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Etude expérimentale de la diffusion thermique dans les monocristaux d'olivine et dans les roches du manteau supérieur

Abstract : The knowledge of the thermal structure of the Earth is a prerequisite to better understand the geological processes observed at the Earth's surface. Conductive and convective heat transport mechanisms within the mantle determine this thermal structure and are mainly controlled by heat transport properties of mantle rocks. This study proposes to investigate these properties by measuring the thermal diffusivity of olivine single-crystals and polycristalline aggregates (rocks) at high temperature and high pressure, using three methods of measurement. Measurements on single-crystals display a strong anisotropy of thermal diffusivity and a significant heat transport by radiation at high temperature. Measurements on naturally-deformed peridotites show that the lattice preferred orientations of minerals lead to a significant anisotropy of thermal diffusivity (25%), which is preserved at high temperature. Comparison between single-crystals and rocks behaviours suggests that heat transfer by phonons is not hindered by grain boundaries and rock imperfections and that heat transport by radiation remains significant at the rock scale, in spite of reflections at grain boundaries. The resulting thermal diffusivity under mantle conditions is close to 1.5 mm2.s-1, which is about 50% higher than the one determined in previous studies. Numerical models of geotherms show that the combination of realistic values of phonon contribution, heat transport by radiation and anisotropy of thermal diffusivity may have major implications on the lithosphere dynamics and mantle convection.
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Contributor : Benoit Gibert <>
Submitted on : Tuesday, October 26, 2004 - 11:48:25 AM
Last modification on : Friday, April 5, 2019 - 8:02:57 PM
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Benoit Gibert. Etude expérimentale de la diffusion thermique dans les monocristaux d'olivine et dans les roches du manteau supérieur. Géologie appliquée. Université Montpellier II - Sciences et Techniques du Languedoc, 2003. Français. ⟨tel-00007214⟩



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