¹Josefin Martell,¹Carl Alwmark,^1,2,3Sanna Holm‐Alwmark,¹Paula Lindgren
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13625]
¹Department of Geology, Lund University, Sölvegatan 12, 223 62 Lund, Sweden
²Niels Bohr Institute, University of Copenhagen, Blegdamsvej, 17, 2100 Copenhagen, Denmark
³Natural History Museum Denmark, University of Copenhagen, Øster Voldgade, 5‐7, 1350 Copenhagen K, Denmark
Published by arrangement with John Wiley & Sons

Recognition of impact‐induced deformation of minerals is crucial for the identification and confirmation of impact structures as well as for the understanding of shock wave behavior and crater formation. Shock deformed mineral grains from impact structures can also serve as important geochronometers, precisely dating the impact event. We investigated zircon grains from the Mien impact structure in southern Sweden with the aim of characterizing shock deformation. The grains were found in two samples of impact melt rock with varying clast content, and in one sample of suevitic breccia. We report the first documentation of so‐called “FRIGN zircon” (former reidite in granular neoblastic zircon) from Mien (pre‐erosion diameter 9 km), which confirms that this is an important impact signature also in relatively small impact structures. Furthermore, the majority of investigated zircon grains contain other shock‐related microtextures, most notably granular and microporous textures, that occur more frequently in grains found in the impact melt than in the suevitic breccia. Our findings show that zircon grains that are prime candidates for establishing a new and improved age refinement of the Mien impact structure are present in the impact melt.

¹Kim V. Fendrich,¹Denton S. Ebel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13623]
¹Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, 10024 USA
Published by arrangement with John Wiley & Sons

The size, distribution, abundance, and physical and chemical characteristics of chondritic inclusions are key features that define the chondrite groups. We present statistics on the size and abundance of the macroscopic components (inclusions) in the Murchison (CM2) and Allende (CV3) chondrites and measure their general chemical trends using established X‐ray mapping techniques. This study provides a fine‐scale assessment of the two meteorites and a semiquantitative evaluation of the relative abundances of elements and their distribution among meteorite components. Murchison contains 72% matrix and 28% inclusions; Allende contains 57% and 43%, respectively. A broad range of inclusion sizes and relative abundances has been reported for these meteorites, which demonstrates the necessity for a more standardized approach to measuring these characteristics. Nonetheless, the characteristic mean sizes of inclusions in Allende are consistently larger than those in Murchison. We draw two significant conclusions (1) these two meteorites sampled distinct populations of chondrules and refractory inclusions, and (2) complementary Mg/Si ratios between chondrules and matrix are observed in both Murchison and Allende. Both support the idea that chondrules and matrix within each chondrite group originated in single reservoirs of precursors with approximately solar Mg/Si ratios, providing a constraint on astrophysical models of the origin of chondrite parent bodies.