Évolution Temporelle et Spatiale du Système d'Interaction entre le point chaud de Tristan da Cunha et la Dorsale de l'Atlantique Sud.

• Main Author: Machado Pessanha, Ivo Bruno
• Other Authors: Domaines Océaniques (LDO), Centre National de la Recherche Scientifique (CNRS)-Institut d'écologie et environnement-Observatoire des Sciences de l'Univers-Université de Brest (UBO)-Institut national des sciences de l'Univers (INSU - CNRS), Université de Bretagne occidentale - Brest, Marcia Maia([e-mail])
• Format: Thesis
• Language: French
• Published: HAL CCSD 2011
• Subjects: hotspot; mid-ocean ridge; South Atlantic; Walvis Ridge; Rio Grande Rise; geoid; kinematics reconstructions; axial jumps; African plate; South America plate; plume flux; isotopic ratio; spherical harmonics; point chaud; Tristan da Cunha; dorsale; Atlantique Sud; chaîne Walvis; élévation du Rio Grande; MBA; RMBA; géoïde; reconstructions cinématiques; sauts d'axes; plaque africaine; plaque sud-américaine; flux de panache; rapport isotopique; harmoniques sphériques; Gough et RSA; geo; envir; Dorsale; Gough; La Dorsale; Mid-Atlantic Ridge; Tristan; Iceland; North Atlantic; South Atlantic Ocean
• Online Access: https://tel.archives-ouvertes.fr/tel-00652905/file/PESSANHA_ivo_2011_these-1.pdf; https://tel.archives-ouvertes.fr/tel-00652905

In this work we have studied the space and time evolution of the Tristan hotspot and south Mid-Atlantic Ridge interaction system. The Tristan hotspot and its associated bathymetrical features (i.e. Walvis Ridge in the African plate and Rio Grande Rise in the South American plate) are ones of the most significant features of the South Atlantic Ocean. However, this system is not as well studied as the systems in the North Atlantic (e.g. Azores and Iceland), and their origin and evolution is an open subject. Data compilation of the available surveys from the National Geophysical Data Center (NGDC) and satellite-derived bathymetry were treated to generate a Digital Elevation Model (DEM) for the entire South Atlantic Ocean. Satellite-derived free-air anomaly data and sediment thickness data were used to calculate the mantle Bouguer anomaly (MBA) and digital isochrons of the ocean floor were used to calculate the residual mantle Bouguer anomaly (RMBA), residual bathymetry and new poles for the South America and Africa relative plate motions. Satellite-derived geoid data and the Earth Gravitational Model - EGM2008 were used for the separation of the different components in the geoid data with the calculation of filters using different levels and degree of spherical harmonics. From kinematic reconstructions based on new rotation poles calculated in this work and using the most accepted hypothesis for the current position of the hotspot, as the volcanic island of Tristan da Cunha, the chronology of the emplacement of the volcanic structures could be detailed. This highlighted the existence of several axes jumps and periodic variations in the magma supply to the axis resulting in a periodic alternation between periods of construction and axial ruptures of the axial plateau. The detailed comparison of the estimated position for the Tristan da Cunha hotspot and the location of the volcanic structures of the Walvis Ridge whose ages are known, underlined that the formation of the Walvis Ridge cannot be explained in its ...