^1,2,3Andrew M. Davis, ^1,2,4Junjun Zhang,^1,2,4Nicolas D. Greber, ^1,2,4Jingya Hu,^1,4,5François L.H. Tissot, ^1,2,3,4Nicolas Dauphas
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.07.032]
¹Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA
²Chicago Center for Cosmochemistry, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA
³Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA
⁴Origins Laboratory, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA
⁵Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139
Copyright Elsevier

Titanium isotopic compositions (mass-dependent fractionation and isotopic anomalies) were measured in 46 calcium-, aluminum-rich inclusions (CAIs) from the Allende CV chondrite. After internal normalization to ⁴⁹Ti/⁴⁷Ti, we found that ε⁵⁰Ti values are somewhat variable among CAIs, and that ε⁴⁶Ti is highly correlated with ε⁵⁰Ti, with a best-fit slope of 0.162±0.030 (95% confidence interval). The linear correlation between ε⁴⁶Ti and ε⁵⁰Ti extends the same correlation seen among bulk solar objects (slope 0.184±0.007). This observation provides constraints on dynamic mixing of the solar disk and has implications for the nucleosynthetic origin of titanium isotopes, specifically on the possible contributions from various types of supernovae to the solar system. Titanium isotopic mass fractionation, expressed as δ′⁴⁹Ti, was measured by both sample-standard bracketing and double-spiking. Most CAIs are isotopically unfractionated, within a 95% confidence interval of normal, but a few are significantly fractionated and the range δ′⁴⁹Ti is from ∼–4 to ∼+4. Rare earth element patterns were measured in 37 of the CAIs. All CAIs with significant titanium mass fractionation effects have group II and related REE patterns, implying kinetically controlled volatility fractionation during the formation of CAIs with those REE patterns.

^1,2Devin L. Schrader, ³Jemma Davidson
Geochmica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.07.031]
¹Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, 781 East Terrace Road, Tempe, AZ 85287-6004, USA
²Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, 10th& Constitution Avenue NW, Washington, D.C. 20560-0119, USA
³Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road NW, Washington, DC 20015-1305, USA
Copyright Elsevier

By investigating the petrology and chemical composition of type II (FeO-rich) chondrules in the Mighei-like carbonaceous (CM) chondrites we constrain their thermal histories and relationship to the Ornans-like carbonaceous (CO) chondrites. We identified FeO-rich relict grains in type II chondrules by their Fe/Mn ratios; their presence indicates chondrule recycling among type II chondrules. The majority of relict grains in type II chondrules are FeO-poor olivine grains. Consistent with previous studies, chemical similarities between CM and CO chondrite chondrules indicate that they had similar formation conditions and that their parent bodies probably formed in a common region within the protoplanetary disk. However, important differences such as mean chondrule size and the lower abundance of FeO-poor relicts in CM chondrite type II chondrules than in CO chondrites suggest CM and CO chondrules did not form together and they likely originate from distinct parent asteroids.

Despite being aqueously altered, many CM chondrites contain pre-accretionary anhydrous minerals (i.e., olivine) that are among the least thermally metamorphosed materials in chondrites according to the Cr2O3 content of their ferroan olivine. The presence of these minimally altered pre-accretionary chondrule silicates suggests that samples to be returned from aqueously altered asteroids by the Hayabusa2 and OSIRIS-REx asteroid sample return missions, even highly hydrated, may contain silicates that can provide information about the pre-accretionary histories and conditions of asteroids Ryugu and Bennu, respectively.

^1,2M. D. Suttle, ^1,2M. J. Genge, ²S. S. Russell
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12927]
¹Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, South Kensington, London, UK
²Department of Earth Science, The Natural History Museum, South Kensington, London, UK
Published by arrangement with John Wiley & Sons

The orientations of dehydration cracks and fracture networks in fine-grained, unmelted micrometeorites were analyzed using rose diagrams and entropy calculations. As cracks exploit pre-existing anisotropies, analysis of their orientation provides a mechanism with which to study the subtle petrofabrics preserved within fine-grained and amorphous materials. Both uniaxial and biaxial fabrics are discovered, often with a relatively wide spread in orientations (40°–60°). Brittle deformation cataclasis and rotated olivine grains are reported from a single micrometeorite. This paper provides the first evidence for impact-induced shock deformation in fine-grained micrometeorites. The presence of pervasive, low-grade shock features in CM chondrites and CM-like dust, anomalously low-density measurements for C-type asteroids, and impact experiments which suggest CM chondrites are highly prone to disruption all imply that CM parent bodies are unlikely to have remained intact and instead exist as a collection of loosely aggregated rubble-pile asteroids, composed of primitive shocked clasts.

¹Adrian R. Muxworthy,²Phillip A. Bland,¹Thomas M. Davison,¹James Moore,¹Gareth S. Collins,³Fred J. Ciesla
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12918]
¹Department of Earth Science and Engineering, Imperial College London, London, UK
²Department of Applied Geology, Curtin University of Technology, Perth, Western Australia, Australia
³Department of Geophysical Science, University of Chicago, Chicago, Illinois, USA
Published by arrangement with John Wiley & Sons

We conducted a paleomagnetic study of the matrix of Allende CV3 chondritic meteorite, isolating the matrix’s primary remanent magnetization, measuring its magnetic fabric and estimating the ancient magnetic field intensity. A strong planar magnetic fabric was identified; the remanent magnetization of the matrix was aligned within this plane, suggesting a mechanism relating the magnetic fabric and remanence. The intensity of the matrix’s remanent magnetization was found to be consistent and low (~6 μT). The primary magnetic mineral was found to be pyrrhotite. Given the thermal history of Allende, we conclude that the remanent magnetization was formed during or after an impact event. Recent mesoscale impact modeling, where chondrules and matrix are resolved, has shown that low-velocity collisions can generate significant matrix temperatures, as pore-space compaction attenuates shock energy and dramatically increases the amount of heating. Nonporous chondrules are unaffected, and act as heat-sinks, so matrix temperature excursions are brief. We extend this work to model Allende, and show that a 1 km/s planar impact generates bulk porosity, matrix porosity, and fabric in our target that match the observed values. Bimodal mixtures of a highly porous matrix and nominally zero-porosity chondrules make chondrites uniquely capable of recording transient or unstable fields. Targets that have uniform porosity, e.g., terrestrial impact craters, will not record transient or unstable fields. Rather than a core dynamo, it is therefore possible that the origin of the magnetic field in Allende was the impact itself, or a nebula field recorded during transient impact heating.

¹Toshiki Koga, ^1,2Hiroshi Naraoka
Scientific Reports 7, 636 Link to Article [doi:10.1038/s41598-017-00693-9]
Department of Earth and Planetray Sciences, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
Research Center for Planetary Trace Organic Compounds, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan

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¹Chaney Lin, ¹Lincoln S. Hollister, ³Glenn J. MacPherson, ^4,5Luca Bindi, ⁶Chi Ma, ⁷Christopher L. Andronicos, ^1,8Paul J. Steinhardt
Scientific Reports 7, 1637 Link to Article [doi:10.1038/s41598-017-01445-5]
¹Department of Physics, Princeton University, Jadwin Hall, Princeton, NJ, 08544, USA
²Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ, 08544, USA
³Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington DC, 20560, USA
⁴Dipartimento di Scienze della Terra, Università di Firenze, Via La Pira 4, I-50121, Florence, Italy
⁵C.N.R. – Istituto di Geoscienze e Georisorse, Via La Pira 4, I-50121, Florence, Italy
⁶Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125, USA
⁷Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, 47907, USA
⁸Princeton Center for Theoretical Science, Princeton University, Princeton, NJ, 08544, USA

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¹J. F. Pernet-Fisher, ¹K. H. Joy, ¹D. J. P. Martin, ²K. L. Donaldson Hanna
Scientific Reports 7, 5888 Link to Article [doi:10.1038/s41598-017-06134-x]
¹School of Earth and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
²Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, OX1 3PU, UK

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¹Timothy J.McCoy, ¹Amy E.Marquardt, ^2,3John T.Wasson, ⁴Richard D.Ash, ^1,5Edward P.Vicenzi
Journal of Archaeological Science 81, 13-22 Link to Article [https://doi.org/10.1016/j.jas.2017.03.003https://doi.org/10.1016/j.jas.2017.03.003]
¹Dept. of Mineral Sciences, National Museum of Natural History, 10th and Constitution Aves NW, Smithsonian Institution, Washington, DC 20560-0119, USA
²Dept. of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA
³Dept. of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1567, USA
⁴Dept. of Geology, University of Maryland, College Park, MD 20742, USA
⁵Museum Conservation Institute, Smithsonian Institution, 4210 Silver Hill Road, Suitland, MD 20746, USA

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¹D.Ray, ¹S.Gosh, ²T.K.Goswami, ³M.J.Jobin
Geoscience Frontiers 8, 413-423 Link to Article [https://doi.org/10.1016/j.gsf.2016.02.005]
¹PLANEX, Physical Research Laboratory, Ahmedabad 380 009, India
²Department of Applied Geology, Dibrugarh University, Assam, India
³Department of Applied Geology, Pondicherry University, India

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^1,2,3Makiko K. Haba, ^2,4Akira Yamaguchi, ¹Hiroyuki Kagi, ^1,5Keisuke Nagao, ^6,7Hiroshi Hidaka
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.07.028]
¹Geochemical Research Center, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
³Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Tokyo 152-8551, Japan
⁴Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo 190-8518, Japan
⁵Korea Polar Research Institute, 26 Songdomirae-ro, Yeonsu-gu, Incheon 21990, South Korea
⁶Department of Earth and Planetary Systems Science, Hiroshima University, Higashi Hiroshima, Hiroshima 739-8526, Japan
⁷Department of Earth and Planetary Sciences, Nagoya University, Nagoya 464-8601, Japan
Copyright Elsevier

Mesosiderites are a group of stony-iron meteorites, which are thought to be the result of mixing of silicates with Fe-Ni metal. In this study, we combined textural observations with geochemical and chronological studies of two zircon grains found in the Estherville mesosiderite. One of the zircons (Zrc1) occurs with pyroxene, plagioclase, troilite, and silica, and the other (Zrc2) is located at a boundary between Fe-Ni metal and a silicate part mainly composed of pyroxene and plagioclase. The textural observations demonstrate that Zrc1 is relatively homogenous, whereas Zrc2 is composed of at least two chemically distinct domains. Trace element analyses of Zrc2 resolve large concentration gradients within this single grain with variations that are an order of magnitude for rare earth elements (REE) and two orders of magnitude for U and Th. The lowest trace element concentration in Zrc2 is more than an order of magnitude lower than those of lunar and eucritic zircons. However, it is similar to those of Zrc1 and a zircon from the Vaca Muerta mesosiderite. The calculated REE composition of the melt in equilibrium with Zrc2 shows that Zrc2 and perhaps also Zrc1 did not crystallize from a melt that was produced by fractional crystallization of the primary magmatic mineral assemblages. The zircons with low REE, U, and Th concentrations can be interpreted to have formed in a residual melt after incorporation of large amounts of REE, U, and Th into secondary phosphate minerals, which formed during the metal-silicate mixing event. The large concentration gradients observed in Zrc2 suggest significant heterogeneities in the melt from which the zircon crystallized. Alternatively, either mixing or diffusion between a relict zircon and a newly formed zircon could explain the observed concentration gradients. However, the REE patterns of Zrc2 cannot be explained by mixing or diffusion between the two distinct generations of zircons. These considerations suggest that Zrc1 and Zrc2 formed during a high-temperature reheating event, which is probably related to the metal-silicate mixing event. The weighted average 207Pb-206Pb age obtained by SIMS from both zircons is 4521 ± 26 Ma (2σ). This age is younger than that of a primary magmatic zircon from Vaca Muerta (4563 ± 15 Ma) and probably corresponds to the timing of the metal-silicate mixing event or a later impact event.