¹Jack Wisdom
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12876]
¹Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
Published by arrangement with John Wiley & Sons

Meteorites are delivered from the asteroid belt by way of chaotic zones (Wisdom 1985a). The dominant sources are believed to be the chaotic zones associated with the ν6 secular resonance, the 3:1 mean motion resonance, and the 5:2 mean motion resonance. Though the meteorite transport process has been previously studied, those studies have limitations. Here I reassess the meteorite transport process with fewer limitations. Prior studies have not been able to reproduce the afternoon excess (the fact that approximately twice as many meteorites fall in the afternoon as in the morning) and suggested that the afternoon excess is an observational artifact; here it is shown that the afternoon excess is in fact consistent with the transport of meteorites by way of chaotic zones in the asteroid belt. By studying models with and without the inner planets it is found that the inner planets significantly speed up the transport of meteorites.

^1,2Vesselin Dekov, ³Pierre Rochette, ³Jérôme Gattacceca
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12879]
¹Tokyo University of Marine Science and Technology, Tokyo, Japan
²Department of Marine Geosciences, IFREMER, Centre de Brest, Plouzané, France
³Aix-Marseille Univ, CNRS, IRD, Coll France, CEREGE, Aix-en-Provence, France
Published by arrangement with John Wiley & Sons

We present a summary of the mineralogy, mineral chemistry, and magnetic characteristics of all the five Bulgarian meteorite falls. We report the first mineralogical descriptions, chemical analyses, and magnetic measurements of the Konevo (1931) and Silistra (1917) meteorites. We classify Konevo as LL5, and Silistra as an ungrouped achondrite with HED affinities. Pavel (1966; previously classified as an H5) is reclassified as H3-anomalous. We also provide precise mineralogy and mineral chemistry of the Virba meteorite (1873, L6), and more details on the mineral chemistry of Gumoschnik (1904, H5).

¹Shigeko Togashi, ²Noriko T. Kita, ¹Akihiko Tomiya, ^1,3Yuichi Morishita
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://doi.org/10.1016/j.gca.2017.04.031]
¹Geological Survey of Japan, AIST, Central 7, Higashi 1-1-1, Tsukuba 305-8567, Japan
²Department of Geoscience, University of Wisconsin-Madison, 1215 W Dayton Street Madison, WI 53706-1692, USA
³Department of Geoscience, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan
Copyright Elsevier

The compositions of host magmas of ferroan anorthosites (FAN-host magmas) were estimated from secondary ion mass spectrometry analyses of plagioclase in lunar highland rocks. The evolution of the magmas was investigated by considering phase relations based on the MELTS algorithm and by re-examining partition coefficients for trace elements between plagioclase and melts. Data little affected by post-magmatic processes were selected by using plagioclase with relatively primitive Sc and Co contents. The FAN-host magma contained 90–174 ppm Sr, 40–119 ppm Ba and 0.5–1.3% TiO2, and had sub-chondritic Sr/Ba and Ti/Ba ratios. It is difficult to account for the formation of FAN-host magma on the basis of magma evolution processes of previously proposed bulk silicate Moon models with chondritic ratios for refractory elements at global scale. Therefore, the source of the FAN-host magma must have had primordial sub-chondritic Sr/Ba and Ti/Ba ratios. The FAN-host magmas were consistent in refractory elements with the estimated host mafic magma for feldspathic crust based on lunar meteorites, and some very-low-Ti mare rocks from lunar meteorites. Here, we propose an alternative bulk silicate Moon model (the cBSM model), which is enriched in crustal components of proto-bodies relative to the present whole Earth–Moon system.

^1,2Lukáš Ackerman, ²Tomáš Magna, ¹Karel Žák, ¹Roman Skála, ¹Šárka Jonášová, ³Jiří Mizera, ³Zdeněk Řanda
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://doi.org/10.1016/j.gca.2017.04.028]
¹Institute of Geology, The Czech Academy of Sciences, Rozvojová 269, CZ-165 00 Prague 6 – Lysolaje, Czech Republic
²Czech Geological Survey, Klárov 3, CZ-118 21 Prague 1, Czech Republic
³Nuclear Physics Institute, The Czech Academy of Sciences, Hlavní 130, CZ-250 68 Husinec-Řež, Czech Republic
Copyright Elsevier

Impact processes are natural phenomena that contribute to a variety of physico–chemical mechanisms over an extreme range of shock pressures and temperatures, otherwise seldomly achieved in the Earth’s crust through other processes. Under these extreme conditions with transient temperatures and pressures ≥3,000K and ≥100 GPa, followed by their rapid decrease, the behavior of elements has remained poorly understood. Distal glassy ejecta (tektites) were produced in early phases of contact between the Earth’s surface and an impacting body. Here we provide evidence for a complex behavior of Os and other highly siderophile elements (HSE; Ir, Ru, Pt, Pd, and Re) during tektite production related to a hyper-velocity impact that formed the Ries structure in Germany. Instead of simple mixing between the surface materials, which are thought to form the major source of central European tektites (moldavites), and impactor matter, the patterns of HSE contents and 187Re/188Os – 187Os/188Os ratios in moldavites, target sediments and impact-related breccias (suevites) can be explained by several sequential and/or contemporary processes. These involve (i) evaporative loss of partially oxidized HSE from the overheated tektite melt, (ii) mixing of target-derived and impactor-derived HSE vapor (plasma) phases, and (iii) early (high-temperature) condensation of a part of the mixed vapor phase back to silicate melt droplets. An almost complete loss of terrestrial Os from the tektite melt and its replacement with extra-terrestrial Os are indicated by low 187Os/188Os ratios in tektites (<0.163) relative to precursor materials (>0.69). This is paralleled by a co-variation between Os and Ni contents in tektites but not in suevites formed later in the impact process.

^1,2,3Levke Kööp, ^4,5Daisuke Nakashima, ^1,2,3Philipp R. Heck, ⁴Noriko T. Kita, ^4,6Travis J. Tenner, ⁷Alexander N. Krot, ⁷Kazuhide Nagashima, ^7,8Changkun Park, ^1,2,3,9Andrew M. Davis
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://doi.org/10.1016/j.gca.2017.04.029]
¹Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA
²Chicago Center for Cosmochemistry, The University of Chicago, Chicago, IL 60637, USA
³Robert A. Pritzker Center for Meteoritics and Polar Studies, Field Museum of Natural History, Chicago, IL, USA
⁴Department of Geoscience, University of Wisconsin, Madison, WI 53706, USA
⁵Division of Earth and Planetary Material Sciences, Faculty of Science, Tohoku University, Aoba, Sendai, Miyagi 980-8578, Japan
⁶Chemistry Division, Nuclear and Radiochemistry, Los Alamos National Laboratory, MSJ514, Los Alamos, NM 87545, USA
⁷Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI
⁸Korea Polar Research Institute, Incheon 21990, Korea
⁹Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA.
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) are the oldest dated objects that formed inside the Solar System. Among these are rare, enigmatic objects with large mass-dependent fractionation effects (F CAIs), which sometimes also have large nucleosynthetic anomalies and a low initial abundance of the short-lived radionuclide 26Al (FUN CAIs). We have studied seven refractory hibonite-rich CAIs and one grossite-rich CAI from the Murchison (CM2) meteorite for their oxygen, calcium, and titanium isotopic compositions. The 26Al-26Mg system was also studied in seven of these CAIs. We found mass-dependent heavy isotope enrichment in all measured elements, but never simultaneously in the same CAI. The data are hard to reconcile with a single-stage melt evaporation origin and may require isotopic reintroduction or reequilibration for magnesium, oxygen and titanium after evaporation for some of the studied CAIs.

The initial 26Al/27Al ratios inferred from model isochrons span a range from <1×10–6 to canonical (∼5×10–5). The CAIs show a mutual exclusivity relationship between inferred incorporation of live 26Al and the presence of resolvable anomalies in 48Ca and 50Ti. Furthermore, a relationship exists between 26Al incorporation and Δ17O in the hibonite-rich CAIs (i.e., 26Al-free CAIs have resolved variations in Δ17O, while CAIs with resolved 26Mg excesses have Δ17O values close to –23‰). Only the grossite-rich CAI has a relatively enhanced Δ17O value (∼–17‰) in spite of a near-canonical 26Al/27Al. We interpret these data as indicating that fractionated hibonite-rich CAIs formed over an extended time period and sampled multiple stages in the isotopic evolution of the solar nebula, including: (1) an 26Al-poor nebula with large positive and negative anomalies in 48Ca and 50Ti and variable Δ17O; (2) a stage of 26Al-admixture, during which anomalies in 48Ca and 50Ti had been largely diluted and a Δ17O value of ∼ –23‰ had been achieved in the CAI formation region; and (3) a nebula with an approximately canonical level of 26Al and a Δ17O value of ∼ –23‰ in the CAI formation region.

¹Shun Ichimura, ¹Yusuke Seto, ¹Kazushige Tomeoka
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://doi.org/10.1016/j.gca.2017.04.025]
¹Department of Planetology, Graduate School of Science, Kobe University, Nada, Kobe 657-8501, Japan
Copyright Elsevier

Nepheline is present as fine grains mainly in refractory inclusions and chondrules in CV and CO carbonaceous chondrites. The nepheline has been formed primarily by replacement of melilite and plagioclase in refractory inclusions and plagioclase and glass in chondrules. The nepheline formation is thought to have occurred during aqueous alteration and thermal metamorphism in the meteorite parent bodies. To verify this hypothesis, we performed the following experiments.

Hydrothermal experiments of gehlenite (Al-rich melilite) and plagioclase (An48) were carried out at 200 °C and ∼15 bar for 168 h using solutions of pH 0, 7, 13, and 14 with a uniform Na concentration. In the gehlenite experiments, various amounts of SiO2 were added. The results revealed that a Na zeolite, analcime, was produced from 10/3 and 10/6 mixtures of gehlenite/SiO2 at pH 7, 13, and14, and from a 10/10 mixture of gehlenite/SiO2 and plagioclase at pH 13 and 14. In particular, at pH 14, in addition to analcime, significant amounts of two other zeolites, fabriesite and hydroxycancrinite, were produced from the 10/6 mixture of gehlenite/SiO2, and fabriesite from plagioclase.

Isothermal heating experiments for 24 h showed that fabriesite, hydroxycancrinite, and analcime transform to nepheline at 600–650, 550–600, and 750–800 °C, respectively. Differential thermal analysis of these zeolites revealed that fabriesite and hydroxycancrinite exhibit exothermic peaks, which correspond to transformation to nepheline, and that the temperatures of those peaks decrease steadily with decreasing heating rate. Kinetic analysis using these data revealed that fabriesite and hydroxycancrinite transform to nepheline at temperatures more than 50–100 degrees lower than determined by the isothermal experiments if heated for durations > 102 and ∼ 1 yr, respectively. Analcime heated non-isothermally at a rate of 1 °C/min transformed to nepheline at temperature higher than that determined by the isothermal experiments, suggesting that its transformation temperature also decreases if it is heated for a much longer duration. From these experiments and analyses, we conclude that fabriesite, hydroxycancrinite, and possibly analcime are capable of transforming to nepheline by heating in meteorite parent bodies.

From our results, we propose that the nepheline in refractory inclusions and chondrules in meteorites formed by a two-stage alteration process: (1) formation of the Na zeolites from melilite, plagioclase, and glass by hydrothermal alteration at low temperature (probably

^1,2,3Hao Sun, ⁴Min Yi, ^1,24Zhigang Shen, ^1,2Xiaojing Zhang, ^1,2Shulin Ma
Planetary and Space Science (in Press) Link to Article [http://doi.org/10.1016/j.pss.2017.04.010]
¹School of Aeronautic Science and Engineering, Beihang University, Beijing 100191, China
²Beijing Key Laboratory for Powder Technology Research and Development, Beijing 100191, China
³Honors College of Beihang University, Beijing 100191, China
⁴Institute of Materials Science, Technische Universität Darmstadt, Darmstadt 64287, Germany

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²Archana M. Nair, ¹George Mathewa
Planetary and Space Science (in Press) Link to Article [http://doi.org/10.1016/j.pss.2017.04.009]
¹Department of Earth Sciences, Indian Institute of Technology (IIT) Bombay, Powai, Mumbai- 400 076
²Department of Civil Engineering, Indian Institute of Technology (IIT) Guwahati, Guwahati -781039

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Benjamin P. Weiss et al. (>10)*
Earth and Planetary Science Letters (in Press) Link to Article [http://doi.org/10.1016/j.epsl.2017.03.026]
¹Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
Copyright Elsevier

Paleomagnetic studies of meteorites have shown that the solar nebula was likely magnetized and that many early planetary bodies generated dynamo magnetic fields in their advecting metallic cores. The surface fields on these bodies were recorded by a diversity of chondrites and achondrites, ranging in intensity from several μT to several hundred μT. In fact, an achondrite parent body without evidence for paleomagnetic fields has yet to be confidently identified, hinting that early solar system field generation and the dynamo process in particular may have been common. Here we present paleomagnetic measurements of the ungrouped achondrite NWA 7325 indicating that it last cooled in a near-zero field (<∼1.7 μT), estimated to have occurred at 4563.09±0.264563.09±0.26 million years ago (Ma) from Al–Mg chronometry. Because NWA 7325 is highly depleted in siderophile elements, its parent body nevertheless underwent large-scale metal-silicate differentiation and likely formed a metallic core. This makes NWA 7325 the first recognized example of an essentially unmagnetized igneous rock from a differentiated early solar system body. These results indicate that all magnetic fields, including those from any core dynamo on the NWA 7325 parent body, the solar nebula, young Sun, and solar wind, were <1.7 μT at the location of NWA 7325 at 4563 Ma. This supports a recent conclusion that the solar nebula had dissipated by ∼4 million years after solar system formation. NWA 7325 also serves as an experimental control that gives greater confidence in the positive identification of remanent magnetization in other achondrites.

¹C.M.O’D. Alexander, ²R.C. Greenwood, ³R. Bowden, ²J.M. Gibson, ⁴K.T. Howard, ²I.A. Franchi
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://doi.org/10.1016/j.gca.2017.04.021]
¹Dept. Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington DC 20015, USA
²Planetary and Space Sciences, Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
³Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington DC 20015, USA
⁴Physical Sciences Department, Kingsborough Community College, City University of New York, 2001 Oriental Blvd., Brooklyn, New York, NY 11235, USA
Copyright Elsevier

As part of a study to identify the most primitive COs and to look for weakly altered CMs amongst the COs, we have conducted a multi-technique study of 16 Antarctic meteorites that had been classified as primitive COs. For this study, we have determined: (1) the bulk H, C and N abundances and isotopes, (2) bulk O isotopic compositions, (3) bulk modal mineralogies, and (4) for some selected samples the abundances and compositions of their insoluble organic matter (IOM). Two of the 16 meteorites do appear to be CMs – BUC 10943 seems to be a fairly typical CM, while MIL 090073 has probably been heated. Of the COs, DOM 08006 appears to be the most primitive CO identified to date and is quite distinct from the other members of its pairing group. The other COs fall into two groups that are less primitive than DOM 08006 and ALH 77307, the previously most primitive CO. The first group is composed of members of the DOM 08004 pairing group, except DOM 08006. The second group is composed of meteorites belonging to the MIL 03377 and MIL 07099 pairing groups. These two pairing groups should probably be combined. There is a dichotomy in the bulk O isotopes between the primitive (all Antarctic finds) and the more metamorphosed COs (mostly falls). This dichotomy can only partly be explained by the terrestrial weathering experienced by the primitive Antarctic samples. It seems that the more equilibrated samples interacted to a greater extent with 16O-poor material, probably water, than the more primitive meteorites.