The Loongana (CL) group of carbonaceous chondrites

1Knut Metzler et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.04.007]
1Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
Copyright Elsevier

A coordinated study of the petrology, mineral chemistry, and bulk chemical and isotopic composition of the five ungrouped carbonaceous chondrites Coolidge, Loongana 001, Los Vientos (LoV) 051, Northwest Africa (NWA) 033, and NWA 13400 reveals that these meteorites have a similar set of properties that distinguishes them from the other carbonaceous chondrite groups and allows definition of the new Loongana (CL) group of carbonaceous chondrites. The basic characteristics of the investigated samples are: (1) Lithophile element ratios (e.g., Al/Mg, Si/Mg) are within the typical range of other carbonaceous chondrite groups. (2) Fe-Ni metal abundances are considerably higher than for CV, but similar to CR chondrites. (3) Chondrule size-frequency distributions are similar to CV, but dissimilar to CR chondrites. (4) The mean CAI abundance is ∼1.4 vol%, i.e., lower than in CV but much higher than in CR chondrites. (5) Very low amounts of matrix (17-21 vol%), the lowest among the main carbonaceous chondrite groups (CI, CM, CO, CV, CR, CK). (6) Olivine is nearly equilibrated, with mean fayalite (Fa) values between 12.5 mol% (Loongana 001) and 14.7 mol% (NWA 13400) as a metamorphic effect. (7) Lower Al2O3 and higher MgO and Cr2O3 concentrations in matrix, compared to matrix in CV, CK, and CR chondrites. (8) Volatile elements (Mn, Na, K, Rb, Cs, Zn, Se, Te, Pb, Tl) are considerably depleted compared to all other main carbonaceous chondrite groups, reflecting the low matrix abundance. (9) Bulk O isotope compositions plot along the CCAM line (Δ17O -3.96 to -5.47‰), partly overlapping with the CV and CK chondrite field but including samples that are more 16O-rich. (10) Unique positions of CL values in the є54Cr-є50Ti isotope plot, with є54Cr values similar to CV, CK, and CO, but є50Ti values similar to CR chondrites. All CL chondrites studied here are of petrologic type 3.9 to 4, indicating that they have been thermally metamorphosed on the parent body. The diagnostic features of CL chondrites detailed here provide a basis for identifying CL members of lower petrologic types. Such samples will be important for determining the pristine state of these meteorites and their components.

Testing models for the composition of chondrites and their components: I. CO chondrites

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.

Resolving the age of the Haughton impact structure using coupled 40Ar/39Ar and U-Pb geochronology

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.

Excellent mechanical properties of taenite in meteoric iron

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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Jarosite formation in deep Antarctic ice provides a window into acidic, water-limited weathering on Mars

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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Suevites and Tagamites of Zhamanshin Astrobleme: Distribution in the Crater and Petrographic Features

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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Microtektites and glassy cosmic spherules from new sites in the Transantarctic Mountains, Antarctica

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.

Heat diffusion in numerically shocked ordinary chondrites and its contribution to shock melting

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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