^1,2Jangmi Han,²Lindsay P.Keller,³Ming-Chang Liu,^1,2Andrew W.Needham,³Andreas T.Hertwig,² Scott Messenger,²Justin I.Simon
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.10.042]
¹Lunar and Planetary Institute, USRA, 3600 Bay Area Boulevard, Houston, TX 77058, USA
²Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
³Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA
Copyright Elsevier

We carried out a coordinated mineralogical and isotopic study of a Wark-Lovering (WL) rim on a Ca,Al-rich inclusion (CAI) from the reduced CV3 chondrite Vigarano. The outermost edge of the CAI mantle is mineralogically and texturally distinct compared to the underlying mantle that is composed of coarse, zoned melilite (Åk_∼10-60) grains. The mantle edge contains fine-grained gehlenite with hibonite and rare grossite that likely formed by rapid crystallization from a melt enriched in Ca and Al. These gehlenite and hibonite layers are surrounded by successive layers of spinel, zoned melilite (Åk_∼0-10), zoned diopside that grades outwards from Al,Ti-rich to Al,Ti-poor, and forsteritic olivine intergrown with diopside. These layered textures are indicative of sequential condensation of spinel, melilite, diopside, and forsterite onto hibonite. Anorthite occurs as a discontinuous layer that corrodes adjacent melilite and Al-diopside, and appears to have replaced them, probably even later than the forsterite layer formation. Based on these observations, we conclude that the WL rim formation was initiated by flash melting and extensive evaporation of the original inclusion edge, followed by subsequent gas-solid reactions under highly dynamic conditions.

All the WL rim minerals are ¹⁶O-rich (Δ¹⁷O = ∼−23‰), indicating their formation in an ¹⁶O-rich nebular reservoir. Our Al-Mg measurements of hibonite, spinel, and diopside from the WL rim, as well as spinel and Al,Ti-diopside in the core, define a single, well-correlated isochron with an inferred initial ²⁶Al/²⁷Al ratio of (4.94 ± 0.12) × 10⁻⁵. This indicates that the WL rim formed shortly after the host CAI. In contrast, the lack of ²⁶Mg excesses in the WL rim anorthite suggest its later formation or later isotopic disturbance in the solar nebula, after ²⁶Al had decayed.

^1,2Bucurica, I.A.,^1,3Radulescu, C.,⁴Poinescu, A.A.,^1,3,5Popescu, I.V.,¹Nicolescu, C.M.,¹Teodorescu, S.,³Bumbac, M.,⁶Pehoiu, G.,⁶Murarescu, O.
Romanian Journal of Physics 64, 906 Link to Article [http://www.nipne.ro/rjp/2019_64_7-8.html]
¹Valahia University of Targoviste, Institute of Multidisciplinary Research for Science and Technology, Targoviste, 130004, Romania
²University of Bucharest, Faculty of Physics, Doctoral School of Physics, Bucharest, 050107, Romania
³Valahia University of Targoviste, Faculty of Sciences and Arts, Targoviste, 130004, Romania
⁴Valahia University of Targoviste, Faculty of Materials Engineering and Mechanics, Targoviste, 130004, Romania
⁵Academy of Romanian Scientists, Bucharest, 050094, Romania
⁶Valahia University of Targoviste, Faculty of Humanities, Targoviste, 130105, Romania

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¹Johnson, B.C.,²Sori, M.M.,³Evans, A.J.
Nature Astronomy (in Press) Link to Article [DOI: 10.1038/s41550-019-0885-x]
¹Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, United States
²Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, United States
³Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, United States

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¹Ke Zhu (朱柯),^1,2Frédéric Moynier,³Daniel Wielandt,³Kirsten K. Larsen,⁴Jean-Alix Barrat,³Martin Bizzarro
The Astrophysical Journal Letters 877, L13 Link to Article [DOI
https://doi.org/10.3847/2041-8213/ab2044]
¹Institut de Physique du Globe de Paris, Université de Paris, CNRS, 1 rue Jussieu, Paris F-75005, France
²Institut Universitaire de France, 103 boulevard Saint-Michel, Paris F-75005, France
³Centre for Star and Planet Formation and Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, Copenhagen DK-1350, Denmark
⁴Laboratoire Géosciences Océan (UMR CNRS 6538), Université de Bretagne Occidentale et Institut Universitaire Européen de la Mer, Place Nicolas Copernic, F-29280 Plouzané, France

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¹Yasuhiro Hasegawa,²Bradley M. S. Hansen,¹Gautam Vasisht
The Astrophysical Journal Letters, 876, L32 Link to Article [https://doi.org/10.3847/2041-8213/ab1b5a]
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
²Mani L. Bhaumik Institute for Theoretical Physics, Department of Physics & Astronomy, University of California Los Angeles, Los Angeles, CA 90095, USA

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¹W. Rapin,^1,2B. L. Ehlmann,³G. Dromart,⁴J. Schieber,¹N. H. Thomas,¹W. W. Fischer,¹V. K. Fox,¹N. T. Stein,⁵M. Nachon,⁶B. C. Clark,⁷L. C. Kah,⁸L. Thompson,¹H. A. Meyer,⁹T. S. J. Gabriel,⁹C. Hardgrove,¹⁰ N. Mangold,¹¹F. Rivera-Hernandez,¹²R. C. Wiens,¹³A. R. Vasavada
Nature Geoscience 12, 889-895 Link to Article [https://doi.org/10.1038/s41561-019-0458-8]
¹California Institute of Technology, Pasadena, CA, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
³Laboratoire de Géologie de Lyon, Université de Lyon, Lyon, France
⁴Indiana University, Bloomington, IN, USA
⁵Texas A&M University, College Station, TX, USA
⁶Space Science Institute, Boulder, CO, USA
⁷University of Tennessee, Knoxville, TN, USA
⁸University of New Brunswick, Fredericton, Canada
⁹School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
¹⁰Laboratoire de Planétologie et Géodynamique, UMR6112, CNRS,
Université Nantes, Université Angers, Nantes, France
¹¹Dartmouth College, Hanover, NH, USA
¹²Los Alamos National Laboratory, Los Alamos, NM, USA
¹³Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

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^1,2Michael J. Henehan,^3,4Andy Ridgwell,^1,5Ellen Thomas,¹Shuang Zhang,⁶Laia Alegret,⁷Daniela N. Schmidt,⁸James W. B. Rae,^9,10James D. Witts,⁹Neil H. Landman,¹¹Sarah E. Greene,¹²Brian T. Huber,¹James R. Super,¹Noah J. Planavsky,¹Pincelli M. Hull
Proceedings of the National Academy of Sciences of teh United States of America (PNAS) (in Press) Link to to Article [https://doi.org/10.1073/pnas.1905989116]
¹Department of Geology & Geophysics, Yale University, New Haven, CT 06520;
²Section 3.3, Deutsches GeoForschungsZentrum GFZ, 14473 Potsdam, Germany;
³School of Geographical Sciences, Bristol University, Bristol BS8 1SS, United Kingdom;
⁴Department of Earth Sciences, University of California, Riverside, CA 92521;
⁵Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06459;
⁶Instituto Universitario de Investigación en Ciencias Ambientales de Aragón, Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain;
⁷School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom;
⁸School of Earth & Environmental Sciences, University of St. Andrews, St. Andrews KY16 9AL, United Kingdom;
⁹Division of Paleontology, American Museum of Natural History, New York, NY 10024;
¹⁰Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131;
¹¹School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom;
¹²Department of Paleobiology, Smithsonian Institution, Washington, DC 20560

Mass extinction at the Cretaceous–Paleogene (K-Pg) boundary coincides with the Chicxulub bolide impact and also falls within the broader time frame of Deccan trap emplacement. Critically, though, empirical evidence as to how either of these factors could have driven observed extinction patterns and carbon cycle perturbations is still lacking. Here, using boron isotopes in foraminifera, we document a geologically rapid surface-ocean pH drop following the Chicxulub impact, supporting impact-induced ocean acidification as a mechanism for ecological collapse in the marine realm. Subsequently, surface water pH rebounded sharply with the extinction of marine calcifiers and the associated imbalance in the global carbon cycle. Our reconstructed water-column pH gradients, combined with Earth system modeling, indicate that a partial ∼50% reduction in global marine primary productivity is sufficient to explain observed marine carbon isotope patterns at the K-Pg, due to the underlying action of the solubility pump. While primary productivity recovered within a few tens of thousands of years, inefficiency in carbon export to the deep sea lasted much longer. This phased recovery scenario reconciles competing hypotheses previously put forward to explain the K-Pg carbon isotope records, and explains both spatially variable patterns of change in marine productivity across the event and a lack of extinction at the deep sea floor. In sum, we provide insights into the drivers of the last mass extinction, the recovery of marine carbon cycling in a postextinction world, and the way in which marine life imprints its isotopic signal onto the geological record.

¹Yves Marrocchi,¹Johan Villeneuve,²Emmanuel Jacquet,¹Maxime Piralla,³Marc Chaussidon
Proceedings of the National Academy of Sciences of the United States of America (PNAS) (in Press) Link to Article [DOI:https://doi.org/10.1073/pnas.1912479116]
¹Centre de Recherches Pétrographiques et Géochimiques (CRPG), CNRS, Université de Lorraine, UMR 7358, 54501 Vandoeuvre-lès-Nancy, France;
²Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), CNRS & Muséum national d’Histoire naturelle, UMR 7590, 75005 Paris, France;
³Institut de Physique du Globe de Paris, Université de Paris, CNRS, 75238 Paris, France

Chondritic meteorites are composed of primitive components formed during the evolution of the Solar protoplanetary disk. The oldest of these components formed by condensation, yet little is known about their formation mechanism because of secondary heating processes that erased their primordial signature. Amoeboid Olivine Aggregates (AOAs) have never been melted and underwent minimal thermal annealing, implying they might have retained the conditions under which they condensed. We performed a multiisotope (O, Si, Mg) characterization of AOAs to constrain the conditions under which they condensed and the information they bear on the structure and evolution of the Solar protoplanetary disk. High-precision silicon isotopic measurements of 7 AOAs from weakly metamorphosed carbonaceous chondrites show large, mass-dependent, light Si isotope enrichments (–9‰ < δ³⁰Si < –1‰). Based on physical modeling of condensation within the protoplanetary disk, we attribute these isotopic compositions to the rapid condensation of AOAs over timescales of days to weeks. The same AOAs show slightly positive δ²⁵Mg that suggest that Mg isotopic homogenization occurred during thermal annealing without affecting Si isotopes. Such short condensation times for AOAs are inconsistent with disk transport timescales, indicating that AOAs, and likely other high-temperature condensates, formed during brief localized high-temperature events.

¹Steven J.Desch,²Katharine L.Robinson
Geochemistry (Chemie der Erde) (In Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125546]
¹School of Earth and Space Exploration, Arizona State University, PO Box 871404, Tempe AZ 85287, United States
²Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston TX 77058, United States
Copyright Elsevier

The Moon is thought to have formed after a planetary embryo, known as Theia, collided with the proto-Earth 4.5 billion years ago. This so-called Giant Impact was the last major event during Earth’s accretion, and its effects on the composition of the Earth and the newly forming Moon would be measureable today. Recent work on lunar samples has revealed that the Moon’s water was not lost as a result of this giant impact. Instead, the Moon appears to contain multiple hydrogen reservoirs with diverse deuterium-to-hydrogen (D/H) ratios. For the first time, we incorporate hydrogen isotopic measurements of lunar samples to help constrain the composition of Theia. We show that the Moon incorporated very low-D/H (δD ≈ -750‰) materials that only could have derived from solar nebula H₂ ingassed into the magma ocean of a large (∼0.4 M_E) planetary embryo that was largely devoid of chondritic water. We infer Theia was a very large body comparable in size to the proto-Earth, and was composed almost entirely of enstatite chondrite-like material. These conclusions limit the type of impact to a “merger” model of similarly-sized bodies, or possibly a “hit-and-run” model, and they rule out models that mix isotopes too effectively.

¹Maxime Piralla,¹Yves Marrocchi,^2,3Maximilien J.Verdier-Paoletti,^1,4Lionel G.Vacher,¹Johan Villeneuve,¹Laurette Piani,²David V.Bekaert,¹Matthieu Gounelle
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.10.041]
¹CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre-lès-Nancy, 54501, France
²IMPMC, CNRS & Muséum national d’Histoire naturelle, UMR 7590, CP52, 57 rue Cuvier, 75005 Paris, France
³DTM, Carnegie Institution for Science, Washington, DC, 20015, USA
⁴Department of Physics, Washington University, St. Louis, MO, 63130, USA
Copyright Elsevier

As the chemical compositions of CI chondrites closely resemble that of the Sun’s photosphere, their oxygen isotopic compositions represent a powerful tool to constrain the origin and dynamics of dust and water ice grains in the protoplanetary disk. However, parent-body alteration processes make straightforward estimation of the primordial isotopic compositions of CI chondritic water and anhydrous minerals difficult. In this contribution, we used in-situ SIMS measurements to determine the oxygen isotope compositions of mechanically isolated olivine and carbonate grains from the CI chondrite Orgueil and carbonates in a polished section of the CI chondrite Ivuna. Most CI olivine grains have Earth-like O isotopic compositions (Δ¹⁷O ≈ 0‰) plotting at the intersection of the terrestrial fractionation line and the primitive chondrule minerals line. Ca-carbonates from Orgueil and Ivuna define a trend with δ¹⁷O = (0.50 ± 0.05) × δ¹⁸O + (0.9 ± 1.4) that differs from mass-independent variations observed in secondary phases of other carbonaceous chondrites. These data show that CIs are chemically solar but isotopically terrestrial for oxygen isotopes. This supports models suggesting that primordial Solar System dust was ¹⁶O-poor (Δ¹⁷O ≈ 0‰) relative to the ¹⁶O-rich nebular gas. Based on results, mass balance calculations reveal that the pristine O isotopic compositions of carbonaceous chondrite matrices differ significantly from the CI composition, except for CR chondrites (calculated Δ¹⁷O values of CM, CO, CV and CR matrices being –3.97 ± 1.19‰, –4.33 ± 1.45‰, –7.95 ± 1.95‰, and –0.07 ± 1.16‰, respectively). This confirms an open chondrule-matrix system with respect to oxygen isotopes where chondrule compositions reflect complex processes of chondrule precursor recycling and gas-melt interactions. As the Mg-Si-Fe chondrule budget is also partially controlled by gas-melt interactions, the complementary formation of chondrules and matrix from a single solar-like reservoir −if it exists− require that (i) this reservoir must have been in a closed system with the gas or (ii) the gas had a CI composition to satisfy the elemental mass balance.