¹R.C.Oligore
Review of Scientific Instruments 89, 024502 Link to Article [https://aip.scitation.org/doi/10.1063/1.5006261]
¹Physics Department, Washington University in St. Louis, Saint Louis, Missouri 63130, USA

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¹Michael Schäfer et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13079]
¹Planetary Geology Department, Institute of Planetary Research, German Aerospace Center (DLR), , Berlin, Germany
Published by arrangement with John Wiley & Sons

Ceres’ surface has commonly been linked with carbonaceous chondrites (CCs) by ground‐based telescopic observations, because of its low albedo, flat to red‐sloped spectra in the visible and near‐infrared (VIS/NIR) wavelength region, and the absence of distinct absorption bands, though no currently known meteorites provide complete spectral matches to Ceres. Spatially resolved data of the Dawn Framing Camera (FC) reveal a generally dark surface covered with bright spots exhibiting reflectance values several times higher than Ceres’ background. In this work, we investigated FC data from High Altitude Mapping Orbit (HAMO) and Ceres eXtended Juling (CXJ) orbit (~140 m/pixel) for global spectral variations. We found that the cerean surface mainly differs by spectral slope over the whole FC wavelength region (0.4–1.0 μm). Areas exhibiting slopes <−10% μm−1 constitute only ~3% of the cerean surface and mainly occur in the bright material in and around young craters, whereas slopes ≥−10% μm−1 occur on more than 90% of the cerean surface; the latter being denoted as Ceres’ background material in this work. FC and Visible and Infrared Spectrometer (VIR) spectra of this background material were compared to the suite of CCs spectrally investigated so far regarding their VIS/NIR region and 2.7 μm absorption, as well as their reflectance at 0.653 μm. This resulted in a good match to heated CI Ivuna (heated to 200–300 °C) and a better match for CM1 meteorites, especially Moapa Valley. This possibly indicates that the alteration of CM2 to CM1 took place on Ceres.

¹F.Tosi et al. (>10)
Meteoritisc & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13078]
¹Instituto Nazionale di Astrofisica, Istituto di Astrofisica e Planetologia Spaziali (INAF‐IAPS), , Rome, Italy
Published by arrangement with John Wiley & Sons

We investigate the region of crater Haulani on Ceres with an emphasis on mineralogy as inferred from data obtained by Dawn’s Visible InfraRed mapping spectrometer (VIR), combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Haulani, which is one of the youngest craters on Ceres, exhibits a peculiar “blue” visible to near‐infrared spectral slope, and has distinct color properties as seen in multispectral composite images. In this paper, we investigate a number of spectral indices: reflectance; spectral slopes; abundance of Mg‐bearing and NH4‐bearing phyllosilicates; nature and abundance of carbonates, which are diagnostic of the overall crater mineralogy; plus a temperature map that highlights the major thermal anomaly found on Ceres. In addition, for the first time we quantify the abundances of several spectral endmembers by using VIR data obtained at the highest pixel resolution (~0.1 km). The overall picture we get from all these evidences, in particular the abundance of Na‐ and hydrous Na‐carbonates at specific locations, confirms the young age of Haulani from a mineralogical viewpoint, and suggests that the dehydration of Na‐carbonates in the anhydrous form Na2CO3 may be still ongoing.

^1,2Eva‐Regine Carl, ³Hanns‐Peter Liermann, ^4,5Lars Ehm, ¹Andreas Danilewsky, ¹Thomas Kenkmann
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13077]
¹Institut für Geo‐ und Umweltnaturwissenschaften, Geologie, Albert‐Ludwigs‐Universität, , Freiburg, Germany
²Institut für Geo‐ und Umweltnaturwissenschaften, Kristallographie, Albert‐Ludwigs‐Universität, , Freiburg, Germany
³Photon Science, DESY, , Hamburg, Germany
⁴Mineral Physics Institute, Stony Brook University, Stony Brook, New York, USA
⁵National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York, USA
Published by arrangement with John Wiley & Sons

Coesite and stishovite are high‐pressure silica polymorphs known to have been formed at several terrestrial impact structures. They have been used to assess pressure and temperature conditions that deviate from equilibrium formation conditions. Here we investigate the effects of nonhydrostatic, dynamic stresses on the formation of high‐pressure polymorphs and the amorphization of α‐quartz at elevated temperatures. The obtained disequilibrium states are compared with those predicted by phase diagrams derived from static experiments under equilibrium conditions. We analyzed phase transformations starting with α‐quartz in situ under dynamic loading utilizing a membrane‐driven diamond anvil cell. Using synchrotron powder X‐ray diffraction, the phase transitions of SiO₂ are identified up to 77.2 GPa and temperatures of 1160 K at compression rates ranging between 0.10 and 0.37 GPa s⁻¹. Coesite starts forming above 760 K in the pressure range between 2 and 11 GPa. At 1000 K, coesite starts to transform to stishovite. This phase transition is not completed at 1160 K in the same pressure range. Therefore, the temperature initiates the phase transition from α‐quartz to coesite, and the transition from coesite to stishovite. Below 1000 K and during compression, α‐quartz becomes amorphous and partially converts to stishovite. This phase transition occurs between 25 and 35 GPa. Above 1000 K, no amorphization of α‐quartz is observed. High temperature experiments reveal the strong thermal dependence of the formation of coesite and stishovite under nonhydrostatic and disequilibrium conditions.

^1,2Jérôme Aléon, ^3,4Johanna Marin-Carbonne, ³Kevin D. McKeegan, ⁵Ahmed El Goresy
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.04.001]
¹Centre de Science Nucléaire et de Science de la Matière, CNRS/IN2P3 – Université Paris-Sud UMR 8609, Bâtiment 104, 91405 Orsay Campus, France
²Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, UMR 7590, Sorbonne Université, Museum National d’Histoire Naturelle, CNRS, Univ. Pierre et Marie Curie, IRD, 61 rue Buffon, 75005 Paris, France
³Department of Earth, Planetary, and Space Sciences, University of California – Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095-1567, USA
⁴Laboratoire Magma et Volcans, UMR 6524, Univ. Lyon, Univ. Jean Monnet Saint-Etienne, CNRS, Univ. Clermont Auvergne, IRD, 23 rue du Dr Paul Michelon, 42023 Saint-Etienne, France
⁵Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany
Copyright Elsevier

Oxygen, magnesium, and silicon isotopic compositions in the mineralogically complex, ultrarefractory (UR) calcium-aluminum-rich inclusion (CAI) E101.1 from the reduced CV3 chondrite Efremovka confirm that E101.1 is a compound CAI composed of several lithological units that were once individual CAIs, free-floating in the solar protoplanetary disk. Each precursor unit was found to have had its own thermal history prior to being captured and incorporated into the partially molten host CAI.

Four major lithological units can be distinguished on the basis of their isotopic compositions. (1) Al-diopside-rich sinuous fragments, hereafter sinuous pyroxene, are ¹⁶O-rich (Δ¹⁷O ≤ -20‰) and have light Mg and Si isotopic compositions with mass fractionation down to -3.5‰/amu for both isotopic systems. We attribute these peculiar isotopic compositions to kinetic effects during condensation out of thermal equilibrium. (2) Spinel clusters are ¹⁶O-rich (Δ¹⁷O ∼ -22‰) and have Mg isotope systematics consistent with extensive equilibration with the host melt. This includes (i) δ²⁵Mg values varying between +2.6 ‰ and +6.5 ‰ close to the typical value of host melilite at ∼+5‰, and (ii) evidence for exchange of radiogenic ²⁶Mg with adjacent melilite as indicated by Al/Mg systematics. The spinel clusters may represent fine-grained spinel-rich proto-CAIs captured, partially melted, and recrystallized in the host melt. Al/Mg systematics indicate that both the sinuous pyroxene fragments and spinel clusters probably had canonical or near-canonical ²⁶Al contents before partial equilibration. (3) The main CAI host (Δ¹⁷O ≤ -2‰) had a complex thermal history partially obscured by subsequent capture and assimilation events. Its formation, referred to as the “cryptic” stage, could have resulted from the partial melting and crystallization of a ¹⁶O-rich precursor that underwent ¹⁶O-depletion and a massive evaporation event characteristic of F and FUN CAIs (Fractionated with Unknown Nuclear effects). Alternatively, a ¹⁶O-rich UR precursor may have coagulated with a ¹⁶O-poor FUN CAI having ⁴⁸Ca anomalies, as indicated by perovskite, before subsequent extensive melting. The Al/Mg systematics (2.4 × 10^-5 ≤  ≤ 5.4 × 10^-5, where  is a model initial ²⁶Al/²⁷Al ratio per analysis spot) are best understood if the FUN component was ²⁶Al-poor, as are many FUN CAIs. (4) A complete Wark-Lovering rim (WLR) surrounds E101.1. Its Mg and Si isotopic compositions indicate that it formed by interaction of the evaporated interior CAI with an unfractionated ¹⁶O-rich condensate component. Heterogeneities in ²⁶Al content in WLR spinels (3.7 × 10^-5 ≤  ≤ 5.7 × 10^-5) suggest that the previously reported age difference of as much as 300,000 years between interior CAIs and their WLRs may be an artifact resulting from Mg isotopic perturbations, possibly by solid state diffusion or mixing between the interior and condensate components.

The isotopic systematics of E101.1 imply that ¹⁶O-rich and ¹⁶O-poor reservoirs co-existed in the earliest solar protoplanetary disk and that igneous CAIs experienced a ¹⁶O-depletion in an early high temperature stage. The coagulation of various lithological units in E101.1 and their partial assimilation supports models of CAI growth by competing fragmentation and coagulation in a partially molten state. Our results suggest that chemical and isotopic heterogeneities of unclear origin in regular CAIs may result from such a complex aggregation history masked by subsequent melting and recrystallization.