Etude de l'expression de surface d'instabilités convectives mantelliques

Earth's lithosphere, which is the upper boundary layer of mantle convection, represents the interface between the external and internal envelopes of our Planet. The multiple interactions between the mantle and lithosphere generate lateral (plate tectonics) and vertical (dynamic topography) deformations of Earth's surface. Understanding the influence of the dynamics of mantle convective instabilities on the surface is fundamental to improve our interpretations of a large range of surface observations, such as the formation of sedimentary basins, continental motions, the location of hotspots, the presence of gravity anomalies or sea-level variations.This thesis aims at developing numerical models of whole-mantle convection self-generating plate-like tectonics in order to study the impacts of the development and the dynamics of mantle convective instabilities (such as slabs or mantle plumes) on the continuous reshaping of the surface.First, I focus on the influence of the coupling between mantle convective motions and plate tectonics on the development of dynamic topography (i.e. surface vertical deformations induced by mantle convection) at different spatial and temporal scales. The results suggest that Earth's surface can deform over large spatial scales (> 104 km) induced by whole-mantle convection to small-scales ( 104 km) ou encore de convection à petite échelle sub-lithosphérique (< 500 km). Les variations temporelles de topographie dynamique s‘étendent de cinq à plusieurs centaines de millions d'années selon la nature des processus convectifs dont elles dérivent. En particulier, la dynamique d'initiation ou d'arrêt des zones de subduction contrôle l'existence d'échelles intermédiaires de topographie dynamique (longueurs d'onde variant entre 500 et 104 km). Ces résultats montrent donc que les interactions entre la dynamique de la lithosphère et la convection mantellique génèrent des motifs spatio-temporels de topographie dynamique complexes et cohérents par rapport aux observations terrestres.Dans un deuxième temps, cette thèse se focalise sur la dynamique des panaches mantelliques, et leurs interactions avec la surface. Je caractérise d'abord précisement le comportement des panaches générés dans nos modèles de convection à la lumière d'observations de surface. Puis, j'étudie la façon dont leurs interactions avec la tectonique de surface et les différentes échelles convectives modifient leurs mouvements latéraux. Enfin, la compréhension de la signature thermique des interactions entre panaches et rides océaniques me permet de proposer une reconstitution des mouvements relatifs entre le panache des Açores et la ride médio-Atlantique

Long-term evolution of a plume-induced subduction in the Neotethys realm

International audienceThe head of a mantle plume can weaken the oceanic lithosphere through the combined action of its buoyancy forces and excess temperature, which eventually induces intra-oceanic subductions. However, the dynamics of plume-induced subductions, their lifetime and their ability to propagate at the scale of an entire ocean remain unknown. Here, we combine a quantitative synthesis of the ophiolitic record of the Neotethys subduction in the Late Cretaceous with 3D spherical modeling of mantle convection self-generating plate-like tectonics to propose that the pre-Deccan plume initiated the Southern Neotethys Subduction. We suggest that this subduction retreated at 5-10 cm yr−1 until it reached the continental margins of Arabia and India. The sequential segmentation of this subduction during its retreat and the diachronous deactivation of the resulting segments drove the Late Cretaceous-Eocene series of plate reorganization events recorded in the Indian Ocean's fabric

Drawing everyday sexism in academia: observations and analysis of a community-based initiative

International audienceAbstract. Sexist behaviour in the workplace contributes to create a hostile environment, hindering the chance of women and gender non-conforming individuals to pursue an academic career, but also reinforcing gender stereotypes that are harmful to their progress and recognition. The Did this really happen?! project aims at publishing real-life, everyday sexism in the form of comic strips. Its major goal is to raise awareness about unconscious biases that transpire in everyday interactions in academia and increase the visibility of sexist situations that arise within the scientific community, especially to those who might not notice it. Through the website didthisreallyhappen.net, we collect testimonies about everyday sexism occurring in the professional academic environment (universities, research institutes, scientific conferences…). We translate these stories into comics and publish them anonymously without any judgement or comments on the website. By now, we have collected over 100 testimonies. From this collection, we identified six recurrent patterns: (1) behaviours that aim at maintaining women in stereotypical feminine roles, (2) behaviours that aim at maintaining men in stereotypical masculine roles, (3) the questioning of the scientific skills of female researchers, (4) situations where women have the position of an outsider, especially in informal networking contexts, (5) the objectification of women, and (6) the expression of neosexist views. We first present a detailed analysis of these categories, then we report on the different ways we interact and engage with the Earth science community, the scientific community at large and the public in this project