¹Andrea Patzer,¹Emma S.Bullock,¹Conel M. O’D.Alexander
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.04.004]
¹Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Rd. NW, Washington D.C. 20015, USA
Copyright Elsevier

We present the first results of a comprehensive investigation aimed at testing the hypothesis of chondrule-matrix complementarity and the four-component model for the compositions of the carbonaceous chondrites and their components. Combining point-counting with electron microprobe analyses, we have determined the bulk compositions of thin sections, as well as the average abundances and compositions of the major chondritic components (chondrules, matrix, refractory inclusions, isolated silicate grains and isolated opaque grains). To minimize the potential for element exchange between components during parent body processing, the two most primitive COs, DOM 08006 and ALH 77307, and the primitive ungrouped CO/CM-like Acfer 094 were selected for this study. To verify our method, we also examined one section of the well-studied CO3.2 Kainsaz, a fall that is free of weathering. We were able to reproduce all major and many minor elemental concentrations reported in the literature for average bulk COs and Kainsaz to better than 10 %. The elements most commonly cited as displaying evidence for complementarity are Mg, Si, Al, Ca, Fe and Ti. Iron, however, can be easily affected by chondrule metal-silicate fractionation, redistribution in the parent body and weathering, and our Ti data for matrix are likely compromised by an analytical artifact. Hence, we focused on Mg, Al, Si and Ca – four elements that we can determine very accurately – and show that their relative abundances in chondrules are on average CI-like within the uncertainties of the method. The matrix is not CI-like, but its composition can be explained by the loss of 10-15 wt.% of forsterite from an initially CI-like material prior to or during parent body accretion. These results are inconsistent with chondrule-matrix complementarity. Our average CO chondrule compositions, as well as chondrule and matrix abundances, are in line with the predictions of the four-component model. However, the four-component model assumes a CI-like composition for matrix, and also predicts refractory inclusion abundances that are higher and compositions that are less refractory than we observe. While similar studies of the other carbonaceous chondrite groups are needed, these differences may indicate the limitations of the simplifying assumptions made in the four-component model.

^1,2Timmons M.Erickson,²Christopher L.Kirkland,^2,3Fred Jourdan,⁴Martin Schmieder,²MichaelI. H. Hartnady,²Morgan A.Cox,²Nicholas E.Timms
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.04.008]
¹Jacobs – JETS Contract, Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX, 77058, USA
²The Institute for Geoscience Research (TIGeR), (Timescales of Mineral Systems Group), School of Earth and Planetary Sciences, Curtin University, GPO Box 1984, Perth, WA, 6845, Australia
³Western Australian Argon Isotope Facility, John de Laeter Centre and Space Science and Technology Centre, Curtin University, GPO Box 1984, Perth, WA, 6845, Australia
⁴HNU Neu-Ulm University of Applied Sciences, Wileystraße 1, D-89231 Neu-Ulm, Germany
Copyright Elsevier

The Haughton Dome located on Devon Island, in the Canadian Archipelago represents a well-preserved, moderate-sized, complex impact crater. Previous age constraints for the 24 km-diameter impact structure have ranged from ca. 21 Ma to ca. 39 Ma. Herein, we present a coordinated microstructural and in situ U-Pb study of zircon and monazite coupled with 40Ar/39Ar laser step heating of shock-melted K-feldspar clasts from shock metamorphosed gneissic fragments collected from the allochthonous impact breccia at Haughton. Moderately shocked zircon and monazite grains yield an age distribution consistent with an Archean protolith metamorphosed at ca. 1.9 Ga, whereas shock recrystallized zircon and monazite yield a lower intercept age of 31.8 ± 1.7 Ma (n=48, MSWD = 0.58, P = 0.99). Four inverse isochron 40Ar/39Ar ages of shocked feldspar clasts yield a weighted mean age of 31.04 ± 0.37 Ma (MSWD = 0.98, P = 0.40), within uncertainty of the U-Pb lower concordia intercept. Ar diffusion modelling supports the interpretation of the impact age and helps resolve impact-driven age resetting. These results highlight the power of coupling multiple geochronologic techniques for determining impact ages, especially from targets with complex geologic histories. Furthermore, they resolve previous discrepancies in the age of the Haughton Dome and the interpretation of the post impact stratigraphy of the crater fill.

^1,2Ueki, S.,¹Mine, Y.,¹Takashima, K.
Scienctific Reports 11, 4750 Link to Article [DOI: 10.1038/s41598-021-83792-y]
¹Department of Materials Science and Engineering, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto, 860-8555, Japan
²Institute of Science and Engineering, Shimane University, 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan

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^1,2Baccolo, G. et al. (>10)
Nature Communications 12, 436 Link to Article [DOI: 10.1038/s41467-020-20705-z]
¹Department of Environmental and Earth Sciences, University of Milano-Bicocca, Milan, 20126, Italy
²INFN, section of Milano-Bicocca, Milan, 20126, Italy

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¹Wang, S.-J. et al. (>10)
Nature Communications 12, 294 Link to Article [DOI: 10.1038/s41467-020-20525-1]
¹State Key Laboratory of Geological Processes and Minerals Resources, China University of Geosciences, Beijing, 100083, China

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¹Sergienko, E.S.,¹Yanson, S.Y.,¹Kosterov, A.,²Kharitonskii, P.V.,³Frolov, A.M.
IOP Conference Series: Earth and Environmental Science 666, 042080 Link to Article [DOI: 10.1088/1755-1315/666/4/042080]
¹St. Petersburg State University, Universitetskaya nab. 7-9, St. Petersburg, 199034, Russian Federation
²Saint Petersburg Electrotechnical University ‘Leti’, Prof. Popova str. 5, St.Petersburg, 197376, Russian Federation
³Far Eastern Federal University, Sukhanova str. 8, Vladivostok, 690950, Russian Federation

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¹Lauren E. Brase,¹Ralph Harvey,^2,3Luigi Folco,²Martin D. Suttle,⁴E. Carrie McIntosh,⁴James M. D. Day,⁵Catherine M. Corrigan
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13634]
¹Department of Earth, Environmental, and Planetary Sciences, Case Western Reserve University, Cleveland, Ohio, 44106 USA
²Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy
³CISUP, Centro per l’Integrazione della Strumentazione dell’Università di Pisa, Lungarno Pacinotti 43, 56126 Pisa, Italy
⁴Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, 92093 USA
⁵Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C., 20560 USA
Published by arrangement with John Wiley & Sons

We report on the geochemical analyses of glassy spherules from sediments at three Transantarctic Mountain locations and the discovery of Australasian microtektites at two of these sites. Australasian microtektites are present at Mt. Raymond (RY) in the Grosvenor Mountains and Meteorite Moraine (MM) at Walcott Névé, in the Beardmore Glacier region of Antarctica. The microtektites were identified based on their pale yellow appearance, the high concentrations of silica (SiO2 = 60 ± 7 wt%) and alumina (Al2O3 = 23 ± 4 wt%), and a K2O/Na2O > 1, which are all characteristics of microtektites and distinct from spherules of meteoritic origin. Additionally, trace element patterns for these microtektites match the upper continental crust compositions with enrichments in refractory elements and depletions in volatile elements, most likely as a result of melting and vaporization of source material. The presence of Australasian microtektites in RY sediment confirms the recent Australasian strewn field extension to Antarctica and the presence of highly volatile depleted microtektites. In addition to microtektites, thousands of chondritic spherules and a few unique differentiated cosmic spherules were identified in RY, MM, and Jacobs Nunatak sediments. Two unique spherules were calculated to have Fe/Mn ratios similar to micrometeorites assumed to be derived from Vesta (Fe/Mn 33.2 ± 0.5 atom%) and two other unique spherules are extremely rich in refractory components (Al2O3 ~ 30% and TiO2 = ~2%). The three sites examined are evidently successful cosmic dust and impact debris collectors, and thus are useful traps for recording and examining the nature of influx events.

¹García, V.M.
Geological Resources of Tierra del Fuego 365-366 Link to Article [DOI
https://doi.org/10.1007/978-3-030-60683-1_19]
¹Centro Austral de Investigaciones Científicas (CADIC-CONICET), c/ B. Houssay n°200, Ushuaia, Tierra del Fuego V9410CAB, Argentina

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^1,2Moreau, J.-G.,³Schwinger, S.
Physics of the Earth and Planetary Interiors 310, 106630 Link to Article [DOI: 10.1016/j.pepi.2020.106630]
¹Department of Geosciences and Geography, University of Helsinki, Finland
²Institute of Ecology and Earth Sciences, Department of Geology, University of Tartu, Estonia
³German Aerospace Center (DLR), Berlin, Germany

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¹Tommasini, S.,^1,2Bindi, L.,^3,6Petrelli, M.,⁴Asimow, P.D.,⁵Steinhardt, P.J.
ACS Earth and Space Chemistry (in Press) Link to Article [DOI: 10.1021/acsearthspacechem.1c00004]
¹Dipartimento di Scienze della Terra, Università Degli Studi di Firenze, Via La Pira 4, Firenze, I-50121, Italy
²CNR-Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via La Pira 4, Firenze, I-50121, Italy
³Dipartimento di Fisica e Geologia, Università Degli Studi di Perugia, Perugia, I-06123, Italy
⁴Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd. M/C 170-25, Pasadena, CA 91125, United States
⁵Department of Physics, Princeton University, Jadwin Hall, Princeton, NJ 08544, United States
⁶INFN, Section of Perugia, Perugia, I-06123, Italy

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