Évolution Temporelle et Spatiale du Système dInteraction entre le point chaud de Tristan da Cunha et la Dorsale de lAtlantique Sud.Report as inadecuate




Évolution Temporelle et Spatiale du Système dInteraction entre le point chaud de Tristan da Cunha et la Dorsale de lAtlantique Sud. - Download this document for free, or read online. Document in PDF available to download.

1 LDO - Domaines Océaniques

Abstract : 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 entirety by the evolution model involving an interaction between the South Atlantic Mid Ocean Ridge and a hotspot whose current position is in the island of Tristan da Cunha. Next, we evaluated the temporal evolution of the influence of the hotspot to the South Atlantic Mid-Ocean Ridge axis with respect to changes in the residual bathymetry RB and the residual mantle Bouguer anomaly RMBA with the analysis of variations in the spreading rate and the hotspot-ridge distance. For the early stages of the South Atlantic opening, the RMBA and BR anomalies are stronger for the African plate then for the South American plate. This suggests that the position of the hotspot was beneath the African plate since the beginning of the opening of the South Atlantic Ocean. In summary, there are three different periods for the Tristan da Cunha hotspot and South Atlantic Mid-Ocean Ridge interaction system. A period of rapprochement of the ridge to the hotspot between 115 Ma and 100 Ma, in which it is observed the influence of the hotspot on the ridge axis for at least the distance of 150 km. Then, between 95 Ma and 60 Ma, we observed that the ridge is directly above or very close



Author: Ivo Bruno Machado Pessanha -

Source: https://hal.archives-ouvertes.fr/



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