Rhéologie du pergélisol de Mars : applications géomorphologiques et structurales ; conséquences sur l'origine des contraintes compressives

Abstract : The climate of planet Mars is dry and cold. The ground is frozen and con tains large amount of ice. The occurrence of groundice has important consequences on the mechanical behavior of the ground. The goal of this study is (1) to measure relative viscosity of ice/rock mixtures using experimental deformation tests and (2) to apply these experimental results to the rheology of the frozen ground, to tectonics and morphology. Climatic and tectonic implications are deduced from the study of rock glaciers morphology and compressional wrinkle ridges. Experimental results show that ice-rock mixtures are viscous when porosity (ice/rock volume ratio), is higher than 28%. The deformation is brittle when porosity is lower than 28%. The frozen ground has then a ductile behavior if porosity is high enough. The strength of this ductile layer is much smaller than the strength of brittle ice-free layers. Porosity limits the depth at which the frozen ground is ductile. The viscous deformation of frozen ground appears at surface as rock glaciers. These morphologies are located between 35 and 50° latitude where current temperatures are about -60°C. Following rheological results and morphological observations, we show that formation of rock glaciers is possible on duration of billions of years without major temperature changes. Therefore no major climatic warming up happened in the recent evolution of Mars for about 2 Ga. Martian wrinkle ridges are compressional structures interpreted as thrusts rooted at shallow depth. Using structural observations and rheological results we show that (1) these structures are rooted on a shallow detachment about 1.5 km deep and (2) this detachment corresponds to the ductile rheological layer created by groundice. Finally we develop the problem of stress origin. Using observations, relative datation by crater counting and planetary secular cooling models, we conclude that compression results from the thermal stress due to the global contraction of the planet.
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Submitted on : Thursday, October 11, 2012 - 11:11:33 AM
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Nicolas Mangold. Rhéologie du pergélisol de Mars : applications géomorphologiques et structurales ; conséquences sur l'origine des contraintes compressives. Planétologie et astrophysique de la terre [astro-ph.EP]. Université Joseph-Fourier - Grenoble I, 1997. Français. ⟨tel-00740850⟩

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