^1,2J. T. Williams, ^1,3C. K. Shearer, ^1,2Z. D. Sharp, ^1,3P. V. Burger, ^3,4F. M. McCubbin, ^1,3A. R. Santos, ^1,3C. B. Agee, ⁵K. D. McKeegan
¹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
²Center for Stable Isotopes, University of New Mexico, Albuquerque, New Mexico, USA
³Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
⁴NASA Johnson Space Center, Mailcode XI2, Houston, Texas, USA
⁵Department of Earth, Planetary, and Space Sciences, UCLA, Los Angeles, California, USA

The Martian meteorites record a wide diversity of environments, processes, and ages. Much work has been done to decipher potential mantle sources for Martian magmas and their interactions with crustal and surface environments. Chlorine isotopes provide a unique opportunity to assess interactions between Martian mantle-derived magmas and the crust. We have measured the Cl-isotopic composition of 17 samples that span the range of known ages, Martian environments, and mantle reservoirs. The 37Cl of the Martian mantle, as represented by the olivine-phyric shergottites, NWA 2737 (chassignite), and Shergotty (basaltic shergottite), has a low value of approximately −3.8‰. This value is lower than that of all other planetary bodies measured thus far. The Martian crust, as represented by regolith breccia NWA 7034, is variably enriched in the heavy isotope of Cl. This enrichment is reflective of preferential loss of 35Cl to space. Most basaltic shergottites (less Shergotty), nakhlites, Chassigny, and Allan Hills 84001 lie on a continuum between the Martian mantle and crust. This intermediate range is explained by mechanical mixing through impact, fluid interaction, and assimilation-fractional crystallization.

Williams JT, Shearer CK, Sharp ZD, Burger PV, McCubbin FM, Santos AR, Agee CB, McKeegan KD (2016) The chlorine isotopic composition of Martian meteorites 1: Chlorine isotope composition of Martian mantle and crustal reservoirs and their interactions. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12647]
Published by arrangement with John Wiley & Sons

¹Dennis Harries,²Michael E. Zolensky
¹Institute of Geosciences, Friedrich Schiller University Jena, Jena, Germany
²Astromaterial Research and Exploration Science—NASA Johnson Space Center, Houston, Texas, USA

The polymict Kaidun microbreccia contains lithologies of C-type chondrites with euhedral iron sulfide crystals of hydrothermal origin. Our FIB-TEM study reveals that acicular sulfides in a CM1 lithology are composed of Fe-rich pyrrhotite with nonintegral vacancy superstructures (NC-pyrrhotite), troilite, and pentlandite, all showing distinct exsolution textures. Based on phase relations in the Fe-Ni-S system, we constrain the temperature of formation of the originally homogeneous monosulfide solid solution to the range of 100–300 °C. In some crystals the exsolution of pentlandite and the microtextural equilibration was incomplete, probably due to rapid cooling. We use thermodynamic modeling to constrain the physicochemical conditions of the extreme hydrothermal alteration in this lithology. Unless the CM1 lithology was sourced from a large depth in the parent body (internal pressure >85 bar) or the temperatures were in the lower range of the interval determined, the water was likely present as vapor. Previously described light δ34S compositions of sulfides in Kaidun’s CM1 lithology are likely due to the loss of 34S-enriched H2S during boiling. Platy sulfide crystals in an adjacent, intensely altered CI1 lithology are composed of Fe-poor, monoclinic 4C-pyrrhotite and NC-pyrrhotite and probably formed at lower temperatures and higher fS2 relative to the CM1 lithology. However, a better understanding of the stability of Fe-poor pyrrhotites at temperatures below 300 °C is required to better constrain these conditions.

Reference
Harries D, Zolensky ME (2016) Mineralogy of iron sulfides in CM1 and CI1 lithologies of the Kaidun breccia: Records of extreme to intense hydrothermal alteration. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12648]
Published by arrangement with John Wiley & Sons

¹Pietrek, A., ¹Kenkmann, T.
¹Institute of Earth and Environmental Sciences—Geology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany

We reassessed two drill cores of the Bunte Breccia deposits of the Ries crater, Germany. The objectives of our study were the documentation of evidence for water in the Bunte Breccia, the evaluation of how that water influenced the emplacement processes, and from which preimpact water reservoir it was derived. The Bunte Breccia in both cores can be structured into a basal layer composed mainly of local substrate material, overlain by texturally and compositionally diverse, crater-derived breccia units. The basal layer is composed of the youngest sediments (Tertiary clays and Upper Jurassic limestone) and has a razor-sharp boundary to the upper breccia units, which are composed of older rocks of Upper Jurassic to Upper Triassic age. Sparse material exchange occurred between the basal layer and the rest of the Bunte Breccia. Fluids predominantly came from the Tertiary and the Upper Triassic sandstone formation. In the basal layer, Tertiary clays were subjected to intense, ductile deformation, indicating saturation with water. This suggests that water was mixed into the matrix, creating a fluidized basal layer with a strong shear localization. In the upper units, Upper Triassic sandstones are intensely deformed by granular flow. The texture requires that the rocks were disaggregated into granular sand. Vaporization of pore water probably aided fragmentation of these rocks. In the Otting core, hot suevite (T > 600 °C) covered the Bunte Breccia shortly after its emplacement. Vertically oriented gas escape pipes in suevite partly emanate directly at the contact to the Bunte Breccia. They indicate that the Bunte Breccia contained a substantial amount of water in the upper part that was vaporized and escaped through these vents.

Reference
Pietrek A, Kenkmann T (2016) Ries Bunte Breccia revisited: Indications for the presence of water in Itzing and Otting drill cores and implications for the emplacement process. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12656]
Published by arrangement with John Wiley & Sons

¹Keita Nagaki, ²Toshihiko Kadono, ¹Tatsuhiro Sakaiya, ¹Tadashi Kondo, ³Kosuke Kurosawa, ⁴Yoichiro Hironaka, ⁵Keisuke Shigemori, ⁵Masahiko Arakawa
¹Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan
²School of Medicine, University of Occupational and Environmental Health, Yahata, Kitakyushu, Japan
³Planetary Exploration Research Center, Chiba Institute of Technology, Narashino, Chiba, Japan
⁴Institute of Laser Engineering, Osaka University, Suita, Osaka, Japan
⁵Graduate School of Science, Kobe University, Nada, Kobe, Japan

We carried out laser shock experiments and wholly recovered shocked olivine and quartz samples. We investigated the petrographic features based on optical micrographs of sliced samples and found that each recovered sample comprises three regions, I (optically dark), II (opaque), and III (transparent). Scanning electron microscopy combined with electron backscattered diffraction shows that there are no crystal features in the region I; the materials in the region I have once melted. Moreover, numerical calculations performed with the iSALE shock physics code suggest that the boundary between regions II and III corresponds to Hugoniot elastic limit (HEL). Thus, we succeeded in the recovery of the entire shocked samples experienced over a wide range of pressures from HEL (~10 GPa) to melting pressure (~100 GPa) in a hierarchical order.

Reference
Nagaki K, Kadono T, SakaiyaT, Kondo T, Kurosawa K, Hironaka Y, Shigemori K, Arakawa M (2016) Recovery of entire shocked samples in a range of pressure from ~100 GPa to Hugoniot elastic limit. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12654]
Published by arrangement with John Wiley & Sons

¹Neva A. Fowler-Gerace, ^1,2Kimberly T. Tait, ³Desmond E. Moser, ³Ivan Barker,⁴Bob Y. Tian
¹Department of Earth Sciences, University of Toronto, Toronto, Ontario, Canada
²Department of Natural History, Mineralogy, Royal Ontario Museum, Toronto, Ontario, Canada
³Department of Earth Sciences, Western University, London, Ontario, Canada
⁴Department of Physics, University of Toronto, Toronto, Ontario, Canada

The mechanism by which olivine grains became embedded within iron-nickel alloy in pallasite meteorites continues to be a matter of scientific debate. Geochemical and textural observations have failed to fully elucidate the origin and history of the olivine crystals; however, little research attention has been devoted to their crystallographic orientations within the metal matrix. Using electron backscatter diffraction, we have collected crystallographic orientation data for 296 crystals within ∼65 cm2 sample surface from Springwater. Though no global crystallographic preferred orientation exists, very low misorientations are observed among [100] axes of olivine crystals within specific texturally defined domains. Combined with a thorough characterization of large-scale Springwater textures, the definitively nonrandom spatial distribution of olivine orientations provides clues regarding the nature of the olivine’s initial formation environment as well as the sequence of events subsequent to metal incorporation.

Reference
Fowler-Gerace NA, Tait KT, Moser DE, Barker I,Tian BY (2016) Aligned olivine in the Springwater pallasite. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12650]
Published by arrangement with John Wiley & Sons

¹Aiden A. Martin, ²Ting Lin, ¹Milos Toth, ³Andrew J. Westphal, ⁴Edward P. Vicenzi, ⁵Jeffrey Beeman,²Eric H. Silver
¹School of Physics and Advanced Materials, University of Technology, Sydney, Ultimo, New South Wales, Australia
²Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA
³Space Sciences Laboratory, University of California at Berkeley, Berkeley, California, USA
⁴Smithsonian Institution, Museum Conservation Institute, Suitland, California, USA
⁵Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA

In 2006, NASA’s Stardust spacecraft delivered to Earth dust particles collected from the coma of comet 81P/Wild 2, with the goal of furthering the understanding of solar system formation. Stardust cometary samples were collected in a low-density, nanoporous silica aerogel making their study technically challenging. This article demonstrates the identification, exposure, and elemental composition analysis of particles analogous to those collected by NASA’s Stardust mission using in-situ SEM techniques. Backscattered electron imaging is shown by experimental observation and Monte Carlo simulation to be suitable for locating particles of a range of sizes relevant to Stardust (down to submicron diameters) embedded within silica aerogel. Selective removal of the silica aerogel encapsulating an embedded particle is performed by cryogenic NF3-mediated electron beam–induced etching. The porous, low-density nature of the aerogel results in an enhanced etch rate compared with solid material, making it an effective, nonmechanical method for the exposure of particles. After exposure, elemental composition of the particle was analyzed by energy-dispersive X-ray spectroscopy using a high spectral resolution microcalorimeter. Signals from fluorine contamination are shown to correspond to nonremoved silica aerogel and only in residual concentrations.

Reference
Martin AA, Lin T, Toth M, Westphal AJ, Vicenzi EP, Beeman J,Silver EH (2016) Exposure and analysis of microparticles embedded in silica aerogel keystones using NF3-mediated electron beam–induced etching and energy-dispersive X-ray spectroscopy. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12655]
Published by arrangement with John Wiley & Sons

¹Kadlag, Y., ¹Becker, H
¹Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany

187Re-187Os systematics, abundances of highly siderophile elements (HSE: Re, PGE, and Au), chalcogen elements (Te, Se, and S), and some major and minor elements were determined in physically separated components of the Allende (CV3) and Murchison (CM2) carbonaceous chondrites. Substantial differences exist in the absolute and relative abundances of elements in the components, but the similarity of calculated and literature bulk rock abundances of HSE and chalcogens indicate that chemical complementarity exists among the components, with CI chondrite-like ratios for many elements. Despite subsequent alteration and oxidation, the overall cosmochemical behavior of most moderately to highly siderophile elements during high-temperature processing has been preserved in components of Allende at the sampling scale of the present study. The 187Re-187Os systematics and element variations of Allende are less disturbed compared with Murchison, which reflects different degrees of oxidation and alteration of these meteorites. The HSE systematics (with the exception of Au) is controlled by two types of materials: Pd-depleted condensates and CI chondrite-like material. Enrichment and heterogeneous distribution of Au among the components is likely the result of hydrothermal alteration. Chalcogen elements are depleted compared with HSE in all components, presumably due to their higher volatility. Small systematic variations of S, Se, and Te in components bear the signature of fractional condensation/partial evaporation and metal–sulfide–silicate partitioning.

Reference
Kadlag Y, Becker H (2016) Highly siderophile and chalcogen element constraints on the origin of components of the Allende and Murchison meteorites. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12653]
Published by arrangement with John Wiley & Sons

¹Martin R. Lee, ¹Paula Lindgren, ²Ashley J. King, ³Richard C. Greenwood, ³Ian A. Franchi, ⁴Robert Sparkes
¹School of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lilybank Gardens, Glasgow G12 8QQ, UK
²Department of Earth Science, Natural History Museum (London), Cromwell Rd, London SW7 5BD
³Planetary and Space Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
⁴Williamson Research Centre for Molecular Environmental Science, School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Road, Manchester M13 9PL

Elephant Moraine (EET) 96029 is a CM carbonaceous chondrite regolith breccia with evidence for unusually mild aqueous alteration, a later phase of heating and terrestrial weathering. The presence of phyllosilicates and carbonates within chondrules and the fine-grained matrix indicates that this meteorite was aqueously altered in its parent body. Features showing that water-mediated processing was arrested at a very early stage include a matrix with a low magnesium/iron ratio, chondrules whose mesostasis contains glass and/or quench crystallites, and a gehlenite-bearing calcium- and aluminium-rich inclusion. EET 96029 is also rich in Fe,Ni metal relative to other CM chondrites, and more was present prior to its partial replacement by goethite during Antarctic weathering. In combination, these properties indicate that EET 96029 is one of the least aqueously altered CMs yet described (CM2.7) and so provides new insights into the original composition of its parent body. Following aqueous alteration, and whilst still in the parent body regolith, the meteorite was heated to ∼400–600 °C by impacts or solar radiation. Heating led to the amorphisation and dehydroxylation of serpentine, replacement of tochilinite by magnetite, loss of sulphur from the matrix, and modification to the structure of organic matter that includes organic nanoglobules. Significant differences between samples in oxygen isotope compositions, and water/hydroxyl contents, suggests that the meteorite contains lithologies that have undergone different intensities of heating. EET 96029 may be more representative of the true nature of parent body regoliths than many other CM meteorites, and as such can help interpret results from the forthcoming missions to study and return samples from C-complex asteroids.

Reference
Lee MR, Lindgren P, King AJ, Greenwood RC, Franchi IA, Sparkes R (2016) Elephant Moraine 96029, a very mildly aqueously altered and heated CM carbonaceous chondrite: implications for the drivers of parent body processing. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.05.008]
Copyright Elsevier

^1,2Stepan M. Chernonozhkin,^1,2Steven Goderis,¹Marta Costas-Rodríguez,²Philippe Claeys,¹Frank Vanhaecke
¹Ghent University, Department of Analytical Chemistry, Krijgslaan, 281 – S12, 9000 Ghent, Belgium
²Vrije Universiteit Brussel, Analytical-, Environmental-, and Geo-Chemistry, Pleinlaan 2, 1050 Brussels, Belgium

Various iron and stony-iron meteorites have been characterized for their Ni and Fe isotopic compositions using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) after sample digestion and chromatographic separation of the target elements in an attempt to further constrain the planetary differentiation processes that shifted these isotope ratios and to shed light on the formational history and evolution of selected achondrite parent body asteroids. Emphasis was placed on spatially resolved isotopic analysis of iron meteorites, known to be inhomogeneous at the μm to mm scale, and on the isotopic characterization of adjacent metal and silicate phases in main group pallasites (PMG), mesosiderites, and the IIE and IAB complex silicate-bearing iron meteorites. In a 3-isotope plot of 60/58Ni versus 62/58Ni, the slope of the best-fitting straight line through the laterally resolved Ni isotope ratio data for iron meteorites reveals kinetically controlled isotope fractionation (βexper = 1.981 ± 0.039, 1 SD), predominantly resulting from sub-solidus diffusion (with the fractionation exponent β connecting the isotope fractionation factors, as View the MathML sourceα62/58=α60/58β). The observed relation between δ56/54Fe and Ir concentration in the metal fractions of PMGs and in IIIAB iron meteorites indicates a dependence of the bulk Fe isotopic composition on the fractional crystallization of an asteroidal metal core. No such fractional crystallization trends were found for the corresponding Ni isotope ratios or for other iron meteorite groups, such as the IIABs. In the case of the IIE and IAB silicate-bearing iron meteorites, the Fe and Ni isotopic signatures potentially reflect the influence of impact processes, as the degree of diffusion-controlled Ni isotope fractionation is closer to that of Fe compared to what is observed for magmatic iron meteorite types. Between the metal and olivine counterparts of pallasites, the Fe and Ni isotopic compositions show clearly resolvable differences, similar in magnitude but opposite in sign (Δ56/54Femet-oliv of +0.178 ± 0.092 ‰ and Δ60/58Nimet-oliv of -0.212 ± 0.082 ‰, 2SD). As such, the heavier Fe isotope ratios for the metal (δ56/54Fe = +0.023 to +0.247 ‰) and lighter values for the corresponding olivines (δ56/54Fe = -0.155 to -0.075 ‰) are interpreted to reflect later-stage Fe isotopic re-equilibration between these phases, rather than a pristine record of mantle-core differentiation. In the case of mesosiderites, the similarly lighter Ni and Fe isotopic signatures found for the silicate phase (-0.149 to +0.023 ‰ for δ60/58Ni, -0.214 to -0.149 ‰ for δ56/54Fe) compared to the metal phase (+0.168 to +0.191 ‰ for δ60/58Ni, +0.018 to +0.120 ‰ for δ56/54Fe) likely result from Fe and Ni diffusion. Overall, the Fe and Ni isotopic compositions of iron-rich meteorites reflect multiple, often superimposed, processes of equilibrium or kinetic nature, illustrating convoluted parent body histories and late-stage interaction between early-formed planetesimal reservoirs.

Reference
Chernonozhkin SM,Goderis S,Costas-Rodríguez M,Claeys P,Vanhaecke F (2016) Effect of parent body evolution on equilibrium and kinetic isotope fractionation: a combined Ni and Fe isotope study of iron and stony-iron meteorites.
Geochimica et Cosmochmica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.04.050]
Copyright Elsevier

^1,2Desireé Cotto-Figueroa, ¹Erik Asphaug, ^1,3Laurence A.J. Garvie, ⁴Ashwin Rai, ⁴Joel Johnston, ⁴Luke Borkowski, ³Siddhant Datta, ⁴Aditi Chattopadhyay, ^1,5Melissa A. Morris
¹School of Earth and Space Exploration, Arizona State University, PO Box 876004, Tempe, Arizona, 85287-6004, USA
²Department of Physics and Electronics, University of Puerto Rico at Humacao, Call Box 860, Humacao, Puerto Rico, 00792
³Center for Meteorite Studies, Arizona State University, PO Box 876004, Tempe, Arizona, 85287-6004, USA
⁴School for Engineering of Matter, Transport and Energy, Arizona State University, PO Box 876106, Tempe, Arizona, 85287, USA
⁵Physics Department, State University of New York, PO Box 2000, Cortland, New York, 13045, USA

Measuring the strengths of asteroidal materials is important for developing mitigation strategies for potential Earth impactors and for understanding properties of in situ materials on asteroids during human and robotic exploration. Studies of asteroid disruption and fragmentation have typically used the strengths determined from terrestrial analog materials, although questions have been raised regarding the suitability of these materials. The few published measurements of meteorite strength are typically significantly greater than those estimated from the stratospheric breakup of meter-sized meteoroids. Given the paucity of relevant strength data, the scale-varying strength properties of meteoritic and asteroidal materials are poorly constrained. Based on our uniaxial failure studies of centimeter-sized cubes of a carbonaceous and ordinary chondrite, we develop the first Weibull failure distribution analysis of meteorites. This Weibull distribution projected to meter scales, overlaps the strengths determined from asteroidal airbursts and can be used to predict properties of to the 100 m scale. In addition, our analysis shows that meter-scale boulders on asteroids are significantly weaker than small pieces of meteorites, while large meteorites surviving on Earth are selected by attrition. Further, the common use of terrestrial analog materials to predict scale-dependent strength properties significantly overestimates the strength of meter-sized asteroidal materials and therefore is unlikely well suited for the modeling of asteroid disruption and fragmentation. Given the strength scale-dependence determined for carbonaceous and ordinary chondrite meteorites, our results suggest that boulders of similar composition on asteroids will have compressive strengths significantly less than typical terrestrial rocks.

Reference
Cotto-Figueroa D, Asphaug E, Garvie LAJ, Rai A, Johnston J, Borkowski L, Datta S, Chattopadhyay A, Morris MA (2016) Scale-Dependent Measurements of Meteorite Strength: Implications for Asteroid Fragmentation. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.05.003]
Copyright Elsevier