Large igneous provinces have been intensively studied, but their architecture, and the processes that create their heterogeneity, are still poorly constrained. The major goal of this thesis is to investigate these processes through the study of two plateaus, Kerguelen and Ethiopia. For the Kerguelen plateau our work focused on Skiff Bank at the western extremity of the plateau. We demonstrated that: (1) the locality contains the oldest alkaline rocks of the plateau, (2) the volcanism is subaerial, (3) the Kerguelen plume is not currently located below Skiff Bank, (4) there is no crustal component in the source of these lavas. In Ethiopia, we showed that the petrology and geochemistry of the lavas of the shield volcanoes are identical to those of the underlying flood basalts. The transition from flood to shield volcanism does not correspond to a change in magma type but to physical evolution of the plumbing system. The lavas of the Ethiopian plateau display two types of bimodality: mafic-felsic and tholeiitic-alkaline. The analysis of these rocks shows that they were derived from a plume that was heterogeneous in terms of temperature and composition. Our dating and mapping show that the Ethiopian plateau is build by several distinct eruptive centers of different ages and petrological/geochemical character. . The emission rates of lavas of these two plateaus evolved differently through time. The magma flux depends on the plume activity and on plate velocity which influences the evolution of the thickness and character of the Iithosphere.
