Geodynamic modelling and tomographic visibility of a mantle plume under La Réunion

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The goal of the German-French experiment RHUM-RUM is to seismologically image a mantle plume - or its absence - under the hotspot of La Réunion, and to understand the results in terms of convective flow at all depth levels of the Earth mantle. Most of the ocean-bottom and island data will become available in late 2013.The work we propose here consists of two kinds of interrelated, a priori modeling studies, meant to accompany the data analysis components of RHUM-RUM. In Work Package 1 (one Ph.D. student) we propose to develop a new geodynamic model of the Réunion mantle plume interacting with large-scale flow, which is commonly considered to be largely driven by subducted slabs, but possibly also by active upwellings under Africa and the Indian Ocean. In Work Package 2 (one Ph.D. student), we will investigate the tomographic observability of such a priori reasonable plume structures.We propose a full-fledged parameter and uncertainty study a priori (Down to which threshold of each rheological / physical parameter should a plume still be detectable, at each depth?), rather than the very topical resolution tests that are typically shown a posteriori in order to justify a preferred model obtained from the real data. Our geodynamic models, and their expected tomographic signatures, can therefore be regarded as a true predictions. As observations become available from the RHUM-RUM data analyses by colleagues, the models will be compared to them, geodynamical parameters will be narrowed down, and modified models will be run. Both work packages contain strong components of computational method development, in terms of mantle convection simulations and broadband waveform inversion.Our overarching objectives are:1. Better geodynamical models in general, of the process of a hypothesized classical plume rising from a Large Low Shear wave Velocity Province (LLSVP) - a generation mechanism currently thought to apply to most oceanic hotspots. 2. A clear and comprehensive understanding of which structures, if present, could or could not be resolved by the actual RHUM-RUM data.3. An immediate geodynamical context for actually observed structures, once they become available, i.e., at a moment when the project experiences its maximum momentum and greatest interest from the scientific community.