
²Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany
³Klaus-Tschira-Labor für Kosmochemie, Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany

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

Reference
Gail H-P, Henke S, Trieloff M (2015) Thermal evolution and sintering of chondritic planetesimals – II. Improved treatment of the compaction process. Astronomy&Astrophysics 576, A60

Link to Article [http://dx.doi.org/10.1051/0004-6361/201424278]

¹Ernesto Palomba et al. (>10)*
¹INAF-IAPS, Via del Fosso del Cavaliere 100, I-00133 Rome, Italy
*Find the extensive, full author and affiliation list on the publishers website

The discovery of olivine on Vesta’s surface by the VIR imaging spectrometer onboard the Dawn space mission has forced us to reconsider our views of Vestan petrogenetic models. Olivines were expected to be present in the interior of Vesta: in the mantle of a vertically layered body as invoked by the magma ocean models, or at the base (or within) the mantle-crust boundary as proposed by fractionation models. Olivines have been detected by VIR-Dawn in two wide areas near Arruntia and Bellicia, regions located in the northern hemisphere. Interestingly, these olivine-rich terrains are far from the Rheasilvia and the more ancient Veneneia basins, which are expected to have excavated the crust down to reach the mantle. In this work we present our attempts to identify other undetected olivine rich areas on Vesta by using spectral parameters sensitive to olivine such as the Band Area Ratio (BAR) and other specific parameters created for the detection of olivines on Mars (forsterite, fayalite and a generic olivine index). As a preliminary step we calibrated these parameters by means of VIS-IR spectra of different HED meteorite samples: behaviors versus sample grain size and albedo were analyzed and discussed. We selected the BAR and the forsterite index as the best parameters that can be used on Vesta. A cross-correlation analysis has been applied in order to detect olivine signature on the VIR hyperspectral cubes. These detections have then been confirmed by an anti-correlation analysis between the BAR and one of the olivine parameters, independent of the first method applied.
In agreement with the recent discovery, Arruntia and Bellicia were found to be as the most olivine-rich areas, i.e. where the parameter values are strongest. In addition we detected 6 new regions, all but one located in the Vesta north hemisphere. This result confirms again that the old petrogenetic models cannot be straightforwardly applied to Vesta and should be reshaped in the view of these new detections. An alternative and very recent option can be represented by the model according to which surface “eruption” of material from the mantle, including olivine can reach the surface of Vesta.

Reference
Palomba E et al. (2015) Detection of new olivine-rich locations on Vesta. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.011]

Copyright Elsevier