¹J.I.Simon,²J.N.Cuzzi^1,2K.A.McCain,⁴M.J.Cato,⁵P.A.Christoffersen,⁶K.R.Fisher⁷P.Srinivasan⁸A.W.Tait⁹D.M.Olson²J.D.Scargle
Earth and Planetary Science Letters 494, 69-82 Link to Article [https://doi.org/10.1016/j.epsl.2018.04.021]
¹Center for Isotope Cosmochemistry and Geochronology, ARES, EISD-XI3, NASA Johnson Space Center, Houston, TX 77058, USA
²NASA Ames Research Center, Moffett Field, CA 94035, USA
³The University of Chicago, Chicago, IL 60637, USA
⁴Western Carolina University, Cullowhee, NC, 28723, USA
⁵St. Lawrence University, Canton, NY, 13617, USA
⁶University of Cincinnati, Cincinnati, OH, 45219, USA
⁷Rutgers University, Piscataway, NJ, 08854, USA
⁸Monash University, Clayton, 3168, VIC, Australia
⁹BAERI, inc., Petaluma, CA 94952, USA
Copyright Elsevier

Magnesium-rich silicate chondrules and calcium-, aluminum-rich refractory inclusions (CAIs) are fundamental components of primitive chondritic meteorites. It has been suggested that concentration of these early-formed particles by nebular sorting processes may lead to accretion of planetesimals, the planetary bodies that represent the building blocks of the terrestrial planets. In this case, the size distributions of the particles may constrain the accretion process. Here we present new particle size distribution data for Northwest Africa 5717, a primitive ordinary chondrite (ungrouped 3.05) and the well-known carbonaceous chondrite Allende (CV3). Instead of the relatively narrow size distributions obtained in previous studies (Ebel et al., 2016, Friedrich et al., 2015, Paque and Cuzzi, 1997, and references therein), we observed broad size distributions for all particle types in both meteorites. Detailed microscopic image analysis of Allende shows differences in the size distributions of chondrule subtypes, but collectively these subpopulations comprise a composite “chondrule” size distribution that is similar to the broad size distribution found for CAIs. Also, we find accretionary ‘dust’ rims on only a subset (∼15–20%) of the chondrules contained in Allende, which indicates that subpopulations of chondrules experienced distinct histories prior to planetary accretion. For the rimmed subset, we find positive correlation between rim thickness and chondrule size. The remarkable similarity between the size distributions of various subgroups of particles, both with and without fine grained rims, implies a common size sorting process. Chondrite classification schemes, astrophysical disk models that predict a narrow chondrule size population and/or a common localized formation event, and conventional particle analysis methods must all be critically reevaluated. We support the idea that distinct “lithologies” in NWA 5717 are nebular aggregates of chondrules. If ≥cm-sized aggregates of chondrules can form it will have implications for planet formation and suggests the sticking stage is where the preferential size physics is operating.

¹Timo Hopp, ¹Thorsten Kleine
Earth and Planetary Science Letters 494, 50-59 Link to Article[https://doi.org/10.1016/j.epsl.2018.04.058]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
Copyright Elsevier

Elevated abundances of highly siderophile elements in Earth’s mantle are thought to reflect the late accretion of primitive material after the cessation of core formation, but the origin of this material, and whether or not it can be linked to specific types of meteorites remain debated. Here, mass-dependent Ru isotopic data for chondrites and terrestrial peridotites are reported to evaluate the chemical nature and type of the late-accreted material. After correction for nucleosynthetic Ru isotope anomalies, enstatite, ordinary and carbonaceous chondrites all have indistinguishable mass-dependent Ru isotopic compositions. Thus, neither distinct formation conditions in the solar nebula nor parent body processes resulted in significant mass-dependent Ru isotope fractionation. All five terrestrial peridotites analyzed have mass-dependent Ru isotopic compositions that are indistinguishable from each other and from the composition of chondrites. The chondritic mass-dependent Ru isotopic composition of Earth’s mantle is difficult to reconcile with prior suggestions that the late accretionary assemblage was a mixture of chondrites with a chemically evolved metal component. Although this mixture can reproduce the suprachondritic Ru/Ir inferred for Earth’s mantle, it consistently predicts a heavy Ru isotopic composition of Earth’s mantle with respect to chondrites. This is because metal components with elevated Ru/Ir are also enriched in heavy Ru isotopes, resulting from isotope fractionation during core crystallization. Thus, if late accretion involved impacts of differentiated protoplanetary bodies, then the projectile cores must have been either homogenized upon impact, or added to Earth’s mantle completely, because otherwise Earth’s mantle would have inherited a non-chondritic mass-dependent Ru isotopic composition from the unrepresentative sampling of core material.

¹E. S. Steenstra, ¹N. Agmon, ²J. Berndt, ²S. Klemme, ³S. Matveev, ¹W. van Westrenen
Scientific Reports 8, 7053 Link to Article [doi:10.1038/s41598-018-25505-6]
¹Faculty of Science, VU Amsterdam, Amsterdam, The Netherlands
²Institute of Mineralogy, University of Münster, Münster, Germany
³Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands

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¹Alex M. Ruzicka, ¹Richard C. Hugo
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.05.014]
¹Cascadia Meteorite Laboratory, Portland State University, Department of Geology, 1721 SW Broadway, Portland, OR 97207
Copyright Elsevier

We used electron backscatter diffraction (EBSD) methods to study the crystallography of olivine and other minerals in seven heavily metamorphosed (petrographic type 6 or 6/7) but variably shocked ordinary chondrites from the H (Kernouvé, Portales Valley), L (Leedey, Bruderheim, Morrow County, Park) and LL (Miller Range (MIL) 99301) groups. MIL 99301 contains a large clast that was analyzed separately. Mesoscale (EBSD) data support and extend inferences based on microscale (TEM) observations and provide good evidence that chondrites were shock-deformed at different temperatures and were variably annealed (sintered) after deformation. Various EBSD deformation intensity metrics adequately and quantitatively represent olivine deformation in meteorites on different scales and in different ways. Mean Grain Orientation Spread (GOS, the average misorientation in a grain) is a robust statistic for overall deformation. We developed an EBSD deformation temperature metric based on olivine misorientation rotation axis data, and an EBSD post-shock annealing metric based on the skewness of olivine GOS distributions. The two parameters together define three groups among the meteorites studied, and these are related to shock stages and 40Ar/39Ar ages that record impact times. Group 1 includes cold-deformed and little-annealed but high-shock-stage (S4 and S5) chondrites (Leedey, Bruderheim, Morrow County) that were affected by impacts at a time (<4 Ga ago) when parent bodies were cold. Troilite was deformed and partly recrystallized, developing a lattice preferred orientation (LPO) in Bruderheim and Morrow County that corresponds to a principal compression direction. Olivine <001> axes in Morrow County were partially re-oriented perpendicular to this compression direction. Group 2 includes the hot-deformed but little-annealed MIL 99301_clast that shows good evidence of having formed as a shock melt, and which represents localized shock heating of material that cooled rapidly at a time when parent bodies may have been cold (∼4230 Ma ago, assuming the younger of two published ages for MIL 99301, 4230 ± 30 and 4520 ± 80 Ma, corresponds to the clast). Group 3 includes hot-deformed and more-annealed low-shock-stage (S1) chondrites (Kernouvé, Portales Valley, MIL 99301 host, Park) that experienced impacts on warm bodies in the oldest epoch (>4425 Ma, assuming the older of two published ages for MIL 99301 corresponds to host). Group 3 chondrites must have been shocked while warm at the time of impact, at temperatures estimated as >700-800 °C and up to ∼1000 °C, i.e., at conditions generally corresponding to thermal metamorphism associated with petrographic type 6 grade, and were subsequently buried and annealed in warm parent bodies. Impact at elevated pre-shock temperature resulted in partly recrystallized troilite in Park and metallic liquids that crystallized as coarse troilite interstitial to silicates in Portales Valley. For Group 3, data are consistent with impact-redistribution on warm parent bodies that were hot at depth, and support a model of early collisional processing of endogenically-heated chondritic planetesimals. In general, EBSD deformation signatures in each of the meteorites studied are dominated by the effects of the prevailing impact, although there is some evidence for multiple impact effects.

¹O. I. Yakovlev, ¹K. M. Ryazantsev, ¹S. I. Shornikov
Geochemistry International 56, 71-74 Link to Article [DOI
https://doi.org/10.1134/S001670291801010X]
¹Vernadsky Institute of Geochemistry and Analytical ChemistryRussian Academy of SciencesMoscowRussia

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¹M.C. De Sanctis et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13104]
¹Istituto di Astrofisica e Planetologia Spaziali, INAF, Rome, Italy
Published by Arrangement with John Wiley & Sons

The Visible and Infrared Spectrometer (VIR) instrument on the Dawn mission observed Ceres’s surface at different spatial resolutions, revealing a nearly uniform global distribution of surface mineralogy. Clearly, Ceres experienced extensive water‐related processes and chemical differentiation. The surface is mainly composed of a dark component (carbon, magnetite?), Mg‐phyllosilicates, ammoniated clays, carbonates, and salts. The observed species suggest endogenous, global‐scale aqueous alteration. While mostly uniform at regional scale, Ceres’s surface shows small localized areas with different species and/or variations in abundances. Few local exposures of water ice are seen, especially at higher latitudes. Sodium carbonates have been identified in several areas on the surface, notably in Occator bright faculae. Organic matter has also been discovered in several places, most conspicuously in a large area close to the Ernutet crater. The observed mineralogies, with the presence of ammoniated species and sodium salts, have a strong resemblance to materials found on other bodies of the outer solar system, such as Enceladus. This poses some questions about the original material from which Ceres accreted, suggesting a colder environment for such material with respect to Ceres’s present position.

¹D. Tirsch, ^2,3J.L. Bishop, ¹J. Yoigt, ⁴L.L. Tornabene, ⁵G. Erkeling, ^1,6R. Jaumann
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.05.006]
¹Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
²Carl Sagan Center, The SETI Institute, Mountain View, CA 94043, USA
³Exobiology Branch, NASA-Ames Research Center, Moffett Field, CA 94035, USA
⁴University of Western Ontario, London, ON, Canada
⁵German National Library of Science and Technology (TIB), Leibniz Information Centre for Science and Technology, Hannover, Germany
⁶Institute of Geological Sciences, Freie Universitaet Berlin, 12249 Berlin, Germany
Copyright Elsevier

We analyze the emplacement chronology and aqueous alteration history of distinctive mineral assemblages and related geomorphic units near Hashir and Bradbury impact craters located within the Libya Montes, which are part of the southern rim of the Isidis Basin on Mars. We derive our results from a spectro-morphological mapping project that combines spectral detections from CRISM near-infrared imagery with geomorphology and topography from HRSC, CTX, and HiRISE imagery. Through this combination of data sets, we were able to use the morphology associated with specific mineral detections to extrapolate the possible extent of the units hosting these compositions. We characterize multiple units consistent with formation through volcanic, impact, hydrothermal, lacustrine and evaporative processes. Altered pyroxene-bearing basement rocks are unconformably overlain by an olivine-rich unit, which is in turn covered by a pyroxene-bearing capping unit. Aqueously altered outcrops identified here include nontronite, saponite, beidellite, opal, and dolomite. The diversity of mineral assemblages suggests that the nature of aqueous alteration at Libya Montes varied in space and time. This mineralogy together with geologic features shows a transition from Noachian aged impact-induced hydrothermal alteration and the alteration of Noachian bedrock by neutral to slightly basic waters via Hesperian aged volcanic emplacements and evaporative processes in lacustrine environments followed by Amazonian resurfacing in the form of aeolian erosion.

^1,2,3Qing-Feng Mei, ^1,2,3Jin-Hui Yang, ^1,2Yue-Heng Yang
Journal of Analytical Atomic Spectroscopy 33, 569-577 Link to Article [DOI:
10.1039/C8JA00024G]
¹State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
²Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China
³ University of Chinese Academy of Sciences, Beijing 100049, China

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¹K. K. Larsen, ¹D. Wielandt, ¹M. Bizzarro
Journal of Analytical Atomic Spectroscopy 33, 613-628 Link to Article [DOI:
10.1039/C7JA00392G]
¹Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Denmark

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¹Quinn R. Shollenberger, ¹Jan Render, ¹Gregory A. Brennecka
Earth and Planetary Science Letters 495, 12-23 Link to Article [https://doi.org/10.1016/j.epsl.2018.05.007]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, Münster, 48149 Germany
Copyright Elsevier

The oldest dated solids in our Solar System, calcium–aluminum-rich inclusions (CAIs), contain isotopic anomalies in a whole suite of elements relative to later formed Solar System materials. Previous work has reported differences in the proportions of nucleosynthetic components between CAIs and terrestrial rocks as a function of mass. However, the nucleosynthetic fingerprint of the CAI-forming region is still lacking significant data in the heavier mass range (A > 154). Therefore, we present the first erbium (Er) and ytterbium (Yb) isotopic data along with hafnium (Hf) isotopic compositions in a wide variety of CAIs derived from a variety of CV and CK chondrites. This work presents new methods for Er and Yb isotopic investigation that were explored using both thermal ionization mass spectrometry (TIMS) and multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). Relative to terrestrial rock standards, CAIs—regardless of host rock, petrologic or chemical classification—have uniform and resolvable Er, Yb, and Hf isotopic compositions. The CAI isotopic patterns correspond to r-process deficits (or s-process excesses) relative to terrestrial values of 9 ppm for Er, 18 ppm for Yb, and 17 ppm for Hf. This new Er, Yb, and Hf data help complete the nucleosynthetic fingerprint of the CAI-forming region, further highlighting the systematic difference between the CAIs and later formed bulk planetary bodies. Such a systematic difference between CAIs and terrestrial rocks cannot be caused by different amounts of any known single presolar phase but is likely the result of a well-mixed reservoir made of diverse stellar sources.