Résumé
Large and permanent uplifts may develop along the flanks of passive rifts, and the most likely mechanism for explaining them is flexural bending of the lithosphere due to an isostatic load resulting from necking of the lithosphere. A numerical model that accounts for the elastic and viscoplastic behaviour of the lithosphere is used to determine the important parameters of this mechanism, in order to explain large uplifts such as those observed in the Red Sea and the Transantarctic Mountains (more than 2000 m). Large uplifts of the flanks and large subsidence in the rift are associated with a thick mechanical lithosphere.