^1,2Daisuke Nakashima,^3,4Keisuke Nagao,⁵Anthony J. Irving
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13039]
¹Department of Earth and Planetary Material Sciences, Faculty of Science, Tohoku University, Sendai, Miyagi, Japan
²Geochemical Research Center, Graduate School of Science, University of Tokyo, Bunkyo, Tokyo, Japan
³Geochemical Research Center, Graduate School of Science, University of Tokyo, Bunkyo, Tokyo, Japan
⁴Division of Polar Earth-System Sciences, Korea Polar Research Institute, Incheon, Korea
⁵Department of Earth & Space Sciences, University of Washington, Seattle, Washington, USA
Published by arrangement with John Wiley & Sons

Noble gases in the five angrites Northwest Africa (NWA) 1296, 2999, 4590, 4801, and 4931 were analyzed with total melting and stepwise heating methods. The noble gases consist of in situ components: spallogenic, radiogenic, nucleogenic, and fission. Cosmic-ray exposure ages of the angrites (including literature data) spread uniformly from <0.2 to 56 Ma, and coarse-grained angrites have longer exposure ages than fine-grained angrites. It is implied that the parent bodies from which the two subgroups of angrites were ejected are different and have distinct orbital elements. The ²⁴⁴Pu-¹³⁶Xe relative ages of the angrites obtained by using ²⁴⁴Pu/¹⁵⁰Nd ratios are as old as that of Angra dos Reis, reflecting their early formation. On the other hand, another method to obtain ²⁴⁴Pu-¹³⁶Xe relative ages, using fission ¹³⁶Xe, spallogenic ¹²⁶Xe, and Ba/REE ratios, yields systematically older ²⁴⁴Pu-¹³⁶Xe ages than those obtained by using ²⁴⁴Pu/¹⁵⁰Nd ratios, which is explained by apparently high Ba/REE ratios caused by Ba contamination during terrestrial weathering. The ²⁴⁴Pu/²³⁸U ratio at 4.56 Ga of angrites is estimated as 0.0061 ± 0.0028, which is consistent with those for chondrules, chondrites, achondrites, and a terrestrial zircon. It is suggested that initial ²⁴⁴Pu/²³⁸U ratio has been spatially homogeneous at least in the inner part of the early solar system.

^1,2,3Surya S. Rout,^1,2,4Philipp R. Heck,^1,5Birger Schmitz
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13041]
¹Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum of Natural History, Chicago, Illinois, USA
²Chicago Center for Cosmochemistry, Chicago, Illinois, USA
³Physikalisches Institut, Space Research and Planetary Sciences, Universität Bern, Bern, Switzerland
⁴Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois, USA
⁵Astrogeobiology Laboratory, Department of Physics, Lund University, Lund, Sweden
Published by arrangement with John Wiley & Sons

Chrome-spinel grains from the fossil ungrouped achondrite Österplana 065 (Öst 065) recovered from Middle Ordovician limestone in Sweden were studied using Raman spectroscopy and TEM. All the studied chrome-spinel grains have a high density of planar fractures and planar features, not seen in chromites from the other L chondritic Ordovician fossil meteorites. Raman spectra of the host chrome-spinel grain and its planar features are similar and no signatures of high-pressure phases of chromite were found. The planar features occur along planar fractures, are enriched in ZnO, and are most probably produced due to enhanced leaching during terrestrial weathering in the marine sediment. Dislocation densities within two FIB sections prepared from two chrome-spinel grains from Öst 065 are similar to the dislocation densities found within chromite grains from the matrix of Tenham L6 chondrite. Using this observation and taking into account the presence of significant fracturing in all the grains, we conclude that the Öst 065 chrome-spinel grains were subjected to moderate to very strong shock corresponding to shock stages of S4–S6. This makes Öst 065 fossil achondrite the highest shocked fossil meteorite studied so far. This is consistent with the hypothesis that Öst 065 is a piece of the impactor that led to the L chondrite parent body breakup.