Chemical zoning of olivines in the Yamato-791717 CO3 chondrite

概要

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The chemical zoning profiles of olivines in the Yamato (Y)-791717 CO3 chondrite have been analyzed in order to explore its thermal history. Two alternative models were applied to distinguish igneous processes from metamorphic features; they are fractional crystallization and diffusive modification of primary composition. It was clarified that chemical zoning of olivines in Y-791717 has been formed by a diffusion process, suggesting that this meteorite has been thermally metamorphosed. Thermal metamorphism of Y-791717 we have shown is consistent with that proposed on the basis of thermoluminescence investigation. A diffusion model also allows us to examine its thermal history in a quantitative way. Using a diffusion model, we have most successfully reproduced measured zoning profiles in isolated and chondrule olivine grains from Y-791717 in the temperature range 800-300℃. The temperature range is broadly consistent with the previously proposed peak metamorphic temperatures for CO3 chondrites.
国立極地研究所の論文