Heating duration of igneous rim formation on a chondrule in the Northwest Africa 3118 CV3oxA carbonaceous chondrite inferred from micro-scale migration of the oxygen isotopes |
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| Institution: | 1. Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan;2. Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo 001-0021, Japan;3. UTokyo Organization for Planetary and Space Science (UTOPS), University of Tokyo, Tokyo 113-0033, Japan;4. ISAS/JAXA, Sagamihara, Kanagawa 252-210, Japan;1. Dept 5.1, Federal Institute for Materials, Research and Testing (BAM), Unter den Eichen 87, 12205 Berlin, Germany;2. Institut für Geowissenschaften (IGW), Friedrich-Schiller-Universität Jena (FSU), Germany;1. Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5-7, DK-1350, Denmark;2. Department of Earth & Planetary Science, University of Tokyo, Tokyo, Japan;1. Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan;2. Department of Earth and Planetary Sciences, Kyoto University, Kyoto 606-8502, Japan;3. Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo 001-0021, Japan;1. Geology and Geophysics, School of Ocean, Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA;2. Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA;3. Department of Natural History Sciences, Hokkaido University, N10 W8, Sapporo 060-0810, Japan;1. Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA;2. Chicago Center for Cosmochemistry, The University of Chicago, Chicago, IL 60637, USA;3. Robert A. Pritzker Center for Meteoritics and Polar Studies, Field Museum of Natural History, Chicago, IL, USA;4. Department of Geoscience, University of Wisconsin, Madison, WI 53706, USA;5. Division of Earth and Planetary Material Sciences, Faculty of Science, Tohoku University, Aoba, Sendai, Miyagi 980-8578, Japan;6. Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Mānoa, Honolulu, HI, USA;7. Korea Polar Research Institute, Incheon 406-840, Republic of Korea;8. Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA;9. Chemistry Division, Nuclear and Radiochemistry, Los Alamos National Laboratory, MSJ514, Los Alamos, NM 87545, USA;1. ETH Zürich, Institute für Geochemie und Petrologie, Clausiusstrasse 25, 8092 Zürich, Switzerland;2. Planetary and Space Sciences, School of Physical Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom;3. Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom |
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| Abstract: | Due to their common occurrence in various types of chondrites, igneous rims formed on pre-existing chondrules throughout chondrule-forming regions of the solar nebula. Although the peak temperatures are thought to reach similar values to those achieved during chondrule formation events, the heating duration in chondrule rim formation has not been well defined. We determined the two-dimensional chemical and oxygen isotopic distributions in an igneous rim of a chondrule within the Northwest Africa 3118 CV3oxA chondrite with sub-micrometer resolution using secondary ion mass spectrometry and scanning electron microscopy. The igneous rim experienced aqueous alteration on the CV parent body. The aqueous alteration resulted in precipitation of the secondary FeO-rich olivine (Fa40–49) and slightly disturbed the Fe-Mg distribution in the MgO-rich olivine phenocrysts (Fa11–22) at about a 1 μm scale. However, no oxygen isotopic disturbances were observed at a scale greater than 100 nm. The MgO-rich olivine, a primary phase of igneous rim formation, has δ17O = −6 ± 3‰ and δ18O = −1 ± 4‰, and some grains contain extreme 16O-rich areas (δ17O, δ18O = ∼−30‰) nearly 10 μm across. We detected oxygen isotopic migration of approximately 1 μm at the boundaries of the extreme 16O-rich areas. Using oxygen self-diffusivity in olivine, the heating time of the igneous rim formation could have continued from several hours to several days at near liquidus temperatures (∼2000 K) in the solar nebula suggesting that the rim formed by a similar flash heating event that formed the chondrules. |
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| Keywords: | Igneous rim Chondrule Oxygen isotopes Carbonaceous chondrite Northwest Africa Diffusion Secondary ion mass spectrometry Olivine Magnesium Iron |
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