¹Qin Zhou,²Qing-Zhu Yin,³Charles K. Shearer,⁴Xian-Hua Li,⁴Qiu-Li Li,⁴Yu Liu,⁴Guo-Qiang Tang,¹Chun-Lai Li
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13026]
¹Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China
²Department of Earth and Planetary Sciences, University of California Davis, Davis, California, USA
³Department of Earth and Planetary Sciences, Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
⁴State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

The Antarctic achondrite Graves Nunataks 06128 (GRA 06128) and Graves Nunataks 06129 (GRA 06129) represent a unique high-temperature, nonbasaltic magmatism in the early solar system. These objects have been interpreted as products of low-degree partial melting of volatile-rich chondritic material, which may have been the asteroid parent bodies of brachinite. Previous studies have investigated their crystallization and metamorphic history with various isotope systematics. Here, we report the U-Pb intercept age of 4466 ± 29 Ma and the weighted-average 207Pb-206Pb age of 4460 ± 30 Ma for the Cl-apatite grains from GRA 06129. Our apatite ages are obviously younger than that of the 26Al-26Mg model age (4565.9 ± 0.3 Ma; Shearer et al. 2010a), but are the same as the 40Ar-39Ar age obtained via step-heating of the bulk rock (4460 ± 28 Ma; Fernandes and Shearer 2010; Shearer et al. 2010a). Based on petrographic observations, merrillites are usually rimmed by apatite and exist as inclusions in apatite. Therefore, the apatite U-Pb age from GRA 06129 probably records a metamorphic event of replacing merrillite with apatite, caused by Cl-rich melts or fluids on their parent body. A collisional event has provided the impact heating for this metamorphic event. Increasing amounts of geochronologic evidence show that the giant impact of the Moon-forming event has affected the asteroid belt at 4450–4470 Ma (Bogard and Garrison 2009; Popova et al. 2013; Yin et al. 2014; Zhang et al. 2016). Considering the contemporary metamorphic events for GRA 06129 (4460 ± 30 Ma), it is likely that the asteroid parent body of GRA 06129 was also affected by the same giant impact as the Moon-forming event.

¹Timothy M. Hahn Jr.,^1,2Nicole G. Lunning,¹Harry Y. McSween Jr.,³Robert J. Bodnar,¹Lawrence A. Taylor
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13036]
¹Department of Earth and Planetary Sciences and Planetary Geoscience Institute, University of Tennessee, Knoxville, Tennessee, USA
²Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C., USA
³Department of Geosciences, Virginia Tech, Blacksburg, Virginia, USA
Published by arrangement with John Wiley & Sons

We describe petrographic, electron microprobe, and laser ablation ICP-MS analyses of Mg-rich harzburgite clasts in the Dominion Range 2010 howardites, and conclude that they are xenolithic samples of the vestan mantle. Key chemical and petrologic characteristics of these rocks provide tests for differentiation models. Our results indicate the mantle of Vesta formed through variable degrees of partial melting, which left behind a harzburgite and possibly dunite residuum. The Mg-rich clasts are composed of orthopyroxene and olivine, with minor clinopyroxene, FeNi metal, and distinctive pyroxene–chromite symplectites. We use mineral chemistry to demonstrate the absence of a genetic link between diogenites and the Mg-rich harzburgites. We propose a secondary origin for the formation of symplectites: interaction of silicate and metallic melts during primordial differentiation and core formation. The occurrence of FeNi metal containing ~1.5 wt% Cr within the assemblage indicates a very reducing environment during mantle differentiation (≪IW). Our study suggests that Vesta did not experience complete melting early in its history, and instead supports the formation of a shallow magma ocean.

¹P. Oliver,¹M. Ralchenko,¹C. Samson,^1,2R. E. Ernst,³P. J. A. McCausland,⁴G. F. West
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13028]
¹Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada
²Faculty of Geology and Geography, Tomsk State University, Tomsk, Russia
³Western Paleomagnetic and Petrophysical Laboratory, Western University, London, Ontario, Canada
⁴Department of Physics, University of Toronto, Toronto, Ontario, Canada
Published by arrangement with John Wiley & Sons

Ordinary chondrites have previously been nondestructively characterized using bulk magnetic susceptibility, broadly reflecting their Fe-Ni alloy content. We seek to expand the information that can be recovered from magnetic susceptibility by using the University of Toronto Electromagnetic Induction Spectrometer (UTEMIS) to measure the complex magnetic susceptibility tensor of 20 ordinary chondrites samples in addition to 16 Gao–Guenie (H5) chondrites at 35 frequencies from 90 Hz to 64 kHz, at variable low applied field strengths <10 A m−1. Following removal of the field-dependent component of susceptibility, frequency dependence, in- and out-of-phase components, and bulk magnetic susceptibility were interpreted. Most meteorites showed no frequency-dependent in-phase responses, but had a frequency-dependent out-of-phase response attributed to eddy currents induced in conductive minerals. Greater in- and out-of-phase frequency dependence correlated with lower fayalite content in olivine and was, in turn, inversely proportional to Fe-Ni alloy content. The uncertainty in the UTEMIS measurements ranges from approximately 0.05% for low-frequency in-phase measurements to a maximum of 3% for low-frequency out-of-phase measurements. This uncertainty level was far lower than the intra-meteorite variability for the Gao–Guenie suite suggesting inhomogeneity at scales of approximately 10 g.

¹C.M.Pieters et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13008]
¹Brown University, Providence, Rhode Island, USA
Published by arrangement with John Wiley & Sons

The geologic context of red organic-rich materials (ROR) found across an elongated 200 km region on Ceres is evaluated with spectral information from the multispectral framing camera (FC) and the visible and near-infrared mapping spectrometer (VIR) of Dawn. Discrete areas of ROR materials are found to be associated with small fresh craters less than a few hundred meters in diameter. Regions with the highest concentration of discrete ROR areas exhibit a weaker diffuse background of ROR materials. The observed pattern could be consistent with a field of secondary impacts, but no appropriate primary crater has been found. Both endogenic and exogenic sources are being considered for these distinctive organic materials.

^1,2Matthias Ebert,^2,3Astrid Kowitz,²Ralf Thomas Schmitt,^2,4,5Wolf Uwe Reimold,⁶Ulrich Mansfeld,⁶Falko Langenhorst
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12948]
¹Institut für Geo- und Umweltnaturwissenschaften, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
²Museum für Naturkunde – Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany
³Department of Earth Sciences, Freie Universität, Berlin, Germany
⁴Humboldt Universität zu Berlin, Berlin, Germany
⁵Geochronology Laboratory, University of Brasilia, Brasilia, Brazil
⁶Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Jena, Germany
Published by arrangement with John Wiley & Sons

Shock-induced recovery experiments were performed to investigate melt formation in porous sandstones in the low shock pressure regime between 2.5 and 17.5 GPa. The sandstone shocked at 2.5 and 5 GPa is characterized by pore closure, fracturing of quartz (Qtz), and compression and deformation of phyllosilicates; no melting was observed. At higher pressures, five different types of melts were generated around pores and alongside fractures in the sandstone. Melting of kaolinite (Kln), illite (Ill), and muscovite (Ms) starts at 7.5, 12, and 15 GPa, respectively. The larger the amount of water in these minerals (Kln ~14 wt%, Ill ~6–10 wt%, and Ms ~4 wt% H₂O), the higher the shock compressibility and the lower the shock pressure required to induce melting. Vesicles in the almost dry silicate glasses attest to the loss of structural water during the short shock duration of the experiment. The compositions of the phyllosilicate-based glasses are identical to the composition of the parental minerals or their mixtures. Thus, this study has demonstrated that phyllosilicates in shocked sandstone undergo congruent melting during shock loading. In experiments at 10 GPa and higher, iron melt from the driver plate was injected into the phyllosilicate melts. During this process, Fe is partitioned from the metal droplets into the surrounding silicate melts, which induced unmixing of silicate melts with different chemical properties (liquid immiscibility). At pressures between 7.5 and 15 GPa, a pure SiO₂ glass was formed, which is located as short and thin bands within Qtz grains. These bands were shown to contain tiny crystals of experimentally generated stishovite.

^1,2,3David Kaeter,¹Martin A. Ziemann,²Ute Böttger,⁴Iris Weber,⁵Lutz Hecht,⁶Sergey A. Voropaev,⁶Alexander V. Korochantsev,⁷Andrey V. Kocherov
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13027]
¹Institute for Earth and Environmental Sciences, University of Potsdam, Potsdam, Germany
²Institute of Optical Sensor Systems, German Aerospace Center, Berlin, Germany
³iCRAG, School of Earth Sciences, University College Dublin, Dublin D04 N2E5, Ireland
⁴Institute of Planetology, University of Münster, Münster, Germany
⁵Museum für Naturkunde, Berlin, Germany
⁶Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia
⁷Chelyabinsk State University, Chelyabinsk, Russia
Published by arrangement with John Wiley & Sons

We present results of petrographic, mineralogical, and chemical investigations of three Chelyabinsk meteorite fragments. Three distinct lithologies were identified: light S3 LL5, dark S4–S5 LL5 material, and opaque fine-grained former impact melt. Olivine–spinel thermometry revealed an equilibration temperature of 703 ± 23 °C for the light lithology. All plagioclase seems to be secondary, showing neither shock-induced fractures nor sulfide-metal veinlets. Feldspathic glass can be observed showing features of extensive melting and, in the dark lithology, as maskelynite, lacking melt features and retaining grain boundaries of former plagioclase. Olivine of the dark lithology shows planar deformation features. Impact melt is dominated by Mg-rich olivine and resembles whole-rock melt. Melt veins (<2 mm) are connected to narrower veinlets. Melt vein textures are similar to pegmatite textures showing chilled margins, a zone of inward-grown elongated crystals and central vugs, suggesting crystallization from supercooled melt. Sulfide-metal droplets indicate liquid immiscibility of both silicate and sulfide as well as sulfide and metal melts. Impact melting may have been an important factor for differentiation of primitive planetary bodies. Graphite associated with micrometer-sized melt inclusions in primary olivine was detected by Raman mapping. Carbon isotopic studies of graphite could be applied to test a possible presolar origin.

¹F. A. J. Abernethy,¹A. B. Verchovsky,¹I. A. Franchi,^1,2M. M. Grady
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13016]
¹Planetary and Space Sciences, The Open University, Walton Hall, Milton Keynes, UK
²Department of Earth Sciences, The Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

Carbon and nitrogen data from stepped combustion analysis of eight angrites, seven eucrites, and two diogenites, alongside literature data from a further nine eucrites and two diogenites, have been used to assess carbon and nitrogen incorporation and isotope fractionation processes on the angrite parent body (APB), for comparison with volatile behavior on the HED parent body (4 Vesta). A subset of the angrite data has been reported previously (Abernethy et al. 2013). Two separate families of volatile components were observed. They were (1) moderately volatile material (MVM), mostly combusting between ~500 and 750 °C and indistinguishable from terrestrial contamination and (2) refractory material (RM), mainly released above 750 °C and thought to be carbon (as math formula) and nitrogen (as N2 or math formula) dissolved within the silicate lattice, fitting with the slightly oxidized (~IW to IW+2) angrite fO2 conditions. Isotopic fractionation trends for carbon and nitrogen within the plutonic and basaltic (quenched) angrites suggest that the behavior of the two volatile elements is loosely coupled, but that the fractionation process differs between the two angrite subgroups. Comparison with results from eucrites and diogenites implies similarities between speciation of carbon and nitrogen on 4 Vesta and the APB, with the latter being more enriched in volatiles than the former.

¹Ansgar Greshake,²Richard Wirth,³Jörg Fritz,⁴Tomasz Jakubowski,⁵Ute Böttger
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13030]
¹Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany
²Helmholtz Centre Potsdam, GFZ German Research Center for Geosciences, Potsdam, Germany
³Saalbau Weltraum Projekt, Heppenheim, Germany
⁴Wroclaw, Poland
⁵Deutsches Zentrum für Luft- und Raumfahrt, Institut für Optische Sensorsysteme, Berlin, Germany
Published by arrangement with John Wiley & Sons

Libyan Desert Glass (LDG) is a SiO₂-rich natural glass whose origin, formation mechanism, and target material are highly debated. We here report on the finding of a lens-shaped whitish inclusion within LDG. The object is dominantly composed of siliceous glass and separated from the surrounding LDG by numerous cristobalite grains. Within cristobalite, several regions rich in mullite often associated with ilmenite were detected. Mineral assemblage, chemical composition, and grain morphologies suggest that mullite was formed by thermal decomposition of kaolinitic clay at atmospheric pressure and T ≥ 1600 °C and also attested to high cooling rates under nonequilibrium conditions. Cristobalite contains concentric and irregular internal cracks and is intensely twinned, indicating that first crystallized β-cristobalite inverted to α-cristobalite during cooling of the SiO₂-rich melt. The accompanied volume reduction of 4% induced the high density of defects. The whitish inclusion also contains several partly molten rutile grains evidencing that at least locally the LDG melt was at T ≥ 1800 °C. Based on these observations, it is concluded that LDG was formed by high-temperature melting of kaolinitic clay-, rutile-, and ilmenite-bearing Cenozoic sandstone or sand very likely during an asteroid or comet impact onto Earth. While melting and ejection occurred at high pressures, the melt solidified quickly at atmospheric pressure.

¹Priscille Cuvillier,^2,3Noël Chaumard,¹Hugues Leroux,^2,4,5Brigitte Zanda,^2,4Roger H. Hewins¹Damien Jacob,⁶Bertrand Devouard
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13032]
¹Unité Matériaux et Transformations, Université Lille 1 and CNRS, Villeneuve d’Ascq, France
²Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Université, Muséum National d’Histoire Naturelle, UPMC Université Paris 06, IRD & CNRS, Paris, France
³WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, USA
⁴Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
⁵Institut de Mécanique Céleste et de Calcul des Ephémérides, Observatoire de Paris, Paris Cedex, France
⁶Aix-Marseille Université, CNRS, IRD, CEREGE UM34, Aix en Provence, France
Published by arrangemenr with John Wiley & Sons

We conducted a transmission electron microscope study of the exsolution microstructures of Ca-rich pyroxenes in type I chondrules from the Paris CM and Renazzo CR carbonaceous chondrites in order to provide better constraints on the cooling history of type I chondrules. Our study shows a high variability of composition in the augite grains at a submicrometer scale, reflecting nonequilibrium crystallization. The microstructure is closely related to the local composition and is thus variable inside augite grains. For compositions inside the pyroxene miscibility gap, with a wollastonite (Wo) content typically below 40 mole%, the augite grains contain abundant exsolution lamellae on (001). For grain areas with composition close to Wo₄₀, a modulated texture on (100) and (001) is the dominant microstructure, while areas with compositions higher than Wo₄₀ do not show any exsolution microstructure development. To estimate the cooling rate, we used the spacing of the exsolution lamellae on (001), for which the growth is diffusion controlled and thus sensitive to the cooling rate. Despite the relatively homogeneous microstructures of augite grains with Wo < 35 mole%, our study of four chondrules suggests a range of cooling rates from ~10 to ~1000 °C h⁻¹, within the temperature interval 1200–1350 °C. These cooling rates are comparable to those of type II chondrules, i.e., 1–1000 °C h⁻¹. We conclude that the formation of type I and II chondrules in the proto-solar nebula was the result of a common mechanism.

¹Tomasz Brachaniec
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13035]
¹Department of Geochemisty, Mineralogy and Petrography, Faculty of Earth Sciences, University of Silesia, Sosnowiec, Poland
Published by arrangement wit John Wiley & Sons

Reworking and redeposition of tektites is a highly complex and multistage geological process including many factors. A tumbling experiment was therefore undertaken with the aim of estimating a distance of transport that such moldavites can withstand. Though the experiment probably did not accurately mimic natural conditions, our results proved that moldavites can withstand considerable transport only over a distance of a few kilometers. Observed abrasion of tektites was significant in the early stage of experimental transport; the rate of abrasion decreased correlatively with increasing distance of transport as usual. Overall, given the results obtained from this experimental study and their state of preservation described in the literature, it is very likely that Polish tektites were reworked and redeposited by rivers from the Sudetes Mountains. Based on the paleoreconstruction of river flows, it can be assumed that the Polish tektites originated from two independent sediment supply areas.