¹A. J. King, ¹P. F. Schofield, ¹S. S. Russell
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12872]
¹Department of Earth Sciences, Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

The CM carbonaceous chondrite meteorites experienced aqueous alteration in the early solar system. They range from mildly altered type 2 to almost completely hydrated type 1 chondrites, and offer a record of geochemical conditions on water-rich asteroids. We show that CM1 chondrites contain abundant (84–91 vol%) phyllosilicate, plus olivine (4–8 vol%), magnetite (2–3 vol%), Fe-sulfide (120 °C), although higher water/rock ratios may also have played a role. The modal data provide constraints for interpreting the composition of asteroids and the mineralogy of samples returned from these bodies. We predict that “CM1-like” asteroids, as has been proposed for Bennu—target for the OSIRIS-REx mission—will have a high abundance of Mg-rich phyllosilicates and Fe-oxides, but be depleted in calcite.

¹Randy L. Korotev
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12869]
¹Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St. Louis, Missouri, USA
Published by arrangement with John Wiley & Sons

This report presents bulk composition data for 10 lunar meteorite stones from Oman for which the names have been approved since June, 2012. On the basis of composition and reported find location, four new meteorites are represented among this group of stones. Data from neutron activation analysis of 371 subsamples of all lunar meteorites from Oman and Saudi Arabia analyzed in this laboratory are presented.

¹Mokkapati Shyam Prasad, ¹N. G. Rudraswami, ¹Agnelo A. De Araujo, ¹Vijay D. Khedekar
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12858]
¹CSIR-National Institute of Oceanography, Dona Paula, Goa, India
Published by arrangement with John Wiley & Sons

Fe-Ni metal is a common constituent of most meteorites and is an indicator of the thermal history of the respective meteorites, it is a diagnostic tool to distinguish between groups/subgroups of meteorites. In spite of over a million micrometeorites collected from various domains, reports of pure metallic particles among micrometeorites have been extremely rare. We report here the finding of a variety of cosmic metal particles such as kamacite, plessite, taenite, and Fe-Ni beads from deep-sea sediments of the Indian Ocean, a majority of which have entered the Earth unaffected by frictional heating during atmospheric entry. Such particles are known as components of meteorites but have never been found as individual entities. Their compositions suggest precursors from a variety of meteorite groups, thus providing an insight into the metal fluxes on the Earth. Some particles have undergone heating and oxidation to different levels during entry developing features similar to I-type cosmic spherules, suggesting atmospheric processing of individual kamacites/taenite grains as another hitherto unknown source for the I-type spherules. The particles have undergone postdepositional aqueous alteration transforming finally into the serpentine mineral cronstedtite. Aqueous alteration products of kamacite reflect the local microenvironment, therefore they have the potential to provide information on the composition of water in the solar nebula, on the parent bodies or on surfaces of planetary bodies. Our observations suggest it would take sustained burial in water for tens of thousands of years under cold conditions for kamacites to alter to cronstedtite.

^1,2Alan E. Rubin, ³Chi Ma
Chemie der Erde – Geochemistry (in Press) Link to Article [http://doi.org/10.1016/j.chemer.2017.01.005]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA
²Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, USA
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
Copyright Elsevier

¹Andrew S. Rivkin, ²Ellen S. Howell, ³Joshua P. Emery, ⁴Jessica Sunshine
Icarus (in Press) Link to Article [http://doi.org/10.1016/j.icarus.2017.04.006]
¹Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Rd, Laurel MD, 20723 USA 443-778-2811
²University of Arizona, Lunar and Planetary Laboratory
³University of Tennessee
⁴University of Maryland
Copyright Elsevier

Water and hydroxyl, once thought to be found only in the primitive airless bodies that formed beyond roughly 2.5-3 AU, have recently been detected on the Moon and Vesta, which both have surfaces dominated by evolved, non-primitive compositions. In both these cases, the water/OH is thought to be exogenic, either brought in via impacts with comets or hydrated asteroids or created via solar wind interactions with silicates in the regolith or both. Such exogenic processes should also be occurring on other airless body surfaces. To test this hypothesis, we used the NASA Infrared Telescope Facility (IRTF) to measure reflectance spectra (2.0 to 4.1 μm) of two large near-Earth asteroids (NEAs) with compositions generally interpreted as anhydrous: 433 Eros and 1036 Ganymed. OH is detected on both of these bodies in the form of absorption features near 3 μm. The spectra contain a component of thermal emission at longer wavelengths, from which we estimate thermal of 167±98 J m−2s−1/2K−1 for Eros (consistent with previous estimates) and 214±80 J m−2s−1/2K−1 for Ganymed, the first reported measurement of thermal inertia for this object. These observations demonstrate that processes responsible for water/OH creation on large airless bodies also act on much smaller bodies.

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.