^1,2Burkhardt, C et al. (>10)*
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12834]
¹Origins Laboratory, Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois 60637, USA
²Institut für Planetologie, Westfälische Wilhelms-Universität M€unster, Wilhelm-Klemm-Str 10, Münster D-48149, Germany
Published by Arrangement with John Wiley & Sons

High-precision isotope data of meteorites show that the long-standing notion of a “chondritic uniform reservoir” is not always applicable for describing the isotopic composition of the bulk Earth and other planetary bodies. To mitigate the effects of this “isotopic crisis” and to better understand the genetic relations of meteorites and the Earth-forming reservoir, we performed a comprehensive petrographic, elemental, and multi-isotopic (O, Ca, Ti, Cr, Ni, Mo, Ru, and W) study of the ungrouped achondrites NWA 5363 and NWA 5400, for both of which terrestrial O isotope signatures were previously reported. Also, we obtained isotope data for the chondrites Pillistfer (EL6), Allegan (H6), and Allende (CV3), and compiled available anomaly data for undifferentiated and differentiated meteorites. The chemical compositions of NWA 5363 and NWA 5400 are strikingly similar, except for fluid mobile elements tracing desert weathering. We show that NWA 5363 and NWA 5400 are paired samples from a primitive achondrite parent-body and interpret these rocks as restite assemblages after silicate melt extraction and siderophile element addition. Hafnium-tungsten chronology yields a model age of 2.2 ± 0.8 Myr after CAI, which probably dates both of these events within uncertainty. We confirm the terrestrial O isotope signature of NWA 5363/NWA 5400; however, the discovery of nucleosynthetic anomalies in Ca, Ti, Cr, Mo, and Ru reveals that the NWA5363/NWA 5400 parent-body is not the “missing link” that could explain the composition of the Earth by the mixing of known meteorites. Until this “missing link” or a direct sample of the terrestrial reservoir is identified, guidelines are provided of how to use chondrites for estimating the isotopic composition of the bulk Earth.

¹Rebecca Querfeld, ¹Mohammad R. Tanha, ²Lars Heyer, ²Franz Renz, ³Georg Guggenberger, ⁴Franz Brandstätter, ⁴Ludovic Ferrière, ^4,5Christian Koeberl, ¹Georg Steinhauser
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12855]
¹Leibniz Universität Hannover, Institute of Radioecology and Radiation Protection, 30419 Hannover, Germany
²Leibniz Universität Hannover, Institute of Inorganic Chemistry, 30167 Hannover, Germany
³Leibniz Universität Hannover, Institute of Soil Science, 30419 Hannover, Germany
⁴Natural History Museum, Burgring 7, 1010 Vienna, Austria
⁵Department of Lithospheric Research, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
Published by Arrangement with John Wiley & Sons

A piece of the 2013 Chelyabinsk meteorite was investigated for its content of anthropogenic radionuclides. In addition to traces of cesium-137 that had been previously reported for this particular fragment, we found an unusually high amount of strontium-90, which indicates that the source of this contamination was the Kyshtym accident (1957). A high Sr-90/Cs-137 activity ratio is characteristic for Kyshtym-derived contaminations. Based on the cesium-137 content in the soil from the finding site, it is estimated that the fragment was contaminated with soil particles in the milligram range upon impact. Investigation of the soil revealed very unusual ferromagnetic characteristics and an iron-rich chemical composition. Mössbauer spectroscopy indicated the presence of steel components in this soil, suggesting that the investigated meteorite fragment was found in an industrial dumping site rather than natural soil.