¹Vacheslav V. Emel’yanenko, ¹Sergey A. Naroenkov, ^2,3Peter Jenniskens,⁴Olga P. Popova
¹Institute of Astronomy of the Russian Academy of Sciences, Moscow, Russia
²SETI Institute, Carl Sagan Center, Mountain View, California, USA
³NASA Ames Research Center, Moffett Field, California, USA
⁴Institute for Dynamics of Geospheres of the Russian Academy of Sciences, Moscow, Russia

The orbit of the Chelyabinsk object is calculated, applying the least-squares method directly to astrometric positions. The dynamical evolution of this object in the past is studied by integrating equations of motion for particles with orbits from the confidence region. It is found that the majority of the Chelyabinsk clones reach the near-Sun state. Sixty-seven percent of these objects have collisions with the Sun for 15 Myr in our numerical simulations. The distribution of minimum solar distances shows that the most probable time for the encounters of the Chelyabinsk object with the Sun lies in the interval from −0.8 Myr to −2 Myr. This is consistent with the estimate of a cosmic ray exposure age of 1.2 Myr (Popova et al. 2013). A parent body of the Chelyabinsk object should experience strong tidal and thermal effects at this time. The possible association of the Chelyabinsk object with 86039 (1999 NC43) and 2008 DJ is discussed.

Reference
Emel’yanenko VV, Naroenkov SA, Jenniskens P, Popova OP (2014) The orbit and dynamical evolution of the Chelyabinsk object. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12382]

Published by arrangement with John Wiley&Sons

¹Nancy L. Chabot, ²E. Alex Wollack, ³Munir Humayun,¹Ellen M. Shank
¹Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
²Department of Physics, Princeton University, Princeton, New Jersey, USA
³Department of Earth, Ocean and Atmospheric Science and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, USA

Oxygen has been considered a potentially important light element in metallic liquids during a range of planetary processes, yet the influence of O in a metallic melt on element partitioning behavior is largely unknown. To investigate the effect of O in such systems, we conducted experiments in the Fe-S-O system, doped with 25 trace elements, which produced two immiscible metallic liquids. Our results indicate that the presence of O in the metallic liquid produces a distinctive chemical signature for W and Ga in particular. Tungsten shows an affinity for O in the metallic liquid and partitions more strongly into the metallic melt in the presence of O. The partitioning of Ga is relatively constant despite the presence of O, which is in contrast to the majority of the other siderophile elements in the study. Our experiments from 1400 to 1600 °C show no significant effect from temperature on the partitioning behavior of any trace elements over this limited temperature range. This distinctive chemical signature due to the presence of O in the metallic liquid has potential implications for modeling core formation, evaluating isotopic signatures produced by core crystallization, and interpreting chemical assemblages observed in meteorites.

Reference
Chabot NL, Wollack EA, Humayun M, Shank EM (2014) The effect of oxygen as a light element in metallic liquids on partitioning behavior. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12383]

Published by arrangement with John Wiley&Sons

¹C. K. Shearer, ¹P. V. Burger, ¹J. J. Papike, ¹F. M. McCubbin,¹A. S. Bell
¹Institute of Meteoritics and Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA

Merrillite is a ubiquitous accessory phase in a variety of Martian meteorite lithologies. The Martian merrillites exhibit a positive correlation between Mg# and Na and a negative correlation between Mg# and both Mn and vacancies in the octahedral Na-site. Their REE patterns are varied and range from LREE-depleted to LREE-enriched. The dominant cation substitutions in the Martian merrillites are Fe2+VI Mg-site[]Mg2+VI Mg-site and Ca2+VI Na-site + □VI Na-site[]2Na+VI Na-site. The REE substitution into the 8-fold coordinated Ca-site is accommodated by the coupled substitution CaVIII Ca-site + (Na)VI Na-site [](Y3+ + REE3+)VIII Ca-site + □VI Na-site. The REE substitution is significantly more prevalent in lunar merrillite and can be used as a “fingerprint” to distinguish lunar from Martian meteorites. The substitution of OH− (whitlockite) and/or F− (bobdownsite) for O2− on one of the phosphate tetrahedrons appears to be rather insignificant. The correlations among Na, Mg#, Mn, and Na-site vacancies are linked to the premerrillite crystallization history of the melt and the crystal chemical behavior of the Mg- and Na-sites. The former reflects the sequence and extent of plagioclase and pyroxene crystallization. The differences in REE pattern shapes among the merrillites reflect source regions for the Martian basalts and the shapes are not greatly perturbed by the crystallization history. The occurrence of merrillite does not imply low-volatile component in the Martian magmas. However, the low whitlockite and bobdownsite contents suggest that these samples were not altered by hydrothermal fluids and therefore not reset owing to aqueous fluid interactions. Consequently, the young ages of the shergottites are probably true igneous crystallization ages.

Reference
Shearer CK, Burger PV, Papike JJ, McCubbin FM, Bell AS (2014) Crystal chemistry of merrillite from Martian meteorites: Mineralogical recorders of magmatic processes and planetary differentiation. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12355]

Published by arrangement with John Wiley&Sons

¹Agnese Fazio, ¹Luigi Folco, ¹Massimo D’Orazio, ²Maria Luce Frezzotti,^3,4Carole Cordier
¹Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
²Dipartimento di Scienze dell’ambiente e del Territorio e di Scienze della Terra (DISAT), Sezione di Scienze Geologiche Geotecnologie, Milano, Italy
³Université de Grenoble Alpes, ISTerre, Grenoble CEDEX 9, France
⁴CNRS, ISTerre, Grenoble CEDEX 9, France

Kamil is a 45 m diameter impact crater identified in 2008 in southern Egypt. It was generated by the hypervelocity impact of the Gebel Kamil iron meteorite on a sedimentary target, namely layered sandstones with subhorizontal bedding. We have carried out a petrographic study of samples from the crater wall and ejecta deposits collected during our first geophysical campaign (February 2010) in order to investigate shock effects recorded in these rocks. Ejecta samples reveal a wide range of shock features common in quartz-rich target rocks. They have been divided into two categories, as a function of their abundance at thin section scale: (1) pervasive shock features (the most abundant), including fracturing, planar deformation features, and impact melt lapilli and bombs, and (2) localized shock features (the least abundant) including high-pressure phases and localized impact melting in the form of intergranular melt, melt veins, and melt films in shatter cones. In particular, Kamil crater is the smallest impact crater where shatter cones, coesite, stishovite, diamond, and melt veins have been reported. Based on experimental calibrations reported in the literature, pervasive shock features suggest that the maximum shock pressure was between 30 and 60 GPa. Using the planar impact approximation, we calculate a vertical component of the impact velocity of at least 3.5 km s−1. The wide range of shock features and their freshness make Kamil a natural laboratory for studying impact cratering and shock deformation processes in small impact structures.

Reference
Fazio A, Folco L, D’Orazio M, Frezzotti ML, Cordier C (2014) Shock metamorphism and impact melting in small impact craters on Earth: Evidence from Kamil crater, Egypt. Meteoritics & Planetary Science (In Press)
Link to Article [doi: 10.1111/maps.12385]

Published by arrangement with John Wiley&Sons

¹S. W. Lehner1, ²W. F. McDonough,³P. Németh
¹School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
²Department of Geology, University of Maryland, College Park, Maryland, USA
³Institute of Materials and Environmental Chemistry, Research Center for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary

We investigated the matrix mineralogy in primitive EH3 chondrites Sahara 97072, ALH 84170, and LAR 06252 with transmission electron microscopy; measured the trace and major element compositions of Sahara 97072 matrix and ferromagnesian chondrules with laser-ablation, inductively coupled, plasma mass spectrometry (LA-ICPMS); and analyzed the bulk composition of Sahara 97072 with LA-ICPMS, solution ICPMS, and inductively coupled plasma atomic emission spectroscopy. The fine-grained matrix of EH3 chondrites is unlike that in other chondrite groups, consisting primarily of enstatite, cristobalite, troilite, and kamacite with a notable absence of olivine. Matrix and pyroxene-rich chondrule compositions differ from one another and are distinct from the bulk meteorite. Refractory lithophile elements are enriched by a factor of 1.5–3 in chondrules relative to matrix, whereas the matrix is enriched in moderately volatile elements. The compositional relation between the chondrules and matrix is reminiscent of the difference between EH3 pyroxene-rich chondrules and EH3 Si-rich, highly sulfidized chondrules. Similar refractory element ratios between the matrix and the pyroxene-rich chondrules suggest the fine-grained material primarily consists of the shattered, sulfidized remains of the formerly pyroxene-rich chondrules with the minor addition of metal clasts. The matrix, chondrule, and metal-sulfide nodule compositions are probably complementary, suggesting all the components of the EH3 chondrites came from the same nebular reservoir.

Reference
Lehner SW, McDonough WF, Németh P (2014) EH3 matrix mineralogy with major and trace element composition compared to chondrules. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12391]

Published by arrangement with John Wiley&Sons

^1,2Haley M. Sapers, ^1,3Gordon R. Osinski, ¹Neil R. Banerjee, ^1,4Ludovic Ferrière, ⁵Philippe Lambert, ^1,6Matthew R. M. Izawa
¹Department of Earth Sciences and the Centre for Planetary Science and Exploration, Western University, London, ON, Canada
²Department of Natural Resource Science, McGill Université, Québec, Canada
³Department of Physics & Astronomy, University of Western Ontario, London, Ontario, Canada
⁴Natural History Museum, Vienna, Austria
⁵Sciences et Applications, Bordeaux, France
⁶Department of Geography, University of Winnipeg, Winnipeg, Manitoba, Canada

The Rochechouart impact structure, south-central France (45o50′N, 0o46′E), is a partly eroded, approximately 200 Myr, complex impact structure. The impactite suite at Rochechouart provides an excellent example of gradational boundaries and transitional lithologies that have been historically difficult to classify with standard impactite nomenclature. Here, we present the first detailed scanning electron microscopy-based description of the Rochechouart impactites integrated with hand-sample and petrographic observations with the goal of understanding the clast-matrix relationships of transitional lithologies. Three main impact-generated hydrothermal alteration assemblages are also recognized: (1) argillic-like, (2) carbonate, and (3) oxide. Our results support the existence of a continuum between clast-rich impact melt rocks and glass-rich clastic breccias (suevites) that must be represented in universal classification schemes. This suite of impactites from the Rochechouart impact structure is used as a test case for a recently published classification scheme based on the nature of the groundmass setting a precedent for classification of impactites with limited to no geological context such as deeply eroded terrestrial impact structures and future sample return missions. The re-evaluation of the melt-bearing Rochechouart impactites questions the currently accepted size of the crater, suggesting a much larger original crater diameter.

Reference
Sapers HM, Osinski GR, Banerjee NR, Ferrière L, Lambert P, Izawa MRM (2014) Revisiting the Rochechouart impact structure, France. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12381]

Published by arrangement with John Wiley&Sons

^1,2Selby Cull, ^2,3Patrick C. McGuire, ²Christoph Gross, ¹Jenna Myers, ¹Nina Shmorhun
¹Department of Geology, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, USA
²Planetary Sciences and Remote Sensing Group, Institute of Geological Sciences, Department of Earth Sciences, Freie Universitaet Berlin, Berlin 12249, Germany
³Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland 20723, USA

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Reference
Cull S, McGuire PC, Gross C, Myers J, Shmorhun N (2014) A new type of jarosite deposit on Mars: Evidence for past glaciation in Valles Marineris? Geology 42, 59-962
Link to Article [doi:10.1130/G36152.1]

¹David W. Mittlefehldt
¹XI3/Astromaterials Research Office, Astromaterials Research and Exploration Sciences Division, NASA/Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, USA

The howardite, eucrite and diogenite (HED) clan of meteorites are ultramafic and mafic igneous rocks and impact-engendered fragmental debris derived from a thoroughly differentiated asteroid. Earth-based telescopic observation and data returned from vestan orbit by the Dawn spacecraft make a compelling case that the asteroid (4) Vesta is the parent asteroid of HEDs, although this is not universally accepted. Diogenites are petrologically diverse and include dunitic, harzburgitic and noritic lithologic types in addition to the traditional orthopyroxenites. Diogenites form the lower crust of Vesta. Cumulate eucrites are gabbroic rocks formed by accumulation of pigeonite and plagioclase from a mafic magma at depth within the crust, while basaltic eucrites are melt compositions that likely represent shallow-level dikes and sills, and flows. Some basaltic eucrites are richer in incompatible trace elements compared to most eucrites, and these may represent mixed melts contaminated by partial melts of the mafic crust. Differentiation occurred within a few Myr of formation of the earliest solids in the Solar System. Evidence from oxygen isotope compositions and siderophile element contents favor a model of extensive melting of Vesta forming a global magma ocean that rapidly (period of a few Myr) segregated and crystallized to yield a metallic core, olivine-rich mantle, orthopyroxene-rich lower crust and basaltic upper crust. The igneous lithologies were subjected to post-crystallization thermal processing, and most eucrites show textural and mineral-compositional evidence for metamorphism. The cause of this common metamorphism is unclear, but may have resulted from rapid burial of early basalts by later flows caused by high effusion rates on Vesta. The observed surface of Vesta is covered by fragmental debris resulting from impacts, and most HEDs are brecciated. Many eucrites and diogenites are monomict breccias indicating a lack of mixing. However, many HEDs are polymict breccias. Howardites are the most thoroughly mixed polymict breccias, yet only some of them contain evidence for residence in the true regolith. Based on the numbers of meteorites, compositions of howardites, and models of magma ocean solidification, cumulate eucrites and their residual ferroan mafic melts are minor components of the vestan crust.

Reference
Mittlefehldt DW (2014) Asteroid (4) Vesta: I. The howardite-eucrite-diogenite (HED) clan of meteorites. Chemie der Erde (in Press)
Link to Article [doi:10.1016/j.chemer.2014.08.002]

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^1,2János Kovacs,²István Sajó, ^3,4Zsuzsanna Márton, ^1,2Viktor Jáger, ⁵Tibor Hegedüs, ⁶Tibor Berecz, ⁴Tamás Tóth, ⁷Péter Gyenizse, ^1,2András Podobni
¹Department of Geology and Meteorology, University of Pécs, H-7624 Pécs, Ifjúság u. 6, Hungary
²Environmental Analytical and Geoanalytical Research Group, Szentágothai Research Centre, University of Pécs, H-7624 Pécs, Ifjúság u. 20, Hungary
³MTA-PTE High-Field Terahertz Research Group, H-7624, Pécs Ifjúság u. 6, Hungary
⁴Institute of Physics, University of Pécs, H-7624, Pécs Ifjúság u. 6, Hungary
⁵Baja Astronomical Observatory, H-6500 Baja, POB 766, Hungary
⁶Department of Materials Science and Engineering, Budapest University of Technology and Economics, H-1111 Budapest, Bertalan L. u. 7, Hungary
⁷Department of Cartography and Geoinformatics, University of Pécs, H-7624 Pécs, Ifjúság u. 6, Hungary

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Reference
Kovacs J, István Sajób, Márton Z, Jáger V, Hegedüs T, Berecz T, Tóth T, Gyenizse P, Podobni A (2014) Csátalja, the largest H4-5 chondrite from Hungary. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2014.11.009]

¹M.C. De Sanctis, ¹A. Frigeri, ^1,2E. Ammannito, ¹F. Tosi, ^1,3S. Marchi, ¹F. Zambon, ⁴C.A. Raymond, ²C.T. Russell
¹INAF, Istituto di Astrofisica e Planetologia Spaziali, Area di Ricerca di Tor Vergata, 00133 Roma, Italy
²Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, USA
³SSERVI Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, CO 80302
⁴Jet Propulsion Laboratory, Pasadena, CA 91109, USA

The young Marcia crater on Vesta displays several interesting features, including pitted and smooth terrains, exposure of relatively bright and dark material, and enrichments of hydrated material in the ejecta. Several questions arise about the origin of Marcia and of the dark material (exogenic material versus volcanic or impact melts) and the smooth and pitted terrains. Here we describe the results of the spectral and thermal analysis of the Marcia crater, with a particular effort to assess the composition of the different units, identifying the presence of OH and its correlation with dark material. Detailed studies of the Marcia crater wall, smooth and floor units reveal a compositional rich terrain with small areas enriched in diogenites with respect to the general eucritic regolith dominating the equatorial region of Vesta. The signature of OH is particularly clear in the pitted floor, dark material, smooth unit, and ejecta. The pitted terrains, beside their appearance, also show thermal anomalies, being colder with respect to the surrounding terrains. The presence of OH, concentrated in darker layers, and the pitted crater floor indicate that the area where the Marcia impact event occurred was rich in volatiles. The results show how the relatively young impact events have modified the surface of Vesta, disrupting a layer of dark material once present on Vesta’s equatorial terrain and exposing fresh, bright material rich in pyroxene.

Reference
De Sanctis MC, Frigeri A, Ammannito E, Tosi F, Marchi S, Zambon F, Raymond CA, Russell CT (2014) Mineralogy of Marcia, the youngest large crater of Vesta: Character and distribution of pyroxenes and hydrated material. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.10.051]

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