^1,2Paulina Skirak,^2,3Gabriela Opiła,¹Adam Piestrzyński,¹Gabriela Kozub-Budzyń,³Czesław Kapusta
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14318]
¹Faculty of Geology Geophysics and Environmental Protection, AGH University of Kraków, Kraków, Poland
²Space Technology Centre, AGH University of Kraków, Kraków, Poland
³Faculty of Physics and Applied Computer Science, AGH University of Kraków, Kraków, Poland
Published by arrangement with John Wiley & Sons

Results of microanalysis study of NWA 869 meteorite, an ordinary chondrite, where silicates, Fe-Ni alloys, and troilite are major constituents, are reported. The presented study of microtextures in metallic and sulfide grains provides information on processes occurring from the asteroid’s accretion, through the impacts until cooling. The presence of metal–silicate emulsion, swiss-cheese texture, and polycrystalline kamacite–troilite aggregates observed indicates very rapid increase in temperature due to impact. Fizzed troilite, slightly homogenized taenite domains, and intergrowth of native copper in plessite imply rapid cooling in isolated regions in space. Agrell effect on the interface of kamacite–taenite grains and non-corroded tetrataenite rims indicates that the sample contains rock fragments from a region unaffected directly by the impact or rapid heating. Diversity of petrological types, lithic clasts with shock grade higher than S3, shock-darkened clasts or impact melting rocks, and variation of microtextures suggest that the parent body of L-type chondrites after accretion, radiogenic metamorphism, and consequent formation of the onion–shell model broke up into debris after the impact of eucrite body.

^1,2Jon M. Friedrich,¹Eva M. Riveros,³Robert J. Macke,^2,4,5Steven J. Jaret,⁶Mark L. Rivers,^2,5,7Denton S. Ebel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14320]
¹Department of Chemistry and Biochemistry, Fordham University, Bronx, New York, USA
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
³Vatican Observatory, Vatican City State
⁴Department of Physical Science, Kingsborough Community College, City University of New York, Brooklyn, New York, USA
⁵Department Earth and Environmental Sciences, CUNY Graduate Center, New York City, New York, USA
⁶GeoSoilEnviroCARS, The University of Chicago, Argonne National Lab, Lemont, Illinois, USA
⁷Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA
Published by arrangement with John Wiley & Sons

CI chondrites are poorly lithified and highly friable regolith breccias. To examine their physical properties and the nature of their breccation, we investigated nine samples of the Ivuna and Orgueil CI chondrites ranging in size from 1 mm to 4 cm in approximate diameter. The combined mass of unique material investigated in this work is 113 g. For our investigations, we use ideal gas pycnometry, 3-D laser scanning, x-ray computed microtomography (μCT), and accompanying digital data extraction techniques. We found that the bulk density of the samples ranged from 1.61 to 2.10 g cm−3. Larger samples tend to have a lower bulk density. Grain density (ranging from 2.44 to 2.55 g cm−3) is significantly less variable than the bulk density in our samples and the quantity of porosity (ranging from 14.6% to 33.8%) is the dominant factor in determining the bulk density of CI chondrite material. Our μCT results show that the visible porosity across all sizes of our CI chondrite samples is in the form of cracks, but these cracks can account for less than two-thirds of the porosity in the CI chondrites. Other porosity is not visible, even at μCT resolutions of 2.7 μm voxel edge−1 and we conclude that it is sub-micron in nature. It is not clear if the cracks seen in our samples are indigenous to the chondrites or are a result of terrestrial processes. We also find that the CI chondrites are excellent examples of the fractal-like nature of brecciation, where clasts can be observed at all scales we imaged. The breccias are composed of sub-equant-shaped and sub-rounded-textured clasts like melt-free impact breccias on other solar system bodies. From our μCT volume and digital data extraction, we determine that the Ivuna CI chondrite breccia is organized: the mostly sub-equant clasts within our ~2 cm chunk of Ivuna have a mean diameter of 1.33 mm and their aligned longest axes define a lineation structure. We speculate that the lineation was imparted after fragmentation of the clasts by slight shear on the parent asteroid which could be the result of seismic-related granular flow or mild non-axial impact-related compaction. These data will help to place returned asteroidal material from asteroids 162173 Ryugu and 101955 Bennu and the CI chondrites into a mutual geological context.