¹G.J. MacPherson, ²C. Defouilloy, ²N.T. Kita
Earth and Planetary Science Letters 491, 238-243 Link to Article [https://doi.org/10.1016/j.epsl.2018.03.039]
¹Dept. of Mineral Sciences, Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA
²WiscSIMS, Dept. of Geoscience, Univ. of Wisconsin–Madison, Madison, WI 53706, USA
Copyright Elsevier

The Allende CAI View the MathML source is the basis for “ALL”, the lowest measured initial 87Sr/86Sr value in any solar system material including other CAIs (Gray et al., 1973). If the value ALL is correct (debated), then View the MathML source must be 1–2 million years older than other CAIs (Podosek et al., 1991). This would require in turn that it have a much higher initial 26Al/27Al value than other CAIs, on the order of 4 × 10−4. Podosek et al. (1991) showed that this is not the case, with initial 26Al/27Al = (4.5 ± 0.7) × 10−5, but their Mg-isotopic data had large error bars and there was clear isotopic disturbance in the data having the highest 27Al/24Mg. Without the latter data, the slope of their isochron is higher (5.10 ± 1.19) × 10−5) and within (large) error of being supracanonical. We used high-precision SIMS to re-determine the initial 26Al/27Al in this CAI and obtained a value of (5.013 ± 0.099) × 10−5, with an intercept δ26Mg⁎=−0.008±0.048 and MSWD = 1.3. This value is indistinguishable from that measured in many other CAIs and conclusively shows that View the MathML source is not uniquely ancient. We also confirmed evidence of later isotopic disturbance, similar to what Podosek et al. found, indicating a re-melting and evaporation event some 200,000 years after initial CAI solidification.

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

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

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.

^1,2Yawooz A.Kettanah, ³Sabah A.Ismail
Journal of African Earth Sciences 139, 260-274 Link to Article [https://doi.org/10.1016/j.jafrearsci.2017.11.015]
¹Department of Applied Geosciences, College of Spatial Planning & Applied Sciences, Duhok University, Duhok, Iraq
²Department of Earth Sciences, Faculty of Graduate Studies, Dalhousie University, Halifax, NS, Canada
³Dean of the College of Education for Pure Sciences, Kirkuk University, Kirkuk, Iraq

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

^1,2F. Thiessen, ^1,3A.A. Nemchin, ¹J.F. Snape, ¹J.J. Bellucci, ^1,2M.J. Whitehouse
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.03.023]
¹Department of Geosciences, Swedish Museum of Natural History, SE-10405 Stockholm, Sweden
²Department of Geological Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
³Department of Applied Geology, Curtin University, Perth, WA 6845, Australia
Copyright Elsevier

Apollo 12 breccia 12013 is composed of two portions, one grey in colour, the other black. The grey portion of the breccia consists mainly of felsite thought to have formed during a single crystallisation event, while the black part is characterized by presence of lithic fragments of noritic rocks and individual plagioclase crystals. In this study, U-Pb analyses of Ca-phosphate and zircon grains were conducted in both portions of the breccia. The zircon grains within the grey portion yielded a large range of ages (4154±7 to 4308±6 Ma, 2σ) and show decreasing U and Th concentrations within the younger grains. Moreover, some grains exhibit recrystallisation features and potentially formation of neoblasts. The latter process requires high temperatures above 1600-1700 ^oC leading to the decomposition of the primary zircon grain and subsequent formation of new zircon occurring as neoblasts. As a result of the high temperatures, the U-Pb system of the remaining original zircon grains was most likely open for Pb diffusion causing partial resetting and the observed range of ²⁰⁷Pb/²⁰⁶Pb ages. The event that led to the Pb loss in zircon could potentially be dated by the U-Pb system in Ca-phosphates, which have a weighted average ²⁰⁷Pb/²⁰⁶Pb age across both lithologies of 3924±3 Ma (95% conf.). This age is identical within error to the combined average ²⁰⁷Pb/²⁰⁶Pb age of 3926±2 Ma that was previously obtained from Ca-phosphates within Apollo 14 breccias, zircon grains in Apollo 12 impact melt breccias, and the lunar meteorite SaU 169. This age was interpreted to date the Imbrium impact. The zircon grains located within the black portion of the breccia yielded a similar range of ages (4123±13 to 4328±14 Ma, 2σ) to those in the grey portion. Given the brecciated nature of this part of the sample, the interpretation of these ages as representing igneous crystallisation or resetting by impact events remains ambiguous since there is no direct link to their source rocks via textural relationships or crystal chemistry. Similarly, the currently available zircon data set for all lunar samples may be distorted by partial Pb loss, resulting in meaningless and misleading age distribution patterns. Therefore, it is crucial to fully understand and recognize the processes and conditions that may lead to partial resetting of the U-Pb system in zircon in order to better constrain the magmatic and impact history of the Moon.

^1,2,3Nicola J. Potts, ^1,4Jessica J. Barnes, ^1,5Romain Tartèse, ¹Ian A. Franchi, ^1,6Mahesh Anand
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.03.022]
¹Planetary & Space Science, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
²Faculty of Earth & Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, NL
³School of GeoSciences, King’s Buildings, University of Edinburgh, Edinburgh, EH9 3JW, UK
⁴ARES NASA Johnson Space Center, Houston, TX 77058, USA
⁵School of Earth and Environmental Sciences, University of Manchester, Manchester M13 9PL, UK
⁶Department of Earth Sciences, The Natural History Museum, Cromwell Road, London, SW7 5BD UK
Copyright Elsevier

Compared to most other planetary materials in the Solar System, some lunar rocks display high δ³⁷Cl signatures. Loss of Cl in a H<<Cl environment has been invoked to explain the heavy signatures observed in lunar samples, either during volcanic eruptions onto the lunar surface or during large scale degassing of the lunar magma ocean. To explore the conditions under which Cl isotope fractionation occurred in lunar basaltic melts, five Apollo 14 crystalline samples were selected (14053,19, 14072,13, 14073,9, 14310,171 along with basaltic clast 14321,1482) for in situ analysis of Cl isotopes using secondary ion mass spectrometry. Cl isotopes were measured within the mineral apatite, with δ³⁷Cl values ranging from +14.6 ± 1.6 ‰ to +40.0 ± 2.9 ‰. These values expand the range previously reported for apatite in lunar rocks, and include some of the heaviest Cl isotope compositions measured in lunar samples to date. The data here do not display a trend between increasing rare earth elements contents and δ³⁷Cl values, reported in previous studies. Other processes that can explain the wide inter- and intra-sample variability of δ³⁷Cl values are explored. Magmatic degassing is suggested to have potentially played a role in fractionating Cl isotope in these samples. Degassing alone, however, could not create the wide variability in isotopic signatures. Our favored hypothesis, to explain small scale heterogeneity, is late-stage interaction with a volatile-rich gas phase, originating from devolatilization of lunar surface regolith rocks ∼4 billion years ago. This period coincides with vapor-induced metasomastism recorded in other lunar samples collected at the Apollo 16 and 17 landing sites, pointing to the possibility of widespread volatile-induced metasomatism on the lunar nearside at that time, potentially attributed to the Imbrium formation event.

^1,2W. Sato, ²M. Nakagawa, ³N. Shirai, ³M. Ebihara
Hyperfine Interactions 239, 13 Link to Article [https://doi.org/10.1007/s10751-018-1489-z]
¹Institute of Science and Engineering, Kanazawa University, Kanazawa, Japan
²Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan
³Graduate School of Science and EngineeringTokyo Metropolitan University, Hachioji, Japan

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