OXYGEN ISOTOPIC DISTRIBUTION IN AN AMOEBID OLIVINE AGGREGATE FROM THE ALLENDE CV CHRONDITE: PRIMARY AND SECONDARY PROCESSES
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dc.contributor.author | Imai H. | |
dc.contributor.author | Yurimoto H. | |
dc.date.accessioned | 2021-12-19T08:43:16Z | |
dc.date.available | 2021-12-19T08:43:16Z | |
dc.date.issued | 2003 | |
dc.identifier | https://www.elibrary.ru/item.asp?id=36253319 | |
dc.identifier.citation | Geochimica et Cosmochimica Acta, 2003, 67, 4, 765-772 | |
dc.identifier.issn | 0016-7037 | |
dc.identifier.uri | https://repository.geologyscience.ru/handle/123456789/33611 | |
dc.description.abstract | The oxygen isotopic distribution in an amoeboid olivine aggregate (AOA), TTA1-02, from the Allende CV3 chondrite has been determined by secondary ion mass spectrometry. The irregular shaped TTA1- 02 (5×3mm) consists mostly of olivine grains of ca. 5μm in diameter. Olivine grains of Mg-rich (Fo95) and Fe-rich (Fo60) composition are in direct contact with each other, with a sharp compositional boundary. Oxygen isotopic compositions of Fe-rich olivine grains are 16O-poor (Δ17O ≅ −5‰), whereas Mg-rich olivine is 16O-rich (Δ17O ≅ −25‰). Several Al-rich inclusions (<ca. 500 μm in diameter) are enclosed by olivine grains in the AOA. Oxygen isotopic compositions of spinel and fassaite in Al-rich inclusions are 16O-rich (Δ17O ≅ −20‰), whereas those of anorthite, nepheline and phyllosilicate are 16O-poor (Δ17O ≅ −5‰). We propose the following sequence of events during the formation of AOAs in the Allende meteorite: 1) Formation of Al-rich inclusions with 16O-rich oxygen isotopic composition; 2) Accretion of Mg-rich olivine grains with 16O-rich oxygen isotopic composition around Al-rich inclusions; 3) Accretion into parent body; and 4) Aqueous alteration in the parent body, which led to crystallization of 16O-poor minerals, Fe-rich olivine, anorthite, nepheline, and phyllosilicate. This is reflecting reactions among primary 16O-rich AOA minerals and aqueous fluid having 16O-poor oxygen isotopic composition. Fe-rich olivine grains precipitated from aqueous fluids, which partially dissolved pre-existing Mg-rich olivine grains. Sintering and Mg-Fe diffusion occurred during thermal metamorphism. Anorthite, nepheline and phyllosilicate in Al-rich inclusions replaced primary anorthite or melilite during the aqueous alteration stage. | |
dc.title | OXYGEN ISOTOPIC DISTRIBUTION IN AN AMOEBID OLIVINE AGGREGATE FROM THE ALLENDE CV CHRONDITE: PRIMARY AND SECONDARY PROCESSES | |
dc.type | Статья |
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