^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

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

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

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

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.

¹Giovanna Serventi, ²Cristian Carli
Icarus (in Press) Link to Article [http://doi.org/10.1016/j.icarus.2017.04.018]
¹Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Viale delle Scienze 157/A Parma 43124, Italy
²IAPS-Inaf, Viale Fosso del Cavaliere Tor Vergata, Roma, 00133 Italy
Copyright Elsevier

The lunar surface consists of a regolith layer that covers the underlying bedrocks, and is generally characterized by particulates

The coarsest sizes of the regolith are chemically and mineralogically similar, while the finest fractions are more feldspathic, probably due to easier fracturing of plagioclase than mafic minerals.

Due to the more feldspathic nature of the very fine lunar soils, in this paper, we quantitatively investigate the influence of very fine (

(1) fine sizes act principally on reflectance and on spectral contrast (with the former increasing and the latter decreasing); (2) very fine plagioclase has a blue slope in the Near Infrared and very shallow 1250 nm band depth, close to zero; (3) consequently, the plagioclase band is always shallower than mafic bands; (4) in mixtures with olivine, the composite band center always shows the typical olivine value, differently from coarser mixtures; and (5) mafic materials have a blue slope in the Short Wavelength Infrared Region, a more V-shaped 1µm pyroxene absorption and the 1µm mafic band centers are shifted by ca. 40 nm vs. coarse sizes, reflecting a different weight within the crystal field absorption of the mafic component in very fine size. We also evidenced that a coarse plagioclase could be overestimated, while a very fine one could be underestimated if compared with the 63-125µm size.

¹Pierrick Roperch, ²Jérôme Gattacceca, ³Millarca Valenzuela, ²Bertrand Devouard, ⁴Jean-Pierre Lorand, ⁵Cesar Arriagada, ²Pierre Rochette,^6,7Claudio Latorre, ⁸Pierre Beck
Earth and Planetary Science Letters 469, 15-26 Link to Article [http://doi.org/10.1016/j.epsl.2017.04.009]
¹Géosciences Rennes, CNRS–INSU, Université de Rennes 1, Rennes, France
²CNRS, Aix Marseille Univ., IRD, Coll France, CEREGE, Aix-en-Provence, France
³Instituto de Astrofísica, P. Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
⁴Laboratoire de Planétologie et Géodynamique, CNRS UMR 6112, Université de Nantes, 2 Rue la Houssinière, 44322, Nantes, France
⁵Departamento de Geología, Facultad de Ciencas Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile
⁶Centro UC del Desierto de Atacama and Departamento de Ecología, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
⁷Institute of Ecology & Biodiversity (IEB), Santiago, Chile
⁸Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 414, Rue de la Piscine, Domaine Universitaire, 38400 St-Martin d’Hères, France
Copyright Elsevier

We describe extended occurrences of unusual silicate glass surface layers from the Atacama Desert (Chile). These glasses, found near the town of Pica at four localities separated by up to 70 km, are neither fulgurites, nor volcanic glasses, nor metallurgical slags related to anthropic activity, but show close similarities to other glasses that have been previously attributed to large airbursts created by meteoroids entering the Earth’s atmosphere. The glasses are restricted to specific Late Pleistocene terrains: paleo-wetlands and soils rich in organic matter with SiO2-rich plant remains, salts and carbonates. 14C dating and paleomagnetic data indicate that the glasses were formed during at least two distinct periods. This rules out the hypothesis of a single large airburst as the cause of surface melting. Instead, burning of organic-rich soils in dried-out grassy wetlands during climate oscillations between wet and dry periods can account for the formation of the Pica glasses. Large oases did indeed form in the hyperarid Atacama Desert due to elevated groundwater tables and increased surface discharge during the Central Andean Pluvial Event (roughly coeval with the Mystery interval and Younger Dryas). Finally, we discuss the implications of our results for the other surface glasses previously attributed to extraterrestrial events.

¹Matthias M. M. Meier,²Kees C. Welten,^1,3My E. I. Riebe,^4,5Marc W. Caffee,^6,7,8Maria Gritsevich,¹Colin Maden,¹Henner Busemann
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12874]
¹ETH Zurich, Institute of Geochemistry and Petrology, Zurich, Switzerland
²Space Sciences Laboratory, University of California, Berkeley, California, USA
³Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC, USA
⁴Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana, USA
⁵Department of Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA
⁶Department of Physics, University of Helsinki, Helsinki, Finland
⁷Finnish Geospatial Research Institute, Masala, Finland
⁸Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russia
Published by arrangement with John Wiley & Sons

The Park Forest (L5) meteorite fell in a suburb of Chicago, Illinois (USA) on March 26, 2003. It is one of the currently 25 meteorites for which photographic documentation of the fireball enabled the reconstruction of the meteoroid orbit. The combination of orbits with pre-atmospheric sizes, cosmic-ray exposure (CRE), and radiogenic gas retention ages (“cosmic histories”) is significant because they can be used to constrain the meteoroid’s “birth region,” and test models of meteoroid delivery. Using He, Ne, Ar, 10Be, and 26Al, as well as a dynamical model, we show that the Park Forest meteoroid had a pre-atmospheric size close to 180 g cm−2, 0–40% porosity, and a pre-atmospheric mass range of ~2–6 tons. It has a CRE age of 14 ± 2 Ma, and (U, Th)-He and K-Ar ages of 430 ± 90 and 490 ± 70 Ma, respectively. Of the meteorites with photographic orbits, Park Forest is the second (after Novato) that was shocked during the L chondrite parent body (LCPB) break-up event approximately 470 Ma ago. The suggested association of this event with the formation of the Gefion family of asteroids has recently been challenged and we suggest the Ino family as a potential alternative source for the shocked L chondrites. The location of the LCPB break-up event close to the 5:2 resonance also allows us to put some constraints on the possible orbital migration paths of the Park Forest meteoroid.