Long-term heliomagnetic field variation based on cosmogenic 44Ti in meteorites

1Mancuso, S.,1,2Taricco, C.,2Colombetti, P.,1,2Rubinetti, S.,3Sinha, N.,4Bhandari, N.,
1,2Barghini, D.,1Gardiol, D.
Nuovo Cimento della Societa Italiana di Fisica C 42, Article number Y Link to Article [DOI: 10.1393/ncc/i2019-19043-8]
1Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Torino – Strada Osservatorio 20, Pino Torinese, 10025, Italy
2Dipartimento di Fisica, Università di Torino -, Via P. Giuria 1, Torino, 10125, Italy
3Wentworth Institute of Technology, Boston, MA, United States

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Mineralogy, Trace Element Composition, and Classification of Onello High-Ni Ataxite

1,2Litasov, K.D.,3Ishikawa, A.,4Kopylova, A.G.,
1Podgornykh, N.M.,1Pokhilenko, N.P.
Doklady Earth Sciences 485, 381-385 Link to Article [DOI: 10.1134/S1028334X19040068]
1Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090, Russian Federation
2Novosibirsk State University, Novosibirsk, 630090, Russian Federation
3Tokyo Institute of Technology, Tokyo, 152-8550, Japan

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Insight into African meteorite finds: Typology, mass distribution and weathering process

1Ouknine, L.,1Khiri, F.,1Ibhi, A.,2Heikal, M.T.S.,3Saint-Gerant, T.,3Medjkane, M.
Journal of African Earth Sciences 158, 103551 Link to Article [DOI: 10.1016/j.jafrearsci.2019.103551]
1Petrology, Metallogeny and Meteorites Team, Faculty of Sciences, Ibn Zohr University, Agadir, Morocco
2Geology Department, Faculty of Science, Tanta University, Egypt
3Identité et Différenciation Des Espaces, de L’environnement et des Sociétés (IDEES), Université de Caen, France

 

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Compositional diversity of ordinary chondrites inferred from petrology, bulk chemical, and oxygen isotopic compositions of the lowest FeO ordinary chondrite, Yamato 982717

1Akira Yamaguchi,1Makoto Kimura,2,3Jean‐Alix Barrat,4Richard Greenwood
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13351]
1National Institute of Polar Research, Tachikawa, Tokyo, 190‐8518 Japan
2Université Européenne de Bretagne, Lorient, France
3CNRS, UMR 6538 (Domaines Océaniques), U.B.O.‐I.U.E.M., Place Nicolas Copernic, 29280 Plouzané Cedex, France
4Planetary and Space Sciences, Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
Published by arrangement with John Wiley & Sons

We performed a petrologic, geochemical, and oxygen isotopic study of the lowest FeO ordinary chondrite (OC), Yamato (Y) 982717. Y 982717 shows a chondritic texture composed of chondrules and chondrule fragments, and mineral fragments set in a finer grained, clastic matrix, similar to H4 chondrites. The composition of olivine (Fa11.17 ± 0.48 (1σ)) and low‐Ca pyroxene (Fs11.07 ± 0.98 (1σ)Wo0.90 ± 0.71(1σ)) is significantly more magnesian than those of typical H chondrites (Fa16.0‐20, Fs14.5‐18.0), as well as other known low‐FeO OCs (Fa12.8‐16.7; Fs13‐16). However, the bulk chemical composition of Y 982717, in particular lithophile and moderately volatile elements, is within the range of OCs. The bulk siderophile element composition (Ni, Co) is within the range of H chondrites and distinguishable from L chondrites. The O‐isotopic composition is also within the range of H chondrites. The lack of reduction textures indicates that the low olivine Fa content and low‐Ca pyroxene Fs content are characteristics of the precursor materials, rather than the result of reduction during thermal metamorphism. We suggest that the H chondrites are more compositionally diverse than has been previously recognized.

 

A vacancy‐rich, partially inverted spinelloid silicate, (Mg,Fe,Si)2(Si,□)O4, as a major matrix phase in shock melt veins of the Tenham and Suizhou L6 chondrites

1Chi Ma,2Oliver Tschauner,3,4Luca Bindi,1John R. Beckett,5,6Xiande Xie
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13349]
1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
2Department of Geoscience, University of Nevada, Las Vegas, Nevada, 89154 USA
3Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira 4, I‐50121 Firenze, Italy
4CNR, Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via G. La Pira 4, I‐50121 Firenze, Florence, Italy
5Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640 China
6Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Chinese Academy of Sciences, Guangzhou, 510640 China
Published by arrangement with John Wiley & Sons

A new high‐pressure silicate, (Mg,Fe,Si)2(Si,□)O4 with a tetragonal spinelloid structure, was discovered within shock melt veins in the Tenham and Suizhou meteorites, two highly shocked L6 ordinary chondrites. Relative to ringwoodite, this phase exhibits an inversion of Si coupled with intrinsic vacancies and a consequent reduction of symmetry. Most notably, the spinelloid makes up about 30–40 vol% of the matrix of shock veins with the remainder composed of a vitrified (Mg,Fe)SiO3 phase (in Tenham) or (Mg,Fe)SiO3‐rich clinopyroxene (in Suizhou); these phase assemblages constitute the bulk of the matrix in the shock veins. Previous assessments of the melt matrices concluded that majorite and akimotoite were the major phases. Our contrasting result requires revision of inferred conditions during shock melt cooling of the Tenham and Suizhou meteorites, revealing in particular a much higher quench rate (at least 5 × 103 K s−1) for veins of 100–500 μm diameter, thus overriding formation of the stable phase assemblage majoritic garnet plus periclase.

The evolution of polycyclic aromatic hydrocarbons under simulated inner asteroid conditions

1,2Claudia‐Corina Giese,2Inge Loes Ten Kate,2Oliver Plümper,2Helen E. King,3Christoph Lenting,2,4,5Yang Liu,6Alexander G. G. M. Tielens
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13359]
1Leiden Observatory, Faculty of Science, Leiden University, 2300 RA Leiden, the Netherlands
2Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD Utrecht, the Netherlands
3Steinmann‐Institut for Geology, Mineralogy und Palaeontology, University of Bonn, 53115 Bonn, Germany
4Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, the Netherlands
5Plymouth Electron Microscopy Centre, University of Plymouth, Devon, PL4 8AA Plymouth, UK
6Leiden Observatory, Faculty of Science, Leiden University, 2300 RA Leiden, the Netherlands
Published by arrangement with John Wiley & Sons

Large polycyclic aromatic hydrocarbons (PAHs) are an important component of the interstellar medium. PAHs have been identified in the soluble and insoluble matter of carbonaceous chondrites (CCs). Here, we study the evolution of PAHs under conditions relevant to the interiors of asteroids and compare our results to PAHs observed in CCs. We have performed long‐term and short‐term hydrothermal experiments, in which we exposed PAH‐mineral mixture analogs of meteorites to temperature conditions representative of those predicted for asteroids interiors. Our results show that small PAHs with melting points within the aqueous alteration temperature of CCs form carbonaceous spherules in the presence of water. In this work, we describe the microstructure and morphology of these spherules. We discuss the similarities and differences compared to globules isolated from CCs.

Bulk chondrite variability in mass independent magnesium isotope compositions – Implications for initial solar system 26Al/27Al and the timing of terrestrial accretion

1Tu-Han Luu,1Remco C.Hin,1Christopher D.Coath,1Tim Elliott
Earth and Planetary Science Letters 522, 166-175 Link to Article [https://doi.org/10.1016/j.epsl.2019.06.033
1Bristol Isotope Group, School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
Copyright Elsevier

We have determined Δ′26 MgDSM-3, the mass-independent variations in 26Mg/24Mg, of primitive, bulk meteorites to precisions better than ±3 ppm (2se). Our measurements of samples from 10 different chondrite groups show Δ′26 MgDSM-3 that vary from −5 to 22 ppm. Our data define an array with a positive slope in a plot of Δ′26 MgDSM-3 against 27Al/24Mg, which can be used to determine (26Al/27Al)0, i.e. initial 26Al/27Al, and (Δ′26 MgDSM-3)0, i.e. initial Δ′26 MgDSM-3. On such an isochron plot, the best fit of our new measurements combined with literature data implies (26Al/27Al)0 of (4.67±0.78)×10−5 and (Δ′26 MgDSM-3)0 of −31.6 ± 5.7 ppm (2se) for ordinary and carbonaceous chondrites, other than CR chondrites, which have anomalously low Δ′26 MgDSM-3. These parameters are within uncertainty of those defined by previous measurements of bulk calcium-, aluminium-rich inclusions (CAIs) that set canonical (26Al/27Al)∼05×10−5 . The most straightforward interpretation of all these observations is that differences in the Al/Mg of bulk ordinary and carbonaceous chondrites are dominantly controlled by variable contributions of early-formed refractory and major silicate components derived from a common, canonical reservoir. The Δ′26 MgDSM-3 of enstatite chondrites are slightly more radiogenic (∼3 ppm) at similar Al/Mg to the ordinary chondrites. We speculate that this is related to the timing of removal of a refractory component from the source reservoirs of these different meteorite groups; the higher Δ′26 MgDSM-3 of the enstatite chondrites suggests later (∼0.5 Ma post CAIs) condensation and loss of this refractory component. Despite inferred consistency of (26Al/27Al)0 and (Δ′26 MgDSM-3)0 across most chondrite groups, some nebular heterogeneity is required to account for the compositions of CR chondrites. Our preferred interpretation is that the CR source region has lower (Δ′26 MgDSM-3)0. As the most appropriate isotopic reference for the Earth, our new mean enstatite chondrite composition allows us to assess possible ingrowth of 26Mg from live 26Al during accretion of the Earth. The Earth has Δ′26 MgDSM-3 within uncertainty of enstatite chondrites, despite its higher Al/Mg. This requires that the terrestrial increase in Al/Mg, which we attribute to vapour loss during accretion, must have happened >1.5 Ma post CAI formation, in an instantaneous fractionation model.