Aims of the project: What is the origin at depth of volcanic plumes? Their geodynamical role and their relationships with oceanic plates and continents?
The mantle plumes, their origin, their surface signature (as hotspots) and their role in global geodynamics are considered as one of the "last frontier" challenges in Earth sciences. To first order, seismic and volcanic activities are well understood by plate tectonics. But mantle plumes cannot be explained by plate tectonics. Their birth, life and death play a fundamental role on the evolution of biological life on Earth, on plate tectonics reorganization. In that respect, La Réunion island is one of the largest hotspot on Earth. Its birth, 65Ma ago, creating the Deccan volcanic traps in India (almost 1million km2) are associated with the Cretaceous-Tertiary boundary and might have provoked the disappearance of more than 90% of life on Earth (including dinosaurs). However, the deep structure of this geological object and the exact geometry of volcanic plumes are still the subject of controversies. The use of seismic data acquired by the French-German RHUM-RUM experiment in the Indian ocean around La Réunion volcanic hotpsot (2012-2016) and the unique collection of broadband seismic data by Indian seismic networks enable us to investigate the deep structure of La Réunion Plume along its complete track from its birth to its present stage in the Indian Ocean around La Réunion. The recent progress in inversion techniques makes it possible a better resolution of these structures, by taking account of the full information of seismograms. During the last twenty years, Jean-Paul Montagner and Barbara Romanowicz worked on the seismic imaging of the Earth mantle at the regional and global scales with a specific interest in the imaging of mantle anisotropy. The main objective of this thesis is to provide an enhanced resolution and a better understanding of the deep structure of volcanic plumes, major actors of the Earth machine. Innovative methods of full waveform inversion will be applied to the unique original seismic datasets obtained in the Indian continent and in the Indian ocean (RHUM-RUM experiments).