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, , Thèse de doctorat, École Normale Supérieure de Lyon, 255 p., (2002)

Élasticité et orientations préférentielles dans la Terre profonde: approche expérimentale

S. Merkel

This thesis is devoted to the development of new experimental techniques for the study of elasticity and rheology under high pressure. These data are of considerable interest for our understanding of seismic anisotropy, convection, and rheology in the deep Earth.

We first perform finite element modeling calculations in order to describe the stresses and strains in the diamond anvil cell. Later, we develop new experimental and theoretical techniques for the study of elastic properties and deformation mechanisms under high pressure.

We then study the yield strength, elastic moduli, texture evolution and deformation mechanisms for several materials : FeS2 pyrite, MgO which is the pure end-member of magnesiowustite that accounts for 10 to 20% of the lower mantle, (Mg,Fe)SiO3 silicate perovskite that accounts for about 70% of the lower mantle, and e-iron which is believed to account for 90% of the Earth inner core.

The full set of elastic moduli and their pressure dependence is estimated for FeS2, MgO, a- iron and e-iron. MgO, a-iron and e-iron in uniaxial compression under ambient temperature and mantle pressures are found to deform by slip and develop strong preferred orientations. However, our measurements show no development of significant lattice preferred orientations in perovskite which indicates that deformation by dislocation glide is not the dominant deformation mechanism in perovskite under these conditions.

These data demonstrate the feasibility of analyzing elastic moduli, shear strength, and deforma- tion mechanisms under pressures relevant for the Earth's interior.

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© Sébastien Merkel, Université de Lille, France

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