¹Ulrich Mansfeld, ¹Falko Langenhorst, ^2,3Matthias Ebert, ²Astrid Kowitz, ²Ralf Thomas Schmitt
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12867]
¹Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Jena, Germany
²Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany
³Institut für Geo- und Umweltnaturwissenschaften, Geologie, Albert-Ludwigs-Universität, Freiburg, Germany
Published by arrangement with John Wiley & Sons

It has been almost exactly half a century since the first synthesis of stishovite in shock experiments on quartz was reported, but its formation conditions during shock is still under debate. Here, we present direct transmission electron microscopic observation of stishovite within material recovered from high-explosive shock experiments on porous sandstone shocked at 7.5 and 12.5 GPa. Our observations allow for new conclusions on the genesis of stishovite in a close-to-nature environment. The formation of stishovite in short-time shock experiments proves that its crystallization is ultrafast <!–(<1 μs). Crystals were found only embedded in amorphous veins indicating homogeneous nucleation. Crystallization from melt rather than from glass can be concluded from the observation of roundish, defect-free crystals up to 150 nm in diameter embedded in nondensified glass. The formation of stishovite at 7.5 GPa is in accordance with the phase diagram of silica, if rapid undercooling is present that becomes only possible by the existence of small hot spots in an otherwise cold material, which is supported by transient heat calculation. The absence of coesite at 7.5 GPa suggests kinetic hindrance of its crystallization from melt and, thus, smaller critical cooling rates compared to stishovite where critical cooling rates are estimated to be as large as 10¹¹ K s⁻¹. While the amorphous veins containing stishovite represent unambiguously hot spots, no associated pressure amplification could be verified within these veins. The rapid liquidus crystallization of stishovite only in hot spots generated in porous material is an alternative formation mechanism to the widely accepted theory of solid–solid transition from quartz to stishovite and might represent the more general mechanism occurring in nature for low shock pressure events.

¹Nancy L. Chabot, ¹E. Alex Wollack, ²William F. McDonough, ²Richard D. Ash, ²Sarah A. Saslow
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12864]
¹Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
²University of Maryland, College Park, Maryland, USA
Published by arrangement with John Wiley & Sons

Experimental trace element partitioning values are often used to model the chemical evolution of metallic phases in meteorites, but limited experimental data were previously available to constrain the partitioning behavior in the basic Fe-Ni system. In this study, we conducted experiments that produced equilibrium solid metal and liquid metal phases in the Fe-Ni system and measured the partition coefficients of 25 elements. The results are in good agreement with values modeled from IVB iron meteorites and with the limited previous experimental data. Additional experiments with low levels of S and P were also conducted to help constrain the partitioning behaviors of elements as a function of these light elements. The new experimental results were used to derive a set of parameterization values for element solid metal–liquid metal partitioning behavior in the Fe-Ni-S, Fe-Ni-P, and Fe-Ni-C ternary systems at 0.1 MPa. The new parameterizations require that the partitioning behaviors in the light-element–free Fe-Ni system are those determined experimentally by this study, in contrast to previous parameterizations that allowed this value to be determined as a best-fit parameter. These new parameterizations, with self-consistent values for partitioning in the endmember Fe-Ni system, provide a valuable resource for future studies that model the chemical evolution of metallic phases in meteorites.

¹Megumi Matsumoto, ¹Kazushige Tomeoka, ¹Yusuke Seto
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.03.032]
¹Department of Planetology, Graduate School of Science, Kobe University, Nada, Kobe 657-8501, Japan
Copyright Elsevier

Ningqiang is an ungrouped carbonaceous chondrite that has a chemical and mineralogical affinity to CV3 chondrites. The Ningqiang matrix has distinctly higher abundances of Na, K, and Al than CV3 matrices. A recent study by Matsumoto et al. (2014) revealed that the major proportions of these elements can be attributed to the presence of nepheline and sodalite.

Scanning electron microscopy revealed that all of the Ningqiang chondrules studied show abundant evidence of extensive Na–Fe metasomatism. Only a small proportion of the chondrules contain primary mesostases in their cores, but the mesostases in their mantles were replaced by fine grains of nepheline, sodalite, Fe-rich olivine, and hedenbergite. The mesostases in the majority of the chondrules were completely replaced by fine grains of the same secondary minerals. Most opaque nodules were also largely replaced by various fine-grained secondary minerals. Nepheline/sodalite form veins penetrating the primary mesostases, providing evidence that aqueous fluids were involved in the alteration reactions. The nepheline/sodalite in the mesostases contain various amounts of inclusions of Fe-rich olivine, diopside, hedenbergite, Fe sulfides, and magnetite. The mineralogical features of the nepheline/sodalite in the mesostases are almost identical to those in the meteorite matrix.

These results suggest that a significant fraction of the nepheline/sodalite grains in the Ningqiang matrix originated from the nepheline/sodalite produced in chondrules and refractory inclusions and that they were disaggregated and mixed into the matrix. These processes can be explained consistently by the model of the dynamic formation of chondrite lithology in a parent body proposed by Tomeoka and Ohnishi (2015). We suggest that after a Ningqiang precursor with a CV3-like lithology was metasomatized, it was fragmented, causing the disaggregation of the fine-grained host matrix and the fine-grained altered mesostases, including nepheline/sodalite, and opaque nodules in the chondrules. The chondrules were thereby separated into multiple fragments. Subsequently, during transportation in a fluidized state, all these materials were homogenously mixed together and later underwent accumulation and lithification.

¹Luke Daly et al. (>10)*
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.03.037]
¹Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
*Find the extensive, full author and affiliation list on the publishers website
Copyright Elsevier

Transmission Kikuchi diffraction (TKD) is a relatively new technique that is currently being developed for geological sample analysis. This technique utilises the transmission capabilities of a scanning electron microscope (SEM) to rapidly and accurately map the crystallographic and geochemical features of an electron transparent sample. TKD uses a similar methodology to traditional electron backscatter diffraction (EBSD), but is capable of achieving a much higher spatial resolution (5-1010 nm) (Trimby, 2012 ; Trimby et al., 2014). Here we apply TKD to refractory metal nuggets (RMNs) which are micrometre to sub-micrometre metal alloys composed of highly siderophile elements (HSEs) found in primitive carbonaceous chondrite meteorites. TKD allows us to analyse RMNs in situ, enabling the characterisation of nanometre-scale variations in chemistry and crystallography, whilst preserving their spatial and crystallographic context. This provides a complete representation of each RMN, permitting detailed interpretation of their formation history.

We present TKD analysis of five transmission electron microscopy (TEM) lamellae containing RMNs coupled with EBSD and TEM analyses. These analyses revealed textures and relationships not previously observed in RMNs. These textures indicate some RMNs experienced annealing, forming twins. Some RMNs also acted as nucleation centres, and formed immiscible metal-silicate fluids. In fact, each RMN analysed in this study had different crystallographic textures. These RMNs also had heterogeneous compositions, even between RMNs contained within the same inclusion, host phase and even separated by only a few nanometres. Some RMNs are also affected by secondary processes at low temperature causing exsolution of molybdenite. However, most RMNs had crystallographic textures indicating that the RMN formed prior to their host inclusion. TKD analyses reveal most RMNs have been affected by processing in the protoplanetary disk. Despite this alteration, RMNs still preserve primary crystallographic textures and heterogeneous chemical signatures. This heterogeneity in crystallographic relationships, which mostly suggest that RMNs pre-date their host, is consistent with the idea that there is not a dominant RMN forming process. Each RMN has experienced a complex history, supporting the suggestion of Daly et al. (2016), that RMNs may preserve a diverse pre-solar chemical signature inherited from the Giant Molecular Cloud.

¹T.Noguchi et al. (>10)*
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.03.034]
¹Faculty of Arts and Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
*Find the extensive, full author and affiliation list on the publishers website
Copyright Elsevier

Micrometeorites (MMs) recovered from surface snow near the Dome Fuji Station, Antarctica are almost free from terrestrial weathering and contain very primitive materials, and are suitable for investigation of the evolution and interaction of inorganic and organic materials in the early solar system. We carried out a comprehensive study on seven porous and fluffy MMs [four Chondritic porous (CP) MMs and three fluffy fine-grained (Fluffy Fg) MMs] and one fine-grained type 1 (Fg C1) MM for comparison with scanning electron microscope, transmission electron microscope, X-ray absorption near-edge structure analysis, and secondary ion mass spectrometer.

They show a variety of early aqueous activities. Four out of the seven CP MMs contain glass with embedded metal and sulfide (GEMS) and enstatite whiskers/platelets and do not have hydrated minerals. Despite the same mineralogy, organic chemistry of the CP MMs shows diversity. Two of them contain considerable amounts of organic materials with high carboxyl functionality, and one of them contains nitrile (C≡N) and/or nitrogen heterocyclic groups with D and 15N enrichments, suggesting formation in the molecular cloud or a very low temperature region of the outer solar system. Another two CP MMs are poorer in organic materials than the above-mentioned MMs. Organic material in one of them is richer in aromatic C than the CP MMs mentioned above, being indistinguishable from those of hydrated carbonaceous chondrites. In addition, bulk chemical compositions of GEMS in the latter organic poor CP MMs are more homogeneous and have higher Fe/(Si+Mg+Fe) ratios than those of GEMS in the former organic-rich CP MMs. Functional group of the organic materials and amorphous silicate in GEMS in the organic-poor CP MMs may have transformed in the earliest stage of aqueous alteration, which did not form hydrated minerals.

Three Fluffy Fg MMs contain abundant phyllosilicates, showing a clear evidence of aqueous alteration. Phyllosilicates in thee MMs are richer in Fe than those in hydrated IDPs, typical fine-grained hydrated (Fg C1) MMs, and hydrated carbonaceous chondrites. One of the Fluffy Fg MMs contains amorphous silicate, which is richer in Fe than GEMS and contains little or no nanophase Fe metal but contains Fe sulfide. Because the chemical compositions of the amorphous silicate are within the compositional field of GEMS in CP IDPs, the amorphous silicate may be alteration products of GEMS. The entire compositional field of GEMS in the CP MMs and the amorphous silicate in the Fluffy Fg MM matches that of the previously reported total compositional range of GEMS in IDPs.

One Fluffy Fg MM contains Mg-rich phyllosilicate along with Fe-rich phyllosilicate and Mg-Fe carbonate. Mg-rich phyllosilicate and Mg-Fe carbonate may have been formed through the reaction of Fe-rich phyllosilicate, Mg-rich olivine and pyroxene, and water with C-bearing chemical species.

These data indicate that CP MMs and Fluffy Fg MMs recovered from Antarctic surface snow contain materials that throw a light on the earliest stages of aqueous alteration on very primitive solar system bodies. Because mineralogy and isotopic and structural features of organic materials in D10IB009 are comparable with isotopically primitive IDPs, its parent body could be comets or icy asteroids showing mass ejection (active asteroids). By contrast, organic-poor CP MMs may have experienced the earliest stage of aqueous alteration and Fluffy Fg MMs experienced weak aqueous alteration. The precursor materials of the parent bodies of Fluffy Fg MMs probably contained abundant GEMS or GEMS-like materials like CP IDPs, which is common to fine-grained matrices of very primitive carbonaceous chondrites such as CR3s. However, highly porous nature of organic-poor CP MMs and Fluffy Fg MMs suggests that parent bodies of these MMs must have been much more porous than the parent bodies of primitive carbonaceous chondrites. Given no phyllosilicate among the returned samples of 81P/Wild 2 comet, the MMs may have been derived from porous icy asteroids such as active asteroids as well as P- and D-type asteroids rather than comets.

¹Elishevah M.M.E. van Kooten, , ¹Martin Schiller, ¹Martin Bizzarro
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.03.033]
¹Centre for Star and Planet Formation and Natural History Museum of Denmark, University of Copenhagen, DK-1350 Copenhagen, Denmark
Copyright Elsevier

Polymict ureilites are meteoritic breccias that provide insights into the differentiation history of the ureilite parent body.We have sampled a total of 24 clasts from the polymict ureilite Dar al Gani 319, representing a variety of lithologies such as mantle residues, cumulates and crustal fragments that are genetically related to monomict ureilites.In addition, we sampled four non-indigenous dark clasts and two chondrule-containing clasts from the same meteorite.We report on the petrology and the bulk mass-dependent and mass-independent magnesium and chromium isotope systematics of these clasts.The DaG 319 polymict ureilite consists predominantly of clasts related to Main Group ureilite residues (MG clasts) with varying Mg#s (0.74-0.91), as well as a significant fraction of olivine-orthopyroxene clasts related to Hughes Type ureilites (HT clasts) with consistently high Mg#s (∼∼0.89).In addition, DaG 319 contains less abundant feldspathic clasts that are thought to represent melts derived from the ureilite mantle.A significant mass-dependent Mg-isotope fractionation totaling ΔΔμμ2525Mg = ∼∼450 ppm was found between isotopically light feldspathic clasts (μμ2525Mg = –305±±25 to 15±±12 ppm), MG clasts (μμ2525Mg = –23±±51 ppm) and HT clasts (μμ2525Mg = 157±±21 ppm).We suggest that this isotopic offset is the result of equilibrium isotope fractionation during melting in the presence of an isotopically light magnesite component.We propose Mg-carbonates to be stable in the upper ureilite mantle, and pure carbon phases such as graphite to be stable at higher pressures.This is consistent with HT clasts lacking carbon-related phases, whereas MG clasts contain abundant carbon.The timing of differentiation events for the ureilitic clasts are constrained by high precision 5353Mn-5353Cr systematics and 2626Al-2626Mg model ages.We show that a dichotomy of ages exist between the differentiation of main group ureilite residues and HT cumulates rapidly after CAI formation and later remelting of cumulates with corresponding feldspathic melts, at 3.8±±1.3 Myr after CAI formation.Assuming an initial 2626Al/2727Al abundance[(2626Al/2727Al)0 = View the MathML source1.33-0.18+0.21×× 10−5] similar to the angrite parent body, the early melting event is best explained by heat production from 2626Al whereas the late event is more likely caused by a major impact. Variations in 5454Cr between MG clasts and HT clasts agree with a carbonaceous chondrite impactor onto the ureilite parent body. This impactor may be represented by abundant dark clasts found in polymict ureilites, which have μμ26Mg∗26Mg∗ and μμ5454Cr signatures similar to CI chondrites. Similar volatile-rich dark clasts found in other meteorite breccias provide insights into the timing of volatile influx to the accretion region of the terrestrial planets.

¹Frédéric Girault, ¹Frédéric Perrier, ¹Manuel Moreira, ²Brigitte Zanda, ³Pierre Rochette, ^1,4Yoram Teitler
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.03.031]
¹Institut de Physique du Globe de Paris, Sorbonne Paris Cité, University Paris Diderot, CNRS UMR 7154, F-75005 Paris, France
²Laboratoire de Minéralogie et de Cosmochimie du Muséum, Muséum National d’Histoire Naturelle, CNRS UMR 7202, F-75005 Paris, France
³Centre Européen de Recherche et d’Enseignement de Géosciences de l’Environnement, CNRS UMR 7330, Aix-Marseille University, BP80 F-13545 Aix en Provence Cedex 4, France
⁴Currently at: Centre de Recherches Pétrographiques et Géochimiques, Université de Nancy, CNRS UMR 7358, Vandœuvre-lès-Nancy, France
Copyright Elsevier

The analysis of noble gases in meteorites provides constraints on the early solar system and the pre-solar nebula. This requires a better characterization and understanding of the capture, production, and release of noble gases in meteorites. The knowledge of transfer properties of noble gases for each individual meteorite could benefit from using radon-222, radioactive daughter of radium-226. The radon-222 emanating power is commonly quantified by the effective radium-226 concentration (ECRa), the product of the bulk radium-226 concentration and of the emanation coefficient E, which represents the probability of one decaying radium-226 to inject one radon-222 into the free porous network. Owing to a non-destructive, high-sensitivity accumulation method based on long photomultiplier counting sessions, we are now able to measure ECRa of meteorite samples, which usually have mass smaller than 15 g and ECRa<0.5 Bq kg^-1. We report here the results obtained from 41 different meteorites, based on 129 measurements on 70 samples using two variants of our method, showing satisfactory repeatability and a detection limit below 10^-2 Bq kg^-1 for a sample mass of 1 g. While two meteorites remain below detection level, we obtain for 39 meteorites heterogeneous EC_Ra values with mean (min–max range) of ca. 0.1 (0.018–1.30) Bq kg^-1. Carbonaceous chondrites exhibit the largest EC_Ra values and eucrites the smallest. Such values are smaller than typical values from most terrestrial rocks, but comparable with those from Archean rocks (mean of ca. 0.18 Bq kg^-1), an end-member of terrestrial rocks. Using uranium concentration from the literature, E is inferred from EC_Ra for all the meteorite samples. Values of E for meteorites (mean 40±4 %) are higher than E values for Archean rocks and reported values for lunar and Martian soils. Exceptionally large E values likely suggest that the ²³⁸U-²²⁶Ra pair would not be at equilibrium in most meteorites and that uranium and/or radium are most likely not uniformly distributed. EC_Ra of meteorites is correlated with E and seems to mainly reflect the gas permeability of the meteorite, which could be one important property, preserved in the meteorite, of its parent body, characterizing its history in space, possibly modified by alteration, shock metamorphism, and eventually weathering on Earth. Larger radon emanation values are associated with larger concentrations of the heaviest noble gases (argon, krypton, xenon), and larger ²⁰Ne/²²Ne and ³⁶Ar/³⁸Ar ratios, suggesting Earth’s atmosphere contamination or solar wind implantation, and probably a similar carrier phase such as Q phase. An unclear correlation is observed with ⁴⁰Ar, which may rule out a purely radiogenic effect on radon emanation. Thus, larger radon emanation suggests a larger capacity of collecting solar and terrestrial gases, which should imply higher loss of gases generated in the meteorite and larger dispersion of Pb/U ratios for age determination. This study provides the first quantification of natural radon-222 loss from meteorites and opens promising perspectives to quantify the relationship between pore space connectivity and the transfer properties for noble gases in meteorites and other extraterrestrial bodies.

^1,3Rachael Hazael, ²Brianna C. Fitzmaurice, ^1,4Fabrizia Foglia, ²Gareth J. Appleby-Thomas, ¹Paul F McMillan
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2017.03.031]
¹Christopher Ingold Laboratories, Department of Chemistry, University College London, London WC1H 0AJ, UK
²Cranfield Defense and Security, Cranfield University, Shrivenham, Swindon SN6 8LA, UK
³Department of Earth Sciences, University College London, London WC1E 6BT
⁴Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK
Copyright Elsevier

The possibility that life can exist within previously unconsidered habitats is causing us to expand our understanding of potential planetary biospheres. Significant populations of living organisms have been identified at depths extending up to several km below the Earth’s surface; whereas laboratory experiments have shown that microbial species can survive following exposure to GigaPascal (GPa) pressures. Understanding the degree to which simple organisms such as microbes survive such extreme pressurization under static compression conditions is being actively investigated. The survival of bacteria under dynamic shock compression is also of interest. Such studies are being partly driven to test the hypothesis of potential transport of biological organisms between planetary systems. Shock compression is also of interest for the potential modification and sterilization of foodstuffs and agricultural products. Here we report the survival of Shewanella oneidensis bacteria exposed to dynamic (shock) compression. The samples examined included: (a) a “wild type” (WT) strain and (b) a “pressure adapted” (PA) population obtained by culturing survivors from static compression experiments to 750 MPa. Following exposure to peak shock pressures of 1.5 and 2.5 GPa the proportion of survivors was established as the number of colony forming units (CFU) present after recovery to ambient conditions. The data were compared with previous results in which the same bacterial samples were exposed to static pressurization to the same pressures, for 15 minutes each. The results indicate that shock compression leads to survival of a significantly greater proportion of both WT and PA organisms. The significantly shorter duration of the pressure pulse during the shock experiments (2-3 μs) likely contributes to the increased survival of the microbial species. One reason for this can involve the crossover from deformable to rigid solid-like mechanical relaxational behavior that occurs for bacterial cell walls on the order of seconds in the time-dependent strain rate.

^1,2Laurence A.J. Garvie, ²L. Paul Knauth, ^2,3Melissa A. Morris
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2017.03.021]
¹Center for Meteorite Studies, Arizona State University, Tempe, Arizona 85287-6004, USA.
²School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287-6004, USA.
³State University of New York, Cortland, NY 13045, USA
Copyright Elsevier

^1,2G.K.Benedix et al. (>10)*
Geochmica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.03.030]
¹Curtin University, Applied Geology, Bentley, Western Australia, Australia
²Western Australia Museum, Department of Earth and Planetary Sciences, Welshpool, Western Australia,
*Find the extensive, full author and affiliation list on the publishers website
Copyright Elsevier

Bunburra Rockhole is the first recovered meteorite of the Desert Fireball Network. We expanded a bulk chemical study of the Bunburra Rockhole meteorite to include major, minor and trace element analyses, as well as oxygen and chromium isotopes, in several different pieces of the meteorite. This was to determine the extent of chemical heterogeneity and constrain the origin of the meteorite. Minor and trace element analyses in all pieces are exactly on the basaltic eucrite trend. Major element analyses show a slight deviation from basaltic eucrite compositions, but not in any systematic pattern. New oxygen isotope analyses on 23 pieces of Bunburra Rockhole shows large variation in both δ17O and δ18O, and both are well outside the HED parent body fractionation line. We present the first Cr isotope results of this rock, which are also distinct from a majority of HEDs. Detailed computed tomographic scanning and back-scattered electron mapping do not indicate the presence of any other meteoritic contaminant (contamination is also unlikely based on trace element chemistry). We therefore conclude that Bunburra Rockhole represents a sample of a new differentiated asteroid, one that may have more variable oxygen isotopic compositions than 4 Vesta. The fact that Bunburra Rockhole chemistry falls on the eucrite trend perhaps suggests that multiple objects with basaltic crusts accreted in a similar region of the Solar System.