Clues to chondrule precursors: An investigation of vesicle formation in experimental chondrules |
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| Institution: | 1. Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St Louis, One Brookings Drive, St. Louis, MO 63130, USA;2. Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA;3. Department of Earth Sciences, Durham University, Science Labs, Durham DH1 3LE, United Kingdom;4. Institut de Physique du Globe de Paris, Institut Universitaire de France, Université Paris Diderot, Sorbonne Paris Cité, 1 rue Jussieu, 75238 Paris Cedex 05, France;1. Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA;2. Chicago Center for Cosmochemistry, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA;3. Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA;4. Origins Laboratory, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA;5. Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;1. Department of Physics, Washington University in St. Louis, St. Louis, MO, USA;2. Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, USA;1. Department of Earth and Planetary Sciences and Planetary Geosciences Institute, University of Tennessee, Knoxville, TN 37996, USA;2. Department of Mineral Sciences, Smithsonian Institution, National Museum of Natural History, Washington, DC 20560, USA;3. Department of Geosciences, University of Wisconsin, Madison, WI 53706, USA;4. Chemistry Division, Nuclear and Radiochemistry, Los Alamos National Laboratory, MSJ514, Los Alamos, NM 87545, USA;5. Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA;1. University of Cologne, Department of Geology and Mineralogy, Zülpicher Str. 49b, 50674, Köln, Germany;2. Natural History Museum, Department of Mineralogy, Cromwell Road, SW7 5BD, London, UK;3. Laboratoire Lagrange, UMR7293, Université de la Côte d''Azur, CNRS, Observatoire de la Côte d''Azur, F-06304, Nice Cedex 4, France |
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| Abstract: | The absence of vesicles in chondrules and their presence in synthetic analogs yields information about the origin of chondrules. A variety of melting-crystallization experiments demonstrate the cause of vesicles in synthetic chondrules. Experiments involving the use of binding agents in sample preparation, samples with residual adsorbed moisture, incompletely melted samples, and the use of fine-grained sizesorted starting powder all generated more vesicles than experiments on control samples. Volatiles such as Na were not responsible for vesicles in our experiments because Na was not lost under our flashheating conditions. Because Wdowiak (1983) assumed chondrule precursors contained volatiles, and his electrical discharge melting generated vesicles, he suggested chondrules were not formed by flashmelting events. However, vesicle-free chondrules are to be expected with flash melting provided that the precursors were poor in highly volatile material. Flash-melting experiments with serpentine in the precursor powder developed extremely porous “popcorn” spherules, as in some meteorite ablation spherules. Chondrule precursors must have consisted of anhydrous phases assembled at low ambient gas pressure above the condensation temperature of ice. The absence of vesicles in all chondrules, including those unlikely to have been heated multiple times, e.g., 16O-rich and granular chondrules, demonstrates that their original precursors, whether interstellar dust or nebular condensates, cannot have consisted of hydrous silicates. |
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