¹Gregory J.Archer,¹Gregory A.Brennecka,² Philipp Gleißner,³Andreas Stracke,²Harry Becker,¹Thorsten Kleine
Earth and Planetary Science Letters 528, 115841 Link to Article [https://doi.org/10.1016/j.epsl.2019.115841]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
²Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstrasse 74-100, 12249 Berlin, Germany
³Institut für Mineralogie, University of Münster, Corrensstrasse 24, 48149 Münster, Germany
Copyright Elsevier

We report ¹⁸²W and ¹⁴²Nd isotopic compositions, ¹⁸⁷Re–¹⁸⁷Os systematics, and abundances of highly siderophile elements (HSE: Re, Os, Ir, Ru, Rh, Pt, Pd, and Au) for a suite of komatiites and basalts from the ∼3.3Ga Ruth Well Formation and the ∼3.45Ga Warrawoona Group of the Pilbara Craton, Western Australia. The ¹⁸²W compositions from all samples are indistinguishable from each other, and more radiogenic than modern bulk silicate Earth, with a mean μ¹⁸²W value of +9.1±4.2 (2SD). By contrast, the ¹⁴²Nd values for all samples are indistinguishable from each other and terrestrial standards, with a mean μ¹⁴²Nd value of −1.6±3.2 (2SD). The ¹⁴⁶Sm–¹⁴²Nd and ¹⁸⁷Re–¹⁸⁷Os systematics are consistent with chondritic Sm/Nd and Re/Os ratios in the mantle source during the lifetime of ¹⁸²Hf, and the observed ¹⁸²W excesses therefore cannot be accounted for by early Hf–W fractionation by magma ocean processes, neither by silicate liquid-crystal fractionation nor by high P–T metal-silicate equilibration. The estimated abundances of HSE in the mantle source, however, are significantly lower than modern bulk silicate Earth, with only 51±9% (1SD) of modern bulk silicate Earth abundances. These results are consistent with a partial lack of late-accreted material within the Pilbara source at ∼3.3Ga to account for the ¹⁸²W excesses. Further, widespread ¹⁸²W excesses of similar magnitude in other Archean mantle-derived rocks worldwide strongly suggests that a common process, most likely incomplete addition of late-accreted material, was responsible. The apparent mismatch between late-accreted ¹⁸²W–HSE systematics for some other localities likely reflects either the inherent difficulties associated with estimating source HSE abundances, and/or dissociation of W and HSE by mantle processes. Finally, the combined average ¹⁸²W–HSE systematics of Archean samples indicate that the pre-late accretion BSE likely had a μ¹⁸²W value similar to that of the lunar mantle, which strongly suggests post-giant impact Earth–Moon equilibration and indicates that the Moon formed after ¹⁸²Hf extinction.

¹Hill, P.J.A.,¹Banerjee, N.R.,^1,2Ali, A.,¹Jabeen, I.,¹Osinski, G.R.,¹Longstaffe, F.J.
Journal of Mass Spectrometry 54, 667-675 Link to Article [DOI: 10.1002/jms.4381]
¹Department of Earth Sciences and Centre for Planetary Science and Exploration, The University of Western Ontario, 1151 Richmond Street N, London, ON N6A 5B7, Canada
²Earth Sciences Research Centre (ESRC), Sultan Qaboos University (SQU), Al-Khoudh, Muscat, Oman

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

¹Balan, E.,¹Créon, L.,¹Sanloup, C.,¹Aléon, J.,²Blanchard, M.,¹Paulatto, L.,¹Bureau, H.
Chemical Geology 525, 424-434 Link to Article [DOI: 10.1016/j.chemgeo.2019.07.032]
¹Sorbonne Université, CNRS, IRD, MNHN, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), 4 place Jussieu, Paris cedex 05, 75252, France
²Géosciences Environnement Toulouse (GET), Observatoire Midi-Pyrénées, Université de Toulouse, CNRS, IRD, UPS, 14 avenue E. Belin, Toulouse, 31400, France

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

^1,2Run-Lia Pang,²Dennis Harries,¹Kilian Pollok,^1,3Ai-Cheng Zhang,^2,4Falko Langenhorst
Geochemistry (Chemie der Erde) (In Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125541]
¹State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China
²Institute of Geosciences, Friedrich Schiller University Jena, D-07745 Jena, Germany
³CAS Center for Excellence in Comparative Planetology, China
⁴Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawai’i 96822, USA
Copyright Elsevier

Shock-induced Ti-rich melt pockets in a basaltic eucrite Northwest Africa (NWA) 8003 were studied using scanning and transmission electron microscopy. Unique mineral assemblages consisting of clinopyroxene, ilmenite, vestaite, corundum, and kyanite are observed. Among them, vestaite and corundum in NWA 8003 are first reported to occur in eucrite meteorites. Petrographic and chemical evidences indicate that the Ti-rich melt pockets have formed by in-situ melting of ilmenite, plagioclase, pyroxene, and possibly minor silica and apatite nearby. The temperature rise and melting were caused by the high shock impedance contrast at interfaces between ilmenite and other phases with a distinctly lower density. Crystallization pressure, temperature and cooling time of the Ti-rich melt pockets in NWA 8003 are constrained to be ∼0.9–∼10 GPa, ∼1300–∼1730 °C, and < 1 ms (5–50 μm in size), respectively.

¹Doreen Schmidt,¹ Kilian Pollok,² Gabor Matthäus,²Stefan Nolte,^1,3FalkoLangenhorst
Geochemistry (Chemie der Erde) (In Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125542]
¹Institute of Geoscience, Friedrich Schiller University, Carl-Zeiss-Promenade 10, 07745, Jena, Germany
²Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University, Albert-Einstein-Straße 15, 07745, Jena, Germany
³Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawai’i, 96822, USA
Copyright Elsevier

Space weathering by micrometeoroid bombardment is a cosmic phenomenon on atmosphere-free celestial bodies, a process that is expected to particularly overprint planetesimals and cosmic dust in debris discs. We reproduced micrometeoroid impact craters by femtosecond pulsed laser irradiation on oriented enstatite single crystals (En₉₃Fs₇) to investigate the deformation behavior and its orientation dependence. All microcraters show typical bowl shaped morphologies, a glass surface layer with splash like ejecta material and subsurface layering. Although we could reproduce melting and vaporization as typical space weathering effects in the enstatite experiments, there is no formation of agglutinate particles or metallic nanoparticles (npFe⁰). The shock effects in the deformation layer consist of planar structures like microfractures and cleavages, amorphous lamellae, stacking faults and clinoenstatite lamellae. Their activation and/or orientation depends on the shock direction. In special orientations we observe the activation of glide systems along specific low indexed crystallographic planes. Due to the short timescale and the high strain rates, the most prominent effect is the failure of enstatite by microfracturing along non-rational crystallographic planes. Common deformation mechanisms reported in meteorites like the formation of clinoenstatite lamellae via shearing along [001] (100) occur less frequently. Shear is apparently the dominant mechanism in the formation of the above-mentioned effects and causes also their modification by frictional heating. The wide-spread formation of amorphous lamellae is, for example, interpreted to be the result of this shear heating along planar structures. We interpret this unconventional deformation behavior as a consequence of the small spatial and temporal scale of the experiments, resulting in a short-lived spherical shock wave with high deviatoric stresses in contrast to a long pressure pulse and quasi-hydrostatic compression in large scale impacts that produce typical shock features.

¹M.Gellissen,¹A.Holzheid,¹Ph.Kegler,²H.Palme
Geochemistr< (Chemie der Erde)  (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125540]
¹Institut für Geowissenschaften, Universität Kiel, Germany
²Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt / Main, Germany
Copyright Elsevier

We have studied the evaporation of Na, K and Mn from Al-Na-K- and Mn-rich silicate at various conditions. Total alkali oxide contents ranged from 5 to 20%. The evaporation rate of Na increases with temperature and decreasing oxygen fugacity and decreases with duration of heating. The loss of K is in all cases less pronounced than for Na. Heating in an evacuated vacuum furnace is more effective in removing Na and K from melt droplets than in furnaces with one atm gas flow of air or gas mixtures controlling the oxygen fugacity. The strong pumping required to keep the vacuum removes Na and K atoms very effectively. In all experiments, the rate of evaporation is determined by quasi-equilibrium between a thin layer of Na and K rich gas above the molten silicates. The results of the experiments are in agreement with several other studies.

In experiments with more than one sample in the furnace, equilibration of Na- and K-rich samples with Na- and K-poor samples occurred rapidly, mediated by the ambient gas phase.

The results of experiments with Mn in starting compositions showed much stronger losses of Na than Mn under a variety of conditions.

Thus the nearly chondritic Mn/Na ratios in the Earth cannot be the result of evaporation of Na and Mn in Earth-making materials, as the Mn/Na ratios in evaporation residues would be much higher than chondritic ratios. Such evaporation processes may have occurred in the parent material of Moon, Vesta and Mars.

The data suggest, in agreement with earlier hypotheses, that the high and variable contents of Na and K in chondrules require a gas phase high in Na and K equilibrating with chondrule melts. The volume of nebular gas parental to a certain type of chondrites was heated and Na and K were lost from the chondrule precursors to the gas phase. Subsequently the nebular parcel was compressed leading to higher partial pressures of Na and K. Flash heating then produced chondrule melts which incorporated some of the gaseous Na and K and then cooled rapidly. The large range of Na and K contents in chondrule melts reflects very local enrichments of Na and K in the gas phase. Despite these variations bulk chondritic meteorites have well defined bulk Na and K contents, implying a closed system during formation of chondrule and matrix.

¹Harry Y.McSweenJr.,²Carol A.Raymond,³Edward M.Stolper,⁴David W.Mittlefehldt,³Michael B.Baker,⁵Nicole G.Lunning,⁶Andrew W.Beck,⁷Timothy M.Hahn
Geochemistry (Chemie der Erde) Link to Article [https://doi.org/10.1016/j.chemer.2019.07.008]
¹Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
⁴NASA Johnson Space Center, Houston, TX 77058, USA
⁵Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854, USA
⁶Department of Petroleum Engineering and Geology, Marietta College, Marietta, OH 45750, USA
⁷Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA
Copyright Elsevier

Quantifying the amounts of various igneous lithologies in Vesta’s crust allows the estimation of petrologic ratios that describe the asteroid’s global differentiation and subsequent magmatic history. The eucrite:diogenite (Euc:Diog) ratio measures the relative proportions of mafic and ultramafic components. The intrusive:extrusive (I:E) ratio assesses the effectiveness of magma ascent and eruption. We estimate these ratios by counting numbers and masses of eucrites, cumulate eucrites, and diogenites in the world’s meteorite collections, and by calculating their proportions as components of crustal polymict breccias (howardites) using chemical mixing diagrams and petrologic mapping of multiple thin sections. The latter two methods yield a Euc:Diog ratio of ∼2:1, although meteorite numbers and masses give slightly higher ratios. Surface lithologic maps compiled from spectra of Dawn spacecraft instruments (VIR and GRaND) yield Euc:Diog ratios that bracket estimates of Euc:Diog from the meteorites. The I:E ratios from HEDs lie between 0.5–2.1:1, due to uncertainties in identifying cumulate eucrite. Gravity mapping of Vesta by the Dawn spacecraft supports the existence of diogenite plutons in the crust. Quantifying the proportion of high-density diogenitic crust in the gravity map yields I:E ratios of 0.8-1:2:1, values which are bracketed by calculations based on HEDs. The I:E ratio for Vesta is lower than for Earth and Mars, consistent with physical modeling of asteroid-size bodies. Nevertheless, it indicates a significant role for pluton emplacement during the formation of Vesta’s crust. These results are inconsistent with simple differentiation models that produce the crust by crystallization of a global magma ocean, unless residual melts are extracted into crustal magma chambers.

¹Emily J.Foote,¹David A.Paige,²Michael K.Shepard,³Jeffrey R.Johnson,⁴Stuart Biggar
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.113456]
¹University of California Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, CA 90095-1567
²Bloomsburg University, 400 E. Second St., Bloomsburg, PA 17815, Bloomsburg, PA
³Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Road, 200-W230, Laurel, MD 20723-6005
⁴College of Optical Sciences, University of Arizona, 1630 E. University Blvd., P.O. Box 210094, Tucson, AZ 85721-0094
Copyright Elsevier

We have acquired a comprehensive laboratory bidirectional measurements of Apollo 11 and Apollo 16 lunar soil samples and have successfully fit photometric models to the laboratory data and have determined the solar spectrum averaged hemispheric reflectance as a function of incidence angle. The Apollo 11 (sample 10084) and 16 (sample 68810) soil samples are two representative end member samples from the Moon, dark lunar maria and bright lunar highlands. We used our solar spectrum averaged albedos in a thermal model and compared our model-calculated normal bolometric infrared emission curves with those measured by the LRO Diviner Lunar Radiometer Experiment. We found excellent agreement at the Apollo 11 site, but at the Apollo 16 site, we found that the albedos we measured in the laboratory were 33% brighter than those required to fit the Diviner infrared data. We attribute this difference at Apollo 16 to increased compaction and decreased maturity of the laboratory sample relative to the natural lunar surface, and to local variability in surface albedos at the Apollo 16 field area that are below the spatial resolution of Diviner.

¹Franck Poitrasson,¹Thomas Zambardi,²Tomas Magna,³Clive R.Neal
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.09.035]
¹Laboratoire Géosciences Environnement Toulouse, Centre National de la Recherche Scientifique UMR 5563 – UPS – IRD – CNES, 14-16, avenue Edouard Belin, 31400 Toulouse, France
²Czech Geological Survey, Klarov 3, CZ-11821 Prague 1, Czech Republic
³Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, USA
Copyright Elsevier

The Fe isotope composition of planetary bodies may provide constraints on their accretion modes and/or differentiation processes, but to do so, the Fe isotope systematics of key planetary reservoirs needs to be determined. To investigate this for the Moon, we measured the Fe isotope compositions for a suite of 33 bulk lunar mare basalts and highland rocks. Combined with published data, a compendium of 73 different lunar bulk rocks reveals a statistically significant Fe isotope difference between low-Ti and high-Ti mare basalts, yielding average δ⁵⁷Fe = 0.127 ± 0.012‰ (2SE; n = 27) and δ⁵⁷Fe = 0.274 ± 0.020‰ (2 SE; n = 25), respectively, relative to the IRMM-14 isotopic reference material. As lunar basalts are thought to reflect the Fe isotope composition of their respective mantle sources, the estimated relative proportion of the low-Ti and high-Ti source mantle suggests that the lunar upper mantle δ⁵⁷Fe value should be close to 0.142 ± 0.026‰. Whilst the composition of highland rocks (ferroan anorthosites and Mg-suite rocks) should provide a more global view of the Moon, the calculation of the mean δ⁵⁷Fe value of 15 available highland rock analyses yields δ⁵⁷Fe = 0.078 ± 0.124‰. Such a value is not defined precisely enough to be of critical use for comparative planetology. Ferroan anorthosites and Mg-suite rocks also give unresolvable means. It appears that Fe isotope heterogeneity among the lunar highland rocks is caused by non-representatively too small sample aliquots of coarse-grained rocks. It can also be the result of mixed lithologies for some. When the (kinetic) effect of olivine tending towards low δ⁵⁷Fe and feldspar with predominantly high δ⁵⁷Fe is cancelled, a more precise δ⁵⁷Fe value of 0.094 ± 0.035‰ is calculated. It is indistinguishable from the mean δ⁵⁷Fe of impact melts and is also similar to the upper lunar mantle estimate obtained from mare basalts. Collectively, this newly determined Fe isotope composition of the bulk Moon is indistinguishable from that of the Earth, and heavier than those reported for other planetary bodies. This planetary isotope relationship is only observed for silicon given the currently available mass-dependent stable isotope database. Because both iron and silicon reside in the Earth’s metallic core in significant quantities, this may point to the involvement of metallic cores of the Earth and Moon in the interplanetary Fe and Si isotope fractionation. Rather than via high-pressure metal–silicate fractionation at the core–mantle boundary, this would more likely be achieved by partial vaporization of the liquid outer metallic core in the aftermath of a Moon-forming giant impact.

¹Tsuyoshi Iizuka,²Fred Jourdan,^3,4Akira Yamaguchi,⁵Piers Koefoed,¹Yuki Hibiya,¹Kengo T.M.Ito,⁵Yuri Amelin
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.09.034]
¹Department of Earth and Planetary Science, The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan
²Western Australian Argon Isotope Facility, JdL Center & Department of Applied Geology, Curtin University, Perth, Western Australia 6845, Australia
³National Institute of Polar Research, Tokyo, Japan
⁴Department of Polar Science, School of Multidisciplinary Science, Graduate University for Advanced Sciences, Tokyo, Japan
⁵Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia
Copyright Elsevier

Eucrites represent samples of mafic crust of the parent body, likely Vesta, and record a complex geologic history involving magmatism, metamorphism, impact processing, and metasomatism. For better understanding of the geologic history, we present combined ²⁰⁷Pb/²⁰⁶Pb and ⁴⁰Ar/³⁹Ar chronology of four basaltic eucrites showing distinct petrologic features: Agoult, an equilibrated eucrite with granulitic textures; Camel Donga, a brecciated equilibrated eucrite enriched in metallic iron; DaG 380, a partially equilibrated monomict eucrite; and NWA 049, a metasomatized polymict eucrite comprising mostly unequilibrated clasts. The ²⁰⁷Pb/²⁰⁶Pb dating in combination with the acid washing technique was applied to pyroxene-rich and plagioclase-rich fractions, while the ⁴⁰Ar/³⁹Ar dating was performed mainly on plagioclase grains using the laser incremental heating method. The Pb isotopic data for acid leaching residues are more radiogenic than those for acid washes, reflecting efficient removal of non-radiogenic Pb components by the acid washing. Among the residues, however, only those of the Agoult and Camel Donga plagioclase-rich fractions yielded isochrons, rather than errorchrons, with ²⁰⁷Pb/²⁰⁶Pb ages of 4532.39 ± 0.87 Ma and 4515.43 ± 0.42 Ma, respectively. The trace element systematics further suggest that these residues essentially represent contaminant oxide minerals such as ilmenite and chromite rather than plagioclase. On the other hand, the Ar isotopic data for Agoult and Camel Donga yielded plateau ages with weighted means of 4494 ± 9 Ma and 3749 ± 25 Ma, in contrast to those for DaG 380 and NWA 049 that did not return any plateau. The ²⁰⁷Pb/²⁰⁶Pb and ⁴⁰Ar/³⁹Ar ages of Agoult are interpreted to reflect the time of the U–Pb and K–Ar system closure during a prolonged thermal metamorphism. By combining the ages reported here and in the literature with the calculated closure temperatures, the cooling rate of Agoult is determined to be 11 ± 2 ˚C/Ma. This cooling rate corresponds to a burial depth of 10–20 km, indicating that granulitic eucrites were originally crystallized near the surface and were subsequently buried and metamorphosed. The ∼20 Ma younger ²⁰⁷Pb/²⁰⁶Pb ages of Camel Donga than Agoult are considered to reflect delayed burial metamorphism in the source region, whereas the plateau ⁴⁰Ar/³⁹Ar age would record the time of an impact causing brecciation and efficient Ar-degassing of the buried crust. Furthermore, the model ²⁰⁷Pb*/²⁰⁶Pb* dates calculated for acid-washed pyroxenes imply that the burial metamorphism of Agoult and DaG 380 were broadly contemporaneous and also that NWA 049 was metasomatized by fluids within the uppermost crust later than 4.4 Ga.