The cosmic-ray exposure history of the Twannberg iron meteorite (IIG)

1Thomas Smith,2Beda A. Hofmann,1Ingo Leya,
3Silke Merchel,3Stefan Pavetich,3Georg Rugel,3Andreas Scharf
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12928]
1Physic Institute, University of Bern, Bern, Switzerland
2Naturhistorisches Museum der Burgergemeinde Bern, Bern, Switzerland
3Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
Published by arrangement with John Wiley & Sons

The Twannberg iron meteorite is one out of only six members of the group IIG. The combined noble gas and radionuclide data obtained in this new systematic study indicate that Twannberg with its ~570 recently recovered specimens was a large object with a preatmospheric radius in the range of ~2 m, which corresponds to ~250 × 106 kg. The cosmic-ray exposure age for Twannberg is 182 ± 45 Ma. The most surprising result is the long terrestrial age of Tterr = math formula ka, which is unexpected considering the humid conditions in Switzerland. However, this age is in accord with glaciation events, indicating that the less shielded samples from Mt. Sujet were found close to the position of the original strewn field, whereas the samples from Gruebmatt and Twannbach, which are from more shielded positions, were glacially transported to the east–northeast during the second last ice age (185–130 ka ago) from an original position west of Mt. Sujet.

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