¹Yuji Matsumoto,²Yasuhiro Hasegawa,³Nozomi Matsuda,³Ming-Chang Liu
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114538]
¹Institute of Astronomy and Astrophysics, Academia Sinica, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
³Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, USA
Copyright Elsevier

Chondrules are often surrounded by fine-grained rims or igneous rims. The properties of these rims reflect their formation histories. While the formation of fine-grained rims is modeled by the accretion of dust grains onto chondrules, the accretion should be followed by the growth of dust grains due to the shorter growth timescale than the accretion. In this paper, we investigate the formation of rims, taking into account the growth of porous dust aggregates. We estimate the rim thickness as a function of the chondrule fraction at a time when dust aggregate accretion onto chondrules is switched to collisions between these chondrules. Our estimations are consistent with the measured thicknesses of fine-grained rims in ordinary chondrites. However, those of igneous rims are thicker than our estimations. The thickness of igneous rims would be enlarged in remelting events.

¹Andreas Bechtold,²Franz Brandstätter,²Lidia Pittarello,²Ludovic Ferrière,³Richard C. Greenwood,¹Christian Koeberl
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13659]
¹Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna, 1090 Austria
²Natural History Museum Vienna, Burgring 7, Vienna, 1010 Austria
³Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
Published by arrangement with John Wiley & Sons

Northwest Africa (NWA) 11962 is a lunar regolith breccia composed of a wide range of different clasts. The lunar origin of this meteorite is confirmed by oxygen isotope analysis and the Fe/Mn ratio in pyroxene and olivine. In the present study, the clasts and the matrix of NWA 11962 are characterized by optical and electron microscopy along with electron microprobe analyses and micro‐Raman spectroscopy. The meteorite has a glassy impact melt matrix, which accounts for 35% of the surface area in the two thin sections examined, and which contains a very large variety of different lithic clasts, monomineralic clasts, and glass fragments. The presence of volcanic and impact‐related glass spherules led to the classification of this meteorite as a regolith breccia. Lithic clasts include numerous fragments of quartz monzogabbro and lunar felsite, which are quite rare lithologies in the lunar alkali suite. However, the most abundant components in the breccia are gabbroic clasts. The mineral chemistry of the pyroxenes in the gabbroic clasts and the chemistry of various types of glass fragments in the breccia indicate an origin of the regolith from an area with low‐Ti to high‐Ti mare basalt volcanism. In addition to the peculiar petrographic characteristics of NWA 11962, the possible pairing relationships with other lunar meteorites are discussed.