Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University/Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University/Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University/Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University
抄録(英)
Spherules collected from deep-sea sediments were analyzed for major chemical compositions and examined for textural relationships. Two main types of internal texture are observed in Ni-bearing I-type spherules : spherules with Ni-free Fe-oxide mantle and Fe-Ni metallic cores and Fe-Ni oxide spherules without metallic cores. Cores are often observed off-centered. S-type spherules show porphyritic, barred, and fine-grained types of texture. Relict olivine grains are found in some porphyritic S-type spherules. A cooling rate of 55℃/s was calculated for one of these grains based on chemical zonal patterns. For I-type spherules, numerical simulations were performed to constrain the relationship between temperatures, radii of spherules, and the apparent gravitational acceleration with the spherule as a stationary frame of reference. Results indicate that a) spherules lose most of their original mass by evaporation over 1900℃, and, b) the apparent gravitational acceleration is at a maximum during the last stage of evaporation. Based on the observations and numerical simulations of I-type spherules, we propose the following model for their formation : during ablation, the metallic core is off-centered, a surface of the core is then exposed to the air due to the strong apparent gravitational acceleration and, finally, oxidation reactions can proceed on the exposed core surface.
雑誌書誌ID
AA10784627
雑誌名
Proceedings of the NIPR Symposium on Antarctic Meteorites
Formation processes of magnetic spherules collected from deep-sea sediments -Observations and numerical simulations of the orbital evolution-
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KJ00000036516
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概要
