¹A. Kereszturi, ²I. Gyollai, ³Zs. Kereszty, ⁴K. Kiss, ²M. Szabó, ^4,6Z. Szalai, ^4,6M. Ringer, ⁵M. Veres
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 173, 637–646 Link to Article [http://dx.doi.org/10.1016/j.saa.2016.10.012]
¹Research Centre for Astronomy and Earth Sciences, Konkoly Thege Miklos Astronomical Institute, H-1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary
²Research Centre for Astronomy and Earth Sciences, Institute for Geological and Geochemical Research, H-1112 Budapest, Budaörsi út 45, Hungary
³International Meteorite Collectors Association (IMCA#6251), H 9024 Győr, Lahner u 1, Hungary
⁴Geographical Institute, H-1112 Budapest, Budaörsi út 45, Hungary
⁵Wigner Research Centre for Physics, H-1121 Budapest, Thege Miklós út 29-33, Hungary
⁶ELTE Department of Environmental and Landscape Geography, Hungary

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^1,2H. M. Sapers, ^1,2,3G. R. Osinski, ^1,2R. L. Flemming, ¹E. Buitenhuis, ¹N. R. Banerjee, ^1,2L. L. Tornabene, ¹S. Blain, ¹J. Hainge
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12796]
¹Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada
²Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario, Canada
³Department of Physics & Astronomy, University of Western Ontario, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

The ~15 Ma, 26 km diameter Ries impact structure in south-central Germany was one of the first terrestrial impact structures where evidence of impact-associated hydrothermal alteration was recognized. Previous studies suggested that pervasive, high-temperature hydrothermal activity was restricted to the area within the “inner ring” (i.e., the crater-fill impactite units). Here we present mineralogical evidence for localized hydrothermal activity in the ejecta beyond the crater rim in two previously unstudied settings: a pervasively altered lens of suevite ejecta directly overlying the Bunte Breccia at the Aumühle quarry; and suevite ejecta at depth overlain by ~20 m of lacustrine sediments sampled by the Wörnitzostheim 1965 drill core. A comprehensive set of X-ray diffraction analyses indicates five distinct alteration regimes (1) surficial ambient weathering characterized by smectite and a minor illitic component; (2) locally restricted hydrothermal activity characterized by an illitic component and minor smectite; (3) hydrothermal activity at depth characterized by smectite, a minor illitic component, and calcite; (4) hydrothermal activity at depth characterized by smectite, a minor illitic component, calcite, zeolites, and clinochlore; and (5) pervasive hydrothermal activity at depth characterized by smectite, a minor illitic component, and minor clinochlore. These data spatially extend the Ries postimpact hydrothermal system suggesting a much more extensive, complex, and dynamic system than previously thought. Constraining the mineralogical alteration regimes at the Ries impact structure may also further our understanding of impact-associated phyllosilicate formation on Mars with implications for climate models and habitability.

¹A. Basu Sarbadhikari,²E. V. S. S. K. Babu,²T. Vijaya Kumar
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12790]
¹Physical Research Laboratory, Ahmedabad, 380009, India
²National Geophysical Research Institute (Council of Scientific and Industrial Research), Hyderabad, India
Published by agreement with John Wiley & Sons

Melting of Martian mantle, formation, and evolution of primary magma from the depleted mantle were previously modeled from experimental petrology and geochemical studies of Martian meteorites. Based on in situ major and trace element study of a range of olivine-hosted melt inclusions in various stages of crystallization of Tissint, a depleted olivine–phyric shergottite, we further constrain different stages of depletion and enrichment in the depleted mantle source of the shergottite suite. Two types of melt inclusions were petrographically recognized. Type I melt inclusions occur in the megacrystic olivine core (Fo76-70), while type II melt inclusions are hosted by the outer mantle of the olivine (Fo66-55). REE-plot indicates type I melt inclusions, which are unique because they represent the most depleted trace element data from the parent magmas of all the depleted shergottites, are an order of magnitude depleted compared to the type II melt inclusions. The absolute REE content of type II displays parallel trend but somewhat lower value than the Tissint whole-rock. Model calculations indicate two-stage mantle melting events followed by enrichment through mixing with a hypothetical residual melt from solidifying magma ocean. This resulted in ~10 times enrichment of incompatible trace elements from parent magma stage to the remaining melt after 45% crystallization, simulating the whole-rock of Tissint. We rule out any assimilation due to crustal recycling into the upper mantle, as proposed by a recent study. Rather, we propose the presence of Al, Ca, Na, P, and REE-rich layer at the shallower upper mantle above the depleted mantle source region during the geologic evolution of Mars.

¹Raphael J. Baumgartner, ¹Marco L. Fiorentini, ^2,3David Baratoux, ⁴Ludovic Ferrière, ⁵Marek Locmelis, ⁶Andrew Tomkins, ⁷Kerim A. Sener
Meteoritics &Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12795]
¹School of Earth and Environment, Centre for Exploration Targeting, ARC Centre of Excellence for Core to Crust Fluid Systems, The University of Western Australia, Crawley, Australia
²Géosciences Environnement Toulouse, CNRS, IRD and University of Toulouse, Toulouse, France
³Institut Fondamental d’Afrique Noire Cheikh Anta Diop, Dakar, Senegal
⁴Natural History Museum Vienna, Vienna, Austria
⁵Department of Geosciences and Geological and Petroleum Engineering, Missouri University of Science & Technology, Rolla, Missouri, USA
⁶School of Geosciences, Monash University, Melbourne, Australia
⁷Matrix Exploration Pty Ltd, Armadale, Australia
Published by arrangement with John Wiley & Sons

The Martian meteorites comprise mantle-derived mafic to ultramafic rocks that formed in shallow intrusions and/or lava flows. This study reports the first in situ platinum-group element data on chromite and ulvöspinel from a series of dunitic chassignites and olivine-phyric shergottites, determined using laser-ablation ICP-MS. As recent studies have shown that Ru has strongly contrasting affinities for coexisting sulfide and spinel phases, the precise in situ analysis of this element in spinel can provide important insights into the sulfide saturation history of Martian mantle-derived melts. The new data reveal distinctive differences between the two meteorite groups. Chromite from the chassignites Northwest Africa 2737 (NWA 2737) and Chassigny contained detectable concentrations of Ru (up to ~160 ppb Ru) in solid solution, whereas chromite and ulvöspinel from the olivine-phyric shergottites Yamato-980459 (Y-980459), Tissint, and Dhofar 019 displayed Ru concentrations consistently below detection limit (<42 ppb). The relatively elevated Ru signatures of chromite from the chassignites suggest a Ru-rich (~1–4 ppb) parental melt for this meteorite group, which presumably did not experience segregation of immiscible sulfide liquids over the interval of mantle melting, melt ascent, and chromite crystallization. The relatively Ru-depleted signature of chromite and ulvöspinel from the olivine-phyric shergottites may be the consequence of relatively lower Ru contents (<1 ppb) in the parental melts, and/or the presence of sulfides during the crystallization of the spinel phases. The results of this study illustrate the significance of platinum-group element in situ analysis on spinel phases to decipher the sulfide saturation history of magmatic systems.

¹Michael S.P. Kelley,, ²Charles E. Woodward, ²Robert D. Gehrz, ³William T. Reach, ⁴David E. Harker
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.11.029]
¹Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
²Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 116 Church Street S. E., Minneapolis, MN 55455, USA
³Universities Space Research Corporation, Stratospheric Observatory for Infrared Astronomy, MS 232-11, NASA Ames Research Center, Moffett Field, CA 94035, USA
⁴Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0424, USA
Copyright Elsevier

Comet nuclei and D-type asteroids have several similarities at optical and near-IR wavelengths, including near-featureless red reflectance spectra, and low albedos. Mineral identifications based on these characteristics are fraught with degeneracies, although some general trends can be identified. In contrast, spectral emissivity features in the mid-infrared provide important compositional information that might not otherwise be achievable. Jovian Trojan D-type asteroids have emissivity features strikingly similar to comet comae, suggesting that they have the same compositions and that the surfaces of the Trojans are highly porous. However, a direct comparison between a comet and asteroid surface has not been possible due to the paucity of spectra of comet nuclei at mid-infrared wavelengths. We present 5–35 µm thermal emission spectra of comets 10P/Tempel 2, and 49P/Arend-Rigaux observed with the Infrared Spectrograph on the Spitzer Space Telescope. Our analysis reveals no evidence for a coma or tail at the time of observation, suggesting the spectra are dominated by the comet nucleus. We fit each spectrum with the near-Earth asteroid thermal model (NEATM) and find sizes in agreement with previous values. However, the NEATM beaming parameters of the nuclei, 0.74 to 0.83, are systematically lower than the Jupiter-family comet population mean of 1.03± 0.11, derived from 16- and 22-µm photometry. We suggest this may be either an artifact of the spectral reduction, or the consequence of an emissivity low near 16 µm. When the spectra are normalized by the NEATM model, a weak 10-µm silicate plateau is evident, with a shape similar to those seen in mid-infrared spectra of D-type asteroids. A silicate plateau is also evident in previously published Spitzer spectra of the nucleus of comet 9P/Tempel 1. We compare, in detail, these comet nucleus emission features to those seen in spectra of the Jovian Trojan D-types (624) Hektor, (911) Agamemnon, and (1172) Aneas, as well as those seen in the spectra of seven comet comae. The comet comae present silicate features with two distinct shapes, either trapezoidal, or more rounded, the latter apparently due to enhanced emission near 8 to 8.5 µm. The surfaces of Tempel 2, Arend-Rigaux, and Hektor best agree with the comae that present trapezoidal features, furthering the hypothesis that the surfaces of these targets must have high porosities in order to exhibit a spectrum similar to a comet coma. An emissivity minimum at 15 µm, present in the spectra of Tempel 2, Arend-Rigaux, Hektor, and Agamemnon, is also described, the origin of which remains unidentified. The compositional similarity between D-type asteroids and comets is discussed, and our data supports the hypothesis that they have similar origins in the early Solar System.

¹Christopher W. Dale, ²Thomas S. Kruijer, ¹Kevin W. Burton
Earth and Planetary Science Letters (in Press) Link to Article [http://dx.doi.org/10.1016/j.epsl.2016.11.001]
¹Department of Earth Sciences, Durham University, Durham, DH1 3LE, UK
²Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
Copyright Elsevier

The higher-than-expected concentrations of highly siderophile elements (HSE) in Earth’s mantle most likely indicate that Earth received a small amount of late accreted mass after core formation had ceased, known as the ‘late veneer’. Small 182W excesses in the Moon and in some Archaean rocks – such as the source of 3.8 billion-year-old Isua magmatics – also appear consistent with the late veneer hypothesis, with a lower proportion received. However, 182W anomalies can also relate to other processes, including early mantle differentiation. To better assess the origin of these W isotope anomalies – and specifically whether they relate to the late veneer – we have determined the HSE abundances and 182W compositions of a suite of mafic to ultramafic rocks from Isua, from which we estimate HSE abundances in the source mantle and ultimately constrain the 182W composition of the pre-late veneer mantle.

Our data suggest that the Isua source mantle had HSE abundances at around 50–65% of the present-day mantle, consistent with partial, but not complete, isolation from the late veneer. These data also indicate that at least part of the late veneer had been added and mixed into the mantle at the time the Isua source formed, prior to 3.8 Ga. For the same Isua samples we obtained a 13±4 ppm13±4 ppm182W excess, compared to the modern terrestrial mantle, in excellent agreement with previous data. Using combined 182W and HSE data we show that the Moon, Isua, and the present-day bulk silicate Earth (BSE) produce a well-defined co-variation between 182W composition and the mass fraction of late-accreted mass, as inferred from HSE abundances. This co-variation is consistent with the calculated effects of various late accretion compositions on the HSE and 182W signatures of Earth’s mantle. The empirical relationship, therefore, implies that the Moon, Isua source and BSE received increasing proportions of late-accreted mass, supporting the idea of disproportional late accretion to the Earth and Moon, and consistent with the interpretation that the lunar 182W value of 27±4 ppm27±4 ppm represents the composition of Earth’s mantle before the late veneer was added. In this case, the Isua source can represent ambient mantle after the giant moon-forming impact, into which only a part of Earth’s full late veneer was mixed, rather than an isotopically distinct mantle domain produced by early differentiation, which would probably require survival through the giant Moon-forming impact.

¹Maximilien J. Verdier-Paoletti, ²Yves Marrocchi, ²Guillaume Avice, ¹Mathieu Roskosz, ²Andrey Gurenko, ^1,3Matthieu Gounelle
Earth and Planetary Science Letters (in Press) Link to Article [http://dx.doi.org/10.1016/j.epsl.2016.10.055]
¹IMPMC, MNHN, UPMC, UMR CNRS 7590, 61 rue Buffon, 75005 Paris, France
²CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre les Nancy, F-54501, France
³Institut Universitaire de France, Maison des Universités, 103 bd. Saint-Michel, 75005 Paris, France
Copyright Elsevier

We report a systematic oxygen isotopic survey of Ca-carbonates in nine different CM chondrites characterized by different degrees of alteration, from the least altered known to date (Paris, 2.7–2.8) to the most altered (ALH 88045, CM1). Our data define a continuous trend that crosses the Terrestrial Fractionation Line (TFL), with a general relationship that is indistinguishable within errors from the trend defined by both matrix phyllosilicates and bulk O-isotopic compositions of CM chondrites. This bulk-matrix-carbonate (BMC) trend does not correspond to a mass-dependent fractionation (i.e., slope 0.52) as it would be expected during fluid circulation along a temperature gradient. It is instead a direct proxy of the degree of O-isotopic equilibration between 17,18O-rich fluids and 16O-rich anhydrous minerals. Our O-isotopic survey revealed that, for a given CM, no carbonate is in O-isotopic equilibrium with its respective surrounding matrix. This precludes direct calculation of the temperature of carbonate precipitation. However, the O-isotopic compositions of alteration water in different CMs (inferred from isotopic mass-balance calculation and direct measurements) define another trend (CMW for CM Water), parallel to BMC but with a different intercept. The distance between the BMC and CMW trends is directly related to the temperature of CM alteration and corresponds to average carbonates and serpentine formation temperatures of 110 °C and 75 °C, respectively. However, carbonate O-isotopic variations around the BMC trend indicate that they formed at various temperatures ranging between 50 and 300 °C, with 50% of the carbonates studied here showing precipitation temperature higher than 100 °C. The average Δ17O and the average carbonate precipitation temperature per chondrite are correlated, revealing that all CMs underwent similar maximum temperature peaks, but that altered CMs experienced protracted carbonate precipitation event(s) at lower temperatures than the least altered CMs. Our data suggest that the Δ17O value of Ca-carbonates could be a reliable proxy of the degree of alteration experienced by CM chondrites.

^1,2A. Stephant, ¹L. Remusat, ¹F. Robert
Geochimica et Cosmochmica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2016.11.031]
¹Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC) Sorbonne Universités – Muséum National d’Histoire Naturelle, UPMC Univ Paris 06, UMR CNRS 7590, IRD UMR 206, 61 rue Buffon, F-75005 Paris, France
²Center for Meteorite Studies, Arizona State University, Tempe, Arizona 85287-6004, USA
Copyright Elsevier

Hydrogen isotopic ratio and water concentration have been measured with the NanoSIMS in olivine, pyroxene and mesostasis phases in individual chondrules from the carbonaceous chondrites Paris (CM2), Renazzo (CR2) and ordinary chondrite Bishunpur (LL3). On average, chondrule pyroxenes in Renazzo, Bishunpur and Paris contain 893±637 ppm (1SD), 879±536 ppm and 791±227 ppm H2O. Chondrule olivines from Renazzo and Bishunpur vary from 156±44 ppm to 222±123 ppm. Olivines in the Paris chondrules have high water concentration (603±145 to 1051±253 ppm H2O) with a minimum mean value of 645±99 ppm. δD ranges from -212±125‰ to 15±156‰ and from -166±133‰ to 137±176‰ in Renazzo and Bishunpur chondrule olivines, pyroxenes and mesostases, respectively. In Paris chondrules, δD ranges from -398±23‰ to 366±35‰; this represents an extreme variation over 764‰. Paris olivines and pyroxenes are either enriched or depleted in deuterium relative to the mesostasis and no systematic isotopic pattern is observed. Simple model of chondrules hydration during parent body hydrothermal alteration is difficult to reconcile with such isotopic heterogeneity. It is proposed that a hydrous component, having a δD of c.a. -400‰, in the chondrule precursors, has been outgassed at 800-900°C in the gas phase. Nevertheless, a residual water fraction remains trapped in Paris chondrules. Quantitative modeling supports this scenario.

¹Connor Brolly, ¹John Parnell, ¹Stephen Bowden
International journal of Astrobiology (in Press) Link to Article [https://doi.org/10.1017/S1473550416000367]
¹Department of Geology & Petroleum Geology, University of Aberdeen, Meston Building, Aberdeen, UK

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¹Richard Matthewman, ²Ian A. Crawford, ³Adrian P. Jones, ⁴Katherine H. Joy, ¹Mark A. Sephton
Astrobiology 16, 900-912 Link to Article [doi:10.1089/ast.2015.1442]
¹Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, London, UK.
²Department of Earth and Planetary Sciences, Birkbeck College, University of London, London, UK.
³Department of Earth Sciences, University College London, London, UK.
⁴School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK.

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