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Some things special about NEAs: Geometric and environmental effects on the optical signatures of hydration

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1S.Potin,1,2P.Beck,1B.Schmitt,3F.Moynier
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.06.026]
1Université Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 414 rue de la Piscine, 38400 Saint-Martin d’Hères, France
2Institut Universitaire de France, Paris, France
3Institut de Physique du Globe de Paris (IPGP), 1 Rue Jussieu, 75005 Paris, France
Copyright Elsevier

Here were report on a laboratory study aiming to reproduce specificities of near-Earth Asteroid. We study how the elevated surface temperature, their surface roughness (rock or regolith), as well as observation geometry can affect the absorption features detected on asteroids. For that purpose, we selected a recent carbonaceous chondrite fall, the Mukundpura CM2 chondrite which fell in India in June 2017. Bidirectional reflectance spectroscopy was performed to analyze the effect of the geometrical configuration (incidence, emergence and azimuth angle) on the measurement. Our results show that reflectance spectra obtained under warm environment (NEA-like) tends to show shallower absorption bands compared to low-temperature conditions (MBA-like), but still detectable in our experiments under laboratory timescales. Irreversible alteration of the sample because of the warm environment (from room temperature to 250 °C) has been detected as an increase of the spectral slope and a decrease of the band depths (at 0.7 μm, 0.9 μm and 2.7 μm). Comparing the meteoritic chip and the powdered sample, we found that surface texture strongly affects the shape of the reflectance spectra of meteorites and thus of asteroids, where a dust-covered surface presents deeper absorption features. We found that all spectral parameters, such as the reflectance value, spectral slope and possible absorption bands are affected by the geometry of measurement. We observed the disappearance of the 0.7 μm absorption feature at phase angle larger than 120°, but the 3 μm band remains detectable on all measured spectra.

New shock microstructures in titanite (CaTiSiO 5 ) from the peak ring of the Chicxulub impact structure, Mexico

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1Timms, N.E. et al. (>10)
Contributions to Mineralogy and Petrology 174, 38 Link to Article [DOI: 10.1007/s00410-019-1565-7]
1The Institute for Geoscience Research (TIGeR), Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, GPO Box U1987, Perth, WA 6845, Australia

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New minerals tsangpoite Ca 5 (PO 4 ) 2 (SiO 4 ) and matyhite Ca 9 (Ca 0.5 □ 0.5 )Fe(PO 4 ) 7 from the D’Orbigny angrite

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1Hwang, S.-L.,2Shen, P.,3Chu, H.-T.,4Yui, T.-F.,5Varela, M.-E.,4Iizuka, Y.
Mineralogical Magazine 83, 293-313 Link to Article [DOI: 10.1180/mgm.2018.125]
1Department of Materials Science and Engineering, National Dong Hwa University, Hualien, Taiwan
2Department of Materials Science and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung, Taiwan
3Central Geological Survey, PO Box 968, Taipei, Taiwan
4Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan
5Instituto de Ciencias Astronómicas de la Tierra y Del Espacio (ICATE), Avenida España 1512 sur, San Juan, J5402DSP, Argentina

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Interplanetary Dust, Meteoroids, Meteors and Meteorites (Review)

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1,2Koschny, D. et al. (>10)
Space Science Reviews 215, 34 Link to Article [DOI: 10.1007/s11214-019-0597-7]
1SCI-S, European Space Agency, Keplerlaan 1, Noordwijk ZH, 2200 AZ, Netherlands
2Lehrstuhl für Raumfahrttechnik, Technische Universität München, Boltzmannstr. 15, Garching, 85748, Germany

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Are hypervelocity impacts able to produce chondrule-like ejecta?

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1Clément Ganino,2,3Guy Libourel,4Akiko M.Nakamura,2Patrick Michel
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2019.06.008]
1Université Côte D’Azur, OCA, CNRS, Géoazur, 250 Rue Albert Einstein, Sophia-Antipolis, 06560, Valbonne, France
2Université Côte D’Azur, OCA, CNRS, Lagrange, Boulevard de L’Observatoire, CS 34229, 06304, Nice Cedex 4, France
3Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, 96821, USA
4Graduate School of Science, Kobe University, 1-1 Rokkoudai-cho, Nada-ku, Kobe, 657-8501, Japan

 

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Deciphering the conditions of tochilinite and cronstedtite formation in CM chondrites from low temperature hydrothermal experiments

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1Lionel G. Vacher,2Laurent Truche,1François Faure,1Laurent Tissandier,3Régine Mosser‐Ruck,1Yves Marrocchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13317]
1CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre‐les‐Nancy, F‐54501 France
2ISTerre, UMR 5275, CNRS, Université Grenoble Alpes, 1381 rue de la Piscine, BP53 38041 Grenoble, CEDEX 9, France
3GeoRessources, UMR 7359, CNRS, Université de Lorraine, Campus Aiguillettes, 54506 Vandoeuvre‐lès‐Nancy, France
Published by arrangement with John Wiley & Sons

Tochilinite/cronstedtite intergrowths are commonly observed as alteration products in CM chondrite matrices, but the conditions under which they formed are still largely underconstrained due to their scarcity in terrestrial environments. Here, we report low temperature (80 °C) anoxic hydrothermal experiments using starting assemblages similar to the constituents of the matrices of the most pristine CM chondrite and S‐rich and S‐free fluids. Cronstedtite crystals formed only in S‐free experiments under circumneutral conditions with the highest Fe/Si ratios. Fe‐rich tochilinite with chemical and structural characteristics similar to chondritic tochilinite was observed in S‐bearing experiments. We observed a positive correlation between the Mg content in the hydroxide layer of synthetic tochilinite and temperature, suggesting that the composition of tochilinite is a proxy for the alteration temperature in CM chondrites. Using this relation, we estimate the mean precipitation temperatures of tochilinite to be 120–160 °C for CM chondrites. Given the different temperature ranges of tochilinite and cronstedtite in our experiments, we propose that Fe‐rich tochilinite crystals resulted from the alteration of metal beads under S‐bearing alkaline conditions at T = 120–160 °C followed by cronstedtite crystals formed by the reaction of matrix amorphous silicates, metal beads, and water at a low temperature (50–120 °C).

Bombardment history of Asteroid 4 Vesta recorded by brecciated eucrites: Large impact event clusters at 4.50 Ga and discreet bombardment until 3.47 Ga

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1Trudi Kennedy,1Fred Jourdan,2Ela Eroglu,1Celia Mayers
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.06.027]
1Western Australian Argon Isotope Facility, JdL Centre & Applied Geology, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
2Department of Chemical Engineering, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
Copyright Elsevier

The thermal/impact histories of sixteen eucrite meteorites were investigated: three monomict eucrites (NWA 999, A-87272,87, and Stannern), five polymict eucrites (NWA 1000, NWA 1666, NWA 5601, Y-980066,100, and Y-980255,100), three quench-textured, eucrite melt rocks (Y-981646,21, Y-981651,105, and MIL 0766214), one eucrite dominantly comprised of quench-textured clasts (QUE 99005,11), three unclassified eucrite breccias (LAP 031316,9, LAR 06870,5, QUE 99799,4) and one unbrecciated eucrite (EET 92004,17), included here due to its shock features. We have measured fifteen high-precision new 40Ar/39Ar plateau ages on plagioclase and matrix for ten of these meteorites with a tight cluster of nine ages obtained from three different polymict breccias. These ages range from 4534 ± 56 Ma to 4491 ± 16 Ma resulting in a concordant age population (P = 0.16). The fact that such a cluster of ages is recorded in unrelated breccias which are made of a priori unrelated components, leads us to propose that those ages recorded a single heating event on a large scale, and is interpreted here as a high-energy impact event, early in the history of Vesta at 4500 ± 4 Ma. We propose that the debris was ejected and isolated from subsequent large impacts in a secondary rubble pile asteroid where the energy of the outgoing shock wave from an impact is significantly reduced as it compacts the target material (Holsapple et al., 2002, and references therein) .

The other analyses define a spread of five plateau ages ranging from 3851± 21 Ma to 3469 ± 35 Ma, over ∼380 Ma. An additional apparent plateau age of 4288 ± 38 Ma, but with a diffusion profile of cumulative 39Ar release, along with published U-Pb apatite age of ∼4.14 Ga, suggests that the data might either define a true continuum (normal background bombardment) from 4.5 Ga to 3.47 Ga or cluster between ∼3.85 Ga and ∼3.47 Ga (excavation of a fresh surface at 3.85 Ga continuously bombarded until 3.47 Ga). Both scenarios are compatible with a final ejection age of 3.47 Ga when a major impact liberates the bulk of the brecciated meteorites into another secondary rubble pile asteroid, where the brecciated eucrites stayed relatively well protected from subsequent major impacts. Based on these results and recent crater counting measurements, we propose that the excavation and bulk ejection were caused by the Rheasilvia (ca. 3.47 Ga) basin-forming impact.

Diffusion models on plagioclase crystals with different Ar age spectrum signatures, from a single breccia (NWA1666; 4501 ± 7 Ma), suggest that either: (1) the formation of the breccia is very young, or (2) different plagioclase crystals have different diffusion characteristics, and/or (3) the porosity caused heterogeneous temperatures during an impact heating event, particularly likely if the 4.5 Ga brecciated eucrites were stored in a rubble pile asteroid. Many or possibly most large asteroids being re-accumulated rubble piles with potential large porosity (Holsapple et al., 2002). Scenarios (2) and (3) preclude the usage of multi-grain aliquots to decipher the time-temperature history of most impact breccia using 40Ar/39Ar thermochronology.

Formation Parameters of High-Pressure Minerals in the Dhofar 717 and 864 Chondrite Meteorites

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1Litasov, K.D.,2Badyukov, D.D.,1Pokhilenko, N.P.
Doklady Earth Sciences 485, 327-330 Link to Article [DOI: 10.1134/S1028334X19030322]
1Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090, Russian Federation
2Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, 119991, Russian Federation

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