Mineralogy,petrography, and oxygen isotopic compositions of ultrarefractory inclusions from carbonaceous chondrites |
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| Institution: | 1. Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, 1680 East-West Road, Honolulu, HI 96822, USA;2. Geoscience Institute, Goethe University, 60438 Frankfurt am Main, Germany;3. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena CA 91125, USA;4. Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA;5. Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA;6. Chicago Center for Cosmochemistry, Chicago, IL 60637, USA;7. Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, USA;8. The Graduate University for Advanced Studies (SOKENDAI), Hayama, Kanagawa 240-0193 Japan;9. Earth Sciences Department, Waseda University, Shinjuku-ku, Tokyo 169-8050, Japan;10. Vernadsky Institute of Geochemistry of Russian Academy of Sciences, Kosygin St. 19, Moscow 119991, Russia;11. Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany;1. Department of Mineral Sciences, Smithsonian Institution, National Museum of Natural History, Washington, DC 20560, USA;2. Department of Earth and Planetary Sciences, Rutgers, State University of New Jersey, 610 Taylor Road, Piscataway, NJ 08854-8066, USA;3. Center for Meteorite Studies, Arizona State University, Tempe, AZ 85287, USA;4. School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA;5. Hawai‘i Institute of Geophysics & Planetology, University of Hawai‘i at Manoa, 1680 East-West Road, POST 602 Honolulu, HI 96822, USA;6. Retired, Iowa State University, Ames, IA 50011, USA;1. Centre de Recherches Pétrographiques et Géochimiques, INSU-CNRS, Université de Lorraine, 15 Rue du Notre Dame des Pauvres, Boite Postale 20, 54501 Vandoeuvre-lès-Nancy, France;1. National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa 403 004, India;2. School of Chemistry, University of Leeds, Leeds LS29JT, UK;3. Institut für Physik, Johannes Gutenberg-Universität, Staudingerweg 7, D-55128 Mainz, Germany;1. WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, 1215 W. Dayton St., Madison, WI 53706, USA;2. Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 200 Monobe-otsu, Nankoku, Kochi 783-8502, Japan;3. Chemistry Division, Nuclear and Radiochemistry, Los Alamos National Laboratory, MSJ514, Los Alamos, NM 87545, USA;4. Department of Earth and Planetary Science, Graduate school of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, 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. Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA;5. Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI, USA;6. Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, USA;1. Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY 10024, USA;2. Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA;3. Graduate Center of the City University of New York, NY, USA;4. Barrick Gold, NV, USA;5. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA;6. Department of Geological Sciences, Indiana University, Bloomington, IN, USA;7. Yale University, 409 Prospect St, New Haven, CT 06511, USA;8. Department of Astronomy and Physics, Williams College, MA, USA;9. SandRidge Energy, Houston, TX, USA;10. Department of Chemistry, Fordham University, 441 East Fordham Road, Bronx, NY 10458, USA;11. Department of Physical Sciences, Kingsborough College, 2001 Oriental Blvd., Brooklyn, NY 11235, USA |
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| Abstract: | We report on the mineralogy, petrography, and in situ oxygen isotopic composition of twenty-five ultrarefractory calcium-aluminum-rich inclusions (UR CAIs) in CM2, CR2, CH3.0, CV3.1–3.6, CO3.0–3.6, MAC 88107 (CO3.1-like), and Acfer 094 (C3.0 ungrouped) carbonaceous chondrites. The UR CAIs studied are typically small, < 100 μm in size, and contain, sometimes dominated by, Zr-, Sc-, and Y-rich minerals, including allendeite (Sc4Zr3O12), and an unnamed ((Ti,Mg,Sc,Al)3O5) mineral, davisite (CaScAlSiO6), eringaite (Ca3(Sc,Y,Ti)2Si3O12), kangite ((Sc,Ti,Al,Zr,Mg,Ca,□)2O3), lakargiite (CaZrO3), warkite (Ca2Sc6Al6O20), panguite ((Ti,Al,Sc,Mg,Zr,Ca)1.8O3), Y-rich perovskite ((Ca,Y)TiO3), tazheranite ((Zr,Ti,Ca)O2?x), thortveitite (Sc2Si2O7), zirconolite (orthorhombic CaZrTi2O7), and zirkelite (cubic CaZrTi2O7). These minerals are often associated with 50–200 nm-sized nuggets of platinum group elements. The UR CAIs occur as: (i) individual irregularly-shaped, nodular-like inclusions; (ii) constituents of unmelted refractory inclusions – amoeboid olivine aggregates (AOAs) and Fluffy Type A CAIs; (iii) relict inclusions in coarse-grained igneous CAIs (forsterite-bearing Type Bs and compact Type As); and (iv) relict inclusions in chondrules. Most UR CAIs, except for relict inclusions, are surrounded by single or multilayered Wark-Lovering rims composed of Sc-rich clinopyroxene, ±eringaite, Al-diopside, and ±forsterite. Most of UR CAIs in carbonaceous chondrites of petrologic types 2–3.0 are uniformly 16O-rich (Δ17O ～ ?23‰), except for one CH UR CAI, which is uniformly 16O-depleted (Δ 17O ～ ?5‰). Two UR CAIs in Murchison have heterogeneous Δ17O. These include: an intergrowth of corundum (～ ?24‰) and (Ti,Mg,Sc,Al)3O5 (～ 0‰), and a thortveitite-bearing CAI (～ ?20 to ～ ?5‰); the latter apparently experienced incomplete melting during chondrule formation. In contrast, most UR CAIs in metamorphosed chondrites are isotopically heterogeneous (Δ17O ranges from ～ ?23‰ to ～ ?2‰), with Zr- and Sc-rich oxides and silicates, melilite and perovskite being 16O-depleted to various degrees relative to uniformly 16O-rich (Δ17O ～ ?23‰) hibonite, spinel, Al-diopside, and forsterite. We conclude that UR CAIs formed by evaporation/condensation, aggregation and, in some cases, melting processes in a 16O-rich gas of approximately solar composition in the CAI-forming region(s), most likely near the protoSun, and were subsequently dispersed throughout the protoplanetary disk. One of the CH UR CAIs formed in an 16O-depleted gaseous reservoir providing an evidence for large variations in Δ17O of the nebular gas in the CH CAIs-forming region. Subsequently some UR CAIs experienced oxygen isotopic exchange during melting in 16O-depleted regions of the disk, most likely during the epoch of chondrule formation. In addition, UR CAIs in metamorphosed CO and CV chondrites, and, possibly, the corundum-(Ti,Mg,Sc,Al)3O5 intergrowth in Murchison experienced O-isotope exchange with aqueous fluids on the CO, CV, and CM chondrite parent asteroids. Thus, both nebular and planetary exchange with 16O-depleted reservoirs occurred. |
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| Keywords: | Ultrarefractory inclusions Mineralogy Petrography Oxygen isotopes Carbonaceous chondrites |
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