Thermochemical stability of low‐iron,manganese‐enriched olivine in astrophysical environments |
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| Authors: | Denton S EBEL Michael K WEISBERG John R BECKETT |
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| Institution: | 1. Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York 10024, USA;2. Department of Earth and Environmental Sciences, Lamont‐Doherty Earth Observatory of Columbia University, New York, New York, USA;3. Graduate Center of the City University of New York, New York, USA;4. Department of Physical Sciences, Kingsborough College of CUNY, 2001 Oriental Blvd., Brooklyn, New York 11235, USA;5. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA |
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| Abstract: | Abstract– Low‐iron, manganese‐enriched (LIME) olivine grains are found in cometary samples returned by the Stardust mission from comet 81P/Wild 2. Similar grains are found in primitive meteoritic clasts and unequilibrated meteorite matrix. LIME olivine is thermodynamically stable in a vapor of solar composition at high temperature at total pressures of a millibar to a microbar, but enrichment of solar composition vapor in a dust of chondritic composition causes the FeO/MnO ratio of olivine to increase. The compositions of LIME olivines in primitive materials indicate oxygen fugacities close to those of a very reducing vapor of solar composition. The compositional zoning of LIME olivines in amoeboid olivine aggregates is consistent with equilibration with nebular vapor in the stability field of olivine, without re‐equilibration at lower temperatures. A similar history is likely for LIME olivines found in comet samples and in interplanetary dust particles. LIME olivine is not likely to persist in nebular conditions in which silicate liquids are stable. |
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