Origin of 16O-rich fine-grained Ca-Al-rich inclusions of different mineralogy and texture |
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| Institution: | 1. Department of Earth and Planetary Sciences, MSC03-2040, University of New Mexico, Albuquerque, NM 87131, USA;2. Lunar and Planetary Institute, USRA, 3600 Bay Area Boulevard, Houston, TX 77058, USA;3. ARES, NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, USA;4. Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA;5. Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA;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. Department of Earth, Planetary, and Space Sciences, UCLA, Los Angeles, CA 90095, United States;2. Origins Lab, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, United States;3. Department of the Earth, Atmospheric and Planetary Sciences, MIT, Cambridge 02139, United States;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. Chemistry Division, Nuclear and Radiochemistry, Los Alamos National Laboratory, MSJ514, Los Alamos, NM 87545, USA;7. Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI, USA;8. Korea Polar Research Institute, Incheon 21990, Republic of Korea;9. Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA;1. School of Ocean, Earth Science and Technology, Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, HI 96822, USA;2. Centre for Star and Planet Formation and Natural History Museum of Denmark, University of Copenhagen, DK-1350 Copenhagen, Denmark;1. Dept. of Mineral Sciences, Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA;2. Carnegie Institution of Washington, Geophysical Laboratory, 5251 Broad Branch Rd., N.W., Washington, DC 20015, USA;3. WiscSIMS, University of Wisconsin, Madison, WI 53706, USA;4. Los Alamos National Laboratory, Los Alamos, NM 87545, USA;5. Tohoku University, Miyagi 980-8578, Japan;6. Vernadsky Institute, Kosygin St. 19, Moscow 119991, Russia;7. University of Hawai''i at Mānoa, Honolulu, HI 96822, USA;8. Harvard University, Cambridge, MA 02138, USA |
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| Abstract: | A coordinated mineralogical and oxygen isotopic study of four fine-grained calcium-, aluminum-rich inclusions (CAIs) from the ALHA77307 CO3.0 carbonaceous chondrite was conducted. Three of the inclusions studied, 05, 1-65, and 2-119, all have nodular structures that represent three major groups, melilite-rich, spinel-rich, and hibonite-rich, based on their primary core mineral assemblages. A condensation origin was inferred for these CAIs. However, the difference in their primary core mineralogy reflects unique nebular environments in which multiple gas-solid reactions occurred under disequilibrium conditions to form hibonite, spinel, and melilite with minor perovskite and Al,Ti-rich diopside. A common occurrence of a diopside rim on the CAIs records a widespread event that marks the end of their condensation as a result of isolation from a nebular gas. An exception is a rare inclusion 2-112 that contains euhedral spinel crystals embedded in melilite, suggesting this CAI had been re-melted. All of the fine-grained CAIs analyzed in ALHA77307 are 16O-rich with an average Δ17O value of ∼−22 ± 5‰ (2σ), indicating no apparent correlation between their textures and oxygen isotopic compositions. We therefore conclude that a prevalent 16O-rich gas reservoir existed in a region of the solar nebula where CO3 fine-grained CAIs formed, initially by condensation and then later, some of them were reprocessed by melting event(s). |
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| Keywords: | Calcium-aluminum-rich inclusions Microstructures Oxygen isotopes Solar nebula |
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