Formation des chondres : précurseurs et chronologie

Abstract : Chondrules are the major constituent of primitive meteorites. The large variability of textures and chemical compositions within chondrules is indicative of a complex history. This work is focused on the chronology of formation of chondrules and of their precursors by using two complementary tools: the short-lived radio-isotopes ²Al-²Mg and the experimental petrology.The development of a high precision analytical methodology for in situ measurements of the Mg and Al isotopic compositions by ion probe allows to demonstrate that the distribution of ²Al was homogeneous within the accretion disk. This result has important implications for the chronology and process of chondrule formation and also for the origin of ²Al in the Solar System. By using the same methodology with relict olivines in chondrules, we were able to constrain their origin and their formation process.From experimental petrology studies, we show that it was easy to form type II PO chondrules analogues from type I PO analogues. Such a process for chondrules formation implies an isothermal heating followed by a quick quench which is incompatible with the classical shock-waves model. Moreover, we show that the chemical compositions for major and trace elements of the different types of porphyritic chondrules can be easily reproduced by a mixing model composed of three refractory phases inherited from chondrules precursors (refractory olivine, refractory liquid and iron metal) and a gas phase enriched in volatile and moderately volatile elements. Finally, we propose a model of genetic linkage between the different types of porphyritic chondrules
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Johan Villeneuve. Formation des chondres : précurseurs et chronologie. Autre. Institut National Polytechnique de Lorraine, 2010. Français. ⟨NNT : 2010INPL032N⟩. ⟨tel-01748829⟩

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