Fall,classification, and exposure history of the Mifflin L5 chondrite |
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Authors: | Noriko T. Kita Kees C. Welten John W. Valley Michael J. Spicuzza Daisuke Nakashima Travis J. Tenner Takayuki Ushikubo Glenn J. MacPherson Linda Welzenbach Philipp R. Heck Andrew M. Davis Matthias M. M. Meier Rainer Wieler Marc W. Caffee Matthias Laubenstein Kunihiko Nishiizumi |
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Affiliation: | 1. Department of Geoscience, University of Wisconsin‐Madison, , Madison, Wisconsin, 53706 USA;2. Space Sciences Laboratory, University of California, , Berkeley, California, 94720 USA;3. Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, , Washington, District of Columbia, 20560 USA;4. Robert A. Pritzker Center for Meteoritics and Polar Studies, Department of Geology, The Field Museum, , Chicago, Illinois, 60605 USA;5. Chicago Center for Cosmochemistry, The University of Chicago, , Chicago, Illinois, 60637–1433 USA;6. Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, , Chicago, Illinois, 60637 USA;7. Department of Earth Sciences, ETH Zürich, , Zürich, CH‐8092 Switzerland;8. Department of Geology, Lund University, , Lund, SE‐22362 Sweden;9. Department of Physics, Purdue University, , West Lafayette, Indiana, 47907 USA;10. Laboratori Nazionali del Gran Sasso, I.N.F.N., , Assergi (AQ), I‐67100 Italy |
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Abstract: | The Mifflin meteorite fell on the night of April 14, 2010, in southwestern Wisconsin. A bright fireball was observed throughout a wide area of the midwestern United States. The petrography, mineral compositions, and oxygen isotope ratios indicate that the meteorite is a L5 chondrite fragmental breccia with light/dark structure. The meteorite shows a low shock stage of S2, although some shock‐melted veins are present. The U,Th‐He age is 0.7 Ga, and the K‐Ar age is 1.8 Ga, indicating that Mifflin might have been heated at the time of the 470 Ma L‐chondrite parent body breakup and that U, Th‐He, and K‐Ar ages were partially reset. The cosmogenic radionuclide data indicate that Mifflin was exposed to cosmic rays while its radius was 30–65 cm. Assuming this exposure geometry, a cosmic‐ray exposure age of 25 ± 3 Ma is calculated from cosmogenic noble gas concentrations. The low 22Ne/21Ne ratio may, however, indicate a two‐stage exposure with a longer first‐stage exposure at high shielding. Mifflin is unusual in having a low radiogenic gas content combined with a low shock stage and no evidence of late stage annealing; this inconsistency remains unexplained. |
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