John A. Grant, Sharon A. Wilson
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12843]
Center for Earth and Planetary Studies, Smithsonian National Air and Space Museum, Washington,District of Columbia 20560, USA
Published by Arrangement with John Wiley & Sons

Hale crater formed in the Early to Middle Amazonian and is one of the best preserved large craters on Mars. We focus on the emplacement of previously mapped distal continuous ejecta and newly recognized discontinuous distal ejecta deposits reaching up to 450 km northeast of Hale. The distal continuous ejecta deposits are typically tens of meters thick, likely water-rich, and subsequent dewatering of some resulted in flow along gradients of 10 m km^-1 for distances of tens of kilometers. The discontinuous distal ejecta are typically <10 m thick with volumes generally <0.5 km³ and embay Hale secondaries, which occur up to ~600 km from Hale. Both continuous and discontinuous distal ejecta deposits are typically smooth at scales of tens to hundreds of meters, relatively dark-toned, devoid of eolian bedforms, inferred to be mostly fine-grained, and were likely emplaced within hours to 1–2 days after impact. The occurrence of well-preserved discontinuous distal ejecta at Hale is unusual compared to other large Martian craters and could be due to impact into an ice-rich substrate that enabled their formation and (or) their survival after minimal postimpact degradation relative to older craters. The pristine nature of distal continuous and discontinuous distal deposits at Hale and the preservation of associated secondaries imply (1) low erosion rates after the Hale impact, comparable to those estimated elsewhere during the Amazonian; (2) the impact did not significantly influence long-term global or regional scale geomorphic activity or climate; and (3) the Hale impact occurred after late alluvial fan activity in Margaritifer Terra.

^1,2Fiona THIESSEN, ^1,3Alexander A. NEMCHIN, ¹Joshua F. SNAPE, ^1,2Martin J. WHITEHOUSE, and ¹Jeremy J. BELLUCCI
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12814]
¹Department of Geosciences, Swedish Museum of Natural History, Stockholm SE-104 05, Sweden
²Department of Geological Sciences, Stockholm University, Stockholm SE-106 91, Sweden
³Department of Applied Geology, Curtin University, Perth, Western Australia 6845, Australia
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Secondary ion mass spectrometry (SIMS) U-Pb ages of Ca-phosphates from four texturally distinct breccia samples (72255, 76055, 76015, 76215) collected at the Apollo 17 landing site were obtained in an attempt to identify whether they represent a single or several impact event(s). The determined ages, combined with inferences from petrologic relationships, may indicate two or possibly three different impact events at 3920 ± 3 Ma, 3922 ± 5 Ma, and 3930 ± 5 Ma (all errors 2σ). Searching for possible sources of the breccias by calculating the continuous ejecta radii of impact basins and large craters as well as their expected ejecta thicknesses, we conclude that Nectaris, Crisium, Serenitatis, and Imbrium are likely candidates. If the previous interpretation that the micropoikilitic breccias collected at the North Massif represent Serenitatis ejecta is correct, then the average 207Pb/206Pb age of 3930 ± 5 Ma (2σ) dates the formation of the Serenitatis basin. The occurrence of zircon in the breccias sampled at the South Massif, which contain Ca-phosphates yielding an age of 3922 ± 5 Ma (2σ), may indicate that the breccia originated from within the Procellarum KREEP terrane (PKT) and the Imbrium basin appears to be the only basin that could have sourced them. However, this interpretation implies that all basins suggested to fall stratigraphically between Serenitatis and Imbrium formed within a short (<11 Ma) time interval, highlighting serious contradictions between global stratigraphic constraints, sample interpretation, and chronological data. Alternatively, the slightly older age of the two micropoikilitic breccias may be a result of incomplete resetting of the U-Pb system preserved in some phosphate grains. Based on the currently available data set this possibility cannot be excluded.

Martin SCHILLER, James N. CONNELLY, and Martin BIZZARRO
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12848]
Centre for Star and Planet Formation, Natural History Museum of Denmark, Copenhagen, Denmark
Published by Arrangement with John Wiley & Sons

The large collection of howardite-eucrite-diogenite (HED) meteorites allows us to study the initial magmatic differentiation of a planetesimal. We report Pb-Pb ages of the unequilibrated North West Africa (NWA) 4215 and Dhofar 700 diogenite meteorites and their mass-independent 26Mg isotope compositions (26Mg*) to better understand the timing of differentiation and crystallization of their source reservoir(s). NWA 4215 defines a Pb-Pb age of 4484.5 ± 7.9 Myr and has a 26Mg* excess of +2.3 ± 1.6 ppm whereas Dhofar 700 has a Pb-Pb age of 4546.4 ± 4.7 Myr and a 26Mg* excess of +25.5 ± 1.9 ppm. We interpret the young age of NWA 4215 as a thermal overprint, but the age of Dhofar 700 is interpreted to represent a primary crystallization age. Combining our new data with published Mg isotope and trace element data suggests that approximately half of the diogenites for which such data are available crystallized within the first 1–2 Myr of our solar system, consistent with a short-lived, early-formed magma ocean undergoing convective cooling. The other half of the diogenites, including both NWA 4215 and Dhofar 700, are best explained by their crystallization in slowly cooled isolated magma chambers lasting over at least ~20 Myr.

¹H. R. LAI, C. T. RUSSELL¹, H. Y. WEI¹, M. CONNORS², and G. L. DELZANNO³
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12854]
¹EPSS and IGPP, UCLA, 603 Charles Young Drive, 3845 Slichter Hall, Los Angeles, California 90095–1567, USA
²Athabasca University, Athabasca, Alberta, Canada
³Los Alamos National Lab, Los Alamos, New Mexico 87545, USA
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Near-Earth objects (NEOs) with diameters of <300 m are difficult to detect from the Earth with radar or optical telescopes unless and until they approach closely. If they are on collisional courses with the Earth, there is little that can be done to mitigate the considerable damage. Although destructive collisions in space are rare for 1 km diameter bodies and above, once hit by a sizeable impactor, such a NEO can develop a relatively dense cloud of co-orbiting material in which destructive collisions are relatively frequent. The gas and nanoscale dust released in the destructive collisions can be detected remotely by downstream spacecraft equipped with magnetometers. In this paper, we use such magnetic disturbances to identify regions of near-Earth space in which high densities of small objects are present. We find that asteroid (138175) 2000EE104 currently may have a cloud of potentially threatening co-orbiting material. Due to the scattered co-orbitals, there can be a finite impact probability whenever the Earth approaches the orbit of asteroid 2000EE104, regardless of the position of the asteroid itself.

^1,2Burkhardt, C et al. (>10)*
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12834]
¹Origins Laboratory, Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois 60637, USA
²Institut für Planetologie, Westfälische Wilhelms-Universität M€unster, Wilhelm-Klemm-Str 10, Münster D-48149, Germany
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High-precision isotope data of meteorites show that the long-standing notion of a “chondritic uniform reservoir” is not always applicable for describing the isotopic composition of the bulk Earth and other planetary bodies. To mitigate the effects of this “isotopic crisis” and to better understand the genetic relations of meteorites and the Earth-forming reservoir, we performed a comprehensive petrographic, elemental, and multi-isotopic (O, Ca, Ti, Cr, Ni, Mo, Ru, and W) study of the ungrouped achondrites NWA 5363 and NWA 5400, for both of which terrestrial O isotope signatures were previously reported. Also, we obtained isotope data for the chondrites Pillistfer (EL6), Allegan (H6), and Allende (CV3), and compiled available anomaly data for undifferentiated and differentiated meteorites. The chemical compositions of NWA 5363 and NWA 5400 are strikingly similar, except for fluid mobile elements tracing desert weathering. We show that NWA 5363 and NWA 5400 are paired samples from a primitive achondrite parent-body and interpret these rocks as restite assemblages after silicate melt extraction and siderophile element addition. Hafnium-tungsten chronology yields a model age of 2.2 ± 0.8 Myr after CAI, which probably dates both of these events within uncertainty. We confirm the terrestrial O isotope signature of NWA 5363/NWA 5400; however, the discovery of nucleosynthetic anomalies in Ca, Ti, Cr, Mo, and Ru reveals that the NWA5363/NWA 5400 parent-body is not the “missing link” that could explain the composition of the Earth by the mixing of known meteorites. Until this “missing link” or a direct sample of the terrestrial reservoir is identified, guidelines are provided of how to use chondrites for estimating the isotopic composition of the bulk Earth.

¹Rebecca Querfeld, ¹Mohammad R. Tanha, ²Lars Heyer, ²Franz Renz, ³Georg Guggenberger, ⁴Franz Brandstätter, ⁴Ludovic Ferrière, ^4,5Christian Koeberl, ¹Georg Steinhauser
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12855]
¹Leibniz Universität Hannover, Institute of Radioecology and Radiation Protection, 30419 Hannover, Germany
²Leibniz Universität Hannover, Institute of Inorganic Chemistry, 30167 Hannover, Germany
³Leibniz Universität Hannover, Institute of Soil Science, 30419 Hannover, Germany
⁴Natural History Museum, Burgring 7, 1010 Vienna, Austria
⁵Department of Lithospheric Research, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
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A piece of the 2013 Chelyabinsk meteorite was investigated for its content of anthropogenic radionuclides. In addition to traces of cesium-137 that had been previously reported for this particular fragment, we found an unusually high amount of strontium-90, which indicates that the source of this contamination was the Kyshtym accident (1957). A high Sr-90/Cs-137 activity ratio is characteristic for Kyshtym-derived contaminations. Based on the cesium-137 content in the soil from the finding site, it is estimated that the fragment was contaminated with soil particles in the milligram range upon impact. Investigation of the soil revealed very unusual ferromagnetic characteristics and an iron-rich chemical composition. Mössbauer spectroscopy indicated the presence of steel components in this soil, suggesting that the investigated meteorite fragment was found in an industrial dumping site rather than natural soil.

¹B. Fritzke, ¹J. Götze, ²J.-M. Lange
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12852]
¹Institut for Mineralogy, TU Bergakademie Freiberg, Brennhausgasse 14, Freiberg 09599, Germany
²Senckenberg Naturhistorische Sammlungen Dresden, Section Petrography, K€onigsbr€ucker Landstraße 159, Dresden 01109,Germany
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A systematic study of a large set of moldavites and the application of cathodoluminescence (CL)-spectroscopy with a detailed discussion of spectral features is presented. Optical CL microscopy and spectroscopy (OM-CL) were performed on 57 moldavite samples from different substrewn-fields in Germany and the Czech Republic. The extracted CL data were supported by SEM-EDX analysis. In general, two different kinds of CL colors can be distinguished: different shades of green in the matrix of the tektite glasses and a variation of blue color for lechatelierite inclusions (a pure silica-glass phase). Spectral analysis of these colors shows three CL emission bands for green and five bands for blue c. Most CL activators are structural defects of the local glass network, influenced by the crystal field. The visible green CL emission is caused by defects related to strong local disorder as well as Al-O⁻-Al defects. The blue CL emission is activated by different types of lattice defects such as nonbridging oxygen-hole center (NBOHC), self-trapped excitons (STE), and oxygen deficiency centers (ODC). Intensity variations of the CL emissions were observed for samples from the different localities, but there is no direct correlation between substrewn-fields and CL characteristics. Nevertheless, CL microscopy is a powerful tool for the high-contrast visualization of internal textures such as streaks and lechatelierite in the tektite matrix due to the luminescence properties of the defect structures in the glassy network.

Matthew J. Genge
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12830]
Impact and Astromaterials Research Centre (IARC), Department of Earth Science and Engineering, Imperial College London, Exhibition Road, London, UK
Department of Earth Science, The Natural History Museum, Cromwell Road, London, UK
Published by Arrangement with John Wiley & Sons

Basaltic micrometeorites (MMs) derived from HED-like parent bodies have been found among particles collected from the Antarctic and from Arctic glaciers and are to date the only achondritic particles reported among cosmic dust. The majority of Antarctic basaltic particles are completely melted cosmic spherules with only one unmelted particle recognized from the region. This paper investigates the entry heating of basaltic MMs in order to predict the relative abundances of unmelted to melted basaltic particles and to evaluate how mineralogical differences in precursor materials influence the final products of atmospheric entry collected on the Earth’s surface. Thermodynamic modeling is used to simulate the melting behavior of particles with compositions corresponding to eucrites, diogenites, and ordinary chondrites in order to evaluate degree of partial melting and to make a comparison between the behavior of chondritic particles that dominate the terrestrial dust flux and basaltic micrometeroids. The results of 120,000 simulations were compiled to predict relative abundances and indicate that the phase relations of precursor materials are crucial in determining the relative abundances of particle types. Diogenite and ordinary chondrite materials exhibit similar behavior, although diogenite precursors are more likely to form cosmic spherules under similar entry parameters. Eucrite particles, however, are much more likely to melt due to their lower liquidus temperatures and small temperature interval of partial melting. Eucrite MMs, therefore, usually form completely molten cosmic spherules except at particle diameters −1) and is more compatible with higher velocities which may suggest a near-Earth asteroid source dominates the current dust production of basaltic MMs.

^aHaolan Tang, ^aMing-Chang Liu, ^aKevin D. McKeegan, ^b,cFrancois L.H. Tissot, Nicolas Dauphas^b

Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.03.001]
^aDepartment of Earth, Planetary, and Space Sciences, UCLA, Los Angeles, CA, 90095
^bOrigins Lab, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago
^cDepartment of the Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, 02139
Copyright Elsevier

The isotopic composition of oxygen as well as ²⁶Al-²⁶Mg and ³⁶Cl-³⁶S systematics were studied in Curious Marie, an aqueously altered Allende CAI characterized by a Group II REE pattern and a large ²³⁵U excess produced by the decay of short-lived ²⁴⁷Cm. Oxygen isotopic compositions in the secondary minerals of Curious Marie follow a mass-dependent fractionation line with a relatively homogenous depletion in ¹⁶O (Δ¹⁷O of -8‰) compared to unaltered minerals of CAI components. Both Mg and S show large excesses of radiogenic isotopes (²⁶Mg∗ and ³⁶S∗) that are uniformly distributed within the CAI, independent of parent/daughter ratio. A model initial ²⁶Al/²⁷Al ratio [(6.2±0.9)×10^-5], calculated using the bulk Al/Mg ratio and the uniform δ²⁶Mg∗∼ +43‰, is similar to the canonical initial solar system value within error. The exceptionally high bulk Al/Mg ratio of this CAI (∼95) compared to other inclusions is presumably due to Mg mobilization by fluids. Therefore, the model initial ²⁶Al/²⁷Al ratio of this CAI implies not only the early condensation of the CAI precursor but also that aqueous alteration occurred early, when ²⁶Al was still at or near the canonical value. This alteration event is most likely responsible for the U depletion in Curious Marie and occurred at most 50 kyr after CAI formation, leading to a revised estimate of the early solar system ²⁴⁷Cm/²³⁵U ratio of (5.6±0.3) ×10^-5. The Mg isotopic composition in Curious Marie was subsequently homogenized by closed-system thermal processing without contamination by chondritic Mg. The large, homogeneous ³⁶S excesses (Δ³⁶S∗∼ +97‰) detected in the secondary phases of Curious Marie are attributed to ³⁶Cl decay (t_1/2=0.3 Myr) that was introduced by Cl-rich fluids during the aqueous alteration event that led to sodalite formation. A model ³⁶Cl/³⁵Cl ratio of (2.3±0.6)×10^-5 is calculated at the time of aqueous alteration, translating into an initial ³⁶Cl/³⁵Cl ratio of ∼1.7-3×10^-5 at solar system birth. The Mg and S radiogenic excesses suggest that ²⁶Al and ³⁶Cl co-existed in the early solar nebula, raising the possibility that, in addition to an irradiation origin, ³⁶Cl could have also been derived from a stellar source.

¹Aya Iwai, ²Yoichi Itoh, ³Tsuyoshi Terai, ⁴Ranjan Gupta, ⁵Asoke Sen, ²Jun Takahash
Research in Astronomy and Astrophysics 17, 17 Link to Article [http://dx.doi.org/10.1088/1674%E2%80%934527%2F17%2F2%2F17]
¹National Institute of Advanced Industrial Science and Technology, Ibaraki 305-8563, Japan
²Nishi-Harima Astronomical Observatory, Center for Astronomy, University of Hyogo, Hyogo 679-5313, Japan
³National Astronomical Observatory of Japan, Hilo, Hawaii 96720, USA
United States
⁴Inter-University Centre for Astronomy and Astrophysics, Ganeshkhind, Pune 411 007, India
⁵Department of Physics, Assam University, Silchar 788 001, India

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