Caractérisation texturale des assemblages Métal-Silicate lors de la différenciation des planétésimaux : Etude de météorites & Approche expérimentale

Abstract : Meteorites are samples of small parent bodies accreted in the first five million years of the solar system. The diversity of meteorites can be related to different thermal evolutions of their parent bodies, from thermal metamorphism to complete mantle/core differentiation. This thesis focuses on the silicate-metal relative mobility during heating, in particular for solid systems which approach or exceed the onset of silicate melting. Two approaches are considered. Firstly, the textural evolutions in natural meteorites have been quantified. Secondly, laboratory experiments have been performed in order to identify and understand the processes which govern these textural changes. A textural study of metal and sulphide grains in H-chondrites shows that as metamorphism grade increases, phases separate, change in shape and grow. This evolution occurs progressively, making it possible to define textural criteria that vary continuously across petrographic boundaries. This evolution is consistent with independent geochemical data and thermal model. We propose a new scale of metamorphism allowing the subdivision of types 4 to 6. Grain growth experiments have been performed in synthetic analogues of meteorites: the system forsterite+nickel±melt silicate (Fo:Ni±M). The synthesis of starting materials required special care. A new sintering technique, seldom used in geosciences, has been developed: Spark Plasma Sintering. Experimental results show that mechanisms of grain growth of Fo and Ni are largely dependent of proportion and composition of each phase. Finally, results are in good agreement with natural observations and can be used to precise thermal history of planetesimals.
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Earth and Planetary Astrophysics. Université Paul Sabatier - Toulouse III, 2011. French


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Submitted on : Thursday, February 2, 2012 - 2:27:53 PM
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Jeremy Guignard. Caractérisation texturale des assemblages Métal-Silicate lors de la différenciation des planétésimaux : Etude de météorites & Approche expérimentale. Earth and Planetary Astrophysics. Université Paul Sabatier - Toulouse III, 2011. French. <tel-00665648>

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