¹Nancy N. Elewa, ¹J. M. Cadogan
Hyperfine Interactions 238, 4 Link to Article [DOI https://doi.org/10.1007/s10751-016-1350-1]
¹School of Physical, Environmental and Mathematical Sciences The University of New South Wales at the Australian Defence Force Academy Canberra Australia

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^1,2Poorna Srinivasan, ^1,3Rhian H. Jones, ¹Adrian J. Brearley
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12921]
¹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
²Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
³School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester, UK
Published by arrangement with John Wiley & Sons

We studied textures and compositions of sulfide inclusions in unzoned Fe,Ni metal particles within CBa Gujba, CBa Weatherford, CBb HH 237, and CBb QUE 94411 in order to constrain formation conditions and secondary thermal histories on the CB parent body. Unzoned metal particles in all four chondrites have very similar metal and sulfide compositions. Metal particles contain different types of sulfides, which we categorize as: homogeneous low-Cr sulfides composed of troilite, troilite-containing exsolved daubreelite lamellae, arcuate sulfides that occur along metal grain boundaries, and shock-melted sulfides composed of a mixture of troilite and Fe, Ni metal. Our model for formation proposes that the unzoned metal particles were initially metal droplets that formed from splashing by a partially molten impacting body. Sulfide inclusions later formed as a result of precipitation of excess S from solid metal at low temperatures, either during single stage cooling or during a reheating event by impacts. Sulfides containing exsolution lamellae record temperatures of ≪600 °C, and irregular Fe-FeS intergrowth textures suggest localized shock melting, both of which are indicative of heterogeneous heating by impact processes on the CB parent body. Our study shows that CBa and CBb chondrites formed in a similar environment, and also experienced similar secondary impact processing.

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.